Journal of the Chilean Chemical Society [4 followers] Follow
Open Access journal
ISSN (Online) 0717-9324
Published by SciELO
[681 journals] [SJR: 0.207] [H-I: 16]
Open Access journalISSN (Online) 0717-9324
Published by SciELO
[681 journals] [SJR: 0.207] [H-I: 16]- FURTHER STUDIES ON HOMO- AND COPOLYMERIZATION OF STYRENE THROUGH
CpTICl3-MAO INITIATOR SYSTEM- Abstract: The copolymerization of styrene with cyclohexene, 1-methyl-1-cyclohexene and with norbornene at various styrene/comonomer molar ratio, using cyclopentadienyltitanium trichloride and methylaluminoxane, CpTiCl3-MAO, initiating system has been tested. Only the couple styrene-norbornene produce real styrene-norbornene copolymers, while comonomers cylohexene and 1-methyl-1-cyclohexene only yielded syndiotactic polystyrene, s-PS. The present paper also report results of exploratory experiments on the synthesis through in-situ polymerization of nanocomposites based on styrene/para-methylstyrene copolymer, S/p-MeS, including SiO2 nanoparticles where nanocomposites with modified SiO2 nanoparticles, showed a better dispersion of nanoparticles in the copolymer matrix.
- Abstract: The copolymerization of styrene with cyclohexene, 1-methyl-1-cyclohexene and with norbornene at various styrene/comonomer molar ratio, using cyclopentadienyltitanium trichloride and methylaluminoxane, CpTiCl3-MAO, initiating system has been tested. Only the couple styrene-norbornene produce real styrene-norbornene copolymers, while comonomers cylohexene and 1-methyl-1-cyclohexene only yielded syndiotactic polystyrene, s-PS. The present paper also report results of exploratory experiments on the synthesis through in-situ polymerization of nanocomposites based on styrene/para-methylstyrene copolymer, S/p-MeS, including SiO2 nanoparticles where nanocomposites with modified SiO2 nanoparticles, showed a better dispersion of nanoparticles in the copolymer matrix.
- WHY HIGH SCHOOL STUDENTS IN CHILE, NOT ACHIEVE SIGNIFICANT LEARNING IN
CHEMISTRY- Abstract: Most of the people who taught chemistry at university level, or secondary, arises as the question of whether their students learn all you are taught. The answer to this question is always the students learned very little. From there, it is logical to wonder then why? The answer focuses on specific teaching of chemistry, showing the different problems of the teaching of this discipline. Among them raises the preconceptions that students bring, mathematization of chemistry, emergent properties and different levels of representation: macroscopic, submicroscopic and symbolic. It is suggested that those who teach chemistry should keep these issues when teaching specific content and try new methodologies and in the future a profound change to the curriculum. Thus, it is proposed here to promote these changes, while modifying the high school curriculum is made, to redress initial chemistry courses in college and taking measurements to provide a basis and endorse the proposed amendments urgent curriculum.
- Abstract: Most of the people who taught chemistry at university level, or secondary, arises as the question of whether their students learn all you are taught. The answer to this question is always the students learned very little. From there, it is logical to wonder then why? The answer focuses on specific teaching of chemistry, showing the different problems of the teaching of this discipline. Among them raises the preconceptions that students bring, mathematization of chemistry, emergent properties and different levels of representation: macroscopic, submicroscopic and symbolic. It is suggested that those who teach chemistry should keep these issues when teaching specific content and try new methodologies and in the future a profound change to the curriculum. Thus, it is proposed here to promote these changes, while modifying the high school curriculum is made, to redress initial chemistry courses in college and taking measurements to provide a basis and endorse the proposed amendments urgent curriculum.
- ARSENIC SPECIES-BINDING PROTEINS IN HUMAN CARDIOVASCULAR AND MUSCLE
TISSUES- Abstract: The intracellular As-protein binding in cytosol and methanol-water extract of the auricle and saphene tissues of As impacted people was evaluated by bidimensional size exclusion FPLC-UV-ICP-MS. The fractionation of cytosol using Superdex, Phenomenex and MonoQ HR 5/5 columns, shows that As was distributed in a wide range of contiguous fractions of each column, being 8, 25, 50 % the percentages of As in the collected fractions, respectively. Arsenic a sulphur coelute when FPLC-UV-ICP-MS was applied, which could implicate that As is bound to bio-compounds of different molecular mass through vicinal sulphur groups. The monitoring of S, Cu and P. In the methanol: water extracts a similar study than performed with the cytosol using preparative gel chromatography on Sephadex G-75 and Shephadex G-100 columns. A very low As and protein contain were found in the different fractions of both SEC fractionating series. A similar As-protein association to that found in the cytosol after fractionating with MonoQ HR 5/5 was observed for auricle and saphene. Inorganic and methylated As speciation in the 20 - 26 cytosol fractions obtained within the Phenomenex column was performed by HPLC-ICP-MS using the Hamilton PRP-X100 column. Only As(III) and As(V) were present and the results obtained shows that the As(III)/As(V) ratio is constant in most cases. Direct evidence of the existence of As-binding peptides in auricle and saphene vein from arsenic impacted human beings has have been obtained which was previously reported by means of novo peptide synthesis.
- Abstract: The intracellular As-protein binding in cytosol and methanol-water extract of the auricle and saphene tissues of As impacted people was evaluated by bidimensional size exclusion FPLC-UV-ICP-MS. The fractionation of cytosol using Superdex, Phenomenex and MonoQ HR 5/5 columns, shows that As was distributed in a wide range of contiguous fractions of each column, being 8, 25, 50 % the percentages of As in the collected fractions, respectively. Arsenic a sulphur coelute when FPLC-UV-ICP-MS was applied, which could implicate that As is bound to bio-compounds of different molecular mass through vicinal sulphur groups. The monitoring of S, Cu and P. In the methanol: water extracts a similar study than performed with the cytosol using preparative gel chromatography on Sephadex G-75 and Shephadex G-100 columns. A very low As and protein contain were found in the different fractions of both SEC fractionating series. A similar As-protein association to that found in the cytosol after fractionating with MonoQ HR 5/5 was observed for auricle and saphene. Inorganic and methylated As speciation in the 20 - 26 cytosol fractions obtained within the Phenomenex column was performed by HPLC-ICP-MS using the Hamilton PRP-X100 column. Only As(III) and As(V) were present and the results obtained shows that the As(III)/As(V) ratio is constant in most cases. Direct evidence of the existence of As-binding peptides in auricle and saphene vein from arsenic impacted human beings has have been obtained which was previously reported by means of novo peptide synthesis.
- SYNTHESIS AND STRUCTURAL CHARACTERIZATION OF NANOCRYSTALLINE
BATIO3 AT VARIOUS CALCINATION TEMPERATURES- Abstract: Barium titanate (BaTiO3) powders with particle sizes about 50 nm in diameter were synthesized using a hydrothermal route. The powders were characterized using various experimental techniques such as XRD, TEM and Raman spectroscopy, and they showed a good crystallinity and homogeneity without heat treatments. Also, Raman spectra showed the presence of the tetragonal phase. In addition, various calcination treatments were made to BaTiO3 powders with the purpose to improve their ferroelectric properties. In general, calcination treatments improved the crystallinity and homogeneity of the samples considerably but did not modify the internal structure of the BaTiO3, which was observed in the Raman spectra. On the other hand, from theoretical calculations were established that the cubic phase should be better dielectric in comparison with the tetragonal phase, but this latter would have better optical properties. However, experimental evidences are indicative that the cubic phase would predominate in the synthesis of the compound.
- Abstract: Barium titanate (BaTiO3) powders with particle sizes about 50 nm in diameter were synthesized using a hydrothermal route. The powders were characterized using various experimental techniques such as XRD, TEM and Raman spectroscopy, and they showed a good crystallinity and homogeneity without heat treatments. Also, Raman spectra showed the presence of the tetragonal phase. In addition, various calcination treatments were made to BaTiO3 powders with the purpose to improve their ferroelectric properties. In general, calcination treatments improved the crystallinity and homogeneity of the samples considerably but did not modify the internal structure of the BaTiO3, which was observed in the Raman spectra. On the other hand, from theoretical calculations were established that the cubic phase should be better dielectric in comparison with the tetragonal phase, but this latter would have better optical properties. However, experimental evidences are indicative that the cubic phase would predominate in the synthesis of the compound.
- NANOTUBULAR ALUMINOSILICATES: A CASE STUDY FOR SCIENCE AND
INDUSTRY- Abstract: The renewed interest in imogolite nanotubes, with structural similarities with carbon nanotubes (CNTs), has led to a new search of the potential of imogolite in the field of nanoscience. The applications of imogolite started being studied at the beginning of the 1970s, but the lack of technological development prevented a detailed study of this aluminosilicate. Furthermore, the strong incursion CNTs, which show exceptional structural characteristics and physical properties, left imogolite as the subject of secondary studies and applications in nanotechnology. This review, revise the scientific interest on imogolite from its discovery until the present, showing the main areas of research and development for this nanotube from a nanotechnological point of view.
- Abstract: The renewed interest in imogolite nanotubes, with structural similarities with carbon nanotubes (CNTs), has led to a new search of the potential of imogolite in the field of nanoscience. The applications of imogolite started being studied at the beginning of the 1970s, but the lack of technological development prevented a detailed study of this aluminosilicate. Furthermore, the strong incursion CNTs, which show exceptional structural characteristics and physical properties, left imogolite as the subject of secondary studies and applications in nanotechnology. This review, revise the scientific interest on imogolite from its discovery until the present, showing the main areas of research and development for this nanotube from a nanotechnological point of view.
- EFFECT OF FLUORINE IN THE SYNERGISM Co-Mo VIA HYDROGEN SPILLOVER ON THE
HYDRODESUL-PHURIZATION OF REFRACTORY MOLECULES- Abstract: The influence of fluorine concentration on the synergism between Co/γ-Al2O3 and MoAy-Al2O3 stacked beds separated by 3-mm of γ-Al2O3Fx (x = 0 - 2.5%), in the hydrodesulphurization of refractory molecules contained in gasoil, under operating conditions similar to those of industry, was studied. The results shown, that the synergism increases with F content, reaching a maximum at 0.8% of fluorine, which it is related to changes in zero point of charge (ZPC) and acid strength, due to the incorporation of fluorine. The conversion of most refractory molecule reported is favoured by fluorine.
- Abstract: The influence of fluorine concentration on the synergism between Co/γ-Al2O3 and MoAy-Al2O3 stacked beds separated by 3-mm of γ-Al2O3Fx (x = 0 - 2.5%), in the hydrodesulphurization of refractory molecules contained in gasoil, under operating conditions similar to those of industry, was studied. The results shown, that the synergism increases with F content, reaching a maximum at 0.8% of fluorine, which it is related to changes in zero point of charge (ZPC) and acid strength, due to the incorporation of fluorine. The conversion of most refractory molecule reported is favoured by fluorine.
- BLENDS OF POLY(N-VINYL-2-PYRROLIDONE) AND DIHYDRIC PHENOLS:
THERMAL AND INFRARED SPECTROSCOPIC STUDIES. PART IV- Abstract: The blending behaviour of binary systems formed by the polymer component poly(N-vinyl-2-pyrrolidone) (PVP) and the low molecular weight compounds 4,4'-biphenol (44BP) and 2,2'-biphenol (22BP) was studied. The blends were characterized in the entire composition range by Differential Scanning Calorimetry (DSC), Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA), and Scanning Electron Microscopy (SEM). Both, the glass transition temperature (Tg) and the melting point (Tm) of the pure components were affected as a consequence of the blending process. It was observed miscibility between the components in both blends and a higher interaction degree in the blend containing 44BP. FTIR analysis detected the hydrogen bonding as intermolecular interaction responsible of the observed miscibility, by means of the variation in the wave number corresponding to the stretching vibration of PVP carbonyl group. TGA and SEM analyses provided coherent and complementary results with both DSC and FTIR.
- Abstract: The blending behaviour of binary systems formed by the polymer component poly(N-vinyl-2-pyrrolidone) (PVP) and the low molecular weight compounds 4,4'-biphenol (44BP) and 2,2'-biphenol (22BP) was studied. The blends were characterized in the entire composition range by Differential Scanning Calorimetry (DSC), Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA), and Scanning Electron Microscopy (SEM). Both, the glass transition temperature (Tg) and the melting point (Tm) of the pure components were affected as a consequence of the blending process. It was observed miscibility between the components in both blends and a higher interaction degree in the blend containing 44BP. FTIR analysis detected the hydrogen bonding as intermolecular interaction responsible of the observed miscibility, by means of the variation in the wave number corresponding to the stretching vibration of PVP carbonyl group. TGA and SEM analyses provided coherent and complementary results with both DSC and FTIR.
- POLYETHYLENE GLYCOL EFFECT ON THE TRANSIENT AND STEADY STATE PHASES OF
P-NITROPHENYLTRIMETHYL ACETATE HYDROLYSIS CATALYZED BY
α -CHYMOTRYPSIN- Abstract: The effect of polyethylene glycol (PEG) on the hydrolytic activity of α-chymotrypsin has been studied using p-nitrophenyltrimethyl acetate (PNTMA) as substrate. This substrate requires long times to reach the steady state condition, allowing the measurement by conventional methods of the fast initial "burst" step present on the biphasic catalytic behaviour exhibited by α-chymotrypsin. The presence of PEG increases both the initial and steady state rates of the reaction. This increase was observed at all the substrate concentrations employed. A formal Michaelis-Menten treatment under steady state conditions shows that K M remains almost constant over the range of PEG concentrations studied (up to 20% w/v), whereas k cat moderately increases with the increment in PEG concentration. The results obtained in this work are interpreted in terms of the following mechanism:
- Abstract: The effect of polyethylene glycol (PEG) on the hydrolytic activity of α-chymotrypsin has been studied using p-nitrophenyltrimethyl acetate (PNTMA) as substrate. This substrate requires long times to reach the steady state condition, allowing the measurement by conventional methods of the fast initial "burst" step present on the biphasic catalytic behaviour exhibited by α-chymotrypsin. The presence of PEG increases both the initial and steady state rates of the reaction. This increase was observed at all the substrate concentrations employed. A formal Michaelis-Menten treatment under steady state conditions shows that K M remains almost constant over the range of PEG concentrations studied (up to 20% w/v), whereas k cat moderately increases with the increment in PEG concentration. The results obtained in this work are interpreted in terms of the following mechanism:
- DEEP DESULFURIZATION BY ADSORPTION OF 4,6-DIMETHYLDIBENZOTHIOPHENE,
- Abstract: In this work the adsorption of 4,6-dimethyldibenzothiophene (4,6-DMDBT) on different supports (SiO2, Al2O3, zeolite 4A, zeolite 13X, natural zeolite, and activated carbon), incorporating on its surface different first series transition metal oxides at different content, was studied. The results indicate that the activated carbon presents a higher adsorption capacity than the other supports studied, which it is assumed to the large number of functional groups present on its surface. The incorporation of the first series transition metal oxides on support, induces in some cases the increase of the adsorption capacities of 4,6-DMDBT and these adsorptions capacities depend on metal content. Finally, the desulfurization by adsorption represents an alternative tool for the elimination of refractory sulfur compounds.
- Abstract: In this work the adsorption of 4,6-dimethyldibenzothiophene (4,6-DMDBT) on different supports (SiO2, Al2O3, zeolite 4A, zeolite 13X, natural zeolite, and activated carbon), incorporating on its surface different first series transition metal oxides at different content, was studied. The results indicate that the activated carbon presents a higher adsorption capacity than the other supports studied, which it is assumed to the large number of functional groups present on its surface. The incorporation of the first series transition metal oxides on support, induces in some cases the increase of the adsorption capacities of 4,6-DMDBT and these adsorptions capacities depend on metal content. Finally, the desulfurization by adsorption represents an alternative tool for the elimination of refractory sulfur compounds.
- SYNTHESIS, THERMAL BEHAVIOR, AND AGGREGATION IN AQUEOUS SOLUTION OF
POLY(METHYL METHACRYLATE)-B-POLY(2-HYDROXYETHYL METHACRYLATE)- Abstract: Amphiphilic block copolymers of poly(methyl methacrylate) PMMA and poly(2-hidroxyethyl methacrylate) PHEMA were synthesized by a two-step atom transfer radical polymerization (ATRP). Copolymers with various degrees of polymerization and different relative block sizes were obtained. The structure of the resulting polymers have been characterized and verified by FT-IR and ¹H-NMR, molecular weight were determined by size exclusion chromatography analyses. The thermal properties of these polymers were investigated by differential scanning calorimetry DSC and thermogravimetric analysis TGA. The glass transition temperature of mono halogenated PMMA increases from 116 °C to 123 °C with increasing molecular weight, whereas the glass transition temperature of block copolymers depends slightly on polymer structure. The derivatives of TGA curves indicate that thermal degradation occurs in one stage. The self-assembly of PMMA-b-PHEMA in aqueous solution have been investigated by fluorescence probing methods. The critical micelle concentrations are in the range 10-6 - 10-7 M. The micropolarity sensed by pyrene is higher than in aggregates formed by block copolymers based on polystyrene.
- Abstract: Amphiphilic block copolymers of poly(methyl methacrylate) PMMA and poly(2-hidroxyethyl methacrylate) PHEMA were synthesized by a two-step atom transfer radical polymerization (ATRP). Copolymers with various degrees of polymerization and different relative block sizes were obtained. The structure of the resulting polymers have been characterized and verified by FT-IR and ¹H-NMR, molecular weight were determined by size exclusion chromatography analyses. The thermal properties of these polymers were investigated by differential scanning calorimetry DSC and thermogravimetric analysis TGA. The glass transition temperature of mono halogenated PMMA increases from 116 °C to 123 °C with increasing molecular weight, whereas the glass transition temperature of block copolymers depends slightly on polymer structure. The derivatives of TGA curves indicate that thermal degradation occurs in one stage. The self-assembly of PMMA-b-PHEMA in aqueous solution have been investigated by fluorescence probing methods. The critical micelle concentrations are in the range 10-6 - 10-7 M. The micropolarity sensed by pyrene is higher than in aggregates formed by block copolymers based on polystyrene.
- ELECTROOXIDATION OF 2,4,6-TRICHLOROPHENOL ON GLASSY CARBON ELECTRODES
MODIFIED WITH COMPOSITE Ni(OH)2-Co(OH)2 FILMS- Abstract: Glassy carbon electrodes coated with a film of electrodeposited cobalt and nickel hydroxides were prepared in order to determine its activity to the 2,4,6-trichlorophenol (TCP) oxidation. The modified electrodes were characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy and Scan Electron Microscopy (SEM) with Energy Dispersive X-ray Spectroscopy (EDS). The results indicate that both hydroxides are homogeneously distributed in the electrode surface. From the viewpoint of electrochemical oxidation of TCP, the presence of cobalt and nickel hydroxides on the electrode surface (i) promotes a more complete oxidation of TCP and (ii) decreases the fouling of the electrode surface in comparison with GC and GC modified with Ni or Co separately.
- Abstract: Glassy carbon electrodes coated with a film of electrodeposited cobalt and nickel hydroxides were prepared in order to determine its activity to the 2,4,6-trichlorophenol (TCP) oxidation. The modified electrodes were characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy and Scan Electron Microscopy (SEM) with Energy Dispersive X-ray Spectroscopy (EDS). The results indicate that both hydroxides are homogeneously distributed in the electrode surface. From the viewpoint of electrochemical oxidation of TCP, the presence of cobalt and nickel hydroxides on the electrode surface (i) promotes a more complete oxidation of TCP and (ii) decreases the fouling of the electrode surface in comparison with GC and GC modified with Ni or Co separately.
- COUMARINS OF HAPLOPAPPUS MULTIFOLIUS AND DERIVATIVE AS
INHIBITORS OF LOX: EVALUATION IN-VITRO AND DOCKING
STUDIES- Abstract: Several natural compounds containing a coumarin moiety have been reported. They have multiple biological activities, e.g., as scavengers of reactive oxygen species (ROS) and to reduce the inflammatory processes by inhibition of enzymes like COX or LOX. A study was made of the inhibitory capacity of seven natural coumarins and one derivative of esculetin, against soybean 15-lipoxygenase (15-sLOX). The studied coumarins showed interesting degrees of inhibition compared to quercetin, a known LOX inhibitor. Docking studies of some compounds into the binding site of 15-sLOX and 5-hLOX were also made.
- Abstract: Several natural compounds containing a coumarin moiety have been reported. They have multiple biological activities, e.g., as scavengers of reactive oxygen species (ROS) and to reduce the inflammatory processes by inhibition of enzymes like COX or LOX. A study was made of the inhibitory capacity of seven natural coumarins and one derivative of esculetin, against soybean 15-lipoxygenase (15-sLOX). The studied coumarins showed interesting degrees of inhibition compared to quercetin, a known LOX inhibitor. Docking studies of some compounds into the binding site of 15-sLOX and 5-hLOX were also made.
- DETERMINATION OF ARSENIC (III) BY DIFFERENTIAL PULSE POLAROGRAPHY IN
THE WATERS OF CAMARONES AREA, CHILE- Abstract: As (III) was determined by differential pulse polarography (DPP) in 1 mol L-1 HCl as supporting electrolyte. For quantification, the -0.35 V peak (versus Ag/ AgCl) was chosen. The obtained detection and quantification limits were 2.7 (3 SD) and 8.9 (10 SD) μg L-1 respectively. The method was used for the determination of As (III) on surface water samples from Camarones River, located in Camarones area, province of Arica, Chile (this area's water contain high levels of salinity). The results indicate that the proposed methodology is a suitable analytical alternative for As determination in natural waters with high levels of dissolved salts, as the waters of Camarones River. The method is not time consuming, nor tedious no prior treatment of the sample is required. The results show that As (III) concentrations in waters of Camarones River are about 10 times higher than the guide values established by WHO for water intended for human consumption.
- Abstract: As (III) was determined by differential pulse polarography (DPP) in 1 mol L-1 HCl as supporting electrolyte. For quantification, the -0.35 V peak (versus Ag/ AgCl) was chosen. The obtained detection and quantification limits were 2.7 (3 SD) and 8.9 (10 SD) μg L-1 respectively. The method was used for the determination of As (III) on surface water samples from Camarones River, located in Camarones area, province of Arica, Chile (this area's water contain high levels of salinity). The results indicate that the proposed methodology is a suitable analytical alternative for As determination in natural waters with high levels of dissolved salts, as the waters of Camarones River. The method is not time consuming, nor tedious no prior treatment of the sample is required. The results show that As (III) concentrations in waters of Camarones River are about 10 times higher than the guide values established by WHO for water intended for human consumption.
- STEROIDAL METABOLITES IN CHILEAN RIVER SEDIMENTS INFLUENCED BY PULP
MILL EFFLUENTS- Abstract: The Biobío River basin (central south of Chile) is highly impacted by a variety of anthropogenic activities such as pulp mills subjected to different treatment processes. The cellulose production has notoriously increased in the Biobío Region in the last years reaching more that 80% of country production. This industrial activity concentrates its production using as raw material fast growing vegetal species like radiata pine (Pinus radiata) and eucaliptus (Eucalyptus globulus). Environmental effects of this massive cellulose production is widely known in countries with major production, but is less addressed in Chile. In this study we report the presence and concentrations of steroidal metabolites, such as sitosterol, campesterol and androstenedione in sediments at the Biobío River basin, considering the Laja, Biobío and Vergara rivers, in points where effluents of cellulose are dumped. Also was detected the presence of coprostanol, which is of human origin.
- Abstract: The Biobío River basin (central south of Chile) is highly impacted by a variety of anthropogenic activities such as pulp mills subjected to different treatment processes. The cellulose production has notoriously increased in the Biobío Region in the last years reaching more that 80% of country production. This industrial activity concentrates its production using as raw material fast growing vegetal species like radiata pine (Pinus radiata) and eucaliptus (Eucalyptus globulus). Environmental effects of this massive cellulose production is widely known in countries with major production, but is less addressed in Chile. In this study we report the presence and concentrations of steroidal metabolites, such as sitosterol, campesterol and androstenedione in sediments at the Biobío River basin, considering the Laja, Biobío and Vergara rivers, in points where effluents of cellulose are dumped. Also was detected the presence of coprostanol, which is of human origin.
- BIOLOGICAL ACTIVITY OF MACROMYCETES ISOLATED FROM CHILEAN SUBANTARCTIC
ECOSYSTEMS- Abstract: Twenty six compounds were identified by GC-MS analysis from culture broth of six Macromycetes growing in subantarctic forests in southern Chile: Mycena hialinotricha, Collybia butyracea, Inocybe geophylla, Entoloma nubigenum, Stropharia semiglobata and Psathyrella sp. Antifungal and antibacterial activity were evaluated through agar diffusion test. This assay showed bioactivity against Penicillium notatum, Fusarium oxysporum, Rhyzoctonia solani, Ceratocistys pilifera, Bacillus subtilis, Pseudomonas aeruginosa, Escherichia coli, Escherichia faecalis and Staphilococcus aureus.
- Abstract: Twenty six compounds were identified by GC-MS analysis from culture broth of six Macromycetes growing in subantarctic forests in southern Chile: Mycena hialinotricha, Collybia butyracea, Inocybe geophylla, Entoloma nubigenum, Stropharia semiglobata and Psathyrella sp. Antifungal and antibacterial activity were evaluated through agar diffusion test. This assay showed bioactivity against Penicillium notatum, Fusarium oxysporum, Rhyzoctonia solani, Ceratocistys pilifera, Bacillus subtilis, Pseudomonas aeruginosa, Escherichia coli, Escherichia faecalis and Staphilococcus aureus.
- RELATIVISTIC-DFT STUDY OF THE ELECTRONIC STRUCTURE, BONDING AND
ENERGETIC OF THE [ReF8] ־ AND
[UF8]2- IONS- Abstract: In this study we evaluated the importance of the relativistic effects (scalar and spin-orbit) on the description of the electronic structure, bonding and the energetic of the [ReF8]- and [UF8]2- ions. We described the bonding interaction between ligands and metal center using the energy decomposition analysis (EDA) proposed by Morokuma and Ziegler, in which it can be appreciated a strong ionic behavior for both ions since the electrostatic interaction energy (∆Ezlestat) is greater than the orbitalic interaction energy (∆E Orb). Furthermore, a qualitative analysis using the mapping of the electrostatic potential over the total electronic density evidence an increase of the ionic character, as well as, the polarization of the electronic density as U > Re. The electron localization function (ELF) corroborates the bonding analysis because of the lack of di-synaptic basins on the metal-ligand bonding region.
- Abstract: In this study we evaluated the importance of the relativistic effects (scalar and spin-orbit) on the description of the electronic structure, bonding and the energetic of the [ReF8]- and [UF8]2- ions. We described the bonding interaction between ligands and metal center using the energy decomposition analysis (EDA) proposed by Morokuma and Ziegler, in which it can be appreciated a strong ionic behavior for both ions since the electrostatic interaction energy (∆Ezlestat) is greater than the orbitalic interaction energy (∆E Orb). Furthermore, a qualitative analysis using the mapping of the electrostatic potential over the total electronic density evidence an increase of the ionic character, as well as, the polarization of the electronic density as U > Re. The electron localization function (ELF) corroborates the bonding analysis because of the lack of di-synaptic basins on the metal-ligand bonding region.
- BIOACTIVE MONOTERPENES FROM ANTARCTIC PLOCAMIUM
CARTILAGINEUM- Abstract: In a chemical analysis of the red seaweed Plocamium cartilagineum collected in Antarctic Peninsula, four polyhalogenated monoterpenes were isolated. Their structures were established by spectroscopic techniques. Two of them are acyclic monoterpenes and the others are cyclic. We report the antimicrobial, insecticide and acaricide activities of compounds.
- Abstract: In a chemical analysis of the red seaweed Plocamium cartilagineum collected in Antarctic Peninsula, four polyhalogenated monoterpenes were isolated. Their structures were established by spectroscopic techniques. Two of them are acyclic monoterpenes and the others are cyclic. We report the antimicrobial, insecticide and acaricide activities of compounds.
- SPINEL LiFexCo2-xO4 (0.25
≤ x ≤ 1) AS CATHODES IN
LITHIUM BATTERIES: RELATIONSHIP BETWEEN IONIC DISTRIBUTION AND
LITHIUM ION INSERTION- Abstract: Spinel LiFe xCo2-xO4 samples with 0.25≤x≤1 were synthesized by the sol-gel Pechini method at 300ºC in order to study the impact on their structural and electrochemical properties due to the substitution of Co by Fe. The specific capacity for lithium insertion into the electrode materials depend on lithium diffusion coefficient DLi which in turn depends on the Fe³+/(Fe³++Co³+ +Co4+) octahedral cationic ratio.
- Abstract: Spinel LiFe xCo2-xO4 samples with 0.25≤x≤1 were synthesized by the sol-gel Pechini method at 300ºC in order to study the impact on their structural and electrochemical properties due to the substitution of Co by Fe. The specific capacity for lithium insertion into the electrode materials depend on lithium diffusion coefficient DLi which in turn depends on the Fe³+/(Fe³++Co³+ +Co4+) octahedral cationic ratio.
- ONE POT SOLVOTHERMAL SYNTHESIS OF ORGANIC ACID COATED MAGNETIC IRON
OXIDE NANOPARTICLES- Abstract: In this work we present the synthesis and characterization of iron oxide nanoparticles (IONPs), which were structurally and magnetically characterized. The use of iron salts and an organic acid (l-serine or ascorbic acid) as precursors under solvothermal conditions yielded these coated IONPs. The powder X-ray diffraction pattern of FeO-1 and FeO-2 is consistent with hematite (α-Fe2O3) and hematite-maghemite ((α-Fe2O3/γ-Fe2O3) respectively. The TEM analysis permits to estimate an average size of 10 nm for the FeO-1 sample. The magnetic characterization of the samples through the M(H) plots showed a very low coercivity value for both samples, being 53 Oe for FeO-1 and 10 Oe for FeO-2, indicating the very weak ferromagnetic character of the synthesized iron oxide species. Even though both organic acids under solvothermal conditions permit to obtain coated IONPs in one pot reaction, l-serine produces a more narrow-size distribution.
- Abstract: In this work we present the synthesis and characterization of iron oxide nanoparticles (IONPs), which were structurally and magnetically characterized. The use of iron salts and an organic acid (l-serine or ascorbic acid) as precursors under solvothermal conditions yielded these coated IONPs. The powder X-ray diffraction pattern of FeO-1 and FeO-2 is consistent with hematite (α-Fe2O3) and hematite-maghemite ((α-Fe2O3/γ-Fe2O3) respectively. The TEM analysis permits to estimate an average size of 10 nm for the FeO-1 sample. The magnetic characterization of the samples through the M(H) plots showed a very low coercivity value for both samples, being 53 Oe for FeO-1 and 10 Oe for FeO-2, indicating the very weak ferromagnetic character of the synthesized iron oxide species. Even though both organic acids under solvothermal conditions permit to obtain coated IONPs in one pot reaction, l-serine produces a more narrow-size distribution.
- SIMPLE STEPS FOR SYNTHESIS OF SILICON OXIDE MESOPOROUS MATERIALS
USED AS TEMPLATE- Abstract: A novel methodology for the synthesis of silicon oxide mesoporous materials has been developed using soft reaction conditions, unlike other synthesis conditions present in the literature. The synthesis involves the use of the lyotropic liquid crystals formed by mixing the surfactant hexadecyltrimethylazanium (CTAB), sodium nitrate as catalyst, water and tetraethyl orthosilicate (TEOS) as the inorganic precursor. The silicon oxide samples were characterized by high-resolution transmission electron microscopy (HRTEM) and EDX analysis. The specific surface area of the powder and the pore size were determined by the BET method and were found to be 587 m²/g and 2-4 nm, respectively. The point of zero charge (pzc) determination using a zeta-meter apparatus was 3.1 showing the acid character of the surface. The template mesoporous SiO2 samples can be used to prepare composite electrodes containing active mixed oxides, e.g. for lithium-ion batteries.
- Abstract: A novel methodology for the synthesis of silicon oxide mesoporous materials has been developed using soft reaction conditions, unlike other synthesis conditions present in the literature. The synthesis involves the use of the lyotropic liquid crystals formed by mixing the surfactant hexadecyltrimethylazanium (CTAB), sodium nitrate as catalyst, water and tetraethyl orthosilicate (TEOS) as the inorganic precursor. The silicon oxide samples were characterized by high-resolution transmission electron microscopy (HRTEM) and EDX analysis. The specific surface area of the powder and the pore size were determined by the BET method and were found to be 587 m²/g and 2-4 nm, respectively. The point of zero charge (pzc) determination using a zeta-meter apparatus was 3.1 showing the acid character of the surface. The template mesoporous SiO2 samples can be used to prepare composite electrodes containing active mixed oxides, e.g. for lithium-ion batteries.
- STRUCTURAL EFFECTS OF THE AU(I) DRUG AURANOFIN ON CELL MEMBRANES AND
MOLECULAR MODELS- Abstract: Auranofin is a gold compound that is widely used for the treatment of rheumatoid arthritis. It is a monomeric linear complex with triethylphosphine and thiolate moieties bounded to an Au(I) center. Gold compounds are well known for their neurological and nephrotoxic implications. However, haematological toxicity is one of the most serious toxic and less studied effects. The lack of information on these aspects of auranofin prompted us to study the structural effects induced on cell membranes, particularly that of human erythrocytes. Auranofin was incubated with intact erythrocytes and molecular models of the erythrocyte membrane. The latter consisted of multibilayers of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE), phospholipids classes located in the outer and inner monolayers of the human erythrocyte membrane, respectively. This report presents evidence in order that auranofin interacts with red cell membranes as follows: a) in scanning electron microscopy studies on human erythrocytes it was observed that auranofin induced shape changes; b) X-ray diffraction studies showed that auranofin induced increasing structural perturbation to DMPC and to a lower extent to DMPE bilayers. Additional experiments were performed in human neuroblastoma cells SH-SY5Y. A statistically significant decrease of cell viability was observed.
- Abstract: Auranofin is a gold compound that is widely used for the treatment of rheumatoid arthritis. It is a monomeric linear complex with triethylphosphine and thiolate moieties bounded to an Au(I) center. Gold compounds are well known for their neurological and nephrotoxic implications. However, haematological toxicity is one of the most serious toxic and less studied effects. The lack of information on these aspects of auranofin prompted us to study the structural effects induced on cell membranes, particularly that of human erythrocytes. Auranofin was incubated with intact erythrocytes and molecular models of the erythrocyte membrane. The latter consisted of multibilayers of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE), phospholipids classes located in the outer and inner monolayers of the human erythrocyte membrane, respectively. This report presents evidence in order that auranofin interacts with red cell membranes as follows: a) in scanning electron microscopy studies on human erythrocytes it was observed that auranofin induced shape changes; b) X-ray diffraction studies showed that auranofin induced increasing structural perturbation to DMPC and to a lower extent to DMPE bilayers. Additional experiments were performed in human neuroblastoma cells SH-SY5Y. A statistically significant decrease of cell viability was observed.
- INCLUSION OF GLUTATHIONE PEROXIDASE ON POLYPYRROLE MODIFIED ELECTRODE,
TO BE ASSAYED AS GLUTATHIONE SENSOR- Abstract: In this work it was obtained a modified electrode by inclusion of the enzyme glutathione peroxidase (GPx) on a conductive polymer, polypyrrole (PPy), deposited on a graphite electrode (GC PPy,GPx) for the amperometric detection of reduced glutathione (GSH) in presence of hydrogen peroxide. Also, working conditions were optimized in order to prepare the electrode GC PPy,GPx, which were tested for different concentrations of monomer and enzyme, electrochemical type of perturbance (by fixed potential or cyclic voltammetry) deposition potential and time (PPy film thickness, GPx), etc. by testing the response of the electrodes versus GSH in presence of hydrogen peroxide at physiological pH and temperature. At optimal experimental conditions, the achieved electrode gives a characteristic response for the analyte, which means that this modified electrode can be proposed as a selective GSH sensor, since it was shown that the enzyme maintains its activity during experimental manipulations and responds in a highly reproducible mode, so its use is proposed as an amperometric biosensor which is highly selective and stable.
- Abstract: In this work it was obtained a modified electrode by inclusion of the enzyme glutathione peroxidase (GPx) on a conductive polymer, polypyrrole (PPy), deposited on a graphite electrode (GC PPy,GPx) for the amperometric detection of reduced glutathione (GSH) in presence of hydrogen peroxide. Also, working conditions were optimized in order to prepare the electrode GC PPy,GPx, which were tested for different concentrations of monomer and enzyme, electrochemical type of perturbance (by fixed potential or cyclic voltammetry) deposition potential and time (PPy film thickness, GPx), etc. by testing the response of the electrodes versus GSH in presence of hydrogen peroxide at physiological pH and temperature. At optimal experimental conditions, the achieved electrode gives a characteristic response for the analyte, which means that this modified electrode can be proposed as a selective GSH sensor, since it was shown that the enzyme maintains its activity during experimental manipulations and responds in a highly reproducible mode, so its use is proposed as an amperometric biosensor which is highly selective and stable.
- BIMETALLIC AU/AG METAL SUPERSTRUCTURES FROM MACROMOLECULAR METAL
COMPLEXES IN SOLID-STATE- Abstract: Novel bimetallic Au/Ag superstructures have been prepared from solid-state pyrolysis of the macromolecular complexes Chitosan(MLn/M'Ln)n y PSP-4-PVPx( MLn/M'Ln)n with MLn = AuCl3 and M'Ln = Ag(CF3SO3)The characterization was made from XRD (X-ray diffraction of powder), SEM and EDS analysis. Morphologies are influenced by both the nature of the polymer and the metal/polymer, molar ratio of the polymer precursor. EDS analysis suggests a core/shell Au/Ag structure for the materials. A probable mechanism of the formation of these superstructures is discussed. Although separated reports of metallic superstructures of Au or Ag have been recently described, the here reported are the first bimetallic Au/Ag.
- Abstract: Novel bimetallic Au/Ag superstructures have been prepared from solid-state pyrolysis of the macromolecular complexes Chitosan(MLn/M'Ln)n y PSP-4-PVPx( MLn/M'Ln)n with MLn = AuCl3 and M'Ln = Ag(CF3SO3)The characterization was made from XRD (X-ray diffraction of powder), SEM and EDS analysis. Morphologies are influenced by both the nature of the polymer and the metal/polymer, molar ratio of the polymer precursor. EDS analysis suggests a core/shell Au/Ag structure for the materials. A probable mechanism of the formation of these superstructures is discussed. Although separated reports of metallic superstructures of Au or Ag have been recently described, the here reported are the first bimetallic Au/Ag.
- BIOTRANSFORMATION OF EVT-BEYERENES WITH MUCOR PLUMBEUS
- Abstract: The microbiological transformation of ent-beyer-15-en-18-ol 1 and ent-beyer-15-en-19-ol 2, using Mucorplumbeus, resulted in hydroxylated products. After nine days of incubation, 15β,16β-epoxide-ent-beyeran-7β,18-diol 3, ent-beyer-15-en-7p,19-diol 4 and 15β,16β-epoxide-ent-beyeran-7β,19-diol 5 were isolated. The metabolites were identified by spectroscopic methods.
- Abstract: The microbiological transformation of ent-beyer-15-en-18-ol 1 and ent-beyer-15-en-19-ol 2, using Mucorplumbeus, resulted in hydroxylated products. After nine days of incubation, 15β,16β-epoxide-ent-beyeran-7β,18-diol 3, ent-beyer-15-en-7p,19-diol 4 and 15β,16β-epoxide-ent-beyeran-7β,19-diol 5 were isolated. The metabolites were identified by spectroscopic methods.
- SULFITE OXIDATION MEDIATED BY ORTHO-PHENYLENEDIAMINE /
CO(II)-TETRAKIS(PARA-AMINOPHENYL)PORPHYRIN COPOLYMERS IN ACID MEDIUM- Abstract: The aim of this work is to study the sulfite oxidation mediated by glassy carbon electrodes modified with copolymers formed by ortho-phenylenediamine (OPD) and Co(II)-tetrakis(para-aminophenyl)porphyrin (CoTAPP). The copolymer was obtained through continuous cycling of potential of a glassy carbon electrode in acid medium containing each respective homopolymer in 1:1 feeding volume, in which the ortho-phenylenediamine concentration was 110-1 M and the CoTAPP concentration was 110-4 M. The film obtained is thin, stable and contains a low amount of porphyrin in comparison to the amount in ortho-phenylenediamine. Its electrocatalytic activity was tested toward the sulfite oxidation. In this case, this film is more electrocatalytic than the modified electrode modified with the CoTAPP electropolymer, even though ortho-phenylenediamine is inactive in this reaction. In this work the electrocatalysis process, the morphology of the film, and the difference of electrocatalytic behavior between the ortho-phenylenediamine and cobalt porphyrin homopolymers and the ortho-phenylenediamine-porphyrin copolymer were studied. The morphologic studies were done using Au electrodes since the electrocatalytic activity on Au and on glassy carbon are quite similar.
- Abstract: The aim of this work is to study the sulfite oxidation mediated by glassy carbon electrodes modified with copolymers formed by ortho-phenylenediamine (OPD) and Co(II)-tetrakis(para-aminophenyl)porphyrin (CoTAPP). The copolymer was obtained through continuous cycling of potential of a glassy carbon electrode in acid medium containing each respective homopolymer in 1:1 feeding volume, in which the ortho-phenylenediamine concentration was 110-1 M and the CoTAPP concentration was 110-4 M. The film obtained is thin, stable and contains a low amount of porphyrin in comparison to the amount in ortho-phenylenediamine. Its electrocatalytic activity was tested toward the sulfite oxidation. In this case, this film is more electrocatalytic than the modified electrode modified with the CoTAPP electropolymer, even though ortho-phenylenediamine is inactive in this reaction. In this work the electrocatalysis process, the morphology of the film, and the difference of electrocatalytic behavior between the ortho-phenylenediamine and cobalt porphyrin homopolymers and the ortho-phenylenediamine-porphyrin copolymer were studied. The morphologic studies were done using Au electrodes since the electrocatalytic activity on Au and on glassy carbon are quite similar.
- WATER-SOLUBLE CATIONIC CELLULOSE COUPLED TO A ULTRAFILTRATION MEMBRANE
FOR THE REMOVAL OF ARSENIC AND CHROMIUM- Abstract: This article describes the retention properties of arsenic (V) and chromium (VI) using a water-soluble polymer based on cationic hydroxyethylcellulose and combined with an ultrafiltration membrane. The polymer was purchased commercially and was characterized by Fourier transform infrared spectroscopy (FTIR). The study of polymer removal capacity of As(V) and Cr(VI) were performed by liquid-phase polymer-based retention technique (LPR). By means of a washing method studied retention as a function of pH, the amount of polymer, and the concentration of As(V) and Cr(VI). The results showed that the retention capacity of both oxy-anions increases with the solution pH. Due to the presence of quaternary ammonium groups in the polymer structure, the retention of As(V) and Cr(VI) was higher at a pH of 9 than that at acidic pH levels, reaching values of 65% for Cr(VI) and 43% for As(V). The study in function of amount of polymer showed that using 75 mg the retention of As(V) was 65%. In the case of Cr(VI) using 50 mg of polymer, 67% retention was obtained. Using low concentrations for arsenic and chromium, maximum retention was found at 65% and 95%, respectively. The maximum retention capacity (MRC) of the polymer was determined by adding As(V) and Cr(VI) to the polymer solution and concentrating in successive steps. FTIR spectra before and after of retention showed differences by the interaction with oxy-anions.
- Abstract: This article describes the retention properties of arsenic (V) and chromium (VI) using a water-soluble polymer based on cationic hydroxyethylcellulose and combined with an ultrafiltration membrane. The polymer was purchased commercially and was characterized by Fourier transform infrared spectroscopy (FTIR). The study of polymer removal capacity of As(V) and Cr(VI) were performed by liquid-phase polymer-based retention technique (LPR). By means of a washing method studied retention as a function of pH, the amount of polymer, and the concentration of As(V) and Cr(VI). The results showed that the retention capacity of both oxy-anions increases with the solution pH. Due to the presence of quaternary ammonium groups in the polymer structure, the retention of As(V) and Cr(VI) was higher at a pH of 9 than that at acidic pH levels, reaching values of 65% for Cr(VI) and 43% for As(V). The study in function of amount of polymer showed that using 75 mg the retention of As(V) was 65%. In the case of Cr(VI) using 50 mg of polymer, 67% retention was obtained. Using low concentrations for arsenic and chromium, maximum retention was found at 65% and 95%, respectively. The maximum retention capacity (MRC) of the polymer was determined by adding As(V) and Cr(VI) to the polymer solution and concentrating in successive steps. FTIR spectra before and after of retention showed differences by the interaction with oxy-anions.
- MOLECULAR AND SOLID STATE STRUCTURE OF THE DOUBLY-SUBSTITUTED
B-DIKETONE 3,3'-BIS(FERROCENYLMETHYL)PENTANE-2,4-DIONE#- Abstract: The ferrocene-containing β-diketone, 3-ferrocenylmethyl-pentane-2,4-dione 1, has been synthesized by reacting ferrocenyl methanol with acetylacetone in the presence of cerium(IV) ammonium nitrate as catalyst in C-C bond formation, and isolated as an orange oily product in 90% yield. The doubly-substituted 1,3-diketone, 3,3'-bis(ferrocenylmethyl)pentane-2,4-dione 2 was isolated as orange crystals in 79% yield, upon standing a dichloromethane solution of 1 at -30 °C for two weeks. Both complexes have been authenticated by spectroscopic methods, mass spectrometry, and cyclic voltammetry. In addition, the molecular identity and geometry of 2 has been confirmed by single-crystal X-ray diffraction analysis. In the crystal lattice, the molecules pack as dimers through C-H---O hydrogen bondings, where weaker C-H---p interactions link the dimeric units to form a chain structure.
- Abstract: The ferrocene-containing β-diketone, 3-ferrocenylmethyl-pentane-2,4-dione 1, has been synthesized by reacting ferrocenyl methanol with acetylacetone in the presence of cerium(IV) ammonium nitrate as catalyst in C-C bond formation, and isolated as an orange oily product in 90% yield. The doubly-substituted 1,3-diketone, 3,3'-bis(ferrocenylmethyl)pentane-2,4-dione 2 was isolated as orange crystals in 79% yield, upon standing a dichloromethane solution of 1 at -30 °C for two weeks. Both complexes have been authenticated by spectroscopic methods, mass spectrometry, and cyclic voltammetry. In addition, the molecular identity and geometry of 2 has been confirmed by single-crystal X-ray diffraction analysis. In the crystal lattice, the molecules pack as dimers through C-H---O hydrogen bondings, where weaker C-H---p interactions link the dimeric units to form a chain structure.
- SYNTHESIS AND CHARACTERIZATION OF COPPER COMPLEXES: INTERACTION
OF METALLICCARBOXYLATES WITH 1,3-THIAZOLE LIGAND- Abstract: Complexes were synthesized from aspirinate of Cu(II) and acetate of Cu(II) dihydrated with the ligand 1,3-thiazole and were characterized through elemental analysis, magnetic moment, FT-IR spectroscopy, and thermogravimetric analysis. Moreover, semiempirical structural PM6 of both compounds were carried out. Ligand 1,3-thiazole coordinates with the Cu(II) ions through the nitrogen without break the dimeric unit Cu2 (RCOO)4 To coordinate with the aspirinate of Cu(II), the ligand must to break tridimensional arrangement and to coordinate with the acetate of Cu(II) dihydrated, it replaced the water molecules. In both compounds, Cu2(asp)4(Tz)2 and Cu2(acetate)4(Tz)2, the PM6 calculations corresponding to the Cu-Cu distances in the dimeric unit Cu2 (RCOO)4 presents a small difference 0.03A°, but the magnetic moments are very different. The complex with aspirinate presents a magnetic moment of 1.79 M.B and that with acetate is 1.4 MB.
- Abstract: Complexes were synthesized from aspirinate of Cu(II) and acetate of Cu(II) dihydrated with the ligand 1,3-thiazole and were characterized through elemental analysis, magnetic moment, FT-IR spectroscopy, and thermogravimetric analysis. Moreover, semiempirical structural PM6 of both compounds were carried out. Ligand 1,3-thiazole coordinates with the Cu(II) ions through the nitrogen without break the dimeric unit Cu2 (RCOO)4 To coordinate with the aspirinate of Cu(II), the ligand must to break tridimensional arrangement and to coordinate with the acetate of Cu(II) dihydrated, it replaced the water molecules. In both compounds, Cu2(asp)4(Tz)2 and Cu2(acetate)4(Tz)2, the PM6 calculations corresponding to the Cu-Cu distances in the dimeric unit Cu2 (RCOO)4 presents a small difference 0.03A°, but the magnetic moments are very different. The complex with aspirinate presents a magnetic moment of 1.79 M.B and that with acetate is 1.4 MB.
- ELECTRODES MODIFIED BY
Π
STACKING OF METALLIC
PHTHALOCYANINES AND ITS ELECTROCATALYTIC ACTIVITY ON NITRITE OXIDATION
- Abstract: In this work, it proposed the developing of a new material, a modified electrode with metallic phthalocyanines stacking columns, MxPc (Mx = Co, Fe and Ni), assembled by π interactions, which have a behavior as a supramolecular system. These electrodes showed an important electrocatalytic activity against nitrite oxidation, compared to the same complexes monomer multilayers adsorbed on the electrode (M-MxPc). It is proposed two new obtaining methods of these systems, S1-MxPc, where the complexes would form a column and would be coordinated with the surface electrode through a covalent bond of 4-aminopyridine (4-AP), and S2-MxPc, where the own functional groups of glassy carbon (GC) would be the covalent unions able to coordinate the complexes and the columns formation. These covalent unions between the electrode surface and phthalocyanines, would give a directional stacking, and therefore, would modify both its electrocatalytical activity and its electrical features. It was also studied the dependence between the activity and the complex central metal (Co, Fe and Ni), finding a great dependence between them. It was found that the S2-MxPc modified electrodes were more stables and actives. The higher activity was found on S2-CoPc, which also performs a linear response. This last feature it is seen on a calibration curve with a large range of concentrations. It is important to notice that there is actually no relative information about the behavior of the new electrodes proposed on this work.
- Abstract: In this work, it proposed the developing of a new material, a modified electrode with metallic phthalocyanines stacking columns, MxPc (Mx = Co, Fe and Ni), assembled by π interactions, which have a behavior as a supramolecular system. These electrodes showed an important electrocatalytic activity against nitrite oxidation, compared to the same complexes monomer multilayers adsorbed on the electrode (M-MxPc). It is proposed two new obtaining methods of these systems, S1-MxPc, where the complexes would form a column and would be coordinated with the surface electrode through a covalent bond of 4-aminopyridine (4-AP), and S2-MxPc, where the own functional groups of glassy carbon (GC) would be the covalent unions able to coordinate the complexes and the columns formation. These covalent unions between the electrode surface and phthalocyanines, would give a directional stacking, and therefore, would modify both its electrocatalytical activity and its electrical features. It was also studied the dependence between the activity and the complex central metal (Co, Fe and Ni), finding a great dependence between them. It was found that the S2-MxPc modified electrodes were more stables and actives. The higher activity was found on S2-CoPc, which also performs a linear response. This last feature it is seen on a calibration curve with a large range of concentrations. It is important to notice that there is actually no relative information about the behavior of the new electrodes proposed on this work.
- ELECTROCHEMICAL AND SPECTROSCOPIC PROPERTIES OF INDOLIZINO[1,2-B]
QUINOLE DERIVATES- Abstract: A series of indolizino[1,2-b] quinole derivates compounds were characterized by various electrochemical and spectroscopic techniques. Electrochemical studies reveal that there are two redox processes controlled by diffusion, the first step corresponds to the formation of a semiquinone radical Q--, while the second step corresponds to the formation of quinone dianion, Q2--. The presence of acceptor groups such as -CN and -COOH shifted reduction potentials, due to a more favorable electronic stabilization. There was no significant effect of the substituents on the absorption spectra of indolizino[1,2-b] quinole derivates. The substituents influenced the fluorescence properties from indolizino[1,2-b] quinole derivates. The emission and excitation spectra obtained of these compounds suggested that the molecule emits from a locally excited state having identical geometry with that of ground state geometry. Finally it was observed that the group with higher acceptor capacity (-CN), has the highest quantum yield, which is indicating that this group always stabilized electronic state with a higher conjugation.
- Abstract: A series of indolizino[1,2-b] quinole derivates compounds were characterized by various electrochemical and spectroscopic techniques. Electrochemical studies reveal that there are two redox processes controlled by diffusion, the first step corresponds to the formation of a semiquinone radical Q--, while the second step corresponds to the formation of quinone dianion, Q2--. The presence of acceptor groups such as -CN and -COOH shifted reduction potentials, due to a more favorable electronic stabilization. There was no significant effect of the substituents on the absorption spectra of indolizino[1,2-b] quinole derivates. The substituents influenced the fluorescence properties from indolizino[1,2-b] quinole derivates. The emission and excitation spectra obtained of these compounds suggested that the molecule emits from a locally excited state having identical geometry with that of ground state geometry. Finally it was observed that the group with higher acceptor capacity (-CN), has the highest quantum yield, which is indicating that this group always stabilized electronic state with a higher conjugation.
- EFFECT OF MO CONTENT IN MO(X)/γ-AL2O3
CATALYSTS OVER THE CONVERSION OF 2-METHOXYPHENOL AS LIGNIN-DERIVATES
COMPONENTS- Abstract: The effect of Mo loading (10, 12, 15, 17 and 20 wt.%) on the physicochemical properties and reactivities of Mo(x)/γ-Al2O3 sulfide catalysts for the conversion of 2-methoxyphenol at 573 K and 5 MPa of hydrogen pressure were studied. The catalysts were characterized by specific area (S BET), electrophoretic migration (EM), X-ray photoelectron spectroscopy (XPS) and surface acidity techniques. The highest conversion observed for the catalyst with a Mo loading of 15 wt.% was attributed to an increase in the number of active sites due to highly dispersed Mo species. At higher Mo loadings, the formation of Mo aggregates led to lower guaiacol conversion. The differences in the phenol/catechol ratio were explained by the acid strengths of the sulfided catalysts.
- Abstract: The effect of Mo loading (10, 12, 15, 17 and 20 wt.%) on the physicochemical properties and reactivities of Mo(x)/γ-Al2O3 sulfide catalysts for the conversion of 2-methoxyphenol at 573 K and 5 MPa of hydrogen pressure were studied. The catalysts were characterized by specific area (S BET), electrophoretic migration (EM), X-ray photoelectron spectroscopy (XPS) and surface acidity techniques. The highest conversion observed for the catalyst with a Mo loading of 15 wt.% was attributed to an increase in the number of active sites due to highly dispersed Mo species. At higher Mo loadings, the formation of Mo aggregates led to lower guaiacol conversion. The differences in the phenol/catechol ratio were explained by the acid strengths of the sulfided catalysts.
- MAGNETIC BEHAVIOR OF LAMELLAR MnPS3 AND CdPS3
COMPOSITES WITH A PARAMAGNETIC MANGANESE(III) MACROCYCLIC GUEST- Abstract: Six new composites derived from the intercalation of the MPS3 phases (M = MnII, CdIII) with the macrocyclic manganese(III) complex [MnL(H2O)2].NO3(H2O) (LH2 = Schiff base macrocyclic ligand derived from the condensation of 2-hydroxy-5-methy1-1,3-benzene-dicarbaldehyde and 1,2-diamine-benzene) were obtained by two different synthetic procedures: a conventional and a microwave assisted method. The composites [MnL]0.25K0.15Mn0.80 PS3(H2O)~1.0 (1), and [MnL]0.25K0.15Cd 0. 80PS3(H2O)~0.5 (2) were obtained by the conventional method, after stirring a suspension of the corresponding potassium precursor and the macrocyclic complex for two weeks, while [MnL]0.35K0.15Mn0.80 PS3(H2O)~1.0 (3) and [MnL]0.25K0.15Cd 0. 80PS3(H2O)~0.5 (4) after stirring for four weeks at room temperature. Using a microwave assisted reaction permitted to obtain in a shorter period of time as compared with the conventional method, composites [MnL]0.20K0.15Mn0.80 PS3(H2O)~1.0 (5) and [MnL]0.15K0.15Cd 0. 80PS3(H2O)~0.5 (6). All the M = MnII, MnIII composites show a bulk antiferromagnetic behavior. However, the spontaneous magnetization present at low temperature in the potassium precursor K0.40Mn0.80 PS3(H2O)~1.0 is observable in composite [MnL]0.20K0.15Mn0.80 PS3(H2O)~1.0 (5), while it is completely absent in composites [MnL]0.25K0.15Mn0.80 PS3(H2O)~1.0 (1) and [MnL]0.35K0.15Mn0.80 PS3(H2O)~1.0 (3).
- Abstract: Six new composites derived from the intercalation of the MPS3 phases (M = MnII, CdIII) with the macrocyclic manganese(III) complex [MnL(H2O)2].NO3(H2O) (LH2 = Schiff base macrocyclic ligand derived from the condensation of 2-hydroxy-5-methy1-1,3-benzene-dicarbaldehyde and 1,2-diamine-benzene) were obtained by two different synthetic procedures: a conventional and a microwave assisted method. The composites [MnL]0.25K0.15Mn0.80 PS3(H2O)~1.0 (1), and [MnL]0.25K0.15Cd 0. 80PS3(H2O)~0.5 (2) were obtained by the conventional method, after stirring a suspension of the corresponding potassium precursor and the macrocyclic complex for two weeks, while [MnL]0.35K0.15Mn0.80 PS3(H2O)~1.0 (3) and [MnL]0.25K0.15Cd 0. 80PS3(H2O)~0.5 (4) after stirring for four weeks at room temperature. Using a microwave assisted reaction permitted to obtain in a shorter period of time as compared with the conventional method, composites [MnL]0.20K0.15Mn0.80 PS3(H2O)~1.0 (5) and [MnL]0.15K0.15Cd 0. 80PS3(H2O)~0.5 (6). All the M = MnII, MnIII composites show a bulk antiferromagnetic behavior. However, the spontaneous magnetization present at low temperature in the potassium precursor K0.40Mn0.80 PS3(H2O)~1.0 is observable in composite [MnL]0.20K0.15Mn0.80 PS3(H2O)~1.0 (5), while it is completely absent in composites [MnL]0.25K0.15Mn0.80 PS3(H2O)~1.0 (1) and [MnL]0.35K0.15Mn0.80 PS3(H2O)~1.0 (3).
- BEHAVIOR OF A POLYMERIC LIQUID MEMBRANE ION- SELECTIVE ELECTRODE FOR
CHLORIDE ION- Abstract: Chloride selective polymeric liquid membrane electrode has been developed by using Bis-(2-ethylhexyl) Sebacate (DOS) as plasticizer and 2-[5-(4-nitrophenyl) furyl]-4,5-diphenyl imidazole (FFDFIN) as ionophore. Some parameters of evaluation of the electrode are presented in this work. The constructed electrode showed fast potentiometric response to chloride ion in the concentration range from 10-6 to 10-2 mol.dm-3 with Nernstian slope of -63.43 ± 0.85 mV/decade, response time of 25 seconds and life time of 15 days.
- Abstract: Chloride selective polymeric liquid membrane electrode has been developed by using Bis-(2-ethylhexyl) Sebacate (DOS) as plasticizer and 2-[5-(4-nitrophenyl) furyl]-4,5-diphenyl imidazole (FFDFIN) as ionophore. Some parameters of evaluation of the electrode are presented in this work. The constructed electrode showed fast potentiometric response to chloride ion in the concentration range from 10-6 to 10-2 mol.dm-3 with Nernstian slope of -63.43 ± 0.85 mV/decade, response time of 25 seconds and life time of 15 days.
- CHEMICAL SYNTHESIS AND CHARACTERIZATION OF POLYANILINE DERIVATIVES:
SUBSTITUENT EFFECT ON SOLUBILITY AND CONDUCTIVITY- Abstract: Polyanilines have different macroscopic properties according to the substituent incorporated into their monomers. Being conducting polymers, one of these properties is conductivity, which may increase or decrease depending on the substituent and its position in the chain. This work is focused on the modification of aniline monomers, which characteristics will vary, enabling thus the effect of the substituent on the respective polymer to be studied. For this purpose monomers substituted with methoxy and bromine, which are commercially available, and thiophenes were prepared using Suzuki and Ullman reactions. It was found that all polymers have conductivities of the order of 10-6 S.cm-1 or less. This demonstrated the performed substitutions had a negative effect on conductivity (although would facilitate their use in solar cells) as compared to aniline (PANI). These modifications also improve the solubility of the respective polymers, as most were more soluble than PANI.
- Abstract: Polyanilines have different macroscopic properties according to the substituent incorporated into their monomers. Being conducting polymers, one of these properties is conductivity, which may increase or decrease depending on the substituent and its position in the chain. This work is focused on the modification of aniline monomers, which characteristics will vary, enabling thus the effect of the substituent on the respective polymer to be studied. For this purpose monomers substituted with methoxy and bromine, which are commercially available, and thiophenes were prepared using Suzuki and Ullman reactions. It was found that all polymers have conductivities of the order of 10-6 S.cm-1 or less. This demonstrated the performed substitutions had a negative effect on conductivity (although would facilitate their use in solar cells) as compared to aniline (PANI). These modifications also improve the solubility of the respective polymers, as most were more soluble than PANI.
- Editorial
- Guest Editor
- Obituary Dra. Elsa Beatriz Abuin Saccomano
- Obituary Dr. Julio Guillermo Contreras Koder
- STRUCTURE AND THERMAL PROPERTIES OF MALEATED LIGNIN-RECYCLED
POLYSTYRENE COMPOSITES- Abstract: In this work, the changes caused by a chemical modification of the properties and chemical structures of lignin are studied. Lignin from a mixture of Eucalyptus globulus and Eucalyptus nitens obtained through the kraft pulping process was used. The lignin was isolated by acid precipitation and modified by a reaction with maleic anhydride. Maleated lignin (ML) was incorporated to recycled polystyrene (rPS) at 2, 5, and 10 wt-% by a melt-blending process. Fourier transformed infrared spectroscopy (FT-IR) was used to determine the ML structure, and the morphology of rPS/ ML composites was studied by scanning electron microscopy (SEM). Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to study the glass-transition temperature (Tg) and the thermal stability of rPS and rPS/ ML composites and were compared with virgin PS. The Tg values of rPS and their composites were higher than those of the virgin PS. TGA revealed that the thermal stability of rPS with 2 and 5% of ML was slightly greater than that of the virgin PS. These results suggest that postconsumer PS can be used to obtain composite materials with good thermal properties.
- Abstract: In this work, the changes caused by a chemical modification of the properties and chemical structures of lignin are studied. Lignin from a mixture of Eucalyptus globulus and Eucalyptus nitens obtained through the kraft pulping process was used. The lignin was isolated by acid precipitation and modified by a reaction with maleic anhydride. Maleated lignin (ML) was incorporated to recycled polystyrene (rPS) at 2, 5, and 10 wt-% by a melt-blending process. Fourier transformed infrared spectroscopy (FT-IR) was used to determine the ML structure, and the morphology of rPS/ ML composites was studied by scanning electron microscopy (SEM). Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to study the glass-transition temperature (Tg) and the thermal stability of rPS and rPS/ ML composites and were compared with virgin PS. The Tg values of rPS and their composites were higher than those of the virgin PS. TGA revealed that the thermal stability of rPS with 2 and 5% of ML was slightly greater than that of the virgin PS. These results suggest that postconsumer PS can be used to obtain composite materials with good thermal properties.
- EFFECT OF COOPER ON THE CATALYTIC ACTIVITY FOR ACETYLACETATE COMBUSTION
OF Ca1-x CuxZrO3 AND
Sr1-xCuxZrO3 PEROVSKITE-TYPE OXIDES- Abstract: The effect of lower Cu (≤ 30%) substitution on alkaline earth zirconate (A1-xCu xZrO3; A=Ca; Sr) perovskites prepared via a citrate route and calcined at 700°C has been investigated as catalysts for total acetyl acetate combustion. The thermal behaviour indicates a beneficial effect of Cu in order to decrease the decomposition temperature of Ca and Sr zirconates. The characterization of the solids by atomic absorption spectroscopy (AAS), BET area, SEM, XRD, O2-DTP and TPR indicates for the Sr series presence crystalline CuO phase in the copper strontium zirconates, meanwhile almost highly dispersed CuO is detected in the Ca series. Two effects explain the increases in the total acetylacetate combustion of Ca and Sr zirconates upon copper content. For one hand, in the Ca series, highly dispersed CuO phase, easier to be reduced increases the catalytic activity, meanwhile for the Sr series, a large extent of oxygen vacancies explains the catalytic effect.
- Abstract: The effect of lower Cu (≤ 30%) substitution on alkaline earth zirconate (A1-xCu xZrO3; A=Ca; Sr) perovskites prepared via a citrate route and calcined at 700°C has been investigated as catalysts for total acetyl acetate combustion. The thermal behaviour indicates a beneficial effect of Cu in order to decrease the decomposition temperature of Ca and Sr zirconates. The characterization of the solids by atomic absorption spectroscopy (AAS), BET area, SEM, XRD, O2-DTP and TPR indicates for the Sr series presence crystalline CuO phase in the copper strontium zirconates, meanwhile almost highly dispersed CuO is detected in the Ca series. Two effects explain the increases in the total acetylacetate combustion of Ca and Sr zirconates upon copper content. For one hand, in the Ca series, highly dispersed CuO phase, easier to be reduced increases the catalytic activity, meanwhile for the Sr series, a large extent of oxygen vacancies explains the catalytic effect.
- ARISTOLOCHIC ACIDS IN THE ROOTS OF ARISTOLOCHIA CHILENSIS, A
DANGEROUS CHILEAN MEDICINAL PLANT- Abstract: The chemical composition of aristolochic acids (AAs) from the roots of A. chilensis was determined by high-performance liquid chromatography with diode-array detection (HPLC-DAD), a technique widely used for the detection and quantification of AAs in herbal medicines. The roots contained a mixture of AA-I (1), AA-II (2), AA-III (3), AA-IV (4), AA-Ia (5), AA-IIIa (6), AA-IVa (7), and aristoloside (8), indicating that A. chilensis is not suitable for use as a medicinal plant due to the harmful effects of the aristolochic acids.
- Abstract: The chemical composition of aristolochic acids (AAs) from the roots of A. chilensis was determined by high-performance liquid chromatography with diode-array detection (HPLC-DAD), a technique widely used for the detection and quantification of AAs in herbal medicines. The roots contained a mixture of AA-I (1), AA-II (2), AA-III (3), AA-IV (4), AA-Ia (5), AA-IIIa (6), AA-IVa (7), and aristoloside (8), indicating that A. chilensis is not suitable for use as a medicinal plant due to the harmful effects of the aristolochic acids.
- CHEMICAL FRACTIONS OF Al IN VOLCANIC SOIL AMENDED WITH CELLULOSE
WASTE- Abstract: The cellulose industry generates a great volume of organic and inorganic waste, one of these wastes are called dreg (D) and grits (G). These residues have a high content of calcium carbonate, positioning them as potential bleachers in acid soils. Due to the important content of Al in the residues, a sequential extraction was done to establish the metal chemical fractions such as exchangeable, adsorbed, organic carbonated, and the ones associated to sulfurs, in incubated samples (2, 4, 8, and 32 days at 60°C) of an Andisol amended soil with Grits, Dregs + Grits and lime in 1, 2 and 3 ton/ha doses. The results revealed that there was a significant increase in the amount of Al in all fractions, in comparison to the control soil. On the other hand the incorporation of these residues through a Dregs (70%) + Grits (30%) mixture provoked a pH increase, always higher than the commercial lime. Finally, the Al present on amended soils was mostly distributed in the residual and carbonated chemical fractions, which would constitute less labile chemical forms to the soil-solution.
- Abstract: The cellulose industry generates a great volume of organic and inorganic waste, one of these wastes are called dreg (D) and grits (G). These residues have a high content of calcium carbonate, positioning them as potential bleachers in acid soils. Due to the important content of Al in the residues, a sequential extraction was done to establish the metal chemical fractions such as exchangeable, adsorbed, organic carbonated, and the ones associated to sulfurs, in incubated samples (2, 4, 8, and 32 days at 60°C) of an Andisol amended soil with Grits, Dregs + Grits and lime in 1, 2 and 3 ton/ha doses. The results revealed that there was a significant increase in the amount of Al in all fractions, in comparison to the control soil. On the other hand the incorporation of these residues through a Dregs (70%) + Grits (30%) mixture provoked a pH increase, always higher than the commercial lime. Finally, the Al present on amended soils was mostly distributed in the residual and carbonated chemical fractions, which would constitute less labile chemical forms to the soil-solution.
- FENTON REACTION DRIVEN BY IRON LIGANDS
- Abstract: One of the most important sources of reactive oxygen species (ROS) in biological systems is the Fenton reaction. In this, the Fe2+ or Fe3+ reacts with H2O2 to produce ROS as the hydroxyl radical (∙OH), superoxide radical (O2-) and singlet oxygen (¹O2). The main ROS, responsible for the high oxidizing power of the Fenton reaction, is not clear. Some authors claim that the principal reactive species is ∙OH, while others propose a ferryl specie (Fe4+ or [FeO]2+)(1,2). Recently, have been proposed that the kind of reaction species produced depends mainly of pH and the iron composition of the coordination sphere. This is highlighted for Fe³+, because in mono and (some) bis-complexes Fe3+ is reduced to Fe2+ and there are some positions occupied by water or hydroxide ligands, readily to be exchanged by H2O2. On the other hand, in tris-complexes there are not any positions occupied by water or hydroxide, avoiding the formation of peroxo-complexes, necessary for Fenton or Fenton like reaction. The 1,2-dihydroxybenzenes (DHBs) have been described as modulators of Fenton reaction. The DHBs driven Fenton reaction have been used for environmental applications as an advanced oxidation process. Furthermore, these systems participate in different biological process, as the wood biodegradation by fungi and oxidative stress in neurodegenerative diseases. In this review, the effect of 1,2-dihydroxybenzenes on the activated species production by the Fenton and Fenton like reaction will be discussed and its participation in different systems.
- Abstract: One of the most important sources of reactive oxygen species (ROS) in biological systems is the Fenton reaction. In this, the Fe2+ or Fe3+ reacts with H2O2 to produce ROS as the hydroxyl radical (∙OH), superoxide radical (O2-) and singlet oxygen (¹O2). The main ROS, responsible for the high oxidizing power of the Fenton reaction, is not clear. Some authors claim that the principal reactive species is ∙OH, while others propose a ferryl specie (Fe4+ or [FeO]2+)(1,2). Recently, have been proposed that the kind of reaction species produced depends mainly of pH and the iron composition of the coordination sphere. This is highlighted for Fe³+, because in mono and (some) bis-complexes Fe3+ is reduced to Fe2+ and there are some positions occupied by water or hydroxide ligands, readily to be exchanged by H2O2. On the other hand, in tris-complexes there are not any positions occupied by water or hydroxide, avoiding the formation of peroxo-complexes, necessary for Fenton or Fenton like reaction. The 1,2-dihydroxybenzenes (DHBs) have been described as modulators of Fenton reaction. The DHBs driven Fenton reaction have been used for environmental applications as an advanced oxidation process. Furthermore, these systems participate in different biological process, as the wood biodegradation by fungi and oxidative stress in neurodegenerative diseases. In this review, the effect of 1,2-dihydroxybenzenes on the activated species production by the Fenton and Fenton like reaction will be discussed and its participation in different systems.
- USE OF ELECTRODEPOSITION OF NICKEL IN THE MANUFACTURE OF LEU ANNULAR
TARGETS- Abstract: This work presents the results of a thin electroplated layer of nickel on the surface of the uranium to achieve deposits 15 to 25 μm thick. Ultrasound tests and electron microscopy showed good adhesion and homogeneity of the Ni deposit, which has high hardness and relatively small grain size, with an orientation in the direction of current flow.
- Abstract: This work presents the results of a thin electroplated layer of nickel on the surface of the uranium to achieve deposits 15 to 25 μm thick. Ultrasound tests and electron microscopy showed good adhesion and homogeneity of the Ni deposit, which has high hardness and relatively small grain size, with an orientation in the direction of current flow.
- EFFECT OF THE INCORPORATION INTO UNILAMINAR VESICLE ON THE
PHOTODEGRADATION OF INDOLES SENSITIZED BY FLAVINS- Abstract: In this work we study the incorporation into dipalmitoylphosphatidylcholine (DPPC) small unilamellar vesicle (SUV), of three indols: Trp, indol-3 acetamide and N-acetyl tryptophan ethyl ester (NATE), and of three flavins: riboflavin (RF), lumiflavin (LF), and 2'3'4'5' riboflavin tetrapropionate (TPRF). The incorporation into the vesicle was determined by selective fluorescence quenching for the indols, and by equilibrium dialysis for the flavins. The more hydrophobic compound, the greater incorporation into the vesicle; therefore, TPRF and indol-3-acetamide and NATE are the flavins and indols, with the higher incorporation. Consequently, the higher efficiency for the indol photodegradation and the photoproducts generation was obtained when the hydrophobic compounds were irradiated with monochromatic light in the presence of the vesicle.
- Abstract: In this work we study the incorporation into dipalmitoylphosphatidylcholine (DPPC) small unilamellar vesicle (SUV), of three indols: Trp, indol-3 acetamide and N-acetyl tryptophan ethyl ester (NATE), and of three flavins: riboflavin (RF), lumiflavin (LF), and 2'3'4'5' riboflavin tetrapropionate (TPRF). The incorporation into the vesicle was determined by selective fluorescence quenching for the indols, and by equilibrium dialysis for the flavins. The more hydrophobic compound, the greater incorporation into the vesicle; therefore, TPRF and indol-3-acetamide and NATE are the flavins and indols, with the higher incorporation. Consequently, the higher efficiency for the indol photodegradation and the photoproducts generation was obtained when the hydrophobic compounds were irradiated with monochromatic light in the presence of the vesicle.
- THEORETICAL CALCULATIONS OF AN OSMIUM MOLECULAR SWITCH
- Abstract: We have investigated the molecular, electronic and optical properties of the [Os(tpy-py)2]2+ complex (tpy-py = 4'-(4-pyridyl)-2,2':6',2"-terpyridine) and its protonated derivative [Os(tpy-pyH)2]4+ through Density Functional Relativistic calculations including Scalar and Spin Orbit corrections. The molecular geometry of the parent complex is not strongly modified by the protonation at the basic nitrogen atoms of the pyridine moieties of the terpyridine ligands in the complex. On the other hand, the optical properties of these complexes can be controlled by a change in the chemical acid-base environment, converting them into suitable materials to act as molecular switches or pH sensor devices.
- Abstract: We have investigated the molecular, electronic and optical properties of the [Os(tpy-py)2]2+ complex (tpy-py = 4'-(4-pyridyl)-2,2':6',2"-terpyridine) and its protonated derivative [Os(tpy-pyH)2]4+ through Density Functional Relativistic calculations including Scalar and Spin Orbit corrections. The molecular geometry of the parent complex is not strongly modified by the protonation at the basic nitrogen atoms of the pyridine moieties of the terpyridine ligands in the complex. On the other hand, the optical properties of these complexes can be controlled by a change in the chemical acid-base environment, converting them into suitable materials to act as molecular switches or pH sensor devices.
- SILICON-CONTAINING POLY(IMIDE-AMIDES) DERIVED FROM ALIPHATIC DIACIDS
WITH NAPHATHALIMIDYL SIDE GROUPS: SYNTHESIS AND THERMAL STUDIES- Abstract: Poly(imide-amides) (PIAs) were obtained from aspartic and glutamic acids containing both a 1,8-naphthlimidyl side group and the diamine bis(4-aminophenyl) diphenylsilane, according to the Yamazaki method and characterized by elemental analysis, optical activity, IR and ¹H, 13C and 29Si NMR spectroscopy. PIAs were soluble at room temperature in common aprotic polar solvents (DMSO, DMAc, DMF, NMP) and in other of lower polarity but low boiling point (CHCl3, THF) after heating. The inherent viscosity values were low, which was indicative of low molecular weight species of oligomeric nature. The Tg values were relatively high considering the aliphatic nature of the diacids and the bulky side groups, which cause an impediment to the rotation. It is possible to suppose a weak hydrogen bond interaction between the NH groups of the amide and the carbonyl groups of the imide. When the Tg of both PIAs was compared, it was possible to see a decrease when the main chain was increased in one -CH2- group. PIAs were not thermostable but the TDT values were relatively high considering the aliphatic nature of the diacid moiety, being PIA-As more thermostable than PIA-Gl with a longer aliphatic chain. Both PIAs showed a similar optical behavior and high transparence at 450 nm, which can be explained by the aliphatic character of the diacid moiety.
- Abstract: Poly(imide-amides) (PIAs) were obtained from aspartic and glutamic acids containing both a 1,8-naphthlimidyl side group and the diamine bis(4-aminophenyl) diphenylsilane, according to the Yamazaki method and characterized by elemental analysis, optical activity, IR and ¹H, 13C and 29Si NMR spectroscopy. PIAs were soluble at room temperature in common aprotic polar solvents (DMSO, DMAc, DMF, NMP) and in other of lower polarity but low boiling point (CHCl3, THF) after heating. The inherent viscosity values were low, which was indicative of low molecular weight species of oligomeric nature. The Tg values were relatively high considering the aliphatic nature of the diacids and the bulky side groups, which cause an impediment to the rotation. It is possible to suppose a weak hydrogen bond interaction between the NH groups of the amide and the carbonyl groups of the imide. When the Tg of both PIAs was compared, it was possible to see a decrease when the main chain was increased in one -CH2- group. PIAs were not thermostable but the TDT values were relatively high considering the aliphatic nature of the diacid moiety, being PIA-As more thermostable than PIA-Gl with a longer aliphatic chain. Both PIAs showed a similar optical behavior and high transparence at 450 nm, which can be explained by the aliphatic character of the diacid moiety.
- SIMULTANEOUS ELECTROCHEMICAL DETECTION OF DOPAMINE, ASCORBIC ACID AND
URIC ACID USING COPPER-PHTHALOCYANINE FUNCTIONALIZED MWCNTS- Abstract: Multiwalled carbon nanotububes functionalized with amino groups (MWCNT-NH2) and further modified with copper-phthalocyaninetetrasulphonate (4ß(SO3) CuPc) were used for preparing a hybrid electrode [MWCNT-NH2/4ß(SO3)CuPc/GC] using glassy carbon (GC) as a support. This hybrid electrode was tested for the detection of dopamine (DA) in the presence of ascorbic acid (AA) and uric acid (UA) in a PBS buffer solution at pH 6.8. The presence of the macrocyclic increased the resolution of the oxidation signals of AA, DA and UA into three very well distinct oxidation peaks. This effect was enhanced when the complex is adsorbed on multiwalled carbon nanotubes. In addition, the hybrid films provide a simple method for selective detection of DA, AA and UA in biological samples. The calibration curves for DA were obtained over the range of 1x10-6-1x10-3M, obtaining a good selectivity and sensitivity.
- Abstract: Multiwalled carbon nanotububes functionalized with amino groups (MWCNT-NH2) and further modified with copper-phthalocyaninetetrasulphonate (4ß(SO3) CuPc) were used for preparing a hybrid electrode [MWCNT-NH2/4ß(SO3)CuPc/GC] using glassy carbon (GC) as a support. This hybrid electrode was tested for the detection of dopamine (DA) in the presence of ascorbic acid (AA) and uric acid (UA) in a PBS buffer solution at pH 6.8. The presence of the macrocyclic increased the resolution of the oxidation signals of AA, DA and UA into three very well distinct oxidation peaks. This effect was enhanced when the complex is adsorbed on multiwalled carbon nanotubes. In addition, the hybrid films provide a simple method for selective detection of DA, AA and UA in biological samples. The calibration curves for DA were obtained over the range of 1x10-6-1x10-3M, obtaining a good selectivity and sensitivity.
- MAGNETIC AND STRUCTURAL STUDY OF UNSOLVATED [Cu(acac)2],
(acac= acetylacetonate)- Abstract: This work is the first of a series of studies on systems with a common basic structure, Cu-b-diketonate, whose ability to bind to other ligands is regulated by the presence of electron-withdrawing groups affecting the electronic density on the copper ion. In this paper the [Cu (acac)2] system is studied. Its structure reveals discrete units linked through H bridges (c.a. 2.7Å). The crystallographic system and space group, are monoclinic and P21/n respectively; the cell parameters are a= 10.34Å, b= 4.71Å, c= 11.38Å, beta= 91.78°. The magnetic behaviour corresponds to a simple paramagnetism with µ= 1.8 [BM]; however, a weak antiferromagnetic interaction is observed at lower temperatures.
- Abstract: This work is the first of a series of studies on systems with a common basic structure, Cu-b-diketonate, whose ability to bind to other ligands is regulated by the presence of electron-withdrawing groups affecting the electronic density on the copper ion. In this paper the [Cu (acac)2] system is studied. Its structure reveals discrete units linked through H bridges (c.a. 2.7Å). The crystallographic system and space group, are monoclinic and P21/n respectively; the cell parameters are a= 10.34Å, b= 4.71Å, c= 11.38Å, beta= 91.78°. The magnetic behaviour corresponds to a simple paramagnetism with µ= 1.8 [BM]; however, a weak antiferromagnetic interaction is observed at lower temperatures.
- CHIRAL Rh/SiO2 CATALYSTS FOR ENANTIOSELECTIVE HYDROGENATION
REACTIONS: THE ROLE OF (S,S)-DIPAMP AS CHIRAL MODIFIER AND
STABILIZER ON METALLIC NANOPARTICLES SYNTHESIS- Abstract: Rhodium nanoparticles were successfully stabilized by the (S,S)-1,2-ethanediylbis[(2-ethoxyphenyl)phenylphosphine] ((S,S)-DIPAMP) deposited on SiO2 prepared by a facile reduction and impregnation method. The chiral catalysts obtained were efficient for the enantioselective hydrogenation reactions of prochiral compounds. The catalysts synthesized from [Rh(µ-OMe)(COD)]2 in the presence of different amounts of a ligand used as chiral stabilizer, showed good metal dispersion. As shown by TEM, the metal particle size ranged between 1 and 2 nm using stabilizer and 9.1 nm was achieved without chiral ligand. Other techniques were used to characterize the chiral catalysts such as X-ray diffraction (XRD), electron diffraction, thermogravimetric analysis (TGA) and N2 adsorption-desorption isotherms. (S,S)-DIPAMP was used as the stabilizer of metal particles to prevent growing and agglomeration, and it also acts as chiral modifier inducing enantioselectivity in the asymmetric hydrogenation of 3,4-hexanodione (HD), ethyl pyruvate (EP), ketopantolactone (KP), and acetophenone (AP). Under specific conditions such as 25 °C, 40 bar of H2 and substrate/Rh=100, 1%Rh-(S,S)-DIPAMP/SiO2 chiral catalysts showed excellent catalytic performance with conversion and enantiomeric excess (ee) levels up to 99% and 54% respectively.
- Abstract: Rhodium nanoparticles were successfully stabilized by the (S,S)-1,2-ethanediylbis[(2-ethoxyphenyl)phenylphosphine] ((S,S)-DIPAMP) deposited on SiO2 prepared by a facile reduction and impregnation method. The chiral catalysts obtained were efficient for the enantioselective hydrogenation reactions of prochiral compounds. The catalysts synthesized from [Rh(µ-OMe)(COD)]2 in the presence of different amounts of a ligand used as chiral stabilizer, showed good metal dispersion. As shown by TEM, the metal particle size ranged between 1 and 2 nm using stabilizer and 9.1 nm was achieved without chiral ligand. Other techniques were used to characterize the chiral catalysts such as X-ray diffraction (XRD), electron diffraction, thermogravimetric analysis (TGA) and N2 adsorption-desorption isotherms. (S,S)-DIPAMP was used as the stabilizer of metal particles to prevent growing and agglomeration, and it also acts as chiral modifier inducing enantioselectivity in the asymmetric hydrogenation of 3,4-hexanodione (HD), ethyl pyruvate (EP), ketopantolactone (KP), and acetophenone (AP). Under specific conditions such as 25 °C, 40 bar of H2 and substrate/Rh=100, 1%Rh-(S,S)-DIPAMP/SiO2 chiral catalysts showed excellent catalytic performance with conversion and enantiomeric excess (ee) levels up to 99% and 54% respectively.
- ELECTRICAL BEHAVIOR OF A
- Abstract: The solid solutions Cu2Fe1-X CoX SnS4, with stannite-type structure are stable up to about 800°C. The electrical properties of the Cu2Fe0.4Co0.6SnS4 ceramic were investigated by complex impedance. The real and imaginary dielectric permittivity dependence with the temperature were measured between 10kHz and 1 MHz in temperature range 77-280K, finding that the ceramic present the characteristics behavior of a dielectric relaxation between 100 and 250 K, with a maximum at approximately 200 K. The electric permittivity found has orders of magnitude between 10² and 10³. A space charge polarization mechanism is suggested to explain the observed electric relaxation.
- Abstract: The solid solutions Cu2Fe1-X CoX SnS4, with stannite-type structure are stable up to about 800°C. The electrical properties of the Cu2Fe0.4Co0.6SnS4 ceramic were investigated by complex impedance. The real and imaginary dielectric permittivity dependence with the temperature were measured between 10kHz and 1 MHz in temperature range 77-280K, finding that the ceramic present the characteristics behavior of a dielectric relaxation between 100 and 250 K, with a maximum at approximately 200 K. The electric permittivity found has orders of magnitude between 10² and 10³. A space charge polarization mechanism is suggested to explain the observed electric relaxation.
- AMINOCARBONYLATION REACTION USING PALLADIUM COMPLEXES CONTAINING
PHOSPHORUS-NITROGEN LIGANDS AS CATALYSTS- Abstract: The catalytic activities of palladium complexes containing phosphorus-nitrogen ligands is reported. The catalysts studied showed high activities in the aminocarbonylation of aryl iodides. The palladium complexes reported activities between 100% and 58% in the aminocarbonylation reaction. The reactions are very selective for the double carbonylative amination of aryl halides. The major product is N,N-diethyl-α-oxo benzeneacetamide (96/4). The reaction was made under mild conditions of temperature and carbon monoxide pressure.
- Abstract: The catalytic activities of palladium complexes containing phosphorus-nitrogen ligands is reported. The catalysts studied showed high activities in the aminocarbonylation of aryl iodides. The palladium complexes reported activities between 100% and 58% in the aminocarbonylation reaction. The reactions are very selective for the double carbonylative amination of aryl halides. The major product is N,N-diethyl-α-oxo benzeneacetamide (96/4). The reaction was made under mild conditions of temperature and carbon monoxide pressure.
- FROM LIMIT EQUATIONS TO GENERAL EQUATIONS: AN ALTERNATIVE
STRATEGY OF DEVELOPING EQUATIONS IN CHEMISTRY AND ITS DIFFERENT STAGES OF
LEARNING- Abstract: The scope of limit equations and their role as starting points to deduce general equations are discussed. Consequently, a general strategy is proposed to go systematically from limit equations to general ones. On the basis of this strategy, the most common general equations in chemistry, like the equation of state for gases, the chemical potential of gases and the equation for the chemical equilibrium constant are illustrated. The method should help to emphasize students' need to think about the validity range of the equations they are learning and to illustrate the way science infers general equations from specific ones. Furthermore, it should allow explaining to students the several steps (introductory, medium and upper level) of their chemistry learning.
- Abstract: The scope of limit equations and their role as starting points to deduce general equations are discussed. Consequently, a general strategy is proposed to go systematically from limit equations to general ones. On the basis of this strategy, the most common general equations in chemistry, like the equation of state for gases, the chemical potential of gases and the equation for the chemical equilibrium constant are illustrated. The method should help to emphasize students' need to think about the validity range of the equations they are learning and to illustrate the way science infers general equations from specific ones. Furthermore, it should allow explaining to students the several steps (introductory, medium and upper level) of their chemistry learning.
- EVALUATION OF THE TOTAL AMOUNT OF PHENOL GROUPS IN COMPLEX MIXTURES BY
FOLIN'S AND ORAC-FLUORESCEIN METHODOLOGIES- Abstract: The total number of phenolic HO groups in a mixture and their average reactivity are fundamental parameters in the evaluation of the capacity of the sample to remove potentially damaging free radicals. The total number of phenolic groups is generally determined by Folin's method and several competitive experiments have been proposed to estimate the reactivity of the sample. Among those stand the Oxygen Radical Absorbance Capacity (ORAC) methodologies. However, when fluorescein is employed as target molecule (ORAC-FL methodology) the index is more related to the number of phenolic groups than to their average reactivity. In the present work it is shown that both indexes correlate with the number of phenolic groups in pure compounds and with the total number of reactive OH groups in complex mixtures (beverages, infusions, fruits and vegetables). This leads to a fair correlation between Folin's and ORAC-FL indexes in these samples.
- Abstract: The total number of phenolic HO groups in a mixture and their average reactivity are fundamental parameters in the evaluation of the capacity of the sample to remove potentially damaging free radicals. The total number of phenolic groups is generally determined by Folin's method and several competitive experiments have been proposed to estimate the reactivity of the sample. Among those stand the Oxygen Radical Absorbance Capacity (ORAC) methodologies. However, when fluorescein is employed as target molecule (ORAC-FL methodology) the index is more related to the number of phenolic groups than to their average reactivity. In the present work it is shown that both indexes correlate with the number of phenolic groups in pure compounds and with the total number of reactive OH groups in complex mixtures (beverages, infusions, fruits and vegetables). This leads to a fair correlation between Folin's and ORAC-FL indexes in these samples.
- QUANTUM CHEMICAL STUDY OF THE RELATIONSHIPS BETWEEN ELECTRONIC
STRUCTURE AND PHARMACOKINETIC PROFILE, INHIBITORY STRENGTH TOWARD
HEPATITIS C VIRUS NS5B POLYMERASE AND HCV REPLICONS OF INDOLE-BASED
COMPOUNDS- Abstract: This paper uses newly developed and extended quantum chemical methods in an attempt to advance the knowledge of the relationship between the variation of several local atomic descriptors of the electronic structure and the variation of the inhibitory capacity of a group of reversible and irreversible inhibitors of hepatitis C virus NS5B polymerase. Good structure-activity relationships were obtained for both kinds of compounds. Some processes are charge-, orbital- and/or steric-controlled. The action mechanisms seem to be different for reversible and irreversible inhibitors. Also, good QSAR equations were obtained for the activities of these compounds in a cellular replicon assay and for pharmacokinetic profiles. The local atomic hardness seems to give a good account of the interaction of the drugs with apolar sites of the partner (enzyme, receptor, etc.). This is the first time that a purely quantum-chemical index is able to deal directly with this kind of interaction.
- Abstract: This paper uses newly developed and extended quantum chemical methods in an attempt to advance the knowledge of the relationship between the variation of several local atomic descriptors of the electronic structure and the variation of the inhibitory capacity of a group of reversible and irreversible inhibitors of hepatitis C virus NS5B polymerase. Good structure-activity relationships were obtained for both kinds of compounds. Some processes are charge-, orbital- and/or steric-controlled. The action mechanisms seem to be different for reversible and irreversible inhibitors. Also, good QSAR equations were obtained for the activities of these compounds in a cellular replicon assay and for pharmacokinetic profiles. The local atomic hardness seems to give a good account of the interaction of the drugs with apolar sites of the partner (enzyme, receptor, etc.). This is the first time that a purely quantum-chemical index is able to deal directly with this kind of interaction.
- THERMODYNAMIC STUDY AND ELECTROCHEMICAL INVESTIGATION OF CALCEIN AS
CORROSION INHIBITOR FOR MILD STEEL IN HYDROCHLORIC ACID SOLUTION- Abstract: The corrosion behaviour of mild steel in 1.0 M HCl solution containing different concentrations of Calcein at different temperatures was investigated using the impedance, potentiodynamic polarization and linear polarization techniques. Long term tests were accomplished by hydrogen gas evolution and impedance measurements. The results showed that inhibition efficiency has increased with the inhibitor concentration and temperature increment. The adsorption of the inhibitor on the mild steel surface obeyed the Langmuir isotherm. Activation energy values at concentrations of Calcein were lower than that of uninhibited system. The thermodynamic parameters of adsorption deduced reveal a strong interaction of Calcein on the mild steel surface.
- Abstract: The corrosion behaviour of mild steel in 1.0 M HCl solution containing different concentrations of Calcein at different temperatures was investigated using the impedance, potentiodynamic polarization and linear polarization techniques. Long term tests were accomplished by hydrogen gas evolution and impedance measurements. The results showed that inhibition efficiency has increased with the inhibitor concentration and temperature increment. The adsorption of the inhibitor on the mild steel surface obeyed the Langmuir isotherm. Activation energy values at concentrations of Calcein were lower than that of uninhibited system. The thermodynamic parameters of adsorption deduced reveal a strong interaction of Calcein on the mild steel surface.
- EVALUATION OF TEA FUNCTIONALITY: DETERMINATION OF L-THEANINE
CONTENT IN GREEN AND BLACK TEAS BY LIQUID CHROMATOGRAPHY- Abstract: L-theanine (γ-glutamyl-L-ethylamide) is a free amino acid classified as functional ingredient because it has shown relevant pharmacological effects such as improving the brain ability to concentrate, learn and memorize. L-theanine is found almost exclusively in tea plants, and its final concentration in commercial tea products mainly depends on the type of raw materials and productive process. Thus, tea infusions could only be considered as functional beverage with respect to L-theanine if an adequate number of tea cups posses the necessary content to produce the desire effect. The objective of this work was to evaluate the functionality of teas marketed in Chile regarding its L-theanine content. A high performance liquid chromatographic method with ultraviolet detection (HPLC/UV) was optimized and validated to quantify L-theanine content in tea infusions. Chromatographic separation was carried out using a mixture of water and phosphoric acid (99.9: 0.1% v/v) as mobile phase and C18 Purospher Hibar-STAR (250 mm x 4.6 mm, 5 μm) column. Detection was performed at 210 nm. The L-theanine content in teas marketed in Chile ranged from 4.21 to 24.83 (2.21 to 12.42 mg g-1), with a mean value of 10.06 mg in 200 mL (5.03 mg g-1). Considering the effective dose reported, only one brand (black tea) presented an adequate L-theanine content to produce the desired effect (two serving cups). Therefore, it is possible to conclude that most teas marketed in Chile do not have an adequate L-theanine content to be considered as functional beverage regarding this amino acid.
- Abstract: L-theanine (γ-glutamyl-L-ethylamide) is a free amino acid classified as functional ingredient because it has shown relevant pharmacological effects such as improving the brain ability to concentrate, learn and memorize. L-theanine is found almost exclusively in tea plants, and its final concentration in commercial tea products mainly depends on the type of raw materials and productive process. Thus, tea infusions could only be considered as functional beverage with respect to L-theanine if an adequate number of tea cups posses the necessary content to produce the desire effect. The objective of this work was to evaluate the functionality of teas marketed in Chile regarding its L-theanine content. A high performance liquid chromatographic method with ultraviolet detection (HPLC/UV) was optimized and validated to quantify L-theanine content in tea infusions. Chromatographic separation was carried out using a mixture of water and phosphoric acid (99.9: 0.1% v/v) as mobile phase and C18 Purospher Hibar-STAR (250 mm x 4.6 mm, 5 μm) column. Detection was performed at 210 nm. The L-theanine content in teas marketed in Chile ranged from 4.21 to 24.83 (2.21 to 12.42 mg g-1), with a mean value of 10.06 mg in 200 mL (5.03 mg g-1). Considering the effective dose reported, only one brand (black tea) presented an adequate L-theanine content to produce the desired effect (two serving cups). Therefore, it is possible to conclude that most teas marketed in Chile do not have an adequate L-theanine content to be considered as functional beverage regarding this amino acid.
- A DETAILED INVESTIGATION ON ENGINEERING PARAMETERS FOR Cd(II) REMOVAL
BY RIPPED CITRUS PARADISI PULP WASTE- Abstract: The contemporary investigation presents a fundamental study on the removal of Cd(II) by ripped Citrus Paradisi pulp waste (RCPW). The effects of various engineering parameters such as initial solution pH, biosorbent dose, agitation, contact time, initial concentration, temperature and different eluents were evaluated on the uptake of Cd(II) by RCPW. Optimum uptake of Cd(II) onto RCPW was observed at 6.5 pH, 0.05 g of biosorbent and 100 rpm. Pseudo second order kinetic model best described the process of Cd(II) uptake by RCPW. Results showed that the sequestration of cadmium on RCPW was in monolayer as described by Langmuir's Model. Increase in temperature negatively affected the biosorption capacity of Cd(II) on RCPW indicating exothermic nature of the phenomenon. 0.1N NaOH was found to be the best desorbent among HNO3, H2SO4, HCl and EDTA.
- Abstract: The contemporary investigation presents a fundamental study on the removal of Cd(II) by ripped Citrus Paradisi pulp waste (RCPW). The effects of various engineering parameters such as initial solution pH, biosorbent dose, agitation, contact time, initial concentration, temperature and different eluents were evaluated on the uptake of Cd(II) by RCPW. Optimum uptake of Cd(II) onto RCPW was observed at 6.5 pH, 0.05 g of biosorbent and 100 rpm. Pseudo second order kinetic model best described the process of Cd(II) uptake by RCPW. Results showed that the sequestration of cadmium on RCPW was in monolayer as described by Langmuir's Model. Increase in temperature negatively affected the biosorption capacity of Cd(II) on RCPW indicating exothermic nature of the phenomenon. 0.1N NaOH was found to be the best desorbent among HNO3, H2SO4, HCl and EDTA.
- LC DETERMINATION OF ROSUVASTATIN AND EZETIMIBE IN HUMAN PLASMA
- Abstract: A simple, precise, sensitive and validated reverse-phase high performance liquid chromatographic (RP-HPLC) method was developed for the simultaneous estimation of rosuvastatin and ezetimibe in human plasma. The method involved protein precipitation and extraction of both drugs from plasma using acetonitrile and then separation on a C-18 column. Both the analytes were detected at a wavelength of 240 nm using diode array detector. Mobile phase for the said separation consists of a mixture of 1.5% phosphoric acid and acetonitrile in 30:70, v/v ratio. Linearity was in the range of 0.32-267 mg/mL for rosuvastatin and 0.08-67 mg/mL for ezetimibe with coefficient of determination between 0.9997 and 0.9967. Limit of detection was 0.106 μg/mL for rosuvastatin and 0.026 mg/mL for ezetimibe whereas limit of quantification was 0.32 mg/mL and 0.08 mg/mL for rosuvastatin and ezetimibe respectively. Recovery of both the analytes was greater than 75% with RSD less than 15 %. The total run time was less than five min for the two components. The developed method can be fruitfully employed for the determination of these two drugs in human plasma.
- Abstract: A simple, precise, sensitive and validated reverse-phase high performance liquid chromatographic (RP-HPLC) method was developed for the simultaneous estimation of rosuvastatin and ezetimibe in human plasma. The method involved protein precipitation and extraction of both drugs from plasma using acetonitrile and then separation on a C-18 column. Both the analytes were detected at a wavelength of 240 nm using diode array detector. Mobile phase for the said separation consists of a mixture of 1.5% phosphoric acid and acetonitrile in 30:70, v/v ratio. Linearity was in the range of 0.32-267 mg/mL for rosuvastatin and 0.08-67 mg/mL for ezetimibe with coefficient of determination between 0.9997 and 0.9967. Limit of detection was 0.106 μg/mL for rosuvastatin and 0.026 mg/mL for ezetimibe whereas limit of quantification was 0.32 mg/mL and 0.08 mg/mL for rosuvastatin and ezetimibe respectively. Recovery of both the analytes was greater than 75% with RSD less than 15 %. The total run time was less than five min for the two components. The developed method can be fruitfully employed for the determination of these two drugs in human plasma.
- POLYELECTROLYTE MODIFIED SILICA GEL MICRO-COLUMN SOLID PHASE EXTRACTION
FOR THE DETERMINATION OF SILVER IN ENVIRONMENTAL WATER SAMPLES BY FLAME
ATOMIC ABSORPTION SPECTROMETRY- Abstract: Silica gel was chemically modified with polyelectrolyte and used as a solid phase extraction adsorbent for the determination of trace silver in environmental water samples by flame absorption spectrometry (FAAS). The effects of pH, sample flow rate and volume, elution conditions and co-existing ions on the recovery of the analyte were investigated. The results showed that silver could be adsorbed at pH 5.0 and eluted by 5.0 mL 2% thiourea in HNO3 (0.1 mol L-1). Under the optimized conditions, the adsorption capacity of modified silica gel was found to be 8.6 mg g-1 for silver. The detection limit of the proposed method was 1.0 ng mL-1 for silver with an enrichment factor of 18.7. The analytical result for the certified reference water sample (GBW08610) was in a good agreement with the certified value. The proposed method has also been successfully applied to the determination of trace silver in drinking water, well water, snow water and waste water with the recoveries for spiked samples between 94% and 105%.
- Abstract: Silica gel was chemically modified with polyelectrolyte and used as a solid phase extraction adsorbent for the determination of trace silver in environmental water samples by flame absorption spectrometry (FAAS). The effects of pH, sample flow rate and volume, elution conditions and co-existing ions on the recovery of the analyte were investigated. The results showed that silver could be adsorbed at pH 5.0 and eluted by 5.0 mL 2% thiourea in HNO3 (0.1 mol L-1). Under the optimized conditions, the adsorption capacity of modified silica gel was found to be 8.6 mg g-1 for silver. The detection limit of the proposed method was 1.0 ng mL-1 for silver with an enrichment factor of 18.7. The analytical result for the certified reference water sample (GBW08610) was in a good agreement with the certified value. The proposed method has also been successfully applied to the determination of trace silver in drinking water, well water, snow water and waste water with the recoveries for spiked samples between 94% and 105%.
- SYNTHESIS, STRUCTURAL CHARACTERIZATION AND ENZYME INHIBITION STUDIES ON
5-(2-NITROSTYRYL)-1,3,4-OXADIAZOLE-2-THIOL DERIVATIVES- Abstract: In the present work, S-substituted derivatives of 5-(2-nitrostyryl)-1,3,4-oxadiazole-2-thiol (4) were synthesized by successive conversions of 3-(2-nitrophenyl) acrylic acid (1) into its respective ester, hydrazide and 1,3,4-oxadiazole. Finally the target compounds were obtained by reaction of 5-(2-nitrostyryl)-1,3,4-oxadiazole-2-thiol (4) with a series of various electrophiles, (5a-I), in NN-dimethyl formamide (DMF) in the presence of sodium hydride (NaH). The structural characterization of these newly synthesized compounds was done by IR, ¹H-NMR, HR-MS and EI-MS spectral data. All these compounds were evaluated for their enzyme inhibitory potentials and found to exhibit broad range spectrum against acetylcholinesterase, butyrylcholinestrase and lipoxygenase enzymes.
- Abstract: In the present work, S-substituted derivatives of 5-(2-nitrostyryl)-1,3,4-oxadiazole-2-thiol (4) were synthesized by successive conversions of 3-(2-nitrophenyl) acrylic acid (1) into its respective ester, hydrazide and 1,3,4-oxadiazole. Finally the target compounds were obtained by reaction of 5-(2-nitrostyryl)-1,3,4-oxadiazole-2-thiol (4) with a series of various electrophiles, (5a-I), in NN-dimethyl formamide (DMF) in the presence of sodium hydride (NaH). The structural characterization of these newly synthesized compounds was done by IR, ¹H-NMR, HR-MS and EI-MS spectral data. All these compounds were evaluated for their enzyme inhibitory potentials and found to exhibit broad range spectrum against acetylcholinesterase, butyrylcholinestrase and lipoxygenase enzymes.
- CYCLIC VOLTAMMETRY OF THE SECOND ORDER CE MECHANISM AT THE THIN MERCURY
FILM COVERED STATIONARY PLANAR ELECTRODE- Abstract: A theoretical model of electrode reaction influenced by the kinetics of complex formation and dissociation is developed for cyclic voltammetry. It is assumed that the electro-reductions of free metal ions and the complex are reversible and totally irreversible, respectively, and that the ligand is not present in great excess. The results show that the stripping peak current and potential depend on the relative bulk concentration of ligand, particularly within the range 1 < c*L,tot / c*M.tot < 3, and on the rate constant of complex formation.
- Abstract: A theoretical model of electrode reaction influenced by the kinetics of complex formation and dissociation is developed for cyclic voltammetry. It is assumed that the electro-reductions of free metal ions and the complex are reversible and totally irreversible, respectively, and that the ligand is not present in great excess. The results show that the stripping peak current and potential depend on the relative bulk concentration of ligand, particularly within the range 1 < c*L,tot / c*M.tot < 3, and on the rate constant of complex formation.
- AN EXPERIMENTAL AND THEORETICAL STUDY ON IMIDAZOLIUM-BASED IONIC LIQUID
PROMOTED CHLOROMETHYLATION OF AROMATIC HYDROCARBONS- Abstract: The chloromethylation of aromatic hydrocarbons proceeded efficiently using the reusable imidazolium-based ionic liquid as promoter. Mild reaction conditions, enhanced rates, improved yields, recyclability of ionic liquids, and reagents' reactivity which is different from that in conventional organic solvents are the remarkable features observed in ionic liquids. The ionic liquids were recycled in three subsequent runs with no decrease in activity. In addition, the results of calculations with the Gaussian 98 suite of program are in good accordance with the experimental outcomes.
- Abstract: The chloromethylation of aromatic hydrocarbons proceeded efficiently using the reusable imidazolium-based ionic liquid as promoter. Mild reaction conditions, enhanced rates, improved yields, recyclability of ionic liquids, and reagents' reactivity which is different from that in conventional organic solvents are the remarkable features observed in ionic liquids. The ionic liquids were recycled in three subsequent runs with no decrease in activity. In addition, the results of calculations with the Gaussian 98 suite of program are in good accordance with the experimental outcomes.
- SOLVENT FREE OXALIC ACID CATALYZED SYNTHESIS OF 1,5-BENZODIAZEPINES
- Abstract: In the present study 1, 5-benzodiazepines were synthesized from a range of α, β-unsaturated ketones and o-phenylendiamine using oxalic acid 10 mol% as a catalyst under solvent free conditions. The yields of the present method are better than the reported method which explains effectiveness of oxalic acid catalyst. The cost effective, resourceful, undemanding and environment friendly are the advantageous aspects of this method.
- Abstract: In the present study 1, 5-benzodiazepines were synthesized from a range of α, β-unsaturated ketones and o-phenylendiamine using oxalic acid 10 mol% as a catalyst under solvent free conditions. The yields of the present method are better than the reported method which explains effectiveness of oxalic acid catalyst. The cost effective, resourceful, undemanding and environment friendly are the advantageous aspects of this method.
- SOLID PHASE EXTRACTION OF Cd(II) AND Pb(II) IONS BY A NEW
CARBOTHIOAMIDE DERIVATIVE- Abstract: An effective, simple, low cost and accurate sorption-spectrophotometric platform for the extractions and subsequent quantifications of Cd(II) and Pb(II) ions in food and environmental samples has been described in this dissertation. The separation and preconcentration of the analyte ions were accomplished by solid phase extraction method based on the adsorption of their N-(4-methylphenyl)-2-{[(4-phenyl-5-pyridin-4-yl-H-1,2,4-triazol-3-yl)thio]acetyl} hydrazinecarbothioamide (MFPTAHK) complex on Amberlite XAD-8 resin in a mini column. The developed method was systematically investigated in different set of experimental parameters that influence the separation and preconcentration of Cd(II) and Pb(II) ions. The precision of the method was determined by reproducibility studies and expressed as relative standard deviations (RSD %) which were less than 4% for both analyte ions. The limits of detections (LODs) for Cd(II) and Pb(II) ions based on the three times the standard deviation of the blanks (N:10) were found to be 0.31 μg L-1 and 0.86 μg L-1, respectively. The developed SPE procedure was utilized for the simultaneous extraction and determinations of Cd(II) and Pb(II) ions levels in rice, cracked wheat and red lentil as food samples and various water samples.
- Abstract: An effective, simple, low cost and accurate sorption-spectrophotometric platform for the extractions and subsequent quantifications of Cd(II) and Pb(II) ions in food and environmental samples has been described in this dissertation. The separation and preconcentration of the analyte ions were accomplished by solid phase extraction method based on the adsorption of their N-(4-methylphenyl)-2-{[(4-phenyl-5-pyridin-4-yl-H-1,2,4-triazol-3-yl)thio]acetyl} hydrazinecarbothioamide (MFPTAHK) complex on Amberlite XAD-8 resin in a mini column. The developed method was systematically investigated in different set of experimental parameters that influence the separation and preconcentration of Cd(II) and Pb(II) ions. The precision of the method was determined by reproducibility studies and expressed as relative standard deviations (RSD %) which were less than 4% for both analyte ions. The limits of detections (LODs) for Cd(II) and Pb(II) ions based on the three times the standard deviation of the blanks (N:10) were found to be 0.31 μg L-1 and 0.86 μg L-1, respectively. The developed SPE procedure was utilized for the simultaneous extraction and determinations of Cd(II) and Pb(II) ions levels in rice, cracked wheat and red lentil as food samples and various water samples.
- EFFECT OF SINGLE-WALLED CARBON NANOTUBES ON
HYDROXYPROPYL- β -CYCLODEXTRIN STATIONARY PHASE- Abstract: In the present work, we describe a novel application of functionalized single-walled carbon nanotubes (SWCNTs) as a stationary phase for the liquid chromatographic separation of polycyclic aromatic hydrocarbons and structurally similar analogues. The SWCNTs were first oxidized to give carboxylic derivatives (SWCNT-COOH), afterwards these were covalently derivatized with hydroxypropyl-β-cyclodextrin (HP-β-CD). Then, the HP-β-CD-SWCNTs were bonded to silica gel with 3-(triethoxysilyl) propyl isocyanate, which were used as a stationary phase to separate the investigated solutes by HPLC. On this stationary phase, eight polycyclic aromatic hydrocarbons were separated using water/methanol (5:5, v/v) as the mobile phase and six structurally similar dipine drugs were also separated using (3:7, v/v) methanol/triethylammonium acetate buffer (0.1%, v/v, pH 4.1) as the mobile phase. The results showed that the HP-β-CD-SWCNTs stationary phase had stronger separation ability for the aromatic hydrocarbons and analogues compared with the HP-β-CD stationary phase. This method can be used to improve the separation efficiency of the β-CD stationary phases, and the HP-β-CD-SWCNTs column can be used for the determination of the aromatic hydrocarbons in wastewater.
- Abstract: In the present work, we describe a novel application of functionalized single-walled carbon nanotubes (SWCNTs) as a stationary phase for the liquid chromatographic separation of polycyclic aromatic hydrocarbons and structurally similar analogues. The SWCNTs were first oxidized to give carboxylic derivatives (SWCNT-COOH), afterwards these were covalently derivatized with hydroxypropyl-β-cyclodextrin (HP-β-CD). Then, the HP-β-CD-SWCNTs were bonded to silica gel with 3-(triethoxysilyl) propyl isocyanate, which were used as a stationary phase to separate the investigated solutes by HPLC. On this stationary phase, eight polycyclic aromatic hydrocarbons were separated using water/methanol (5:5, v/v) as the mobile phase and six structurally similar dipine drugs were also separated using (3:7, v/v) methanol/triethylammonium acetate buffer (0.1%, v/v, pH 4.1) as the mobile phase. The results showed that the HP-β-CD-SWCNTs stationary phase had stronger separation ability for the aromatic hydrocarbons and analogues compared with the HP-β-CD stationary phase. This method can be used to improve the separation efficiency of the β-CD stationary phases, and the HP-β-CD-SWCNTs column can be used for the determination of the aromatic hydrocarbons in wastewater.
- GREEN SYNTHESIS AND CHARACTERIZATION OF GRAPHITE OXIDE BY ORTHOGONAL
EXPERIMENT- Abstract: Graphite oxide (GO) was prepared with graphite flakes, KMnO4, and a mixture of concentrated H2SO4/H3PO4 by an improved green synthesis method. To obtain fully oxidized GO, an orthogonal array design L9 was applied to select the optimum preparing conditions. The effects of the quantity of graphite, the quantity of KMnO4, reaction time, and temperature on the degree of oxidization of GO were evaluated by the orthogonal array design (OAD). The results show that the factors arranged in important order as the follows: reaction time, reaction temperature, the quantity of KMnO4, the quantity of graphite. Graphite oxide obtained at the optimal parameters by the improved method was characterized by UV-Vis, FT-IR, Raman spectrum, and XRD techniques, and compared with GO produced by the modified Hummers' method. The results indicate that the GO obtained by the improved green synthesis method has fewer defects in the basal plane and is more oxidized than the modified Hummers' method.
- Abstract: Graphite oxide (GO) was prepared with graphite flakes, KMnO4, and a mixture of concentrated H2SO4/H3PO4 by an improved green synthesis method. To obtain fully oxidized GO, an orthogonal array design L9 was applied to select the optimum preparing conditions. The effects of the quantity of graphite, the quantity of KMnO4, reaction time, and temperature on the degree of oxidization of GO were evaluated by the orthogonal array design (OAD). The results show that the factors arranged in important order as the follows: reaction time, reaction temperature, the quantity of KMnO4, the quantity of graphite. Graphite oxide obtained at the optimal parameters by the improved method was characterized by UV-Vis, FT-IR, Raman spectrum, and XRD techniques, and compared with GO produced by the modified Hummers' method. The results indicate that the GO obtained by the improved green synthesis method has fewer defects in the basal plane and is more oxidized than the modified Hummers' method.
- QUANTUM MECHANICAL STUDY OF THE INSERTION REACTION BETWEEN
- Abstract: To further reveal the reactivity of cyclopropenylidene with R-H compounds, mechanisms of four reactions between cyclopropenylidene and R-H (R=F, OH, NH2, CH3) have been systematically investigated employing the second-order Møller-Plesset perturbation theory (MP2) method. Geometry optimization, vibrational analysis, and energy property for the involved stationary points on the potential energy surface have been calculated. All the mechanisms of four reactions are identical to each other. Based on the calculated results, there are three steps (step a, b, and c) along the reaction between cyclopropenylidene and R-H. For the first step, cyclopropenylidene is inserted into R-H to form an three-membered ring intermediate. For the second step, the three-membered ring is opened to form a carbene intermediate. With regard to the third step, it is H-transfered processes, the ultimate product is alkyne.
- Abstract: To further reveal the reactivity of cyclopropenylidene with R-H compounds, mechanisms of four reactions between cyclopropenylidene and R-H (R=F, OH, NH2, CH3) have been systematically investigated employing the second-order Møller-Plesset perturbation theory (MP2) method. Geometry optimization, vibrational analysis, and energy property for the involved stationary points on the potential energy surface have been calculated. All the mechanisms of four reactions are identical to each other. Based on the calculated results, there are three steps (step a, b, and c) along the reaction between cyclopropenylidene and R-H. For the first step, cyclopropenylidene is inserted into R-H to form an three-membered ring intermediate. For the second step, the three-membered ring is opened to form a carbene intermediate. With regard to the third step, it is H-transfered processes, the ultimate product is alkyne.
- SYNTHESES AND CHARACTERISATION OF DIUREA MOLECULAR TWEESORS FOR THE
RECOGNITION OF ANION- Abstract: Two novel urea anion receptors (11) and (12) were synthesized from building block 3,3' methylene diamine and was characterized via the techniques of ¹H NMR, 13CNMR, DEPT- 135 ¹H-¹H COSY, HMQC and HMBC spectroscopy. The ¹H NMR profile of both compounds reveals diagnostic peaks. For compound (11), the urea NH protons resonate as two singlets downfield at 8.706 ppm and 8.635 ppm, whereas for compound (12) these two urea -NHCONH protons resonate together at 8.614 ppm. There seem to be no rotation of the structure on the NMR time scale as the bridged CH2 protons resonate as a singlet. The integration pattern for the aromatic hydrogens for both compounds is: 2: 4: 2: 4: 4, consistent with the structure. 13CNMR spectrums reveal fourteen signals for both structures in accordance with fourteen different types of carbon. Dept-135 indicates eight different CH protons. Preliminary anion binding studies via ¹HNMR spectroscopy revealed complexation with dicarboxylate anions in the highly competitive solvent, d6-DMSO.
- Abstract: Two novel urea anion receptors (11) and (12) were synthesized from building block 3,3' methylene diamine and was characterized via the techniques of ¹H NMR, 13CNMR, DEPT- 135 ¹H-¹H COSY, HMQC and HMBC spectroscopy. The ¹H NMR profile of both compounds reveals diagnostic peaks. For compound (11), the urea NH protons resonate as two singlets downfield at 8.706 ppm and 8.635 ppm, whereas for compound (12) these two urea -NHCONH protons resonate together at 8.614 ppm. There seem to be no rotation of the structure on the NMR time scale as the bridged CH2 protons resonate as a singlet. The integration pattern for the aromatic hydrogens for both compounds is: 2: 4: 2: 4: 4, consistent with the structure. 13CNMR spectrums reveal fourteen signals for both structures in accordance with fourteen different types of carbon. Dept-135 indicates eight different CH protons. Preliminary anion binding studies via ¹HNMR spectroscopy revealed complexation with dicarboxylate anions in the highly competitive solvent, d6-DMSO.
- APPLICATION OF MULTIVARIATE IMAGE ANALYSIS - QUANTITATIVE STRUCTURE
TOXICITY RELATIONSHIP STUDY FOR MODELING THE TOXICITY OF PHENOL
DERIVATIVES- Abstract: The toxicity of some phenol derivatives over tetrahymena pyriformis were modeled by using multivariate image analysis (MIA) descriptors applied to quantitative structure-toxicity relationship (QSTR) method. MIA descriptors are derived from pixels of two-dimensional (2D) chemical structures that may be built by using any appropriate drawing software. QSTR analysis has been done by using partial least square regression (PLS), correlation ranking-principal component regression (CR-PCR) and correlation ranking-principal component-artificial neural network (CR-PC-ANN) modeling methods. For the ANN models two different weight update functions of Levenberg-Marquardt (LM) and Scaled Conjugate Gradient (SCG) were investigated. Finally, obtained results using different linear and nonlinear modeling methods were compared, showing that PLS and CR-PC-ANN-SCG methods present high performance for prediction of the toxicity of phenol derivatives. Also, these results indicated that MIA descriptors may be useful to predict toxicity of phenol derivatives. Squared correlation coefficient (R²) and standard error using the PLS method for the training set were 0.996 and 0.042 and for the test set were 0.996 and 0.048, respectively. Squared correlation coefficient (R²) and standard error using the CR-PC-ANN-SCG method were respectively, 0.999 and 0.002 for the training set, 0.999 and 0.001 for the test set and 0.999 and 0.002 for the validation set.
- Abstract: The toxicity of some phenol derivatives over tetrahymena pyriformis were modeled by using multivariate image analysis (MIA) descriptors applied to quantitative structure-toxicity relationship (QSTR) method. MIA descriptors are derived from pixels of two-dimensional (2D) chemical structures that may be built by using any appropriate drawing software. QSTR analysis has been done by using partial least square regression (PLS), correlation ranking-principal component regression (CR-PCR) and correlation ranking-principal component-artificial neural network (CR-PC-ANN) modeling methods. For the ANN models two different weight update functions of Levenberg-Marquardt (LM) and Scaled Conjugate Gradient (SCG) were investigated. Finally, obtained results using different linear and nonlinear modeling methods were compared, showing that PLS and CR-PC-ANN-SCG methods present high performance for prediction of the toxicity of phenol derivatives. Also, these results indicated that MIA descriptors may be useful to predict toxicity of phenol derivatives. Squared correlation coefficient (R²) and standard error using the PLS method for the training set were 0.996 and 0.042 and for the test set were 0.996 and 0.048, respectively. Squared correlation coefficient (R²) and standard error using the CR-PC-ANN-SCG method were respectively, 0.999 and 0.002 for the training set, 0.999 and 0.001 for the test set and 0.999 and 0.002 for the validation set.
- SOLID FLY-ASH:H2SO4 CATALYZED MICROWAVE ASSISTED
SOLVENT-FREE CONDENSATION:SYNTHESIS OF SOME TRIFLUOROMETHYL-IMINES- Abstract: Good yield of trifluoromethyl-imines have been synthesized by Fly-ash:H2SO4 catalyzed condensation of anilines and phenyl trifluoromethyl ketone in microwave irradiation under solvent free conditions.
- Abstract: Good yield of trifluoromethyl-imines have been synthesized by Fly-ash:H2SO4 catalyzed condensation of anilines and phenyl trifluoromethyl ketone in microwave irradiation under solvent free conditions.
- GREEN SYNTHESIS OF CALCIUM CARBONATE WITH UNUSUAL MORPHOLOGIES IN THE
PRESENCE OF FRUIT EXTRACTS- Abstract: In the present investigation, we reported a novel green strategy for the biological synthesis of calcium carbonate crystals using water-soluble polysaccharides extracted from the apple and pear. The resultant crystals were characterized by scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, and X-ray powder diffractometry (XRD). The results showed that water-soluble polysaccharides as a soft template were easy to induce calcium carbonate with unusual morphologies (such as straw bundles-like). Based on the time-dependent growth of CaCC3 particles, possible mechanisms were proposed for the formation of straw bundle-like CaCC3 microspheres with secondary structures in the presence of water-soluble polysaccharides.
- Abstract: In the present investigation, we reported a novel green strategy for the biological synthesis of calcium carbonate crystals using water-soluble polysaccharides extracted from the apple and pear. The resultant crystals were characterized by scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, and X-ray powder diffractometry (XRD). The results showed that water-soluble polysaccharides as a soft template were easy to induce calcium carbonate with unusual morphologies (such as straw bundles-like). Based on the time-dependent growth of CaCC3 particles, possible mechanisms were proposed for the formation of straw bundle-like CaCC3 microspheres with secondary structures in the presence of water-soluble polysaccharides.
- TRICHLOROTRIAZINE AS A SIMPLE AND EFFICIENT CATALYST PROMOTER FOR THE
SYNTHESIS OF NEW GENERATION OF COUMARINS- Abstract: The first synthesis of azo bearing coumarins from azo aldehydes and malononitrile in the presence of an efficient catalyst, trichlorotriazine under ultrasound irradiation in high yield and short reaction time is reported. In the other study, the first electrophilic substitution under ultrasound irradiation for the synthesis of azo bearing coumarins was developed. All of synthesized compounds were characterized by FTIR, NMR and elemental analysis.
- Abstract: The first synthesis of azo bearing coumarins from azo aldehydes and malononitrile in the presence of an efficient catalyst, trichlorotriazine under ultrasound irradiation in high yield and short reaction time is reported. In the other study, the first electrophilic substitution under ultrasound irradiation for the synthesis of azo bearing coumarins was developed. All of synthesized compounds were characterized by FTIR, NMR and elemental analysis.
- STUDY BASED ON ELECTRONIC DESCRIPTORS OF THE DIASTEREOSELECTIVE
AZA-DIELS-ALDER CYCLOADDITION OF [(1R)-10-(N,N-DIETHYLSULFAMOYL)ISOBORNYL]
2H-AZIRINE-3-CARBOXYLATE TO E,E-1,4-DIACETOXY-1,3-BUTADIENE- Abstract: Cycloaddition of chiral [(1R)-10-(N,N-diethylsulfamoyl)isobornyl] 2H-azirine-3-carboxylate to E,E-1,4-diacetoxy-1,3-butadiene shows complete diatereoselectivity giving a single cycloadduct (-)-(2S,5R,6R)-6-[(1R)-10-(N,N-diethylsulfamoyl)isobornyloxycarbonyl]-1-azabicyclo[4.1.0]hept-3-ene-2,5-diyldiacetate. Our main objective is to identify electronic/steric parameters capable of describing the observed tendencies of this reaction. The results of the calculations conclude that: even though the steric factors can play an important role at the initial steps of the reaction, at the transition states the behavior of several electronic parameters; like hardness, polarizability, aromaticity, charge transfer, etc is decisive enough to justify the obtained product. Finally, this work summarizes an exhaustive analysis of electronic descriptors and empirical reactivity principles, reaching a definitive and comprehensive explanation to the observed experimental result.
- Abstract: Cycloaddition of chiral [(1R)-10-(N,N-diethylsulfamoyl)isobornyl] 2H-azirine-3-carboxylate to E,E-1,4-diacetoxy-1,3-butadiene shows complete diatereoselectivity giving a single cycloadduct (-)-(2S,5R,6R)-6-[(1R)-10-(N,N-diethylsulfamoyl)isobornyloxycarbonyl]-1-azabicyclo[4.1.0]hept-3-ene-2,5-diyldiacetate. Our main objective is to identify electronic/steric parameters capable of describing the observed tendencies of this reaction. The results of the calculations conclude that: even though the steric factors can play an important role at the initial steps of the reaction, at the transition states the behavior of several electronic parameters; like hardness, polarizability, aromaticity, charge transfer, etc is decisive enough to justify the obtained product. Finally, this work summarizes an exhaustive analysis of electronic descriptors and empirical reactivity principles, reaching a definitive and comprehensive explanation to the observed experimental result.
