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1.
Complex formation equilibria between Ag(I) and thiourea or N-alkyl-substituted thioureas have been investigated in n-propanol by potentiometry at 10 °C intervals from 5 to 50 °C. Stepwise formation of tris-coordinated AgLn (n = 1-3) complexes has been found for the majority of the ligands. ΔH and ΔS values for the complex formation reactions have been evaluated from the dependence of ln βn on temperature. The alkyl-substituents affect the ligand affinities in different ways in relation with the coordination level n.The reactions are exothermic with few exceptions. Enthalpy favoured complex formation with negative dependence of ΔG on temperature (ΔS > 0) have been found.The enthalpy and entropy changes for the stepwise complex formation equilibria are correlated by two linear compensative relationships with the same isoequilibrium temperature 50-51 °C. 相似文献
2.
Ibrahim Shehatta 《Helvetica chimica acta》2002,85(7):2125-2137
Dissociation constants (pKa) of trazodone hydrochloride (TZD⋅HCl) in EtOH/H2O media containing 0, 10, 20, 30, 40, 50, 60, 70, and 80% (v/v) EtOH at 288.15, 298.15, 308.15, and 318.15 K were determined by potentiometric techniques. At any temperature, pKa decreased as the solvent was enriched with EtOH. The dissociation and transfer thermodynamic parameters were calculated, and the results showed that a non‐spontaneous free‐energy change (ΔdissGo>0) and unfavorable enthalpy (ΔdissHo>0) and entropy (ΔdissSo<0) changes occurred on dissociation of trazodone hydrochloride. The free‐energy change or pKa varied nonlinearly with the reciprocal dielectric constant, indicating the inadequacy of the electrostatic approach. The dissociation equilibria are discussed on the basis of the standard thermodynamics of transfer, solvent basicity, and solute‐solvent interactions. The values of ΔtransGo and ΔtransHo increased negatively with increasing EtOH content, revealing a favorable transfer of trazodone hydrochloride from H2O to EtOH/H2O mixtures and preferential solvation of H+ and trazodone (TZD). Also, ΔtransSo values were negative and reached a minimum, in the H2O‐rich zone that has frequently been related to the initial promotion and subsequent collapse of the lattice structure of water. The pKa or ΔdissGo values correlated well with the Dimroth‐Reichardt polarity parameter ET(30), indicating that the physicochemical properties of the solute in binary H2O/organic solvent mixtures are better correlated with a microscopic parameter than the macroscopic one. Also, it is suggested that preferential solvation plays a significant role in influencing the solvent dependence of dissociation of trazodone hydrochloride. The solute‐solvent interactions were clarified on the basis of the linear free‐energy relationships of Kamlet and Taft. The best multiparametric fit to the Kamlet‐Taft equation was evaluated for each thermodynamic parameter. Therefore, these parameters in any EtOH/H2O mixture up to 80% were accurately derived by means of the obtained equations. 相似文献
3.
Molar conductance of lithium acetate, sodium acetate and potassium acetate were studied in aqueous 2-butanol solutions with an alcohol mass fraction (w2) of 0.70, 0.80 and 0.90 at 298.15, 303.15 and 308.15 K. The conductance data were analyzed with the Fuoss conductance-concentration equation to evaluate the limiting molar conductances (Λ0), association constants (KA,c) and cosphere diameter (R) for ion-pair formation. Gibbs energy (ΔG0), enthalpy (ΔH0) and entropy (ΔS0) for ion-association reaction were derived from the temperature dependence of KA,c. Activation energy for ionic movement (ΔH#) was derived from the temperature dependence of Λ0. Based on the composition dependence of Walden products (Λ0η0) and different thermodynamic properties (ΔG0,ΔH0, ΔS0 and ΔH#), the influence of the solvent composition on ion-association and solvation behavior of ions were discussed in terms of ion-solvent, ion-ion interactions and the structural changes in the mixed solvent media. 相似文献
4.
Hydrophobic interaction chromatography of proteins: Thermodynamic analysis of conformational changes
Rene Ueberbacher Agnes Rodler Rainer Hahn Alois Jungbauer 《Journal of chromatography. A》2010,1217(2):184-190
For BSA and β-lactoglobulin adsorption to hydrophobic interaction chromatography (HIC) stationary phases leads to conformational changes. In order to study the enthalpy (ΔHads), entropy (ΔSads), free energy (ΔGads) and heat capacity (Δcp,ads) changes associated with adsorption we evaluated chromatographic data by the non-linear van’t Hoff model. Additionally, we performed isothermal titration calorimetry (ITC) experiments. van’t Hoff analysis revealed that a temperature raise from 278 to 308 K increasingly favoured adsorption seen by a decrease of ΔGads from −12.9 to −20.5 kJ/mol for BSA and from −6.6 to −13.2 kJ/mol for β-lactoglobulin. Δcp,ads values were positive at 1.2 m (NH4)2SO4 and negative at 0.7 m (NH4)2SO4. Positive Δcp,ads values imply hydration of apolar groups and protein unfolding. These results further corroborate conformational changes upon adsorption and their dependence on mobile phase (NH4)2SO4 concentration. ITC measurements showed that ΔHads is dependent on surface coverage already at very low loadings. Discrepancies between ΔHads determined by van’t Hoff analysis and ITC were observed. We explain this with protein conformational changes upon adsorption which are not accounted for by van’t Hoff analysis. 相似文献
5.
Attempts have been made to determine the enthalpy and entropy of transfer of H+ ion from water to mixed solvents using the calorimetric data of earlier experiments. The results are in qualitative agreement with the facts that ΔH t 0 (H+) passes through an exothermic maximum andTΔS t 0 passes through a minimum at about 20 to 30 wt% of organic solvent indicating the initial structure formation and the ultimate breakdown of the solvent structure with the addition of organic solvent. 相似文献
6.
Rong Li Yan Wang Guo‐Liang Chen Mei‐Shi Xiao‐Gang Wang Jian‐Bin Zheng Bin Chen 《中国化学会会志》2011,58(2):215-221
The chromatographic behaviors of proteins on iminodiacetic acid (IDA) column with and without immobilized metal ion were examined in detail. Comparing the effects of pI, solution pH, and salt concentration on retention of proteins in cation‐exchange chromatography (CEC) and metal chelate affinity chromatography (MCAC), the retention mechanism of proteins was investigated in MCAC. By aid of observing the retention characteristics of proteins on naked IDA and metal chelate columns in high concentration salt‐out salt solution, the hydrophobic interaction in MCAC and the influence of metal ion on it were proved. In terms of the comparison of the thermodynamics of proteins in CEC and MCAC, the thermostability, the conformational change entropy Δ(ΔS0) and enthalpy Δ(ΔH0), compensation temperature β, the driving force and caloritic effect of proteins in MCAC were discussed. The identity of retention mechanism at protein thermal denaturation in CEC and MCAC was demonstrated by using the compensation relationship between ΔH0 and ΔS0. 相似文献
7.
Hindered internal rotation about the C‐N single bonds joining the thiuram disulfide was studied by 1H NMR complete line‐shaped analysis in different dimethyl sulfoxide‐chloroform (DMSO‐CDCl3) mixtures. From the temperature dependence of methyls proton spectra, activation parameters (Ea, ΔH≠, ΔS≠, and ΔG≠) were obtained. The Arrhenius plots showed a distinct isokinetic temperature at about 35 °C at which the exchange rate is more or less independent of the solvent composition. The resulting ΔH≠ against TΔS≠ plot showed a firmly good linear correlation, indicating the existence of an enthalpy‐entropy composition in an exchange process. 相似文献
8.
Heats of fusion of polyethylene-adipate, pimelate, suberate and azelaate have been determined by two methods, viz. DTA and the pressure dependence of the melting point up to 6000 bar. Degrees of crystallization were measured dilatometrically. Entropies of fusion were divided into volume and conformational entropy terms, only the latter alternates. Alternation of melting points depends on enthalpy of fusion ΔHm, entropy of fusion ΔSm and volume change Δυ on melting; influence of the functions increases thus ΔVm < ΔHm < ΔSm and ΔSm is dominant. Entropy and heat of fusion alternation is explained by the conformational change on melting governed by the driving force of maximum H-bridge formation. 相似文献
9.
10.
N. M. Viktorova S. P. Knyazev N. S. Zefirov Yu. D. Gavrilov G. M. Nikolaev V. F. Bystrov 《Magnetic resonance in chemistry : MRC》1974,6(4):236-239
The vicinal 3Jaa and 3Jee spin-spin coupling constants of a number of deuterated trans-1,2-disubstituted cyclohexenes and the ΔH and ΔS values of the conformational equilibria of these compounds have been determined by computer optimisation of the 3J(HH) = f(T) function. Compounds with —CF3 and CCl3 substituents were shown to have an enhanced proportion of the diaxial conformer. 相似文献
11.
The pressure dependence of the melting temperature of six aliphatic polyesters belonging to two different homologous series, poly(x-succinate) and poly(x-adipate) having even number of methylene groups (2,4,6) in the alkylene segment (x) was investigated by high pressure differential thermal analysis (HP-DTA) up to 500 MPa. The phase diagrams of these polyesters were newly determined except for poly(ethylene adipate). The dTm/dpo at atmospheric pressure was obtained from the quadratic equation and the trend of dTm/dpo with respect to the number of methylene groups in the monomer unit in each homologous series is discussed. Amorphous densities at 25 °C, expansion and compressibility coefficients in the melt of these polyesters are also reported. The entropy of fusion (ΔSm), enthalpy of fusion (ΔHm), volume change on melting (ΔVm), conformational entropy (ΔSor) and volume entropy (ΔSv) were correlated with respect to the number of methylene groups in the alkylene segment. ΔVm and ΔSv displayed a similar trend as that of dTm/dpo while ΔSm, ΔSor and ΔHm showed an increasing trend. The influence of these parameters on dTm/dpo is discussed in the context of the Clapeyron equation. 相似文献
12.
Mohsen Irandoust Hiua DaraeiMohammad Joshaghani Khodayar GholivandMohammad B. Gholivand 《Polyhedron》2011,30(2):228-232
The complexation reaction between uranyl (II) nitrate, and N-methyliminobis(methylenephosphonic acid) (MIDPH) was investigated in two different binary solvent mixtures of D2O-DMSO-d6 at various temperatures using 31P NMR spectroscopy. The exchange between the free ligand and the 1:1 complexed ligand was slow on the NMR timescale and two 31P NMR signals were observed. The formation constant of the resulting complex was evaluated from integration of the two 31P NMR signals. The values of thermodynamic parameters of the resulting complex (ΔH, ΔS and ΔG) were determined from the temperature dependence of the formation constants. In the two solvent mixtures studied, the resulting complex is enthalpy stabilized but entropy destabilized. 相似文献
13.
Hamideh Sharifi Noghabi Gholam Hossein Rounaghi Mohammad Hossein ArbabZavar Javad Ebrahimi 《Russian Journal of General Chemistry》2014,84(7):1429-1433
We report on conductometric study of complexation between benzylbisthiosemicarbazone [(2E,2′E)-2,2′-(1,2-diphenylethane-1,2-diylidene)bis(hydrazine-1-carbothioamide)] with Zn2+, Cr3+, Co2+, and Ni2+ cations at different temperatures in acetonitrile-dimethylformamide binary solvents of varied composition. The equilibrium constant and standard thermodynamic parameters (Δc H 0 and Δc S 0) of the complexes formation have been determined and found to be dependent on the binary solvent composition, the metal ion nature, and temperature. 相似文献
14.
Alwyn S. Gilbert 《Thermochimica Acta》2007,452(2):135-139
Using published data, the symmetry effect on the entropy of fusion, ΔSf, of rigid organic molecules has been investigated by comparing structural isomers. Because ΔSf is dependent on the enthalpy of fusion, ΔHf, [A.S. Gilbert, Thermochim. Acta 339 (1999) 131-142] this dependence must be allowed for as ΔHf values can vary quite widely. When this is done, it is found that more symmetric isomers usually have lower than expected values of ΔSf, in relation to ΔHf, than their less symmetric counterparts. This is the reason that more symmetric isomers generally melt at higher temperatures, a fact noted by many workers over the years. 相似文献
15.
Using dynamic method and the laser monitoring observation technique, the solubility of cefodizime disodium in water + (ethanol, 1-propanol, and 2-propanol) was measured as a function of temperature from 278.15 K to 318.15 K under atmospheric pressure. The experimental data were correlated with a simple model of molecular thermodynamics for solubility of solid in liquid. The model parameters were fitted, and the solution enthalpies ΔsolH and solution entropies ΔsolS were estimated. ΔsolH and ΔsolS are all positive. The endothermic effect of solution process may be due to the fact that the newly bond energy between cefodizime disodium and solvent molecules is not powerful enough to compensate the energy needed to break the original association bond in various solvents, and the system needs to absorb heat from surroundings and manifests as ΔsolH > 0. The reason for the entropy increase during the dissolution process is that the solutes disrupt the alignment of solvent molecules and therefore reduced the degree of order of the system while they were dissolved in various solvents. The positive ΔsolH and ΔsolS revealed that the dissolution process of cefodizime disodium was an entropy-driven process. 相似文献
16.
I. N. Mezhevoi V. G. Badelin 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2013,87(12):2023-2026
Integral enthalpies of dissolution Δsol H m of DL-valine are measured via calorimetry of dissolution in aqueous solutions of glycerol, ethylene glycol, and 1,2-propylene glycol. Standard values of the enthalpies of dissolution (Δsol H ○) and transfer (Δtr H ○) of amino acid from water to mixed solvent are calculated from the resulting experimental data. The enthalpy coefficients for pair interactions hxy of amino acid with polyatomic alcohol molecules are calculated using the McMillan-Meyer theory and have positive values. The obtained results are discussed in light of the theory of the predomination of various types of interactions in mixed solutions and the effect of structural features of interacting biomolecules on the thermochemical parameters of the dissolution of amino acids. 相似文献
17.
The influence of interaction enthalpy (ΔHMOD/BuLi) of μ, σ, σ+μ and σ-μ complexing polar modifiers with n-butyllithium on the 1,3-butadiene anionic polymerization enthalpy (ΔHBD), polymerization reaction rate (kp) and polybutadiene microstructure was studied. It has been found that enthalpy of interaction depends on complex type, molar ratio of polar modifier to n-butyllithium (MOD/BuLi) and temperature. For the first time it has been proven that with increasing ΔHMOD/BuLi the content of 1,2 butadiene (vinyl) units in the chain increases individually for each complex type but the value of ΔHBD decreases similarly for all complexes containing σ-donor groups, exhibiting linear nature. Since ΔHMOD/BuLi controls the content of butadiene isomeric structures in the chain its value was compared with polymerization reaction rate, ranging from ∼46 to ∼5500 moL/L·min, and discussed on mechanistic level. 相似文献
18.
The integral enthalpies of solution Δsol H m of L-cysteine and L-asparagine in mixtures of water with ethanol, n-propanol, and isopropanol at a mole fraction of alcohol of up to 0.32 were determined by calorimetry of solution. The standard enthalpies of solution (Δsol H 0) of L-serine and of its transfer (Δtr H 0) from water to a mixed solvent were calculated. The dependences of Δsol H 0 and Δtr H 0 on the composition of water-alcohol mixtures pass through a maximum. The calculated enthalpy coefficients of pair interaction of amino acids with alcohol molecules are positive and increase in the order ethanol, n-propanol, isopropanol. The data obtained were interpreted from the viewpoint of various types of interaction in solution and effect of the amino acid residue on the thermochemical characteristics of solution. 相似文献
19.
A direct determination of enthalpy of mixing (ΔH mix) is of interest in predicting miscibility in polymer—polymer systems. Such measurements present, however, working difficulties, so a reliable indirect approach has been attempted. The enthalpy of mixing ΔH m is obtained by application of Hess law to heat of solution measurement for blends and their components in a common solvent. For SAN/PMMA blend, corresponding to the weight ratio 50∶50, the experiments were performed by the Hess law approach at 29.4 and 49.3°C on dilute polymer solutions, for various concentrations, getting very good correlation data. This leads to a negative value of the interaction parameterFH χ(1,2) and by ΔG mix diagram it is possible to make a comparison for each temperature in accordance with the LCST behaviour of these mixtures. 相似文献
20.
《Colloids and Surfaces》1993,69(4):265-269
The thermodynamics of the adsorption of phosphamidon on antimony(V) phosphate cation exchanger has been studied at 30, 45 and 50°C and the thermodynamic equilibrium constant (K0), standard free energy change (ΔG°), enthalpy change (ΔH°) and entropy change (ΔS°) have been calculated to predict its adsorption behaviour. All the data are adequately represented by the Freundlich isotherms. 相似文献