α-氨基酸在水-乙醇中羧基质子化热力学

Enthalpy changes for the protonation of carboxyl group of four α-amino acids(glycine,L-α-alanine,L-valine and L-serine) were measured in water-ethanol mixtures (10－ 70wt％) at 298.15K using LKB-2277 Bioactivity Monitor.The corresponding entropy and Gibbs energy changes were also calculated.The results show that both enthalpy changes and entropy changes are favorable to the protonation of carboxyl groups of the investigated amino acids in water-ethanol mixtures.However,the influence of the composition of ethanol in the mixed solvents on the enthalpy change and entropy changes is complicated.Both sδ and sδ ,the differences of enthalpy changes and entropy changes in mixed solvents and in pure water respectively,show a minimum approximately at xEtOH=0.1.The effects of side chains on the enthalpy change and entropy changes were also investigated using the proton transfer process between glycine and the other three amino acids.The results demonstrate that the proton transfer processes for alanine and valine are spontaneous but not for serine,which could be interpreted in terms of the electrostatic interaction between amino group and carboxyl group within the molecule and the interaction between carboxyl group and the solvent.     

α-氨基酸-丁醇-水三元体系中分子间的异系焓相互作用

利用2277热活性检测仪的流动测量系统获得了298.15K时甘氨酸、L-丙氨酸、L-缬氨酸和L-脯氨酸分别与n-丁醇在水溶液中混合过程的焓变以及各自的稀释焓,依据McMillan-Mayer理论关联得到异系焓相互作用系数,讨论了不同氨基酸与n-丁醇分子的作用机理.对hxy值分析结果表明,不同氨基酸与n-丁醇分子间的异系焓作用系数的大小主要取决于氨基酸分子结构的差异,氨基酸的不同侧基(非极性或极性)对焓作用系数有着不同的贡献,焓作用系数值的相对大小最终取决于各基团之间竞争平衡的结果.脯氨酸特殊的五元吡咯环结构对hxy值有较大的正贡献;n-丁醇的疏水性比尿素或甲脲大得多.     

α-氨基酸在丁酸钠水溶液中的体积性质(308.15K)

盐溶液对蛋白质的结构和性质（例如蛋白质的溶解度、变性、解离为次级结构以及酶的活性’‘’等）有很大的影响．由于蛋白质是一个结构复杂的大分子,直接研究它与电解质的相互作用比较困难．因而,对蛋白质的模型化合物氨基酸和肽的研究具有重要的意义．关于氨基酸在氯化钙、碱金属卤化物（LICI,NaCI,KCI,CsCI,KBr,KI）、硫氨酸钾和氯化控水溶液中的体积性质已有文献报导’‘－”．丁酸钠是一种有机盐,丁酸根离子具有疏水的丙基和亲水的核基,因而它对氨基酸的作用与简单阴离子的作用可能会有所不同．另外,丁酸钠在水溶液中…     

α -羟基-α -氨甲酰基酰胺类化合物的合成新方法

N, N-二甲氨酰基三甲基硅烷与一系列α -羰基酰胺在无水无氧、105 ℃的条件下反应, 较高产率地合成了α -羟基-α -氨甲酰基酰胺类化合物或α -三甲基硅氧基-α -氨甲酰基酰胺衍生物。 其结构用元素分析、¹H NMR、¹³C NMR和IR等技术手段进行了表征。 通过研究反应机理和影响反应的因素发现, 在α -羰基上连的烃基的空间位阻是该加成反应的重要影响因素, 而电子效应则影响反应的速率。 提出了可能的反应机理。     

L-丝氨酸在乙醇-水混合溶剂中的稀释焓

氨基酸是重要的生物活性物质,是组成蛋白质的基本结构单位．氨基酸的稀释焓是氨基酸溶液热力学性质研究的一个重要方面［１,２］,即溶质 溶质相互作用．目前氨基酸的稀释焓研究大多集中在纯水溶液中．然而,大多数蛋白质的天然环境并不是单纯的水溶液,而是含有许多有机物质的复杂环境．有机溶剂对蛋白质的溶解度、变性行为、解缔成次一级结构和酶的活性等都有很大影响［３］,蛋白质在非水介质环境条件下的热力学性质与其在水溶液环境条件下的性质是大不相同的．由混合溶剂中稀释焓的研究可以获得溶剂介入的溶质分子间的相互作用信息．…     

氮羟基邻苯二甲酰亚胺催化的α-紫罗兰酮的氧化反应

以分子氧（O₂）为氧化剂,在无溶剂条件下,研究了N-羟基邻苯二甲酰亚胺/乙酰丙酮亚钴(Ⅱ)体系对α-紫罗兰酮的催化氧化反应,分析了氧化产物,主要得到α-紫罗兰酮的烯丙位氧化产物5-氧代-α-紫罗兰酮,同时生成少量环氧α-紫罗兰酮及重排产物4-氧代-β-紫罗兰酮和环氧β-紫罗兰酮,提出了可能的反应机理,化合物的结构经IR, ¹H NMR, MS和EA等手段得以表征;为了提高5-氧代-α-紫罗兰酮的选择性和催化氧化反应的转化率,优化了催化氧化反应的工艺条件：当反应温度为70 ℃,氧气压力为1.0 MPa,N-羟基邻苯二甲酰亚胺和乙酰丙酮亚钴(Ⅱ)用量分别为α-紫罗兰酮的25%和1.0%,反应10 h,5-氧代-α-紫罗兰酮的产率达53.4%,反应转化率达95.0%以上,平行实验表明,实验重复性良好。     

α-羟基化吡咯烷亚硝胺代谢及形成DNA加合物反应机理的理论研究

采用密度泛函理论, 在B3LYP/6-31G**水平上, 研究了气相和水溶剂中, α-羟基化吡咯烷亚硝胺(α-hydroxylation-NPYR, A)代谢为终致癌物重氮氢氧化物(B)、重氮烷阳离子(C)和氧离子(D), 以及C与鸟嘌呤碱基相互作用的反应机理. 化合物A代谢为终致癌物, 涉及异构化和质子化过程, 是相对容易进行的放热反应. 终致癌物C与鸟嘌呤在N7位形成DNA加合物F和G的反应, 遵循S_N2机理. 加合物G由F异构形成, 且有相对高的异构化能(气相: 244.77 kJ/mol; 水溶剂中: 234.83 kJ/mol), 这与实验上得到加合物G是主要癌变物的结果一致.     

4-羟基脯氨酸立体异构对α-芋螺毒素溶液构象的影响

在α-芋螺毒素及其它家族的芋螺毒素中, 脯氨酸的羟基化是非常普遍的后转录修饰方式. 在天然芋螺毒素中脯氨酸的羟基常采用反式构型, 且该残基对芋螺毒素的结构与生物活性产生了重要的影响, 而顺式构型的羟脯氨酸对α-芋螺毒素的折叠与生物活性的影响还鲜有研究. 本工作通过二维(2D)溶液核磁共振方法测定了经过化学修饰的三个含有反式或顺式羟脯氨酸的α-芋螺毒素的溶液结构, 它们是α4/7亚家族芋螺毒素肽[γ15E]Sr1B、[O7O'/γ15E]Sr1B和[O6O'/γ14E]Vc1A. 研究表明, 羟基顺反异构化学修饰对芋螺毒素的结构影响显著. 羟脯氨酸羟基的反式到顺式修饰导致α-芋螺毒素肽明显的溶液构象变化, 这些变化包括二级结构的改变、关键残基的侧链取向变化以及氢键性质的改变. [O7O'/γ15E]Sr1B与[γ15E]Sr1B相比, 典型的α-芋螺毒素ω弯曲结构发生形变. 而[O6O'/γ14E]Vc1A不同于Vc1A的是末端转角结构的缺失. 本工作加深了对α-芋螺毒素肽的化学修饰法的理解, 该方法是阐明α-芋螺毒素结构-生物活性关系的有用工具.     

α-氨基丁酸对映异构体在DMF+水混合溶剂中的焓对作用

利用等温滴定微量热法(ITC)分别测定了298.15K时L-α-氨基丁酸和D-α-氨基丁酸两种对映异构体在不同组成的二甲基甲酰胺(DMF)+水混合溶剂中的稀释焓.根据统计热力学的McMillan-Mayer理论计算各溶剂组成下的同系焓对作用系数(hxx).从溶质-溶质和溶质-溶剂相互作用的观点出发探讨了三元水溶液中疏水-疏水、疏水-亲水和亲水-亲水作用的竞争平衡.实验发现,在所研究的混合溶剂组成范围内(wDMF=0-0.3),α-氨基丁酸两种对映体的hxx都是较大的正值,且都随wDMF的增大而逐渐减小,而有趣的是L型对映体的hxx值普遍比D型的大(hLLhDD),说明ITC可以区分对映异构体的同手性焓对作用.结果表明:在α-氨基丁酸+水+DMF三元溶液体系中,疏水-疏水和疏水-亲水作用在分子对作用过程中占优势;在α-氨基丁酸的同种对映体发生分子对作用时,L-L分子对比D-D分子对在构型上更有利于α-碳上疏水侧链(CH3CH2-)的靠拢,疏水基团的水合壳层发生交盖,局部破坏而释放出部分结构化的水,过程自发、吸热且伴随显著熵增(ΔG0,ΔH0,ΔS=(ΔH-ΔG)/T0),因而在稀释时释放出更多热量,hxx具有较大的正值.     

氯苯甲酸在水-DMF混合溶剂中的电离热力学

结构上彼此相关的取代苯甲酸在非水溶剂中电离热力学性质研究一直受到广泛的重视［‘一句，但是这类酸在水一DMF混合溶剂中的电离热力学性质的研究少见报导．DMF（N，N一二甲基甲酸胺）由于其独特性质，在许多化学、化工领域中已得到广泛的应用．本文对苯甲酸和。、。一、p氯苯甲酸在水一DMF混合溶剂中的电离热力学性质进行研究，以此深入地了解溶剂和取代基对弱酸电离的影响．1实验1．11热仪器用LKB－2277BioActivityMonitor问的流动混合测量系统部分，测量精度为0．2％（300Pw量程）1．2试剂苯甲酸为分析纯试剂，含量＞99．5％质…     

Enthalpies of Solution of Some L-α-amino Acids in Aqueous Solutions of Urea at 298.15 K

The standard molar enthalpies of solution of glycine, L-α-alanine, L-α-valine and L-α-leucine in aqueous solutions of urea at 298.15 K were determined by calorimetry. The results obtained were used to calculate the heterogeneous enthalpic interaction coefficients between the zwitterions of the L-α-amino acids and a molecule of urea in water. The values of the resultant enthalpic interaction coefficients are interpreted in terms of the effects of the hydrophobic alkyl groups on the interactions between the zwitterions of the L-α-amino acids and a polar molecule of urea in aqueous solutions. This revised version was published online in August 2006 with corrections to the Cover Date.     

Enthalpic Interactions of Amino Acids with Glucose in Aqueous Solutions at 298.15 K

The enthalpies of mixing of aqueous glucose solutions and six kinds of aqueous amino acid solutions (glycine, L-alanine, L-serine, L-valine, L-proline, and L-threonine) and their respective enthalpies of dilution have been determined at 298.15 K using flow microcalorimetry. The experimental data have been analyzed in terms of the McMillan–Mayer model to obtain the heterotactic interaction coefficients. The results have been interpreted from the point of view of solute–solute interactions.     

Enthalpic Interaction of Amino Acids with 2-Chloroethanol in Aqueous Solutions at 298.15 K

The enthalpies of mixing have been determined for five kinds of aqueous amino acids solutions (glycine, L-alanine, L-valine, L-serine, and L-proline) with 2-chloroethanol by an LKB-2277 Bio Activity Monitor at 298.15 K. In addition, the enthalpies of dilution at 298.15 K of aqueous solutions containing the five kinds of amino acids and 2-chloroethanol have been obtained. The heterotactic enthalpic pairwise interaction coefficients of the virial expansion of excess enthalpy were evaluated and interpreted from the point of view of solute–solute interactions. In comparison with ethanol, 2-chloroethanol shows a stronger exothermic interaction with amino acids because of its hydrophilic Cl atom and a more acidic –OH group. Using the additivity groups concept by Savage and Wood (SWAG), contributions of each of functional group of the amino acids and ethanol and 2-chloroethanol have been estimated.     

Interactions of Some Amino Acids with Aqueous Osmoprotectant Proline at 298.15 K: Volumetric and Calorimetric Studies

Apparent molar volumes of a homologous series of amino acids in aqueous proline solutions have been obtained from densities at 298.15 K, measured with a vibrating-tube digital densimeter. These data have been used to deduce the partial molar volumes of transfer from water to aqueous proline solutions; these partial molar volumes of transfer are found to be positive for glycine, alanine, α-amino-n-butyric acid and valine, whereas they are negative for leucine. The number of water molecules hydrated to the amino acids was estimated from the partial molar volume data. In order to supplement this information, enthalpies of transfer of aqueous amino acids from water to 0.1, 2.25 and 1 mol⋅dm⁻³ aqueous proline have been determined at 298.15 K using a VP-ITC titration calorimeter. The data on the partial molar volumes and enthalpies of transfer are discussed in terms of various interactions operating in the ternary mixtures of amino acids, water and proline.     

Enthalpies of transfer of amino acids from water to aqueous solutions of sodium nitrate and sodium perchlorate at T = 298.15 K

Enthalpies of solution of glycine, l-alanine and l-serine in water and aqueous solutions of NaNO₃ and NaClO₄ have been determined at T = 298.15 K with a calorimeter. Enthalpies of transfer (Δ_trH) from water to aqueous solutions of salts were derived and interpreted in terms of electrostatic interaction and structural interaction. Δ_trH decreases with increasing salt concentration in the composition range studied. The transfer enthalpies of amino acids from water to NaNO₃ solution and low concentration NaClO₄ solution vary in the sequence l-serine < glycine < l-alanine while glycine < l-serine < l-alanine in NaClO₄ solution above 2 mol kg⁻¹. The difference may be due to ion association at high concentration, weakening the interaction with l-serine more than with glycine.     

Interactions of Some Amino Acids with Aqueous N,N-Dimethylacetamide Solutions at 298.15 and 308.15 K: A Volumetric Approach

The apparent molar volumes, V _φ , of glycine, L-alanine and L-serine were obtained in aqueous 0 to ∼4 mol⋅kg⁻¹ N,N-dimethylacetamide (DMA) solutions from density measurements at 298.15 and 308.15 K. The standard partial molar volume, V _φ ^o, and standard partial molar volumes of transfer, Δ_tr V _φ ^o, were determined for these amino acids. It has been shown that hydrophilic-hydrophilic interactions between charged groups of the amino acids and the —CON= group of DMA are predominant in the case of glycine and L-serine, but for L-alanine the interactions between its side group (—CH₃) and DMA are predominant. An increase in temperature increases the standard partial molar volumes but decreases the transfer volumes of the amino acids. The results have been interpreted in terms of cosphere overlap model.     

Enthalpies of solution of l-threonine in a (water + alcohol) mixture at 298.15 K

The enthalpies of solution of l-threonine in the (water + methanol), (water + ethanol), (water + n-propanol), and (water + i-propanol) mixtures, with an alcohol content up to 0.4 mol fractions, have been measured calorimetrically at T = 298.15 K. The standard enthalpies of solution and transfer of l-threonine from water to an aqueous alcohol have been calculated. The effect of the structure properties of the mixed solvent on the specified enthalpy characteristics of l-threonine is discussed. The enthalpy coefficients of pairwise interactions between amino acid and alcohol molecules have been computed. It has been found that these coefficients become increasingly positive in the methanol, ethanol, n-propanol, and i-propanol consequence. A comparative analysis of the thermodynamic characteristics of dissolution of l-threonine and some other amino acids (glycine, l-alanine and l-valine) in the mixtures studied has been made.     

Enthalpic interactions of some α-amino acids with glycol in aqueous solutions at 298.15 K

The enthalpies of mixing of six kinds of aqueous amino acid solutions (Glycine, l-alanine, l-valine, l-serine, l-threonine and l-proline) and aqueous glycol solution and their respective enthalpies of dilution have been determined at 298.15 K using flow microcalorimetry. The experimental data have been analyzed according to the McMillan–Mayer formalism to obtain the heterotactic enthalpic interaction coefficients (h_xy). h_xy coefficients have been discussed from the points of view of solute–solute interactions.