Electrical Conductance Studies in Aqueous Solutions with Ascorbate Ions

Conductivity measurements in dilute aqueous solutions of L-ascorbic acid, sodium-L-ascorbate, magnesium-L-ascorbate, calcium-L-ascorbate and ferrous-L-ascorbate were performed in the (288.15 to 323.15) K temperature range. The limiting molar conductances of the ascorbic anion, λ^∘(HAsc⁻, T), and the dissociation constants of ascorbic acid, K(T), were derived by the use of the Debye-Hückel equation for the activity coefficients and the Onsager and Quint and Viallard conductivity equations.     

Electrical Conductance Studies in Aqueous Solutions with Glutamic Ions

Conductivity measurements in dilute aqueous solutions of L-glutamic acid, DL-glutamic acid, sodium-L-glutamate and magnesium-L-glutamate, were performed in the 288.15 to 323.15 K temperature range. The limiting molar conductivities of glutamic anions, λ ^o(HGlu⁻,T) and the dissociation constants of glutamic acid, K ₂(T) were derived by the use of the Debye–Hückel equation for the activity coefficients and the Onsager, and Quint and Viallard conductivity equations.     

Electrical Conductance Studies in Aqueous Solutions of Glutaric Acid,Disodium Glutarate and Sodium Hydrogen Glutarate

Conductivity measurements of glutaric acid and disodium glutarate in dilute aqueous solutions were performed in the 288.15 to 323.15 K temperature range. The limiting equivalent conductances of glutarate anions, λ ^o(HGlut⁻,T) and λ ^o(1/2Glut²⁻,T), and the dissociation constants of glutaric acid, K ₁(T) and K ₂(T), were derived by the use of the Onsager and the Quint and Viallard conductivity equations. The applied molecular model was successfully confirmed by analyzing the conductivities of sodium hydrogen glutarate at 298.15 K.     

Electrical Conductance and Volumetric Studies in Aqueous Solutions of DL-Pyroglutamic Acid

Conductivity measurements of DL-pyroglutamic acid and sodium pyroglutamate in dilute aqueous solutions were performed in the 288.15–323.15 K temperature range. The limiting molar conductances of pyroglutamate anion, λ^o(pGlu⁻, T) and the dissociation constants of pyroglutamic acid, K(T) were derived from the Onsager, and the Quint and Viallard conductivity equations. Densities of aqueous solutions with molalities lower than 0.5 mol-kg⁻¹ were determined at 5 K intervals from T = 288.15 K to 333.15 K. Densities served to evaluate the apparent molar volumes, V_2,φ(m, T), the cubic expansion coefficients, α (m,T) and the changes of the isobaric heat capacities with respect to pressure, (∂ C_P/∂ P)_T,m. They were correlated qualitatively with the changes in the structure of water when pyroglumatic acid is dissolved in it.     

Electrical Conductance and Volumetric Studies in Aqueous Solutions of Nicotinic Acid

Conductivity measurements of nicotinic acid and sodium nicotinate in dilute aqueous solutions were performed in the (288.15 to 323.15) K temperature range. The limiting equivalent conductances of the nicotinate anion, λ⁰(Nic⁻, T), and the dissociation constants of nicotinic acid, K(T), were derived by the use of the Onsager and the Quint and Viallard conductivity equations. Densities of aqueous solutions with molalities lower than 0.2 mol-kg⁻¹ were determined at 5 K temperature intervals, from T = (288.15 to 333.15) K. The measured densities were used to evaluate the apparent molar volumes, V_{2, φ}(m, T), the cubic expansion coefficients, α(m, T), and the changes of isobaric heat capacities with respect to pressure, (∂C_P/∂p)_{T, m}. They were qualitatively correlated with the changes in the structure of water when nicotinic acid is dissolved in it.     

Electrical Conductivity Studies of Quinic Acid and its Sodium Salt in Aqueous Solutions

The electrical conductivities of aqueous solutions of quinic acid and its sodium salt were measured from 293.15 to 328.15 K in steps of 5 K. The molar conductivities of the sodium salt were treated by the Lee–Wheaton equation, in the form of Pethybridge and Taba, and the Kohlrausch equations. The limiting molar conductivities of the quinate anion were estimated, as well as the corresponding ionic association constants and standard thermodynamic functions of the ionic association reaction. The hydrodynamic radius of the quinate anion was calculated from the Walden rule and compared with the van der Waals radius. The dissociation constant of quinic acid was evaluated from the known value of the limiting molar conductivity of quinic acid using the conductivity equation of Pethybridge and Taba. The standard thermodynamic functions of the dissociation process, i.e., the Gibbs energy, enthalpy, entropy and heat capacity, were obtained using the non-empirical procedure given by Clarke and Glew. The standard thermodynamic functions of dissociation of quinic acid are discussed in terms of solute–solvent interactions and stabilization of the quinate anion due to hydrogen bonding of the α-hydroxyl group to the carboxyl group.     

肌醇在碱金属氯化物溶液中的体积性质

使用精密数字密度计测定了298.15和308.15 K肌醇在不同浓度的LiCl-H2O、NaCl-H2O或KCl-H2O溶液中的密度, 计算了肌醇的表观摩尔体积Vφ和极限偏摩尔体积Vθφ , 得到了其由纯水溶剂转移至混合溶剂中的迁移偏摩尔体积⊿trsVθ椎 .结果表明, LiCl, NaCl和KCl在溶液中对肌醇的体积性质影响显著, 极限偏摩尔体积Vθφ和极限迁移偏摩尔体积⊿trsVθφ都随盐浓度的增大而增加;温度对肌醇的极限偏摩尔体积和极限迁移偏摩尔体积只有轻微影响. 从分子-离子间的相互作用角度对实验结果进行了讨论.     

Interactions of Phenylalanine,Tyrosine and Histidine in Aqueous Caffeine Solutions at Different Temperatures

Densities, ρ, viscosities, η, and refractive indices, n_D of aqueous caffeine (0.5 M) and of solutions of amino acids, l‐phenylalanine (Phe), l‐tyrosine (Tyr) and l‐histidine (His), (0.01–0.05 M) in aqueous‐caffeine have been measured at 298.15, 303.15, 308.15 and 313.15 K. From these experimental data, apparent molar volume, ?_v, limiting partial molar volume, ?^º_ν and the slope, S_v, transfer volume, ?^º_ν,tr, Falkenhagen coefficient, A, Jones‐Dole coefficients, B, free energies of activation per mole of solvent, Δμ^o#₁ and per mole of solute, Δμ^o#₂, enthalpy, ΔH^* and entropy, ΔS^* of activation of viscous flow, and molar refraction, R_m were calculated. The results are interpreted from the point of view of solute‐solvent and solute‐solute interactions in these systems. It has been observed that there exist strong solute‐solvent and weak solute‐solute interactions in these systems. Further, the solute‐solvent interactions decrease, whereas solute‐solute interactions increase with rise in temperature. It is observed that these amino acids act as structure‐makers in aqueous‐caffeine solvent. The thermodynamics of viscous flow have also been discussed.     

丙氨酸在葡萄糖和蔗糖水溶液中的体积性质

利用精密数字密度计分别测定了丙氨酸在不同组成的葡萄糖和蔗糖水溶液中的密度,计算了丙氨酸的表观摩尔体积、极限偏摩尔体积和理论水化数,根据结构水合作用模型讨论了迁移偏摩尔体积的变化规律,并与乙二醇-水和丙三醇-水等多羟基体系作了比较.结果表明,丙氨酸分子在多羟基化合物-水体系中体积效应的大小与多羟基化合物所含OH基数目有关.     

Temperature and Concentration Dependence of the Electrical Conductance,Diffusion, and Kinetics Parameters of the Ions in Aqueous Solutions of Sulfuric Acid,Selenic Acid,and Potassium Tellurate

The temperature and concentration dependences of the electrical conductance of aqueous solutions of sulfuric acid, selenic acid, and potassium tellurate were studied. The coefficients of the corresponding empirical equations were determined, and the values of equivalent conductances of the anions were evaluated at infinite dilution at the experimental temperatures. The values of the coefficients in the Fuoss and Onsager equation were evaluated for the three electrolytes at 298 K. The values of the molecular and ionic coefficients of self-diffusion at infinite dilution were calculated in the temperature range 288–318 K. The change of the translational energy Δ E∘_tr. of water molecules in the ionic hydration sphere was determined. The number of water molecules participating in the ionic hydration sphere at 298 K and the changes of Gibbs free energy, enthalpy, and entropy of activation of ionic conductance were calculated. The results obtained were interpreted according to the Samoylov’s theory of positive and negative hydration of ions. The differences observed in the temperature dependences of the mentioned parameters were explained in terms of the different radii and hydration numbers of the ions.     

Studies on 1,2-Bis(O-Aminophenoxy)Ethane-N,N,N′,N′;-Tetraacetic Acid Chelates of the Tripositive Lanthanide Ions

The acid dissociation constants of 1,2-bis(cis-aminophenoxy)ethane-N,N,N′,N′;-tetraacetic acid (H₄BAPAT or H₄Z), and the stability constants of its chelates with tripositive rare-earth metal ions have been determined by the potentiometric titration and mercury indicator electrode methods at 15°, 25′ and 35°C and an ionic strength of 0.1 (KNO₃). The existence of a monohydrogen chelate species, LnHZ, and the normal chelate, LnZ^?, is illustrated. Enthalpy and entropy changes characterizing the formation of the normal chelates and the dissociation of the last two protons of chelating acid have been calculated at 25°C. These functions have been compared with corresponding values for related chelating agents.     

氨基酸在木糖醇水溶液中的体积性质

应用精密数字密度计测定了298.15 K时甘氨酸、L-丙氨酸或L-缬氨酸与不同组成的木糖醇-水混合溶剂构成的三元系溶液的密度, 计算了氨基酸的表观摩尔体积、极限偏摩尔体积、迁移偏摩尔体积和水化数. 根据结构水合作用模型讨论了迁移偏摩尔体积和水化数的变化规律. 结果表明, 氨基酸两性离子部分与木糖醇羟基间的相互作用占主导地位, 且随木糖醇浓度的增大而增大. 氨基酸在木糖醇水溶液中的迁移偏摩尔体积为正值, 甘氨酸的迁移偏摩尔体积大于L-丙氨酸和L-缬氨酸的. 氨基酸在木糖醇水溶液中的水化数随溶液中木糖醇浓度的增加而减小.     

有机试剂的结构与性质研究(Ⅴ)——5-Br-PADAP的酸碱平衡及其在溶液中存在形式的研究

本文用分光光度法研究了2-[2-(5-溴-吡啶)偶氮]-5-二乙胺基酚(5-Br-PADAP)的酸碱平衡,实验测得的pH和A的数据,用最小二乘法处理得到了5-Br-PADAP在30％乙醇溶液中的离解常数:pK_a1=-0.12,PK_a2=1.66,pK_a3=12.30;并用HMO量子化学计算法确定了5-Br-PADAP在溶液中可能存在的各种形式.     

Tetraalkylammonium Ions in Aqueous and Non-aqueous Solutions

Property data for tetraalkylammonium cations, [H(CH₂) _n ]₄N⁺, are reviewed. They pertain to the isolated cations and their transfer from the gas phase into aqueous solutions. Various properties of these cations in aqueous and non-aqueous solutions and data for their transfer between these are also reviewed. Emphasis is placed on the dependence of data on the length n of the alkyl chains rather than on the absolute values. Most of the data are available only for the first four members of the series. The properties of the isolated ions increase linearly with the chain length. Molar enthalpies of formation of the gaseous and aqueous cations, and absolute standard molar enthalpies of hydration, are derived. Standard molar entropies of dissolution of several salts in water are obtained from their solubilities and enthalpies of solution. The molar entropies of the crystalline iodides of the first four members of the series then give the standard partial molar entropies of the aqueous cations and their molar entropies of hydration. The standard partial molar volumes in aqueous and non-aqueous solutions are quite linear with n and in non-aqueous solutions the molar volume hardly depends on the nature of the solvent. On transfer from water to non-aqueous solvents the volume of Me₄N⁺ suffers some shrinkage, that of Et₄N⁺ appears to be unaffected, but from Pr₄N⁺ onwards an increasing expansion takes place. This unexpected result is tentatively explained by hydrophobic intra-molecular association of pairs of alkyl chains in aqueous solutions, resulting in a tightening of the structure. The transfer of the R₄N⁺ cations from water into non-aqueous solvents is governed by a large positive entropy change, outweighing the smaller positive enthalpy change. The transport properties of the aqueous R₄N⁺ cations are non-linear with n. A major impediment to movement is thus the sticking of the water molecules to the ice-like hydrophobic hydration sheaths of the larger cations. The number of water molecules affected by the hydrophobic cations is open to widely differing estimates resulting from various approaches, and constitute an open issue.     

298.15 K下氨基酸在D-木糖水溶液中的体积性质

报道了甘氨酸、L-丙氨酸和L-丝氨酸3种典型氨基酸在D-木糖水溶液中的体积性质.     

Studies on Complexation of ATMP, PBTCA, PAA and PMAAA with Ca^2＋ in Aqueous Solutions

By means of acid-base potentiometric titration and the advanced BEST computer program developed by Martell et al., the deprotonation constants of four inhibitors [Aminotrimethylenephosphoinic acid(ATMP), 2-phosphino-tutane-1,2, 4-tricarboxylic acid (PBTCA), polyacrylic acid (PAA, Mw=2000), poly (maleic, acrylic) acid(PMAAA, Mw=3000)], and the stability constants of the complexes of these inhibitors with Ca^2 have been determined. And the distribution curves of ATMP at different pH values in aqueous solutions have also been given out. The result of this study can be applied to explaining the inhibition mechanism.     

多环芳烃在盐溶液中盐析常数和活度系数的研究

研究盐类对多环芳烃溶解度的影响,不仅涉及盐效应各种理论的研究,而且在化工分离、环境治理上也有重要的实际意义。本文研究了25℃下7种多环芳烃在NaCl水溶液中的活度系数和盐析常数。计算并比较了萘和联苯的盐析常数以及5种多环芳烃在被正辛醇饱和的NaCl水溶液中的活度系数和盐析常数。     

甘氨酸、L-丙氨酸和L-丝氨酸在尿素水溶液中的体积性质

蛋白质的折叠与解折叠、稳定性、变性行为和酶的活性等都受到环境中其它各种物质影响.作为蛋白质模型分子,氨基酸在混合溶液中的热力学研究近年来引起了广泛重视.尿素在生物体系中的独特地位主要表现在:它是水结构的破坏者,同时又是许多球状蛋白的变性剂.然而,尿素对球状蛋白的变性作用尚未达成共识.     

Complexation of Calcium Ions with Dicarboxylic Acids in Aqueous Solutions

Complexation of calcium ion with malonic, succinic, glutaric, adipic acids at 25°C, ionic strength I = 0.3 (KCl) was studied by pH-potentiometric titration.     

Ion association and solvation behavior of some alkali metal acetates in aqueous 2-butanol solutions at T = 298.15, 303.15 and 308.15 K

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 (K_A,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 K_A,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.