Enthalpies of mixing of acetonitrile with isomeric butanols: Enthalpies of hydrogen-bonded complexes

The enthalpies of mixing of four isomeric butanols with acetonitrile were determined at 30°C by a Calvet type microcalorimeter. All the four systems showed endothermic behaviour. The enthalpies of hydrogen bonded complex formation were determined by means of a thermochemical cycle. 1-butanol formed a stronger bonding (−13kJ/mole) than the other three isomers (−11.20kJ/mole). The strength of the H-bond of alcohol with C ≡ N is much less than that with C-N. NCL communication no. 4883     

Interplay of Thermochemistry and Structural Chemistry, the Journal (Volume 11, 2000), and the Discipline

As practiced disciplines, structural chemistry and thermochemistry need not be related. In the current study they are: the entire contents of the journal Structural Chemistry (Vol. 11) for the year 2000 has been reviewed and then each and every article that appeared therein was given a thermochemical commentary, spin or slant.     

三甲醇丙烷—季戊四醇固体溶液的热容和相变焓

前曾报道季戊四醇在461.60K有一个固-固相变,其相交含为41.37kJmol~(-1)。但是,作为低温储能材料,该物质的相变温度偏高。从有关固-固相变储能材料的热力学研究中,我们发现三甲醇丙烷-季戊四醇固体溶液具有较低的固-固相变温度。本文测定了三甲醇丙烷-季戊四醇(摩尔比60:40)固体溶液的相变热参数和热容。     

The role of protein “Stability patches” in molecular recognition: A case study of the human growth hormone‐receptor complex

Dynamic characteristics of protein surfaces are among the factors determining their functional properties, including their potential participation in protein‐protein interactions. The presence of clusters of static residues—“stability patches” (SPs)—is a characteristic of protein surfaces involved in intermolecular recognition. The mechanism, by with SPs facilitate molecular recognition, however, remains unclear. Analyzing the surface dynamic properties of the growth hormone and of its high‐affinity variant we demonstrated that reshaping of the SPs landscape may be among the factors accountable for the improved affinity of this variant to the receptor. We hypothesized that SPs facilitate molecular recognition by moderating the conformational entropy of the unbound state, diminishing enthalpy–entropy compensation upon binding, and by augmenting the favorable entropy of desolvation. SPs mapping emerges as a valuable tool for investigating the structural basis of the stability of protein complexes and for rationalizing experimental approaches, such as affinity maturation, aimed at improving it. © 2015 Wiley Periodicals, Inc.     

Thermodynamics of the Second Dissociation Constant and Standards for pH of 3-(NMorpholino) Propanesulfonic Acid (MOPS) Buffers from 5 to 55°C

The second dissociation constant pK2 of 3-(N-morpholino)propanesulfonic acid (MOPS) has been determined at eight temperatures from 5 to 55°C by measurements of the emf of cells without liquid junction, utilizing hydrogen electrodes and silver–silver chloride electrodes. The pK2 has a value of 7.18 ± 0.001 at 25°C and 7.044 ± 0.002 at 37°C. The thermodynamic quantities G°, H°, S°, and C _p ^o have been derived from the temperature coefficients of the pK ₂. This buffer at ionic strength I = 0.16 mol-kg^–1 close to that of blood serum, has been recommended as a useful secondary pH standard for measurements of physiological fluids. Five buffer solutions with the following compositions were prepared: (a) equimolal mixture of MOPS (0.05 mol-kg^–1) + NaMOPS, (0.05 mol-kg^–1); (b( MOPS (0.05 mol-kg^–1) + NaMOPS (0.05 mol-kg^–1) + NaCl (0.05 mol-kg^–1); (c) MOPS (0.05 mol-kg^–1) + NaMOPS (0.05 mol-kg^–1); + NaCl (0.11mol-kg^–1); (d) MOPS (0.08 mol-kg^–1) + NaMOPS (0.08 mol-kg^–1); and (e)MOPS (0.08 mol-kg^–1) + NaMOPS (0.08 mol-kg^–1) + NaCl (0.08 mol-kg^–1).The pH values obtained by using the pH meter + glass electrode assembly are compared with those measured from a flow–junction calomel cell saturated with KCl (cell B), as well as those obtained from cell (A) without liquid junction at 25 and 37°C. The conventional values of the liquid junction potentials E _j have been obtained at 25 and 37°C for the physiological phosphate reference solution as well as for the MOPS buffers (d) and (e) mentioned above.     

氨基酸从水到尿素水溶液中的迁移焓研究

用微量量热法测定甘氨酸、L-丙氨酸、L-丝氨酸在水和尿素水溶液中的溶解焓, 计算得到氨基酸从水到尿素水溶液的迁移焓, 并根据水合结构相互作用模型予以讨论. 结果表明, 氨基酸两性离子与尿素分子的静电作用以及两性离子头部与尿素分子的结构相互作用对氨基酸迁移焓有负贡献, 氨基酸侧链与尿素分子的结构相互作用依其亲水性或疏水性分别对迁移焓有负贡献或正贡献. 在实验浓度范围(0～13 mol/kg)内, 三种氨基酸的迁移焓总体上随尿素浓度的增加而下降, 其大小依次为L-丝氨酸＜甘氨酸＜L-丙氨酸, 氨基酸迁移焓的差异反映了溶质-溶剂结构相互作用的变化.     

The hydration of anions in nonaqueous media

A very simple isopiestic method based on that of S. Christian is used for measuring the salting-in of water into nonpolar, low-volatility solvents by tetraalkylammonium salts. The quantity of excess water which is dissolved in such solvents is directly proportional to the salt concentration and is sharply dependent on the nature of the anion but is nearly insensitive to that of the R₄N⁺ cation. The hydration ratioH, which we define as the moles of excess solubilized water per mole of R₄N⁺ X^–, is directly relatable to the enthalpy of hydration of the anion X^– in several solvents and in the gas phase. The quantityH is also correlated with many free-energy terms including those for the Hofmeister lyotropic series, for the ability of the anions to salt nonelectrolytes out of water, for the free-energy terms for separation of these ions by reverse osmosis membranes, and for their nucleophilicities. A surprising (but not unprecedented) feature of the hydration ratio is that it, rather than its logarithm, behaves as a free-energy term. It is proposed that all these properties have in common the free energy of hydration of the anions, and this notion is supported by a close correspondence between the anionic hydration ratio and their hydrogen-bonding energies with proton donors in aprotic solvents. The results support scattered observations by other workers that isolated water molecules do not have an unusual inherent affinity for anions. Accordingly, large anionic hydration energies in bulk aqueous media reflect extensive cooperative interactions in the solvent. Implications for nucleophilic activity in phase transfer catalysis and enzyme activity are mentioned.     

聚氧化乙烯和聚醋酸乙烯酯共混热力学参数的理论估算

实验测定了聚氧化乙烯（ＰＥＯ）和聚醋酸乙烯酯（ＰＶＡｃ）的共混热以及共混组分的热压系数和热膨胀系数．并由上述实测值计算了状态方程参数．用Ｈａｍａｄａ~［１－２］等改进的Ｆｌｏｒｙ状态方程理论估算了ＰＥＯ／ＰＶＡｃ混体系的交换能参数（Ｘ_１２）、相互作用参数（ｘ_１２／ｒ_１）和剩余混合体积（Ｖ~Ｅ／Ｖ~０）．     

The effect of temperature and pressure on the protonation ofo-phosphate ions at 348.15 and 398.15 K,and at 1.52 and 12.50 MPa

Flow calorimetry has been used to study the interaction of HPO ₄ ^2– and H₂PO ₄ ^– with H⁺ in water at temperatures of 348.15 and 398.15 K and at pressures of 1.52 and 12.50 MPa. The protonations of HPO ₄ ^2– and H₂PO ₄ ^– are exothermic and endothermic, respectively, under these experimental conditions. Under the conditions of this study, the effect of pressure on the enthalpy changes for both reactions is small. Equilibrium constant K, enthalpy change H, and entropy change S values are given for the protonation reactions at each temperature. These values are compared with those reported in the literature. Incorporation into the calculation procedure of reactions involving association between protonated phosphate species to form hydrogen-bonded dimers does not result in better fits of the experimental data.     

Crystallization in the SiO2-Al2O3 System from Amorphous Powders

The crystallization of amorphous chemically homogeneous powders in the SiO₂.Al₂O₃ system has been studied by differential scanning calorimetry and X-ray diffraction. Up to 1300°C only one exotherm has been observed. Only mullite crystallizes for compositions ≤69 mol% Al₂O₃ and spinel for those ≤80%. The crystallizations into mullite and spinel are sharp and exothermic, with an enthalpy of 250–300 J/g. The chemical composition of the crystallized mullite regularly increases from 68 to 76 mol% Al₂O₃ with increasing bulk composition from 60 to 75 mol% Al₂O₃.