Thermochemical properties from ab initio calculations: π- and σ-Free radicals of importance in soot formation: •C3H3 (propargyl), •C4H3, •C13H9 (phenalenyl), •C6H5 (phenyl), •C10H7 (naphthyl), •C14H9 (anthryl), •C14H9 (phenanthryl), •C16H9 (pyrenyl), •C12H7 (acenaphthyl), and •C12H9 (biphenylyl)

The calculated difference in the standard heat of formation Δ Δ_fH°(298.15) of n- and i-C₄H₃^• free radicals is 37.9 kJ mol⁻¹ for G3MP2B3 and 45.0 kJ mol⁻¹ for CCSD(T)-CBS (W1U) calculations, which seems to preclude the direct even-carbon radical pathway to benzene and higher PAH (polycyclic aromatic hydrocarbon) formation including soot in a hydrocarbon flame. For the phenyl-type σ-radicals listed in the title, absolute values of Δ_fH°(298.15) have been calculated using G3MP2B3-computed values of bond dissociation energies D°(298.15) and combined with experimental values of Δ_fH° (298.15) for the parent hydrocarbon because of a slight systematic overprediction of the thermodynamic stability of large PAHs by the applied computational G3MP2B3 method. Standard enthalpies of formation Δ_fH°(298.15) as well as absolute entropies S° and heat capacities C°_p are given for a series of π- and σ-free radicals important to combustion as a function of temperature. A spread of roughly 40 kJ mol⁻¹ in the average C H bond strength of PAH leading to σ-radicals has been calculated, the lowest leading to 4-phenanthryl (463.6 kJ mol⁻¹), the highest leading to 2-biphenylyl radical (502.5 kJ mol⁻¹). © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 395–415, 2008     

Steric and Inductive Effects on Ionic Association in Aqueous Solutions Using an ion Selective Electrode Technique. II. Magnesium Salts

The stoichiometric association constants, K, the thermodynamic association constants, K_A, and the thermodynamic parameters ΔS°, ΔH°, ΔG° for the association between Mg(II) ion with o-, m and p-toluates,o-,m, and p-chlorobenzoates, and o-, m- and p-bromobenzoates have been determined at 15°C, 25°C, 35°C and 45°C in aqueous media. Ion selective electrodes were used to measure the Mg^{2 +} activities. The trends in the association behavior of Mg(II) salts of aromatic acids connot be explained on the basis of steric effects but can be explained according to the trend of the pKa of the parent organic acids, and the Hammett function, σ, of the salts themselves relative to the corresponding benzoate salt.     

Spectrophotometric Studies of Nickel(II) Chelate of 2-Picolylamine

Nickel(II) chelate of 2–picolylamine has been studied spectrophotometrically in aqueous solution at 25°C and at an ionic strength of 0.3 M. The formation of pink color chelate was pH dependent, and the optimum pH range was between 7.0 to 8.5. Its mole ratio of ligand to nickel(II) ion was found to be 3 to 1 stoichiometry and the formation constant, logK, was determined as 13.31 ± 0.10. By using the wavelength 535 run, determination of trace amount of nickel(II) ion with the sensitivity of 5.28 τ/Cm² was possible. Enthalpy and entropy changes characterizing the formation of the chelate have been calculated as follows: ΔG°=–8.15Kcal mole^-1, ΔH°=–9.65 Kcal mole^-1, ΔS°=28.5eu mole^-1.     

Thermodynamics of binding of methyl orange and its homologs by poly(vinylpyrrolidone): The effect of inorganic electrolytes

The extent of binding of methyl orange, ethyl orange, propyl orange, and butyl orange by poly(vinylpyrrolidone) has been measured in aqueous solutions of inorganic electrolytes such as NaCl, LiCl, NaSCN, and NaClO₄ by an equilibrium dialysis method. The effect of the salts on the first binding constants and the thermodynamic functions which are accompanied by the dye—polymer association process was investigated relative to the corresponding values in the absence of such salts. It was found that in aqueous solutions of NaCl and LiCl the enthalpy change accompanying the binding is small and the largest contribution to the free energy of binding is from the positive entropy gain. For NaSCN and NaClO₄, the values of ΔF° and ΔH° were both large and negative and the value of ΔS° was small and negative. Thus, the favorable free energy for the complex formation was due entirely to the negative enthalpy term. These characteristics of the thermodynamic quantities are discussed in terms of changes in structural properties of water in the vicinity of the binding entities and conformational changes of the polymer to which the dye is bound due to the added foreign electrolytes.     

Structure and thermodynamics of polystyrene-block-poly(ethylene/propene) micelles in selective solvents

The concentration and temperature dependencies of micelle formation by a polystyrene-block-poly(ethylene/propene) copolymer in several ketones (2-butanone, 3-pentanone, 4-methyl-2-pentanone, 4-heptanone, 5-methyl-2-hexanone and 5-methyl-3-heptanone) were studied by static and dynamic light scattering, viscometry and size exclusion chromatography. No micelles were detected in solutions of 5-methyl-3-heptanone. The standard Gibbs energy, ΔG°, the standard enthalpy, ΔH°, and the standard entropy, ΔS°, of micellization were estimated. The values of ΔG° and ΔH° were negative for all ketones studied and depended on the polar character of the ketone. The micelles showed larger association numbers and densities independent of the ketone. Micelle dimensions hardly depended on the ketone.     

The thermodynamic investigation of inclusion complexations between β—cyclodextrin and hyoscyamine drugs

The inclusion complexations of β-cyclodextrin with four hyoscyamine drugs were investigated by microcalorimetric technique and ¹HNMR. All the inclusion complexes were found to be 1:1 and their thermodynamic parameters of formation constant K, ΔG°, ΔH° and ΔS° were obtained. The ¹HNMR spectra strongly suggested that the drug molecule is included in the hydrophobic cavity of β-cyclodextrin. The properties of binding force and effects of steric hindrance and chirality of the drugs on the inclusion complexation were also discussed.     

Correlation of thermodynamic stabilities of charge transfer complexes of anthracene and chloranil with those of tetra-cyanoethylene

The formation constants of charge-transfer complexes of a number of 9- and 9,10-substituted anthracenes with chloranil have been measured by a spectrophotometric method and the corresponding thermodynamic parameters ΔG°_c, ΔH°_c and ΔS°_c evaluated in various solvents. v_max values of the chargetransfer band for chloranil were linearly related to those for tetracyanoethylene (TCNE). Good correlations were also obtained between v_max and the corresponding ionisation potentials Ip of the donor molecules. In addition ΔG°_c varied linearly with Ip and from these correlations, values of ΔG°_c, etc. for the corresponding TCNE complexes could be calculated. These values are otherwise very difficult to obtain due to the high reactivity of TCNE.     

Substituent effects on the tautomer ratios between the hydra-zone imine and diazenyl enamine forms in 3-(arylhydra-zono)methyl-2-oxo-1,2-dihydroquinoxalines. Correlation of the hammett constants σp with the tautomeric equilibrium constants KT

The 3-(arylhydrazono)methyl-2-oxo-1,2-dihydroquinoxalines 1a-e and 2a-i showed tautomeric equilibria between the hydrazone imine A and diazenyl enamine B forms in dimethyl sulfoxide media. The sub-stituent effects on the tautomer ratios of A to B in compounds 1a-e and 2a-i were studied by the nmr spec-troscopy. The electron-donating or electron-withdrawing p-substituents R¹ in compounds 2a-i represented a tendency to increase the ratios of the tautomer A or the tautomer B , respectively, exhibiting the linear correlation of the Hammett constants σ_p (-0.17 to +0.78) with the tautomer ratios of A to B or the tautomeric equilibrium constants K_T. However, the presence of the ester group R² in compounds 1a-e induced the exclusive existence of the tautomer A regardless of the nature of the p-substituents R¹. In the tautomeric thermodynamic study, the elevating temperature increased the ratios of the hydrazone imine tautomer A in compounds 2a-i . The tautomeric thermodynamic parameters ΔG°, ΔH° and ΔS° were derived from the van't Hoff plots for compounds 2a , b , h , i , wherein the entropy term dominated the free-energy difference between the A and B tautomers.     

Studies on the Equilibria of α-Phthalic and Phosphoric Acids in Mixed Methanol — Water Mixture (50% w/w)

The secondary dissociation constants of α-phthalic and phosphoric acids have been determined in 50% w/w methanol-water mixture from the e.m.f measurements of the cell of the type: Pt; H₂(1 atm), M₂A(m), MHA(m), MCl, AgCl; Ag at different temperatures (288.15–308.15 K) and at different ionic strengths. The thermodynamic values ΔG°, ΔH°, ΔS° for the respective equilibria are estimated. The possibility of using these acids as basis for some buffer solutions in 50% methanol – water mixture is discussed.     

Spectrophotometric Studies of Cerium(III) Chelate of 7-Iodo-8-Hydroxyquinoline-5-Sulphonic Acid

Cerium(III) chelate of 7-iodo-8-hydroxyquinoline-5-sulphonic acid(ferron) has been studied spectrophotometrically in aqueous solution at 25°C and at an ionic strength of 0.1M. The formation of this chelate was pH dependent, and the optimum pH range was between 5.5 to 6.0. Its mole ratio of ligand to cerium(III) ion was found to be 2 to 1 stoichiometry and the formation constant, logK, was determined as 10.15. Enthalpy and entropy changes characterizing the formation of the chelate have been calculated as follows: ΔG° =-13.85kcal mole^-1, ΔH°= ?5.03 kcal mole^-1, ΔS°=29.56 eu mole^-1. By using the wavelength of 370 nm, determination of trace amount of cerium(III) ion with the sensitivity of 0.056 was possible.     

Study on the Interaction between Theasinesin and Bovine Serum Albumin by Fluorescence Method

Theasinesin (TS), a polymer of epigallocatechin gallate, is the main active component of tea polyphenols. Several studies indicate that tea polyphenols have extensive pharmacology activity. However, there is little research about the transportation and metabolism of tea polyphenols in vivo. Serum albumin is a most important protein serving as a depot protein and as a transport protein for many drugs and other bioactive small molecules. This study observed the interaction between TS and bovine serum albumin (BSA) by fluorescence and absorption spectroscopy. The results showed that both static and dynamic quenching occurred in the fluorescence quenching of BSA by TS. The binding sites number is 1.1845 and the binding sites may close to the tyrosine residues. The thermodynamic parameters ΔH°, ΔG°, ΔS° at temperatures 310 K were calculated 1.7 KJ, ?35.4 KJ, and 0.12 KJ. The negative sign of free energy (ΔG°) means that the interaction process is spontaneous. The positive enthalpy (ΔH°) and entropy (ΔS°) values of the interaction of TS and BSA indicate that the binding is mainly entropy-driven and the enthalpy is unfavorable for it, the hydrophobic forces playing a major role in the reaction. A distance of 4.037 nm was found between donor (BSA) and acceptor (TS), obtained according to the F?rster theory of non-radiation energy transfer, which indicates that the energy transfer from BSA to TS occurs with high probability. The results of synchronous fluorescence spectra and UV–vis absorption spectra showed that the peptide strands of BSA molecules extended more and the hydrophobicity decreased with the addition of TS.     

蛋白质在疏水色谱中的变性热力学

研究21-80℃温度范围内一些蛋白质和小分子在疏水相互作用色谱中的热行为。利用Van't Hoff作图(lnk'-1/T)测定蛋白质分子的热力学参数(ΔH°, ΔS°和ΔG°), 根据标准熵变(ΔS°)和标准自由能变(ΔG°)判断蛋白质在色谱过程中的构象变化, 通过ΔH°-ΔS°的线性关系估计蛋白质变性时的"补偿温度"(β), 鉴定蛋白质在疏水相互作用色谱中保留机理的同一性。     

Thermodynamics of Ion-Association of NaClO4 in Aqueous-Methanol and Aqueous-Glycerol Using Conductance Measurements

The conductance of NaClO₄ at (25–45)°C in methanol-H₂O, and glycerol-H₂O mixtures in a concentration range up to 10^?2 M has been measured. The association constant, K_A, values have been determined, where the conductometric data were analysed by a M S X computer using the Fuoss-Aprano method. The K_A values for NaClO₄ in methanol-H₂O are higher than in glycerel-H₂O mixtures, Also K_A values increase as the proportional of methanol or glycerol increases in mixture. The thermodynamic parameters ΔH°, ΔG°, and ΔS° were also calculated. It is obvious that the entire process of the ionic association in those systems are endothermic ones. The Walden products, Λ_oη were calculated for all systems investigated.     

Influence of β-cyclodextrin on the protolytic and complexing ability of p-aminobenzoic acid

UV spectroscopy was used to study the protolytic properties and determine the ionization constants of p-aminobenzoic acid in the presence of β-cyclodextrin. Formation of supramolecular structures of 1: 1 composition was established. Stability constants of the β-cyclodextrin-p-aminobenzoic acid inclusion complex were calculated, as were the thermodynamic parameters (ΔG°, ΔH°, and ΔS°) of its formation. The complexing process between β-cyclodextrin and p-aminobenzoic acid was found to occur spontaneously in the temperature range under investigation while being accompanied by energy liberation and leading to a reduction in the system’s entropy.     

Hydrophobic effect for anionic dye - cationic surfactant interaction in aqueous and mixed solvent

Abstract

The interaction between anionic dyes [Reactive Orange 122 (R.O 122), Reactive Blue 19 (R.B 19), Reactive Violet 5 (R.V 5) and Acid Green 20 (A.G 20)] with cationic surfactant cetyltrimethylammoniun bromide (CTAB) has been investigated by spectrophotometry and conductance technique. The used dyes are characterized by tautomeric behavior which affects the mechanism of the interaction. Various parameters such as dye structure, surfactant composition, solvent composition, temperature and pH of the medium were studied. The spectral data were applied for calculating the binding constant between dye and surfactant (K_b), fraction of micellization (?_mic), and standard free energy change of binding (ΔG°_b) in 0,10,20 and 30 v/v % acetonitile (AN). Conductance technique was constructed to estimate the ion pairing constant (K_a) at different temperatures and v/v % AN. Thermodynamic parameters (ΔG°, ΔH° and ΔS°) for ion pair formation were evaluated. The role of hydrophobic and electrostatic effect on dye-surfactant interaction was discussed.     

Synthesis of a MnO2/multiwalled carbon nanotube nanocomposite and its application as a sorbent for removing Cu2+ ions from aqueous media

In this research, a manganese dioxide/multiwalled carbon nanotube (MnO₂/MWCNT) was firstly synthesized and characterized and then was applied as an effective sorbent for removing Cu²⁺ ions from aqueous solution. The effects of initial concentration, temperature, contact time, pH solution, and sorbent dosage were investigated and the optimum value of each was determined. The Langmuir isotherm model, Freundlich model, and Temkin model were used to fit our experimental results. Ultimately, using the Van't Hoff approach, the thermodynamic functions of the intended adsorption phenomenon such as ΔH°_ad, ΔS°_ad, and ΔG°_ad were estimated.     

Beiträge zur Chemie der Oxidhalogenide von Molybdän und Wolfram. I. Sättigungsdruck und Bildungsenthalpie von MoO2Br2 und MoO2CI2

Molybdenum dioxiddibromide and -dichloride have been prepared from MoO₂, Br₂, und Cl₂, respectively, and their chemical and thermochemival behaviour was studied. Their enthalpies of formation, ΔH°, have been determined from the solution enthalpies of MoO₂Br₂, and MOo₂Cl₂, in aqueous NaOH (data see ?Inhaltsübersicht”?). From their sublimation pressures, p, the enthalpies, ΔH° (subl.), and entropies, ΔS° (subl.), of sublimation have been evaluated (data see above).     

Beiträge zur Chemie der Oxidhalogenide von Molybdän und Wolfram. IX. Bildungsenthalpie und Sättigungsdruck des MoOBr3

From the enthalpy of solution of MoOBr₃ in NaOH/H₂O₂ the enthalpy of formation ΔH°(MoOBr₃,f,298) = ?109,5(±0,4) kcal/mol was derived. The sublimation of MoOBr₃ is connected with simultaneous decomposition (see “Inhaltsübersicht”). From the temperature function of the saturated vapor pressure the values ΔH°(subl., MoOBr₃, 298) = 36(±1,5) kcal/mol and ΔS°(subl., MoOBr₃, 298) = 56(±3) cl are calculated.     

Proprietes thermodynamiques des fluorotellurates alcalins. I. Pentafluorotellurate (IV) de sodium

The heat capacity of sodium pentafluorotellurate (IV) was determined between 10 and 300 K. No anomalous region was observed in this range. The behaviour of NaTeF₅ at low temperature was explained by a molecular solid model. The Cp = f(T) curve recalculated from spectroscopic data is in good agreement with the experimental curve.The thermodynamic functions Cp, S°, (H°(T) - H°(O) and −{G°(T) - H°(O)}/T tabulated from 10 to 300 K.     

Thermodynamic studies of sitting-atop complexation between free base meso-tetraarylporphyrins and antimony(III) chloride in chloroform

Interaction of para, meta and ortho-substituted meso-tetraarylporphyrins, (H₂t(X)pp, X: OMe, Me, H and Cl) with SbCl₃ in chloroform solution afforded 1 : 1 sitting-atop (SAT) complexes ([(SbCl₃)(H₂t(X)pp)]). The formation constants were calculated by KINFIT and found to decrease with increasing temperature. The thermodynamic parameters, ΔH°, ΔS° and ΔG°, were obtained. Formation constants of these complexes change with changing substituent (X) on the aryl rings of H₂t(X)pp in the following order: (SbCl₃)H₂t(4-OMe)pp >?(SbCl₃)H₂t(4-Me)pp >?(SbCl₃)H₂tpp >?(SbCl₃)H₂t(4-Cl)pp >?(SbCl₃)H₂t(3-OMe)pp >?(SbCl₃)H₂t(3-Me)pp> (SbCl₃)H₂t(2-OMe)pp >?(SbCl₃)H₂t(2-Me)pp.