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Thermodynamic Study (thermodynamic + study)
Selected AbstractsThermodynamic Study of the Binding of Methyltrioxorhenium with Pyridine and Its Derivatives in Benzene SolutionEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 12 2005S. Masoud Nabavizadeh Abstract A spectrophotometric study of the interaction of methyltrioxorhenium (MTO) with pyridine and its derivatives in benzene solution has been carried out at various temperatures. The stability constants of the resulting 1:1 complexes were determined by analysis of spectrophotometric data and found to vary in the order 3,4-Me2Py > 4- tBuPy > 4-MePy > 3-MePy > 4-BenzylPy > Py > 3-PhPy > 3-C(O)OMePy > 3-ClPy. The enthalpy and entropy of adduct formation were determined from the temperature dependence of the stability constants. All complexes formed were enthalpy stabilized but entropy destabilized. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Thermodynamic Study of ,H Complexes in Nucleophilic Aromatic Substitution Reactions: Relative Stabilities of Electrochemically Generated RadicalsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 14 2008Iluminada Gallardo Abstract The mechanism for the electrochemical oxidation of ,H complexes, such as 1-hydro-1-alkoxy/sulfoxy or -fluoro-2,4-dinitro/2,4,6-trinitrocyclohexadienyl anions, has been widely studied by means of cyclic voltammetry and controlled-potential electrolysis. Previous studies have shown that the electrochemical oxidation of ,H complexes, formed by the addition of carbon or nitrogen nucleophiles followed by a two electron mechanism, corresponding to the formal elimination of the hydride anion (nucleophilic aromatic substitution of hydrogen mechanism, the NASH mechanism). For these ,H complexes (Nu, = OH,, ,OR, ,SR, ,F), the electrochemical reaction takes place by a one-electron mechanism and is followed by the radical elimination of the leaving group with the consequent recovery of the starting material. This mechanism is similar to that proposed for the electrochemical oxidation of ,X complexes (nucleophilic aromatic substitution of a heteroatom, the NASX mechanism). The operating mechanism in each case, the NASH or NASX, can be rationalized in terms of thermodynamics. The standard potentials of the , complex and/or the leaving group as well as the bond dissociation energies (BDEs) are determinant factors. This study has not led to a significant improvement in the electrochemical preparation of aromatic-substituted compounds, but does help to understand and predict the usefulness or uselessness of using the nucleophilic aromatic substitution route to obtain a desired product. Finally, the current approach extends the electrochemical methodology to different chemical fields, for example, to general nondestructive methods for the detection, identification, and quantification of either organic pollutants or explosives in different solvents. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Binding and Catalysis: A Thermodynamic Study on a Catalytic Antibody SystemCHEMBIOCHEM, Issue 6 2003Herschel Wade Dr. Binding versus catalysis: Attempts to obtain efficient catalysts by using conventional screening methods raise a question concerning the connection between binding and catalysis. To address this issue, we have determined the thermodynamic parameters for the binding of several phosphonates to the esterolytic antibody 17E8 (see scheme). Our results suggest that there may be thermodynamic differences between a binding site selected from a screen for tight transition-state-analogue binding and one that is designed for efficient catalysis. [source] A High Performance Theory for Thermodynamic Study on the Binding of Human Serum Albumin with Erbium ChlorideCHINESE JOURNAL OF CHEMISTRY, Issue 2 2009G. Rezaei BEHBEHANI Abstract A thermodynamic study of the interaction between erbium(III) chloride (Er3+) and human serum albumin (HSA) was studied at pH=7.0, 27 and 37 °C in phosphate buffer by isothermal titration calorimetry (ITC). The present study reports the thermodynamic parameters that govern HSA-Er3+ interactions. The extended solvation theory was used to reproduce the enthalpies of HSA-Er3+ interactions over the whole range of Er3+ concentrations. The binding parameters recovered from the new model were attributed to the structural change of HSA and its biological activity. The results obtained indicate that there is a set of two identical binding sites for Er3+ ions with negative cooperativity. The enhancement of complex formation by Er3+ and concomitant increase in ?S suggest that the metal ion plays a role in increasing the number of hydrophobic contacts. The binding parameters discovered from the extended solvation model indicate that the stability of HSA molecule is increased as a result of its interaction with Er3+ ions. [source] Thermodynamic study of capillary pressure curves based on free energy minimizationGEOFLUIDS (ELECTRONIC), Issue 3 2001Y. Deng Abstract This paper presents a new method for pore level network simulation of the distribution of two immiscible phases in a permeable medium. The method requires that the Helmholtz free energy of the system , the medium and the two phases contained within the pore space , be a minimum at all saturation states. We describe the method here and show some typical results from a computer algorithm that implements it. The results include (i) an explanation of the ,scanning' behaviour of capillary pressure curves based wholly on the free energy minimization, (ii) predictions of capillary pressure at arbitrary wetting states, including negative capillary pressures, and (iii) illustrations of how the minimized free energy changes along the scanning curves. The method also predicts the known dependency of the capillary pressure on the pore size distribution and interfacial tension. The current work is restricted to two-dimensional networks, but the free energy minimization appears to be generalizable to three dimensions and to more than two fluid phases. Moreover, functions generated through the minimization, specifically contact areas between the medium surface and the phases, appear to have applications predicting other multiphase petrophysical properties. [source] Thermodynamic study of wet cooling tower performanceINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 6 2006V. D. Papaefthimiou Abstract An analytical model was developed to describe thermodynamically the water evaporation process inside a counter-flow wet cooling tower, where the air stream is in direct contact with the falling water, based on the implementation of the energy and mass balance between air and water stream describing thus, the rate of change of air temperature, humidity ratio, water temperature and evaporated water mass along tower height. The reliability of model predictions was ensured by comparisons made with pertinent experimental data, which were obtained from the literature. The paper elaborated the effect of atmospheric conditions, water mass flow rate and water inlet temperature on the variation of the thermodynamic properties of moist air inside the cooling tower and on its thermal performance characteristics. The analysis of the theoretical results revealed that the thermal performance of the cooling tower is sensitive to the degree of saturation of inlet air. Hence, the cooling capacity of the cooling tower increases with decreasing inlet air wet bulb temperature whereas the overall water temperature fall is curtailed with increasing water to air mass ratio. The change of inlet water temperature does not affect seriously the thermal behaviour of the cooling tower. Copyright © 2005 John Wiley & Sons, Ltd. [source] Kinetic and thermodynamic study of thiolato and sulfenato Co(III) complexes in water,acetonitrile mixturesINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 1 2004Monika Aranyosiová Rate constants are reported for peroxodisulfate as well as periodate oxidation of[Co(en)2{SCH2CH(COO)NH2}]+, [Co(en)2(SCH2CH2NH2)]2+, and [Co(en)2(SOCH2CH2NH2)]2+ in water,acetonitrile mixtures. The dependence of rate constants on the acetonitrile concentration is established and discussed. Ancillary information relevant to solvation of reactants has been obtained from solvatochromism and from Gibbs transfer functions. The solvent effect is discussed from the viewpoint of change in solvation of initial and transition state on going from water to water,acetonitrile mixtures. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 36: 34,40, 2004 [source] Thermodynamic analysis of two-step solar water splitting with mixed iron oxidesINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 10 2009Martin Roeb Abstract A two-step thermochemical cycle for solar production of hydrogen from water has been developed and investigated. It is based on metal oxide redox pair systems, which can split water molecules by abstracting oxygen atoms and reversibly incorporating them into their lattice. After successful experimental demonstration of several cycles of alternating hydrogen and oxygen production, the present work describes a thermodynamic study aiming at the improvement of process conditions and at the evaluation of the theoretical potential of the process. In order to evaluate the maximum hydrogen production potential of a coating material, theoretical considerations based on thermodynamic laws and properties are useful and faster than actual tests. Through thermodynamic calculations it is possible to predict the theoretical maximum output of H2 from a specific redox-material under certain conditions. Calculations were focussed on the two mixed iron oxides nickel,iron-oxide and zinc,iron-oxide. In the simulation the amount of oxygen in the redox-material is calculated before and after the water-splitting step on the basis of laws of thermodynamics and available material properties for the chosen mixed iron oxides. For the simulation the commercial Software FactSage and available databases for the required material properties were used. The analysis showed that a maximum hydrogen yield is achieved if the reduction temperature is raised to the limits of the operation range, if the temperature for the water splitting is lowered below 800°C and if the partial pressure of oxygen during reduction is decreased to the lower limits of the operational range. The predicted effects of reduction temperature and partial pressure of oxygen could be confirmed in experimental studies. The increased hydrogen yield at lower splitting temperatures of about 800°C could not be confirmed in experimental results, where a higher splitting temperature led to a higher hydrogen yield. As a consequence it can be stated that kinetics must play an important role especially in the splitting step. Copyright © 2009 John Wiley & Sons, Ltd. [source] Behaviour and mechanism of Zn(II) adsorption on Chinese loess at dilute slurry concentrationsJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 5 2008Xiaowu Tang Abstract BACKGROUND: Zn(II) is commonly present in mining drainage in developing countries. Since loess is abundant and always located near mining sites in China, it would be useful to investigate the possibility and efficiency of using loess to remove Zn(II) from aqueous solution. RESULTS: The Zn(II) adsorption capacity of Chinese loess was determined as 215.9 mg g,1. The adsorption followed pseudo-second-order kinetics and took place mainly by surface diffusion. Generally, higher initial pH and solute concentration resulted in higher % Zn(II) removal, while higher temperature and slurry concentration led to lower % Zn(II) removal. A thermodynamic study revealed that the adsorption process was exothermic, with the predicted enthalpy change ranging from ,20.87 to ,4.06 kJ mol,1. With the assistance of X-ray photoelectron spectroscopy and X-ray diffraction, the high adsorption capacity was ascribed to the growth of micro-organisms and mineral constituents such as kaolinite and goethite. CONCLUSION: Chinese loess proved effective for Zn(II) adsorption in this study. The optimal adsorption conditions included pH > 3.0, temperature ,15 °C and contact time , 400 min. As an abundant natural soil in arid areas with very low population density, it would be appropriate to develop this material into a wastewater-purifying agent. Copyright © 2008 Society of Chemical Industry [source] Stabilization of lysozyme by benzyl alcohol: Surface tension and thermodynamic parametersJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 10 2010Monu Kumari Goyal Abstract The aim of the study was to understand the effect of benzyl alcohol on biological activity, aggregation behavior, denaturant and heat-induced unfolding of lysozyme. Compatibility studies of lysozyme carried out with a number of anti-microbial preservatives, indicated benzyl alcohol to be the best suppressor of protein aggregation against heat stress. The effect of this preservative was checked at various pH values ranging from 4.0 to 9.0. In spite of reducing the thermal denaturation temperature (Tm) at all pH values, benzyl alcohol had a stabilizing effect on lysozyme in terms of retaining the biological activity when the enzyme was incubated at 75°C. The reduction in Tm with increasing benzyl alcohol concentration was correlated with decreasing surface tension of surrounding medium. A detailed thermodynamic study of lysozyme in the presence of benzyl alcohol was carried out at pH 6.2. Change in Gibb's free energy of thermal unfolding at 25°C was found to remain constant in the presence of benzyl alcohol, indicating no interaction of benzyl alcohol with the native protein at room temperature. Both the enthalpy and entropy change at mid point of thermal unfolding were found to increase in the presence of benzyl alcohol indicating the stabilization of partially unfolded state. © 2010 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:4149,4161, 2010 [source] Extent and mechanism of solvation and partitioning of isomers of substituted benzoic acids: A thermodynamic study in the solid state and in solutionJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 9 2008German L. Perlovich Abstract Temperature dependency of saturated vapour pressure and thermochemical characteristics of fusion processes for 2-, 3- and 4-methoxybenzoic acids (anisic acids) were measured and thermodynamic functions of sublimation, fusion, and evaporation calculated. A new approach to split specific and nonspecific energetic terms in the crystal lattice was developed. For methoxybenzoic acid isomers as well as for a number of analogous molecules, a parameter describing molecular packing density by the ratio of free volume of the molecules in the crystal lattice and van der Waals molecular volume is defined. Its relationship to Gibbs energy of sublimation and to the respective melting points was analysed. Temperature dependencies of solubility in buffers with pH 2.0 and 7.4, n -octanol and n -hexane were measured. The thermodynamic functions of solubility, solvation and transfer processes were deduced. Concentration dependence of partition coefficients for the outlined isomers was measured. Specific and nonspecific solvation terms were distinguished using the transfer from the ,inert' n -hexane to the other solvents. Comparison analysis of specific and nonspecific interactions in the solid state and in solution was carried out. A diagram enabling analysis of the mechanism of the partitioning process was applied. It was found that position of substituents essentially affects the mechanism of partitioning in buffer pH 2.0, however, at pH 7.4, the mechanism is independent of the position of the substituent. © 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 97:3883,3896, 2008 [source] Kinetic and thermodynamic study of methanolysis of poly(ethylene terephthalate) waste powderPOLYMER INTERNATIONAL, Issue 3 2003S Mishra Abstract Depolymerization of poly(ethylene terephthalate) waste (PETW) was carried out by methanolysis using zinc acetate in the presence of lead acetate as the catalyst at 120,140,°C in a closed batch reactor. The particle size ranging from 50 to 512.5,µm and the reaction time 60 to 150,min required for methanolysis of PETW were optimized. Optimal percentage conversion of PETW into dimethyl terephthalate (DMT) and ethylene glycol (EG) was 97.8% (at 120,°C) and 100% (at 130 and 140,°C) for the optimal reaction time of 120,min. Yields of DMT and EG were almost equal to PET conversion. EG and DMT were analyzed qualitatively and quantitatively. To avoid oxidation/carbonization during the reaction, methanolysis reactions were carried out below 150,°C. A kinetic model is developed and the experimental data show good agreement with the kinetic model. Rate constants, equilibrium constant, Gibbs free energy, enthalpy and entropy of reaction are also evaluated at 120, 130 and 140,°C. The methanolysis rate constant of the reaction at 140,°C (10.3 atm) was 1.4,×,10,3,g PET mol,1 min,1. The activation energy and the frequency factor for methanolysis of PETW were 95.31,kJ,mol,1 and 107.1,g PET mol,1 min,1, respectively. © 2003 Society of Chemical Industry [source] A High Performance Theory for Thermodynamic Study on the Binding of Human Serum Albumin with Erbium ChlorideCHINESE JOURNAL OF CHEMISTRY, Issue 2 2009G. Rezaei BEHBEHANI Abstract A thermodynamic study of the interaction between erbium(III) chloride (Er3+) and human serum albumin (HSA) was studied at pH=7.0, 27 and 37 °C in phosphate buffer by isothermal titration calorimetry (ITC). The present study reports the thermodynamic parameters that govern HSA-Er3+ interactions. The extended solvation theory was used to reproduce the enthalpies of HSA-Er3+ interactions over the whole range of Er3+ concentrations. The binding parameters recovered from the new model were attributed to the structural change of HSA and its biological activity. The results obtained indicate that there is a set of two identical binding sites for Er3+ ions with negative cooperativity. The enhancement of complex formation by Er3+ and concomitant increase in ?S suggest that the metal ion plays a role in increasing the number of hydrophobic contacts. The binding parameters discovered from the extended solvation model indicate that the stability of HSA molecule is increased as a result of its interaction with Er3+ ions. [source] | ||||||||||