【作者】 庞现红；

【导师】 于丽；

【作者基本信息】 山东大学 ， 物理化学， 2008， 硕士

【摘要】 蛋白质是许多生物现象的重要物质基础。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，被认为是理论研究中最重要的生物模型化合物；酰胺因为含有一些多肽链单元，多肽链单元含有酰基和非极性残基，已成为研究水溶液里肽链性质的模型化合物。糖类和羟基化合物能够稳定球形蛋白质的天然构象，而有机溶剂对蛋白质的溶解性、变性行为、折叠和解折叠及酶的活性等都有很大影响。通过研究水溶液中氨基酸、酰胺与有机溶剂化合物的热力学性质，既可以获得水溶液中溶剂化的溶质分子间的相互作用方面的信息，又有助于了解有机溶剂化合物对蛋白质的稳定机理及氨基酸、酰胺在蛋白质中的构象稳定性和解折叠过程中所担当的角色。本论文主要由以下几部分组成：第一部分：概述了蛋白质模型分子体系溶液热力学的研究状况。第二部分：选择六种典型氨基酸——甘氨酸、L-丙氨酸、L-丝氨酸、L-缬氨酸、L-脯氨酸、L-苏氨酸为研究对象，用LKB-2277热活性检测仪的流动混合测量系统测定了298．15 K、303．15 K和310．15 K时它们与2,2,2-三氟乙醇（TEF）在水溶液中的混合焓及各自的稀释焓，根据McMillan-Mayer理论关联得到各级异系焓相互作用系数，从溶质一溶质相互作用角度，研究了氨基酸与2,2,2-三氟乙醇分子间的相互作用机制，并探讨了温度的影响。结果表明：（1）氨基酸与2,2,2-三氟乙醇分子间的h_xy均为正值，说明两种溶质分子混合过程中吸热效应占优势，不同氨基酸与2,2,2-三氟乙醇分子间的h_xy值的不同主要取决于不同氨基酸分子侧链结构的差异。（2）三个温度下氨基酸与2,2,2-三氟乙醇分子间的h_xy值有较大的差异。310．15 K时氨基酸与2,2,2-三氟乙醇分子间的焓对相互作用系数均大于298．15 K和303．15 K时的数值。说明当温度升高时，由于氢键的协同作用加大了分子间的疏水相互作用，增强了羟基的部分去水化作用，且温度越高，氢键的协同作用越明显，所以310．15 K时氨基酸与2,2,2-三氟乙醇的h_xy出现较大的正值，这可能是2,2,2-三氟乙醇可以作为可逆变性剂的一个主要原因。（3）脯氨酸具有独特的吡咯环结构，它们在确定多肽性质方面具有特殊的重要性。结果表明吡咯环具有较大的疏水作用，而且脯氨酸与2,2,2-三氟乙醇分子作用的h_xy值是随着温度的递增而递增的。第三部分：研究氨基酸298．15K（甘氨酸、L-丙氨酸、L-丝氨酸、L-缬氨酸、L-脯氨酸、L-苏氨酸）和N，N-二甲基乙酰胺（DMAC）分别与二甲亚砜分子间的异系焓相互作用，根据得到的焓对相互作用系数讨论了氨基酸和N，N-二甲基乙酰胺分别与二甲亚砜分子的作用机制，得到结论如下：（1）水溶液中上述六种氨基酸、DMAC与二甲亚砜的相互作用均为吸热过程，焓对作用系数表现为正值。在298．15 K时，模型化合物与二甲亚砜异系焓对相互作用系数出现了以下顺序：h_xy（Gly）<h_xy（Ala）<h_xy（Val）<h_xy（Ser）<h_xy（Thr）<h_xy（DMAC）。并从各自的结构上解释了产生此顺序的原因。（2）与氨基酸相比，DMAC分子中极性的酰胺键是一个共轭体系，而且这个共轭体系受3个甲基的包围，产生很大的位阻效应，这大大降低了DMAC与二甲亚砜分子间的亲水-亲水相互作用；而与氮原子相连的两个甲基大大增强了两者之间的疏水-疏水相互作用；所以，h_xy（DMAC）表现出较大的正值。第四部分：采用2277热活性检测仪的流动混合测量系统测定了298．15 K时N,N-二甲基乙酰胺与葡萄糖、蔗糖分子的混合过程焓变及各自的稀释焓，根据McMillan-Mayer理论关联得到各级焓作用系数，探讨了其相互作用机理。研究结果表明：在水溶液中DMAC与葡萄糖、蔗糖相互作用均为吸热过程，焓对作用系数表现为正值。在298．15 K时，DMAC与葡萄糖、蔗糖异系焓对相互作用系数出现了h_xy（葡萄糖）<h_xy（蔗糖）的大小顺序。蔗糖虽然是—分子D-葡萄糖和—分子D-果糖通过1，4-苷键形成的的二聚体，但由于分子间氢键和位阻效应等复杂因素，相对于单糖来说，苷键的形成消耗了2个羟基，表现出特有的热力学性质，而不是2分子单糖简单的热力学性质的加和。更多还原

【Abstract】 Amino acids, which have been used extensively as the most important biological model compounds, are not only the basic building blocks of proteins, but also the typical zwiterionic compounds and important active materials in living things.Sugars and polyols help in stabilizing the naitve conformation of globular proteins.There has been significant interest in the investigation on the interaction in aqueous solutions between amino acids and organic molecules present in living organisms or possessing functional group identical. The principle reasons for studying such systems are to obtain （i） the information that contributes to the growing body of knowledge aboutsolute solvation and solute-solute interactions in aqueous media, and （ii） a beter understanding of their role played in the conformational stability and unfolding behavior of proteins.This paper mainly consists of the following four parts.The first part summarizes the current status of studies on the thermodynamic properties of sytems containing portein model molecules.In the second part.enthalpies of mixing of aqueous amino acids solutions （glycine, L-alanine, L-serine, L-valine, L-proline, L-threonine）with aqueous 2,2,2-Trifluoroethanol （TEF） solutions have been determined at 298.15 K ,303.15 K and 310.15 K by the LKB-2277 flow microcalorimetric system. These results along with enthalpies of dilution of these aqueous solutions have been used to obtain the enthalpic interaction coefficients (h_xy,h_xxy, etc.) in terms of the McMillan-Mayer theory. The enthalpic pairwise interactions between amino acids and TEF have been discussed by solute-solute interactions.The results show: （1） The disprepancy of h_xy values between amino acids and TEF can were determined by the side-chain of amino acids. Amino acids with different side-group can make different contributions to h_xy. （2） Under the three temperatures there has a big difference for the h_xy values between amino acids and TEF molecules. For the same kind of amino acid, the h_xy value between amino acid and TEF molecules at 310.15 K is larger than that of 298.15 K and 303.15 K. Because of the synergistic effect of the hydrogen bonds, the intermolecular hydrophobic interactions strengthen and subsequently the partial dehydration of the dydroxyl groups enhance when the temperature increases. The higher the temperature, the synergistic effect of the hydrogen bonds more obvious. Therefore, the h_xycoefficients between amino acids and TEF at 310.15 K appear relatively larger positive values. This probably is the main reason that TEF is used as a reversible denaturant. （3） Proline is a natural amino acid that has one pyrrole ring. Its special structure makes it important to the properties of polypeptide. On one hand, the cyclic structure weakens the attracting interactions between proline molecules due to the steric effect, which makes solvation easy. The results indicate that the pyrrole ring has the bigger hydrophobic interaction. The hxy value between Proline and TEF molecules increases with the increment of temperature.In the third part, the heterotactic enthalpic interactions have been investigated between the six kinds of amino acids studied above, DMAC and DMSO and the interaction mechanism has been discussed.The results show: （1） The h_xy values between the six kinds of amino acids, DMAC and DMSO molecules are all positive. The h_xy coefficients at 298.15 K are in the following sequence: h_xy（Gly） <h_xy（Ala） <h_xy（Val） < h_xy（Ser）<h_xy（Thr）< h_xy（DMAC）. This can be ascribed to the the different structures of the protein model molecules. （2） Compared with the amino acids, the DMAC polar part is a conjugated system, which is surrounded by three methyl groups. This can lead to a very big steric effect and subsequently the hydrophilic-hydrophilic interaction between DMAC and DMSO molecules weaken. But the hydrophobic-hydrophobic interaction between them strengthen greatly because of the existence of the two methyl groups connected with the nitrogen atom. Therefore, the h_xy（DMAC） coefficient displays a larger positive value.The forth part, the enthalpies of mixing of the DMAC aqueous solution with the saccharides （glucose, sucrose） aqueous solutions have been determined at 298.15 K by the LKB-2277 flow microcalorimetric system. These results along with enthalpies of dilution of these aqueous solutions have been used to obtain the enthalpic interaction coefficients (h_xy,h_xxy, etc.) in terms of the McMillan-Mayer theory. The enthalpic pairwise interactions between DMAC and saccharides have been discussed from the point view of solute-solute interactions.The results show: The h_xy values between DMAC and glucose and sucrose molecules are all positive. At 298.15 K, the h_xy coefficients increase in the order: h_xy （glucose） < h_xy（sucrose）. Sucrose is a dimer formed by a glucose molecule and a fructose molecule through the 1,4-glucoside bond. But owing to many complex factors, such as the intermolecular hydrogen bonding or steric hindrance between two monomers, two hydroxyl groups have been consumped during the course of the formation of glucoside bond for the monosaccharide. So the thermodynamic property of sucrose is between glucose and fructose, not the simple adduct of these two monosaccharide molecules.更多还原