Advances in Physical Chemistry
[SJR: 0.297] [H-I: 7] [11 followers] Follow
Open Access journal
ISSN (Print) 1687-7985 - ISSN (Online) 1687-7993
Published by Hindawi [333 journals]
- Synthesis and Characterization of System In(O,OH)S/i-ZnO/n+-ZnO
Abstract: In this work, we fabricated system In(O,OH)S/i-ZnO/n+-ZnO to be used as potential optical window in thin films solar cells. i-ZnO/n+-ZnO thin films were synthesized by reactive evaporation (RE) method and In(O,OH)S thin films were synthesized by chemical bath deposition (CBD) method; all thin films were deposited on soda lime glass substrates. Thin films were characterized through X-ray diffraction (XRD), atomic force microscopy (AFM), and spectral transmittance measurements. Structural results indicated that both thin films were polycrystalline; furthermore, morphological results indicated that both thin films coated uniformly soda lime glass substrate; besides, optical characterization indicated that system had more than 80% of visible radiation transmittance.
PubDate: Wed, 15 Mar 2017 07:39:41 +000
- The Effect of Concentration of Lawsonia inermis as a Corrosion Inhibitor
for Aluminum Alloy in Seawater
Abstract: Lawsonia inermis also known as henna was studied as a corrosion inhibitor for aluminum alloy in seawater. The inhibitor has been characterized by optical study via Fourier transform infrared spectroscopy (FTIR). The FTIR proves the existence of hydroxyl and carbonyl functional groups in Lawsonia inermis. Aluminum alloy 5083 immersed in seawater in the absence and presence of Lawsonia inermis was tested using electrochemistry method, namely, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PP). EIS and PP measurements suggest that the addition of Lawsonia inermis has caused the adsorption of inhibitor on the aluminum surface. The adsorption behavior of the inhibitor follow Langmuir adsorption model where the value of free energy of adsorption, , is less than 40 kJ/mol indicates that it is a physical adsorption. Finally, it was inferred that Lawsonia inermis has a real potential to act as a corrosion inhibitor for aluminum alloy in seawater.
PubDate: Thu, 16 Feb 2017 00:00:00 +000
- Superparamagnetic Iron Oxide (Fe3O4) Nanoparticles Coated with PEG/PEI for
Biomedical Applications: A Facile and Scalable Preparation Route Based on
the Cathodic Electrochemical Deposition Method
Abstract: Cathodic electrochemical deposition (CED) is introduced as an efficient and effective method for synthesis and surface coating of superparamagnetic iron oxide nanoparticles (SPIONs). In this way, bare Fe3O4 nanoparticles were electrosynthesized through CED method from aqueous solution Fe3+ : Fe2+ chloride (molar ratio of 2 : 1). In the next step, the surface of NPs was coated with polyethyleneimine (PEI) and polyethylene glycol (PEG) during the CED procedure, and PEG/PEI coated SPIONs were obtained. The prepared NPs were evaluated by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), dynamic light scattering (DLS), vibrating sample magnetometer (VSM), and field-emission scanning electron microscopy (FE-SEM). The pure magnetite phase and nanosize (about 15 nm) of the prepared NPs were confirmed by XRD and FE-SEM. The presence of two coats (i.e., PEG and PEI) on the surface of electrosynthesized NPs was proved via FTIR results. The percentage of polymer coat (37.5%) on the NPs surface was provided by TGA analysis. The high magnetization value, negligible coercivity, and remanence measured by VSM indicate the superparamagnetic nature of both prepared NPs. The obtained results confirmed that the prepared Fe3O4 nanoparticles have suitable physicochemical and magnetic properties for biomedical applications.
PubDate: Mon, 13 Feb 2017 00:00:00 +000
- Corrosion Inhibition of Mild Steel in 1 mol L−1 HCl Using Gum
Exudates of Azadirachta indica
Abstract: The ability of gum exudates of Azadirachta indica (GAI) to inhibit corrosion on mild steel in 1 mol L−1 HCl has been studied using mass loss, polarization, and impedence measurements. The effect of temperature (303–323 K) and immersion time of 1, 2, 4, 6, and 12 hours on corrosion behavior of mild steel was examined. Gum exudates decrease the corrosion rate up to a concentration of 80 ppm and at 323 K temperature. GAI adsorb chemically onto the surface of the mild steel while it obeys Langmuir adsorption isotherms. Polarization studies show GAI as mixed mode inhibitor. Surface studies ascertain that a shielding layer was formed on the mild steel surface.
PubDate: Thu, 22 Dec 2016 14:37:03 +000
- New Homologues Series of Heterocyclic Schiff Base Ester: Synthesis and
Abstract: A homologous series of liquid crystal bearing with heterocyclic thiophene Schiff base ester with alkanoyloxy chain (CH3(CH2)nCOO–, where , 6, 8, 10, 12, 14, 16) was successfully synthesized through the modification of some reported methods. The structural information of these compounds was isolated and characterized through some spectroscopic techniques, such as FTIR, 1H, and 13C NMR and elemental analysis. Textural observation was carried out using a polarizing optical microscope (POM) over heating and cooling cycles. It was found that all synthesized compounds (3a–g) exhibited an enantiotropic nematic phase upon the heating and cooling cycle with high thermal stability. Moreover, a characteristic bar transition texture was observed for compounds 3f and 3g which have shown transition of nematic-to-smectic C phase. This has been further confirmed by obtaining relative phase transition temperature using the differential scanning calorimetry (DSC).
PubDate: Thu, 08 Dec 2016 15:04:24 +000
- Investigation of Antileishmanial Activities of Acridines Derivatives
against Promastigotes and Amastigotes Form of Parasites Using Quantitative
Structure Activity Relationship Analysis
Abstract: In a search of newer and potent antileishmanial (against promastigotes and amastigotes form of parasites) drug, a series of 60 variously substituted acridines derivatives were subjected to a quantitative structure activity relationship (QSAR) analysis for studying, interpreting, and predicting activities and designing new compounds by using multiple linear regression and artificial neural network (ANN) methods. The used descriptors were computed with Gaussian 03, ACD/ChemSketch, Marvin Sketch, and ChemOffice programs. The QSAR models developed were validated according to the principles set up by the Organisation for Economic Co-operation and Development (OECD). The principal component analysis (PCA) has been used to select descriptors that show a high correlation with activities. The univariate partitioning (UP) method was used to divide the dataset into training and test sets. The multiple linear regression (MLR) method showed a correlation coefficient of 0.850 and 0.814 for antileishmanial activities against promastigotes and amastigotes forms of parasites, respectively. Internal and external validations were used to determine the statistical quality of QSAR of the two MLR models. The artificial neural network (ANN) method, considering the relevant descriptors obtained from the MLR, showed a correlation coefficient of 0.933 and 0.918 with 7-3-1 and 6-3-1 ANN models architecture for antileishmanial activities against promastigotes and amastigotes forms of parasites, respectively. The applicability domain of MLR models was investigated using simple and leverage approaches to detect outliers and outsides compounds. The effects of different descriptors in the activities were described and used to study and design new compounds with higher activities compared to the existing ones.
PubDate: Tue, 22 Nov 2016 13:47:23 +000
- Electrochemical Investigation of Catechol at Poly(niacinamide) Modified
Carbon Paste Electrode: A Voltammetric Study
Abstract: A polymeric thin film modified electrode, that is, poly(niacinamide) modified carbon paste electrode (MCPE), was developed for the electrochemical determination of catechol (CC) by using cyclic voltammetric technique. Compared to bare carbon paste electrode (BCPE), the poly(niacinamide) MCPE shows good electrocatalytic activity towards the oxidation of catechol in phosphate buffer solution (PBS) of physiological pH 7.4. All experimental parameters were optimized. Poly(niacinamide) modified carbon paste electrode gave a linear response between concentration of CC and its anodic peak current in the range within 20.6–229.0 μM. The limit of detection (3S/M) and limit of quantification (10S/M) were 1.497 μM and 4.99 μM, respectively. From the study of scan rate variation, the electrode process was found to be adsorption-controlled. The involvement of protons and electrons in the oxidation of CC was found to be equal. The probable electropolymerisation mechanism of niacinamide was proposed. Finally, this method can be used in development of a sensor for sensitive determination of CC.
PubDate: Mon, 07 Nov 2016 13:53:10 +000
- Theoretical Studies of the Stone-Wales Defect in C36 Fullerene Embedded
inside Zigzag Carbon Nanotube
Abstract: We apply density functional theory at PBE/6-311G(d) level as well as nonorthogonal tight-binding model to study the Stone-Wales transformation in C36 fullerene embedded inside the (14,0) zigzag carbon nanotube. We optimize geometries of two different isomers with the and the symmetries and the transition state dividing them. The mechanism of Stone-Wales transformation from to symmetry for the encapsulated C36 is calculated to be the same as for the isolated one. It is found that the outer carbon wall significantly stabilizes the isomer. However, carbon nanotube reduces the activation barrier of Stone-Wales rearrangement by 0.4 eV compared with the corresponding value for the isolated C36.
PubDate: Tue, 01 Nov 2016 09:08:05 +000
- Remediation of Rhodamine B Dye from Aqueous Solution Using Casuarina
equisetifolia Cone Powder as a Low-Cost Adsorbent
Abstract: The removal of toxic dye rhodamine B (RB) from aqueous solution was achieved by using Casuarina equisetifolia cone (CEC) as an adsorbent. Batch experiment method was used in order to investigate the effects of contact time, pH, temperature, ionic strength, and dye concentration on the adsorption process. Kinetics and isotherm theoretical models were applied on the experimental data and it was found that the pseudo-2nd-order kinetics and the Langmuir isotherm model best fitted into the data. The Langmuir maximum adsorption capacity for CEC was determined as 49.5 mg g−1. The adsorption of RB onto CEC is thermodynamically favourable, feasible, and endothermic in nature.
PubDate: Mon, 17 Oct 2016 13:14:45 +000
- General Randić, Sum-Connectivity, Hyper-Zagreb and Harmonic Indices, and
Harmonic Polynomial of Molecular Graphs
Abstract: We present explicit formula for the general Randić connectivity, general sum-connectivity, Hyper-Zagreb and Harmonic Indices, and Harmonic polynomial of some simple connected molecular graphs.
PubDate: Sun, 25 Sep 2016 13:43:12 +000
- Removal of Phosphate Using Red Mud: An Environmentally Hazardous Waste
By-Product of Alumina Industry
Abstract: The industrial waste, bauxite residue generated in the Bayer chemical process of alumina production, commonly known as red mud (RM) has been used as the adsorbent for selective removal of phosphate in aqueous solutions. RM collected from the storage area of alumina industry was characterized by chemical analysis and physical methods such as BET surface area, Scanning Electron Microscopy (SEM), particle size analysis, and X-ray diffraction (XRD) methods. Among the various red mud samples (0.2–200 μ) studied, the samples treated with 1 M HCl for 2 h were found better for the selective adsorption of phosphate in comparison with untreated and heat treated RM samples. The presence of phosphate in the aqueous samples collected after adsorption studies with red mud was determined by standard spectrophotometric procedure using ammonium molybdate and ascorbic acid in nitrate medium at 880 nm. The studies reported significant adsorption of phosphate on acid treated red mud in comparison with adsorption of phosphate on untreated and heat treated red mud, respectively. The adsorption of phosphate on raw red mud and activated red mud was further investigated with respect to stirring time, pH of the solution, dose of adsorbent, and varying phosphate concentration. Acid treated RM is observed as an efficient and cost-effective adsorbent for selective removal of phosphate in aqueous solutions.
PubDate: Mon, 29 Aug 2016 16:35:46 +000
- Kinetics and Mechanistic Study of Permanganate Oxidation of Fluorenone
Hydrazone in Alkaline Medium
Abstract: The oxidation kinetics of fluorenone hydrazone (FH) using potassium permanganate in alkaline medium were measured at a constant ionic strength of 0.1 mol dm−3 and at 25°C using UV/VIS spectrophotometer. A first-order kinetics has been monitored in the reaction of FH with respect to [permanganate]. Less-than-unit order dependence of the reaction on [FH] and [OH−] was revealed. No pronounced effect on the reaction rate by increasing ionic strength was recorded. Intervention of free radicals was observed in the reaction. The reaction mechanism describing the kinetic results was illustrated which involves formation of 1 : 1 intermediate complex between fluorenone hydrazones and the active species of permanganate. 9H-Fluorenone as the corresponding ketone was found to be the final oxidation product of fluorenone hydrazone as confirmed by GC/MS analysis and FT-IR spectroscopy. The expression rate law for the oxidation reaction was deduced. The reaction constants and mechanism have been evaluated. The activation parameters associated with the rate-limiting step of the reaction, along with the thermodynamic quantities of the equilibrium constants, have been calculated and discussed.
PubDate: Mon, 25 Jul 2016 09:52:01 +000
- Energy Landscape of Pentapeptides in a Higher-Order Conformational
Abstract: The potential energy landscape of pentapeptides was mapped in a collective coordinate principal conformational subspace derived from principal component analysis of a nonredundant representative set of protein structures from the PDB. Three pentapeptide sequences that are known to be distinct in terms of their secondary structure characteristics, (Ala)5, (Gly)5, and Val.Asn.Thr.Phe.Val, were considered. Partitioning the landscapes into different energy valleys allowed for calculation of the relative propensities of the peptide secondary structures in a statistical mechanical framework. The distribution of the observed conformations of pentapeptide data showed good correspondence to the topology of the energy landscape of the (Ala)5 sequence where, in accord with reported trends, the α-helix showed a predominant propensity at 298 K. The topography of the landscapes indicates that the stabilization of the α-helix in the (Ala)5 sequence is enthalpic in nature while entropic factors are important for stabilization of the β-sheet in the Val.Asn.Thr.Phe.Val sequence. The results indicate that local interactions within small pentapeptide segments can lead to conformational preference of one secondary structure over the other where account of conformational entropy is important in order to reveal such preference. The method, therefore, can provide critical structural information for ab initio protein folding methods.
PubDate: Mon, 16 May 2016 07:35:06 +000
- Corrigendum to “(Photo)electrochemical Methods for the Determination of
the Band Edge Positions of TiO2-Based Nanomaterials”
PubDate: Thu, 28 Apr 2016 07:26:38 +000
- Simulation of Ni-MH Batteries via an Equivalent Circuit Model for Energy
Abstract: Impedance measurement was conducted at the entire cell level for studying of the Ni-MH rechargeable batteries. An improved equivalent circuit model considering diffusion process is proposed for simulation of battery impedance data at different charge input levels. The cell capacity decay was diagnosed by analyzing the ohmic resistance, activation resistance, and mass transfer resistance of the Ni-MH cells with degraded capacity. The capacity deterioration of this type, Ni-MH cell, is considered in relation to the change of activation resistance of the nickel positive electrodes. Based on the report and surface analysis obtained from the energy dispersive X-ray spectroscopy, the composition formula of metal-hydride electrodes can be closely documented as the AB5 type alloy and the “A” elements are recognized as lanthanum (La) and cerium (Ce). The capacity decay of the Ni-MH cell is potentially initiated due to starved electrolyte for the electrochemical reaction of active materials inside the Ni-MH battery, and the discharge product of Ni(OH)2 at low state-of-charge level is anticipated to have more impeding effects on electrode kinetic process for higher power output and efficient energy delivery.
PubDate: Wed, 16 Mar 2016 06:32:12 +000
- Calculating Heat of Formation Values of Energetic Compounds: A Comparative
Abstract: Heat of formation is one of several important parameters used to assess the performance of energetic compounds. We evaluated the ability of six different methods to accurately calculate gas-phase heat of formation () values for a test set of 45 nitrogen-containing energetic compounds. Density functional theory coupled with the use of isodesmic or other balanced equations yielded calculated results in which 82% (37 of 45) of the values were within ±2.0 kcal/mol of the most recently recommended experimental/reference values available. This was compared to a procedure using density functional theory (DFT) coupled with an atom and group contribution method in which 51% (23 of 45) of the values were within ±2.0 kcal/mol of these values. The T1 procedure and Benson’s group additivity method yielded results in which 51% (23 of 45) and 64% (23 of 36) of the values, respectively, were within ±2.0 kcal/mol of these values. We also compared two relatively new semiempirical approaches (PM7 and RM1) with regard to their ability to accurately calculate . Although semiempirical methods continue to improve, they were found to be less accurate than the other approaches for the test set used in this investigation.
PubDate: Mon, 14 Mar 2016 09:59:21 +000
- Hydrogen Abstraction from Fluorinated Ethyl Methyl Ether Systems by OH
Abstract: A systematic computational investigation of hydrogen abstraction by OH from the full series of fluorinated ethyl methyl ethers (EME) containing at least one H and one F, (, ; and not allowed), including 147 reactants and 469 transition states, has been carried out, employing the MP2/6-31G(d) level of theory. Results for optimized geometries, including evidence of intramolecular hydrogen bonding in transition states, and barrier heights are presented. Trends pertaining to the number of fluorines substituted, key bond lengths, barrier heights, and key bond angles were found with good correlations and were investigated. An increase in the number of F increases the barrier height of the reaction. An increase in some parameters such as C–H length of TS, relative change in C–H from reactants to TS, ∠COC of reactants, ∠HOH in the TS, and relative change in ∠HOH between TS and free water bond angle also correlates with increased barrier height. An increase in other parameters like C–H length in the reactants and hydrogen bonding can decrease the barrier height.
PubDate: Wed, 10 Feb 2016 08:39:06 +000
- A Group Theoretical and Quantum Chemical Study of Electronic Absorption
and Fluorescence, Vibrational Spectra, and Conformations of Trimethine
Cyanine Dye Molecules
Abstract: The energetic structures and conformations of trimethine cyanine dye molecules were investigated. For research, group theoretical and quantum chemical calculation methods were used. The theoretical group analysis of electronic and vibrational structure of molecules was carried out. Also, the energetic structures and conformations of the molecule of this dye were studied. Research shows that the investigated molecule may reside in three different conformational states, one of which is highly symmetric (symmetry ) and the other two with low symmetry. The third conformer is characterized by lowering of binding energy of the electronic system by 0.23 eV, and the long-wavelength absorption band is shifted to lower energies. Also the group theoretical analysis of the trimethine cyanine molecule had allowed systematizing the vibrational and electronic quantum transitions and identifying the bands in the absorption spectra. It is shown that the excitation of the molecule in -state causes trans-cis-isomerization. The presence of the barrier of ~0.1 eV allows the fluorescence process to compete with isomerization process, but isomerization causes a decrease in the fluorescence quantum yield of the dye.
PubDate: Mon, 18 Jan 2016 11:55:30 +000
- Decay of Metastable State with Account of Agglomeration and Relaxation
Abstract: Theoretical description of the metastable phase decay kinetics in the presence of specific connections between the embryos of small sizes has been given. The theory of the decay kinetics in the presence of relaxation processes is constructed in analytical manner. The -mers nucleation is investigated and the global kinetics of decay is also constructed in this case analytically.
PubDate: Tue, 05 Jan 2016 14:16:18 +000
- DFT Study of a Novel Organic Film: The Structural versus Magnetic Effects
Abstract: Unsaturated fatty acids have great interest by their activities as industrial materials in novel applications. In the present work, the cis-3-hexenoic acid (HA) adsorbed on the Ni(111) surface was studied by first-principles calculations using the Vienna Ab Initio Simulation Package (VASP). The most stable location for HA is presented on top site of Ni(111), although the energies are very similar for all the adsorption sites. The surface-molecule interaction takes place between the carboxyl group of HA and surrounding Ni atoms. The adsorption is weak and consequently the metal-molecule length is enhanced. The carboxyl group is elongated and weakened after adsorption giving rise to a shift in stretching frequencies. There are notable changes on the magnetic moments values of Ni surface atoms neighboring to the molecule that mainly induced magnetic moments on O and H atoms. Noticeable charge transfer occurs in 3d 4s, p Ni orbitals and 2s C, 2s p O, 1s H orbitals of carboxyl group. The surface presents positive work function changes after adsorption as a consequence of an electron back-donation. During interaction, the significance of the magnetic effects over the structural effects is evidenced. This sets the stage for a future adsorption process improvement based on the modification of the surface magnetic properties.
PubDate: Sun, 29 Nov 2015 13:00:44 +000
- Geometry, Energy, and Some Electronic Properties of Carbon Polyprismanes:
Ab Initio and Tight-Binding Study
Abstract: We report geometry, energy, and some electronic properties of [n,4]- and [n,5]prismanes (polyprismanes): a special type of carbon nanotubes constructed from dehydrogenated cycloalkane C4- and C5-rings, respectively. Binding energies, interatomic bonds, and the energy gaps between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) have been calculated using density functional approach and nonorthogonal tight-binding model for the systems up to thirty layers. It is found that polyprismanes become more thermodynamically stable as their effective length increases. Moreover, they may possess semiconducting properties in the bulk limit.
PubDate: Mon, 26 Oct 2015 14:24:12 +000
- DFT Study on the Oxidative Addition of 4-Substituted Iodobenzenes on
Abstract: The oxidative addition of 4-substituted iodobenzenes on Pd(0)-PMe3 complexes has been studied at the BP86 level of theory including dispersion correction and solvation effect, with tetrahydrofuran as solvent. The bisphosphine pathway was found to be barrierless, whereas the monophosphine route is hampered by the high dissociation energy of trimethylphosphine. The reaction free energy of this step shows linear correlation with the Hammett constants of the para substituents with the most electron withdrawing groups being the most exergonic.
PubDate: Sun, 04 Oct 2015 13:06:56 +000
- Revisiting Oxidative Dehydrogenation of Ethane by W Doping into MoVMn
Mixed Oxides at Low Temperature
Abstract: The catalytic performance of MoVMnW mixed oxides was investigated in the oxidative dehydrogenation of ethane at three different reaction temperatures (235, 255, and 275°C) using oxygen as an oxidant. The catalysts were characterized by using X-ray diffraction, temperature-programmed reduction, and scanning electron microscopy. The MoVMnW mixed oxide catalyst showed the 70–90% of ethylene selectivity at the reaction temperatures. However, a significant decrease in the selectivity of ethylene was observed by increasing the reaction temperature from 235°C to 275°C.
PubDate: Tue, 27 Jan 2015 09:12:27 +000
- Preparation of Zirconium Oxide Powder Using Zirconium Carboxylate
Abstract: Zirconia was prepared at low temperatures (
PubDate: Wed, 31 Dec 2014 00:10:16 +000
- Adsorption of Polyanion onto Large Alpha Alumina Beads with Variably
Abstract: Adsorption of strong polyelectrolyte, poly(styrenesulfonate), PSS, of different molecular weights onto large α-Al2O3 beads was systematically investigated as functions of pH and NaCl concentrations. The ultraviolet (UV) absorption spectra of PSS at different pH and salt concentrations confirmed that the structure of PSS is independent of pH. With the change of molecular weight from 70 kg/mol (PSS 70) to 1000 kg/mol (PSS 1000), adsorption amount of PSS increases and proton coadsorption on the surface of α-Al2O3 decreases at given pH and salt concentration. It suggests that higher molecular weight of PSS was less flat conformation than lower one. The adsorption density of PSS 70 and PSS 1000 decreases with decreasing salt concentrations, indicating that both electrostatic and nonelectrostatic interactions are involved. Experimental results of both PSS 70 and PSS 1000 adsorption isotherms onto α-Al2O3 at different pH and salt concentrations can be represented well by two-step adsorption model. The effects of molecular weight and salt concentration are explained by structure of adsorbed PSS onto α-Al2O3. The influence of added SDS on the isotherms is evaluated from the sequential adsorption. The SDS uptake onto α-Al2O3 in the presence of hemimicelles can prevent the adsorption of PSS at low concentration so that adsorption of PSS reduces with preadsorbed SDS.
PubDate: Mon, 15 Dec 2014 08:57:29 +000
- Evaluation of Density Matrix and Helmholtz Free Energy for Harmonic
Oscillator Asymmetric Potential via Feynmans Approach
Abstract: We apply a Feynmans technique for calculation of a canonical density matrix of a single particle under harmonic oscillator asymmetric potential and solving the Bloch equation of the statistical mechanics system. The density matrix and kinetic energy per unit length can be directly evaluated from the solving solutions. From the evaluation, it was found that both of the density matrix and kinetic energy per unit length depended on the parameter of the value of asymmetric potential , the value of axes-shift potential , and temperature (T). Comparison of the Helmholtz free energy was derived by the Feynmans technique and the path-integral method. The results illustrated are slightly different.
PubDate: Sun, 02 Nov 2014 08:03:57 +000
- Effect of Concentration on Isomerization of Rhodanine Derivatives of
Merocyanine Dyes in Polar Solvents
Abstract: Rhodanine derivatives of merocyanine dyes with residues of 1,3,3-trimethyl-3H-indole and 3-ethylbenzothiazoline have been found to possess two molecular forms in diluted solutions of polar solvents such as dimethylformamide, dimethyl sulfoxide, and N-methylpyrrolidinone. The first molecular form was observed to prevail at low concentrations of the dyes, normally up to 10−5 M. The second one prevails at higher concentrations and is displayed through a new band in the electronic absorption spectrum, which is red-shifted with respect to the absorption band of the first form. No similar effect was found for these dyes by use of nonpolar solvents or upon alkyl-substitution of the molecules at nitrogen atom in the rhodanine moiety. We assign the above two forms to different molecular isomers and the analogous spectral changes were shown to take place by light or heat influence which correspond to a typical isomerization effect for the related merocyanine dyes. It is discussed that the isomer transformation is facilitated by the increased mobility of the proton bonded to the nitrogen atom of the rhodanine moiety in the polar environment and the increased amount of dye-dye collisions.
PubDate: Wed, 27 Aug 2014 12:05:51 +000
- Ruthenium(III) Catalysis in Perborate Oxidation of 5-Oxoacids
Abstract: Ruthenium(III) catalyzes perborate oxidation of substituted 5-oxoacids in acidic solution. The catalyzed oxidation is first order with respect to the oxidant and catalyst. The rate of ruthenium(III) catalyzed oxidation displays the Michaelis-Menten kinetics on the reductant and is independent of [H+] of the medium. Hydrogen peroxide is the reactive species of perborate and the kinetic results reveal formation of ruthenium(III) peroxo species-5-oxoacid complex. Electron-releasing substituents accelerate the reaction rate and electron-withdrawing substituents retard it. The order of reactivity among the studied 5-oxoacids is p-methoxy p-methyl > p-phenyl > −H > p-chloro > p-bromo > m-nitro. Activation parameters are evaluated using Arrhenius and Eyring’s plots. A mechanism consistent with the observed kinetic data is proposed and discussed. A suitable rate law is derived based on the mechanism.
PubDate: Sun, 24 Aug 2014 06:23:47 +000
- Full Kinetics and a Mechanistic Investigation of the Green Protocol for
Synthesis of β-Aminoketone in the Presence of Saccharose as a Catalyst by
a One-Pot Three-Component Reaction
Abstract: For the first time, in a green protocol, an investigation of the kinetics and mechanism of the reaction between benzaldehyde 1, 4-chloroanilinne 2, and acetophenone 3 compounds in the presence of saccharose as a catalyst was performed for generating β-aminoketone. For determining the kinetic parameters, the reaction was monitored by using the UV/Vis spectrophotometry technique. The second order rate constant () was automatically calculated by the standard equations contained within the program. In the studied temperature range, the second order rate constant (, ) depended on reciprocal temperature that was in good consistent with Arrhenius and Eyring equations, respectively. These data provided the suitable plots for calculating the activation energy and parameters (Ea, , , and ) of the reaction. Furthermore, useful information was obtained from studying the effects of solvent, concentration, and catalyst on the reaction mechanism. The results showed that the first step of the reaction mechanism is a rate determining step (RDS). The obtained experimental data and also the steady state assumption confirmed the proposed mechanism.
PubDate: Mon, 16 Jun 2014 00:00:00 +000
- A Development of Ethanol/Percarbonate Membraneless Fuel Cell
Abstract: The electrocatalytic oxidation of ethanol on membraneless sodium percarbonate fuel cell using platinum electrodes in alkaline-acidic media is investigated. In this cell, ethanol is used as the fuel and sodium percarbonate is used as an oxidant for the first time in an alkaline-acidic media. Sodium percarbonate generates hydrogen peroxide in aqueous medium. At room temperature, the laminar-flow-based microfluidic membraneless fuel cell can reach a maximum power density of 18.96 mW cm−2 with a fuel mixture flow rate of 0.3 mL min−2. The developed fuel cell features no proton exchange membrane. The simple planar structured membraneless ethanol fuel cell presents with high design flexibility and enables easy integration of the microscale fuel cell into actual microfluidic systems and portable power applications.
PubDate: Thu, 29 May 2014 08:34:05 +000