Journal of the Chilean Chemical Society
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Open Access journal
ISSN (Online) 0717-9324
Published by SciELO [724 journals]
- MESO AND RACEMIC 1,1-BIS (BENZYLSULFINYL)-2-ETHYLBUTANE. A b-DISULFOXIDE
PRO-LIGAND WITH STERIC RESTRICTIONS
Abstract: Coordination chemistry of disulfoxides is of interest in inorganic chemistry given the well-known metal coordination through oxygen or sulfur atoms.¹ Ethylene and propylene bridged disulfoxide pro-ligands, coordinate to metals, forming coordinated and chelated complexes, demonstrating its flexibility in the formation of such complexes.² Some of these compounds have demonstrated interesting properties in medicinal chemistry³ and asymmetric catalysis4 and their synthesis is of importance for bioorganic studies. The presence of two stereogenic centers allows the existence of the meso and racemic forms in disulfoxides. Previous studies on b-disulfoxides5 in our laboratories have led to the synthesis and spectroscopic study (¹H-NMR, FT-IR) of both diastereomeric forms. In this work we report the synthesis and structural analysis of meso-(2)- and racemic-(3)-1,1-bis(benzylsulfinyl)-2-ethylbutane (Scheme1), with high steric requirement around both sulfinyl groups when a branched aliphatic carbon chain is introduced in the a-carbon. An increase in selectivity for small radius metal ions was achieved by compression of the pro-ligand coordination radius. These kind of compounds have not been previously studied.
- THERMODYNAMIC CYCLE FOR CALCULATING AB-INITIO pKa VALUES OF TYPE
(Me)2-N-Phenyl-(HC=CH)n-CHO (n = 0, 1, 2 and 3) MOLECULAR SYSTEMS
Abstract: Based on a thermodynamic cycle the pKa in aqueous phase of the series of molecules of the type (Me)2-N-Phenyl-(HC=CH)n-CHO with n = 0, 1, 2 and 3 have been determined. To that end the SM5.4 solvation model has been considered. The calculated pKa have been compared with the pKa measured experimentally. A study has also been made of the proton affinity in the gas phase and in aqueous phase. The calculation scheme agrees favorably, in a qualitative manner, considering favorably the molecular and solute-solvent interaction characteristics that determine the free energy that governs the acid-base properties of the molecules in the series
- SIMULTANEOUS DETERMINATION OF DIFFERENT FLAVONOIDS IN HUMAN PLASMA BY A
SIMPLE HPLC ASSAY
Abstract: A simple HPLC method for simultaneous determination of five flavonoids in human plasma was developed. Following addition of catechin as internal standard (IS), luteolin-7-glucoside, rutin, apigenin-7-glucoside, quercetin and baicalein were isolated from human plasma by liquid-liquid extraction with acetone. The chromatographic separation was achieved in a DAD-HPLC equipment on a reversed-phase C18 column using a gradient mobile phase consisting of 0.1% acetic acid + methanol: acetonitrile: acetic acid (90:10:1, v/v) and running at a flow rate of 1 mL/min. The effluent was monitored at a wavelength of 280 ƞm, as well as IS was well separated from each other and free from interference from blank plasma and other components in plasma. The calibration curve was constructed by plotting peak area ratio of analytes to IS vs. concentration. The method showed good linearity over range of 5 - 30 μg/mL for the five standards used (r>0.996). The developed method may be used not only to identify the analytes assayed but, simultaneously measure plasma concentrations of these herbal compounds.
- SUPPORT EFFECT ON CONVERSION OF QUINOLINE OVER ReS2
Abstract: The conversion of quinoline over ReS2 supported on y-Al2O3, SiO2, ZrO2 and TiO2 catalysts in a batch reactor at 300ºC and 5 MPa of hydrogen pressure was studied. The catalysts were prepared by wet impregnation with a loading of 1.5 atoms of Re per nm² of support. The catalysts were characterized by N2 adsorption, X-ray photoelectron spectroscopy (XPS) and X-ray powder diffraction (XRD). The Re(x)/supports catalysts displayed high activities for the conversion of quinoline, although negligible formation of N-free compounds (hydrodenitrogenation) were observed. The intrinsic activities of ReS2 were modified by the support decreased in the order: Re/TiO2 > Re/ZrO2 > Re/SiO2 > Re/y-Al2O3. The highest activity displayed by the Re/TiO2 catalyst was correlated with the Re dispersion and formation of ReS2 species. Meanwhile, the lower conversion of quinoline over the Re/ZrO2, Re/SiO2 and Re/y-Al2O3 catalysts was related to the combined effect of the textural properties of catalysts and the formation of ReS species on the supports.
- EFFECT OF GAMMA-IRRADIATION ON BIODEGRADABLE MICROSPHERES LOADED WITH
Abstract: In the present study, the influence of gamma-irradiation was evaluated on the physicochemical characteristics and in vitro release of rasagiline mesylate (RM), a selective MAO-B inhibitor used in Parkinson’s disease, from poly(D,L-lactide-co-glycolide) (PLGA) microspheres. Microspheres were prepared using PLGA 50:50 by the solvent evaporation technique (O/W emulsion). Microspheres were sterilized by gamma-irradiation and their influence was assessed by scanning electron microscopy (SEM), laser light diffraction, differential scanning calorimetry (DSC), X-ray diffraction (XRD), gel permeation chromatography (GPC), encapsulation efficiency (EE) and in vitro drug release. Gamma-irradiation of RM-loaded microspheres did not affect EE, DSC and XRD patterns. After gamma-irradiation, changes on the surface were observed by SEM, but no significant difference in mean particle size was observed. GPC measurements showed a decrease in molecular weight of the polymer after five days of in vitro release. The similarity factor value between irradiated and non-irradiates microspheres was
- DISTRIBUTION OF ARSENIC AND MERCURY IN THE AQUATIC ECOSYSTEM OF THE FIVE
Abstract: Arsenic and mercury are among the metals and metalloids more toxic to the ecosystem. A quantification method by atomic absorption spectroscopy with hydride generator (AAS-HG) to determine total As and cold steam to determine Hg was optimized and validated in various matrices: superficial water, interstitial or pore water, sediments and in gill, liver and muscle of two fish species, a silverside (Basilichthys microlepidotus) and a catfish (Trichomycterus areolatus). The quality of the results was tested using certified reference materials (Water: ERM-CA615; Fish: DOLT-4; Sediment: BCR-320R). Samples were collected in the affluent and effluent of five reservoirs: Cogotí (31°00’S, 71°05’W); Corrales (31°54°S, 70°54’W); La Paloma (30°44’S, 71°00’W); Rapel (34°08’S, 71°29’O); Recoleta (30°28’S, 71°06’W). ), in two campaigns during high flow (winter 2010) and low flow (summer 2011). The results show a clear difference in the distribution of As and Hg in the different matrices; higher concentrations were found in the order sediment > interstitial water > surface water. Catfish showed higher accumulation of both metals, and metal concentrations generally decreased in the order liver > gill > muscle. No significant effect of reservoirs and zones was observed in As and Hg content. However, Arsenic (As) was found in higher concentration in the different matrices of the five reservoirs and zones. The concentrations of As and Hg in all samples did not exceed international standards in the case of sediment and the Chilean norm in the case of water, while in both fish species concentrations of As and Hg in muscle exceeded international standards.
- STRUCTURE AND THERMAL BEHAVIOR OF TANNINS FROM Acacia dealbata BARK AND
THEIR REACTIVITY TOWARD FORMALDEHYDE
Abstract: The objective of this study was to evaluate the tannin extraction potential taken from the bark of Acacia dealbata. This tannins were extracted with water at 90°C. An extraction yield of 17.2% solids with a Stiasny number of 82% was obtained from the bark extract of Acacia dealbata. The structure was studied by Fourier transform infrared spectroscopy (FTIR). The thermal behavior of tannins was studied by DSC and a glass-transition temperature (Tg) of 116,77°C was determined. The thermal stability of tannins was studied by TGA. At 196.91°C the decomposition is 3.7% and the maximum of the weight loss rate (DTG) of the degradation was 257.77°C. The curing with formaldehyde showed an exotherm reaction in the range of 100-120°C, which is similar to tannins of other species.
- ANTIPROLIFERATIVE ACTIVITY OF NEW 6-BROMINE DERIVATIVES OF
Abstract: A variety of 6-bromine-containing 7-anilino-1-arylisoquinolinequinones 2a-g were synthesized to evaluate their half-wave potentials and in vitro antiproliferative activity on gastric and leukemia cancer cell lines. The new compounds displayed significant IC50 values in the range: 1.31 to 11.04 μM. The structure activity relationship analysis of the new series suggest that the antiproliferative activity is dependent, in part, on the push-pull electronic effects of the nitrogen and bromine substituents inserted into the redox fragment of the 1-arylisoquinolinequinone scaffold. Linear regression analysis provided satisfactory relationships between the log IC50 and ClogP values for the AGS gastric cancer cell line.
- DETERMINATION OF TRICLABENDAZOLE IN CATTLE PLASMA AS ITS SULPHOXIDE AND
SULPHONE METABOLITES BY ROTATING DISK SORPTIVE EXTRACTION COMBINED WITH
HIGH-PERFORMANCE LIQUID CHROMATOGRAPHY AND ITS APPLICATION TO
Abstract: In this study, a new method for determination of triclabendazole (TCB) as its main metabolites, triclabendazole sulfoxide (TCB-SO) and triclabendazole sulfone (TCB-SO2) in animal plasma was developed. TCB is widely used as antiparasitic in the veterinary industry. Rotating disk sorptive extraction (RDSE) was the selected sample preparation technique for extraction/clean up of the compounds from the samples followed by high performance liquid chromatography coupled to diode array detection (HPLC-DAD) for quantification. Optimization of physicochemical variables was performed using a multivariate experimental design. Following the recommendations given in the Veterinary International Conference on Harmonization guides (VICH GL02 and VICH GL49), the validation of the method was performed, given rise to improved analytical features compared with those provided by other methods based on solid phase extraction (SPE). Linearity (r > 0.99) was achieved for both compounds when calibration was performed not only in standard solutions but also in animal spiked plasma. Selectivity, defined as the response ratio between blank and analyte at the limit of quantification, was 11.8% and 3.4% for TCB-SO and TCB-SO2, respectively. Accuracy and precision, expressed in percentage, were always lower than -16.7% and 8.1%, respectively. Eco-efficiency was quantitatively assessed indicating that the method is an excellent green method. The proposed analytical method was applied to the determination of the pharmacokinetic of two commercial products of TCB in cattle plasma after oral administration. The good analytical performance, eco-efficiency and economy, make the method interesting for alternative use in routine laboratories.
- PREPARATION, IDENTIFICATION AND BIOLOGICAL PROPERTIES OF NEW
Abstract: Nanoparticles (NPs) of new fluoride (SrF2 and MgF2) nanocompounds were synthesized by the simple chemical method of precipitation in ethanol. Synthesis of the strontium fluoride (SrF2)-magnesium oxide (MgO) nanocomposite was achieved through the ultrasonic method. These prepared nanopowders were characterized through Fourier transform infrared (FT-IR) spectroscopy, ultraviolet-visible (UV-Vis) spectroscopy, Powder X-ray Diffraction (PXRD) and Scanning Electron Microscopy (SEM). FT-IR confirmed the purity of the synthesized fluoride NPs by evaluation of the vibrations, and UV-Visible showed the intense absorption peaks of NPs. PXRD analysis indicated the average of particle size, and SEM demonstrated a nearly spherical morphology of the NPs. The antibacterical properties of the nanopowders on Staphylococcus Aureus, Bacillus Subtilis and E. Aklay bacteria were studied, with the strongest effect by the magnesium fluoride (MgF2) NPs and the SrF2-MgO nanocomposite.
- ELECTROCHEMICAL METHOD FOR SULFITE DETERMINATION IN WINES BY
ELECTROCHEMICAL RESPONSE USING A MEMBRANE ABSORBER SYSTEM
Abstract: This research demonstrates how the sulfite content can be measured by cyclic voltammetry using a previously reported membrane absorber system, which separates efficiently sulfite present in wine. Results obtained show notably similar values to those obtained for the same wine samples using modified Monier-Williams method (aspiration method) and Ripper method. The membrane absorber system allows the release of the free SO2 and can be used to determine the sulfur dioxide present in juices and other foods that contain high concentrations of phenols, polyphenols and other structurally related compounds that act as interferers in the electrochemical oxidation of sulfite. The absorber solution allows a direct measurement without change in pH or added electrolyte, facilitating the determination of great amounts of samples from diverse wines using only one calibration curve. In this way, a system that allows the detection of sulfite and that can be used in vineyards is obtained. Finally, the method was assessed on linearity, sensitivity, accuracy, reproducibility and repeatability, obtaining values that account for the applicability of the method.
- DENITROGENATION BY ADSORPTION OF PYRIDINE ON NI/SUPPORT
Abstract: In this work we have carried out the adsorption of pyridine using three different supports (activated carbon, SiO2 and y-Al2O3). After choosing the best support, due to its higher adsorption capacity, we have impregnated the support with nickel at three different concentrations (2, 4 and 6% w/w) by wet impregnation to study the adsorption of pyridine by π-complexation. All the samples (supports and adsorbents) were characterized by N2 adsorption-desorption by the BET method and electrophoretic migration. The experimental results, for the three different supports, show that the adsorption capacity is better for y-Al2O3 due to its higher isoelectric point. With the incorporation of nickel, no better adsorption capacities are observed, due that the nickel incorporation diminish the zero point charges of the adsorbents.
- IMPLEMENTATION OF AN ANALYTICAL METHOD FOR THE DETERMINATION OF INORGANIC
ARSENIC SPECIES IN OCCUPATIONALLY EXPOSED HUMAN URINE SAMPLES AND ITS
TOXIC EFFECTS ON EPITHELIAL CELLS OF RENAL COLLECTING TUBULE
Abstract: In this study a method was implemented for the determination of total As and its inorganic species in human urine by HPLC-HG-AFS. The method was applied to workers occupationally exposed to mining and thermoelectric operations. Results shows high levels of As in urine up to 188±4 μg L-1 and As(III) up to 10.7±0.6 μg L-1. Toxic effects of As(III) at the concentration levels founded in human urine were evaluated over the morphology and fibrosis of renal epithelial collecting duct cells in vitro. Our results suggest that urinary tract epithelial renal tubular cells exposed to this concentration of As(III) result in epithelial-mesenchymal transition.
- EFFECT OF CHLORIDE IONS ON THE STRUCTURAL, OPTICAL, MORPHOLOGICAL, AND
ELECTROCHEMICAL PROPERTIES OF Cu2O FILMS ELECTRODEPOSITED ON
FLUORINE-DOPED TIN OXIDE SUBSTRATE FROM A DMSO SOLUTION
Abstract: This study shows the results attained during the electrodeposition of Cu2O films on fluorine-doped tin oxide (FTO) substrate from a dimethyl sulfoxide (DMSO) solution in the presence of chloride ions. Before the film electrodeposition and in order to establish the best conditions for the Cu2O electrodeposition, a detailed electrochemical study of the precursors in the presence of chloride ions was performed. The voltammetric profiles obtained show significant differences compared to those previously obtained during the study of the Cu2O electrodeposition from a free-chloride DMSO solution. These differences are the result of the coordination complexes formation between chloride ions and the different copper species in solution. The films were potentiostatically electrodeposited between -1.4 V and -1.6 V vs Ag/AgCl reference electrode. Then, these films were characterized through different techniques: X-ray diffraction, scanning electron microscopy, optical characterization, and capacitance measurements through electrochemical impedance spectroscopy.
- CHANGES IN SECONDARY METABOLITES PROFILES AND BIOLOGICAL ACTIVITY OF THE
FRESH FRUITING BODIES OF Stereum hirsutum EXPOSED TO HIGH-DOSE UV-B
Abstract: The present study aims to investigate the effects of ultraviolet radiation (type B) on the steroid and fatty acids content, phenolic compounds and biological activities of Stereum hirsutum wild fruiting bodies, which has been used by both Chinese and Korean folk medicine to treat cancer and recently as functional food. From another perspective, the distribution of steroid derivatives as well as fatty acids underwent significant changes after UV exposure over time. In our model of study UV-B radiation induced a decrease in the relative abundance of ergosterol derivatives while squalene increased. We also detected that UVB radiation (1.2 W m-2) enhanced the antioxidant activity of Stereum hirsutum, with the acetonic extract after 48 hours of radiation the most efficient with a half-maximal inhibitory concentration (IC50) of 339.9 μg/mL. Gas-mass chromatography (GC-MS) analysis at this 48 hours stage revealed a high content of phenolic compounds (70%). We observed a decrease in the antibacterial activity against Escherichia coli, Salmonella typhi and Salmonella typhimurium compared to their respective controls. The study concludes that UV-B influences the pathway of secondary metabolites to induce changes metabolic in the composition of sterols and fatty acids and increasing the abundance of antioxidant compounds in S. hirsutum.
- A CHEMOMETRIC APPROACH TO THE INFLUENCE OF THE SYNTHESIS PARAMETERS ON THE
OPTICAL RESPONSE OF GOLD NANOPARTICLES AND STUDY OF THEIR ELECTROPHORETIC
DEPOSITION ON SILICON
Abstract: This study describes gold nanoparticle synthesis in an aqueous solution by reducing tetrachloroauric acid (HAuCl4), using sodium citrate as a reducing agent. Synthesis was optimized through an experimental design, and particle characterization was obtained through UV-Vis spectroscopy. In a first stage, a factorial design was conducted to establish the significance of the variables used in the synthesis, i.e. reducer concentration, temperature, stirring rate. In the second stage, the obtained nanoparticles were positioned on a silicon p-type substrate through electrophoretic deposition. The modified substrates were characterized by means of reflectance measurements and their morphology using transmission electron microscopy (TEM) and atomic force microscopy (AFM). Finally, a brief discussion was carried out concerning the sizes of the determined nanoparticles based on a model taken from the literature that relates maximum absorption with the nanoparticle diameter, comparing these with the sizes obtained through AFM and TEM observation.
- ZrO2-SUPPORTED ALKALI METAL (Li, Na, K) CATALYSTS FOR BIODIESEL PRODUCTION
Abstract: We studied the effect of the alkali metal type (Li, Na, and K) and the calcination temperature (500, 600 and 700 °C) in the activity for biodiesel production of catalysts prepared by impregnation method, with constant metal content of 10%w/w using ZrO2 as support. The results of the catalytic activity allowed to find an activity sequence regarding the alkali tested metals: Na > Li > K, with this sequence remaining constant independent of the calcination temperature. The high activity of the Na/ZrO2 system, and slightly lower activity of Li/ZrO2, can be explained by the fact that higher calcination temperatures promote the formation of alkali-based zirconate species, M2ZrO3 (M = Na or Li). The presence of these species is correlated with the higher activity of these catalysts, specifically with the Na and Li-based catalyst calcined at high temperatures (600-700 °C). These M2ZrO3 species show higher basicity respect to other alkali metal oxide species, as was demonstrated with CO2-TPD results. The higher activity corresponded to 10% Na supported on ZrO2 and calcined at 700 °C, which reached full conversion within just 30 minutes of reaction, which makes this system a promising heterogeneous replacement for the regular homogeneous systems.
- STUDY OF THE CATALYTIC CONVERSION AND ADSORPTION OF ABIETIC ACID ON
ACTIVATED CARBON: EFFECT OF SURFACE ACIDITY
Abstract: This study reports the adsorption and catalytic conversion of abietic acid as representative compound of tall oil, using activated carbons. Acid functional groups present on CGRAN activated carbons favored the adsorption of abietic acid, probably through a physical adsorption mechanism. In contrast, the conversion of abietic acid was not favored in DARCO activated carbon by increase of acid sites thought HNO3 treatment. The detection of neoabietic, palustric and/or levopimaric acids as reaction products indicate that the transformation of abietic acid was by dehydrogenation and/or isomerization routes. The negative influence of acid sites on the catalytic activity, in addition to the non-detection of volatile products, suggests that the cracking pathway for the conversion of abietic acid over these catalysts can be ruled out. Contrasting effects of the surface groups on the adsorption capacity and the conversion was observed: strong acid sites of CGRAN activated carbon favor the adsorption of abietic acid and decrease competitive adsorption between substrate and solvent, while conversion is not favored by these acid sites.
- CHEMICAL COMPOSITION AND ANTIBACTERIAL ACTIVITY OF ESSENTIAL OILS FROM
AZORELLA SPINOSA (APIACEAE) AGAINST WILD PHYTOPATHOGENIC BACTERIA
Abstract: The aim of the present investigation was to appraise variation in the chemical composition and antimicrobial activity against phytopatogenic bacterial of essential oils from Azorella spinosa. Three samples of A. spinosa were collected in different date in the same area. The essential oils were obtained for hydro-destillation using a Clevenger-type apparatus. The chemical composition of essential oils were analysed using Gas chromatography-mass spectrometry showed variation in the yield and composition, the main detected compounds were monoterpenes such as limonene (10.66-12.30%), tricyclene (10.81-16.99%) and sabinene (9.10-11.49%), the most abundant sesquiterpene was γ-gurjenene (5.48-8.47%). The biological activity of essential oils from A. spinosa against wild phytopatogenic microorganisms showed selectivity over Pseudomonas syringae. This is the first report of the essential oil composition of A. spinosa, and confirms that natural products obtained from aromatic plants represent an important source of bioactive molecules that could be used as new alternatives for the treatment of phytopatogenic bacteria infections.
- A BOX-MODEL APPROACH TO MOLECULAR SHAPE
Abstract: In this work, using the length-width-height ratios of a rectangular box in which the molecule under study is enclosed, two descriptors for the characterization of molecular shape are introduced. The molecular shape analysis of the set of molecules under study is facilitated by the introduction of a diagram where the extreme cases (i.e. cubic-box, prolate-box and oblate-box) are clearly located. The method is illustrated by the analysis of fifty molecules including normal alkanes, acenes, alkynes, oblate molecules and the eighteen octane isomers. The geometry of each molecule was optimized by AM1 semiempirical method, and van der Waals molecular surface was used to define the molecular shape contour. The length, the width, and the height of the enclosing box were extracted using VEGA ZZ software. A regular behaviour of the shape descriptors for homologous series was observed. Finally, using the present descriptors, a molecular shape similarity analysis of the octane isomer molecules was included.
- SYNTHESIS, CHARACTERIZATION, AND GAS TRANSPORT PROPERTIES OF NEW
Abstract: Three new copoly(ether-amide)s based on polyether segments of different molecular weight (average molecular weight 400, 900 and 2000 g/mol) and polyamide segments obtained from 4,4’-diamine benzophenone (DBF) and isophthalic acid (ISO) are reported. The resulting new copoly(ether-amide)s have inherent viscosities ranging of 0.32 to 0.35 dL/g at concentration of 0.5 g/dL, and form dense membranes by solvent casting method. The gas transport properties of the new copoly(ether-amide) membranes for pure gases (He, CO2, O2, CH4, and N2) are studied at different pressures (2.0, 5.0, 7.5, and 10.0 atm) and at different temperatures (35-75 °C). The soft segment of polyether allows an increase in gas permeability coefficients, mainly CO2, in comparison with the values reported for DBFISO aromatic polyamide. However, an increase in polyether segment length decreases the overall permeability coefficients, because the polyether shows a strong tendency to crystallize.
- NEW APPROACH FOR DETERMINATION OF FLUMEQUINE AND OXOLINIC ACID IN AQUEOUS
SAMPLES BYIONIC LIQUID-BASED DISPERSIVE LIQUID-LIQUID MICROEXTRACTION AND
HIGH-PERFORMANCE LIQUID CHROMATOGRAPHY-FLUORESCENCE DETECTION
Abstract: A rapid and sensitive analytical method for the determination of oxolinic acid and flumequine in aqueous samples based on dispersive liquid-liquid microextraction using ionic liquids (ILs) was developed. Based on the structural properties of the antibiotic agents studied, two ILs with different functionalities were required: ethyl-dimethyl-(2-methoxyethyl) ammonium tris(pentafluoroethyl)trifluorophosphate ([MOEDEA][FAP]) for extraction and 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BFJ) to adjust the polarity of the medium. The significant experimental factors involved in DLLME were identified and optimized using the experimental design methodology. A Plackett-Burman design was initially used for screening, and a central composite design was used for optimization. The optimized method exhibited good precision, with relative standard deviation values of less than 5 % and limits of detections on the order of 0.1 and 0.3 ng mL-1 for the two drugs. The enrichment factors for both antibiotics were 13-33 fold. The proposed method was applied to the analysis of the two antibiotic in spiked surface, river, and wastewater samples.
- ELECTRONIC AND STRUCTURAL PROPERTIES OF 5-HYDROXY-7-METOXYFLAVANONE: A
Abstract: Electronic and structural properties of two polymorphic modifications of 5-hydroxy-7-methoxyflavanone (pinostrobin) were theoretically investigated and compared with experimental crystallographic data. In the literature, four polymorphic modifications of pinostrobin had been reported. The present study has established that only two of them are relevant as they differ only in the position of the methoxy group whereas other structures are derived from the rotation of the phenyl group. Both structures differ in about 1.5 kJ/mol, but the activation energy of methoxy torsion was greater than 16 kJ/mol. In addition, both have similar electronic structures but it was established with slight differences in reactivity.
- OXIDATION FACILITY BY A TEMPERATURE DEPENDENCE ON THE METAL NOBLE
NANOSTRUCTURED M°/MxOy PHASE PRODUCTS USING A SOLID STATE METHOD: THE
CASE OF Pd
Abstract: Pyrolysis at 800°C under air of the macromolecular precursor Chitosan•(PdCl2)n and PS-co-4-PVP•(PdCl2)n in solid state afford the mixture phases Pt/PdO depending on the molar ratio metal/polymer. For the 1:1 Chitosan•PdCl2)n and PS-co-4-PVP•(PdCl2)n precursors the pure phase PdO was obtained while that for another molar ratios 1:5 and 1:10, the mixture phase Pt/PdO were obtained. For the 1:10 PS-co-4-PVP•(PdCl2)n precursor the core/shell PdO@Pd nanoparticles as small as 4 nm were observed. Optical properties for the PdO indicate an insulator behavior.
- FERROCENYL ALKYLAMMONIUM N-SUBSTITUTED POLYPYRROLE CONTAINING Pt AND Pd
AND ITS APPLICATION ON ELECTROANALYSIS OF ARSENITE
Abstract: Arsenic occurs in a variety of forms and oxidation states and is a very toxic element. The main inorganic arsenic species present in natural waters are arsenate (oxidation state V) and arsenite ions (oxidation state III). Arsenite is more toxic and mobile than arsenate. Therefore, it is important the development of new materials for analysis and control of these toxic species. This research proves that polymer-metal composite electrode materials synthesized by incorporation of Pt0 and Pd0 nanoparticles into a poly(pyrrole-ferrocenyl alkylammonium) matrix present electrocatalytic properties towards the oxidation of arsenite to arsenate. The polymer films displayed a stable electrochemical response in aqueous solution. However, when the polymer film modified electrode were transferred to aqueous solution in presence of arsenite anions, the CV curves for polymer films were deeply modified by the decrease in the electroactivity of the film. It can be concluded that the cationic polymer films present a strong affinity toward arsenite anions. The composite films containing Pt0 or Pd0 showed catalytic activity towards oxidation of As(III) to As(V) due to the presence of metal catalyst particles into the polymer films.
- MECHANISTIC STUDY OF A RUTHENIUM HYDRIDE COMPLEX OF TYPE
[RuH(CO)(N-N)(PR3)2]+ AS CATALYST PRECURSOR FOR THE HYDROFORMYLATION
REACTION OF 1-HEXENE
Abstract: The catalytic activity of systems of type [RuH(CO)(N-N)(PR3)2]+ was evaluated in the hydroformylation reaction of 1-hexene. The observed activity is explained through a reaction mechanism on the basis of the quantum theory. The mechanism included total energy calculations for each of the intermediaries of the elemental steps considered in the catalytic cycle. The deactivation of the catalyst precursors takes place via dissociation of the polypyridine ligand and the subsequent formation of thermodynamically stable species, such as RuH(CO)3(PPh3)2 and RuH3(CO)(PPh3)2, which interrupt the catalytic cycle. In addition, the theoretical study allows to explain the observed regioselectivity which is defined in two steps: (a) the hydride migration reaction with an anti-Markovnikov orientation to produce the alkyl-linear-complex (3.1a), which is more stable by 19.4 kJ/mol than the Markovnikov orientation (alkyl-branched-complex) (3.1b); (b) the carbon monoxide insertion step generates the carbonyl alkyl-linear specie (4.1a) which is more stable by 9.5 kJ/mol than the alternative species (4.1b), determining the preferred formation of heptanal in the hydroformylation of 1-hexene.
- INTERMOLECULAR ASSOCIATION OF AMPHIPATHIC POLYELECTROLYTES IN
Abstract: The intermolecular association of amphipathic polyelectrolytes is studied using fluorescence and conductivity methods. This type of interaction is evidenced by the decrease in the average distances between charges as the polyelectrolyte side chain increases in length. This modify the dissociation degree and consequently, the linear charge density parameter. These distances were calculated with the Manning counterion condensation theory for the conductivity of polyelectrolyte solutions. The determination of the ratio I1/I3 of the fluorescence bands of pyrene with polymer content reveals the formation of hydrophobic microdomains at very low concentrations, smaller than the required concentration to produce a significant change in the average distances between charges. These distances and also the I1/I3 ratio vary with polymer concentration and their values were dependent on the size of the side chain in the polyelectrolyte. Finally, the experimental behavior of the solution viscosity and electrical conductivity of polyelectrolytes, which increase drastically with dilution, can be explained as a continuous change in the average distances between charges which produce conformational changes.
- EFFECT OF THE SELENIUM CONTENT IN THE OPTICAL PROPERTIES OF THE KESTERITE
Abstract: Polycrystalline Cu2ZnSnS4-xSe x (X=1, 2, 3) compounds were synthesized by conventional solid-state reactions. The samples were characterized by powder X-ray diffraction (XRD), energy-dispersive X-ray analysis (SEM-EDS), Raman spectroscopy, diffuse reflectance UV-vis and Photoluminescence. All ofphases crystallize in the tetragonal kesterite-type structure. The powder X-ray diffraction (XRD) pattems were indexed in the space group . No secondary phases were detected in XRD pattems. The results from diffuse reflectance show band gap between 1.26 - 1.17 eV, when S is gradually replaced by Se. The PL spectrum of Cu2ZnSnS4-xSe x phases shows nearly symmetrical band, which shifted linearly to the lower energy with increasing Se content. The selenized (CZTSSe) phases are promising candidates to be used as absorbing material in solar cells.
- SYNTHESIS AND CHARACTERIZATION OF POLY([(2-methacryloyloxy) ethyl])
TRIMETHYLAMONNIUM CHLORIDE) RESIN WITH REMOVAL PROPERTIES FOR VANADIUM(V)
Abstract: It was successful synthesized the ion exchange resin poly([(2-methacryloyloxy) ethyl]) trimethylammonium chloride) PClMETA by radical polymerization to study the removal properties towards vanadium (V) and molybdenum (VI) and compared with the commercial resin AmberliteIRA-402 which contains the same functional group. The resin was characterized by FT-IR and SEM. Parameters including water adsorption capacity, effect of the pH, maximum retention capacity of the metal ions, elution, regeneration, adsorption time, and adsorption isotherms were studied. All the studies were carried out in Batch and Column equilibrium procedures. Thermodynamic parameters such as enthalpy, entropy, and free energy were calculated. The PClMETA resin showed higher capacity to remove V(V) and Mo(VI) from water solution than Amberlite IRA-402 commercial resin. The higher capacity displayed by PClMETA resin was attributed to the higher degree of swelling and different structure that Amberlite IRA-402 resin.
- HOMO- AND COPOLYMERIZATION OF STYRENE AND STYRENE RELATED MONOMERS:
SYNTHESIS AND CHARACTERIZATION
Abstract: Systems including diphenylzinc, metallocene, and methylaluminoxane, at various combinations has been attempted, as initiating systems for homo- and copolymerization of styrene and various styrene related comonomers including : substituted styrenes, styrene derivatives, a-olefins, dienes and more recently cycohexenes including norbornene. The used metallocenes were those containing titanium, zirconium and for comparatives reasons hafnium. The metallocene efficiency towards syndiotactic polystyrene polymerization showed the order : titanocene > zirconocene > hafnocene. While the polymerization as well the copolymerization of Styrene with related to styrene compounds resulted to be much influenced by both electrical and steric hindrance effect. For styrene substituted derivative those group or element having I+ inductive effect depending its position at styrene’s its phenyl ring favours homopolymerization as well their copolymerization with styrene. The steric hindrance also showed a determinant influence on reactivity, so methyl and tert-butyl group, having a I+ effect, when at para-position improve activity and stereoregularity of their polymerization processes. But when placing at orto-position showed a very low capacity to polymerize. The present and previous results indicate that polymerization processes are initiated by monomer coordination to active metal species either of the binary metallocene-MAO or of the ternary Ph2Zn-metallocene-MAO.