【作者】 林贵梅；

【导师】 林瑞森；

【作者基本信息】 浙江大学 ， 物理化学， 2006， 博士

【摘要】 蛋白质是生物形态结构和生命活动的物质基础,具有特定的立体结构。由于蛋白质分子结构的复杂性直接测量其热力学性质非常困难。二肽分子结构简单便于研究,分子中侧基所处的化学环境与蛋白质分子相近,能够真实地反映蛋白质分子中侧基与其它官能团或共溶质间的相互作用,是一种理想的蛋白质模型分子。通过对水溶液中二肽的各种热力学性质研究,可以获得各种蛋白质分子中侧基与水分子之间相互作用的方式,为进一步探索水化作用对蛋白质天然结构的稳定作用提供丰富的信息。然而大多数蛋白质的天然环境并不是单纯的水溶液,而是含有许多无机和有机物质的复杂环境。因此,有关蛋白质分子在生物功能分子水溶液中的热力学性质研究具有特别重要的意义。 T.E.Creighten在他的著作(Proteins,Structures and Molecular Properties)中提到,对水结构起破坏作用的溶质能够稳定蛋白质立体结构,而对水结构起形成作用的溶质破坏蛋白质立体结构使其变性。大量的实验证明电解质和尿素对水结构都有破坏作用,电解质溶液可以稳定蛋白质的立体构型而尿素则是显著的蛋白质变性剂,与T.E.Creighten的理论相悖;另外正负离子半径的变化对肽分子热力学性质有不同影响。基于以上两点本论文将围绕二肽模型分子体系与不同生物功能分子(NaX[X=F、Cl、Br和I]、KCI和尿素)之间的相互作用展开工作,通过对混合溶液中模型分子迁移性质的研究,分析和讨论离子及尿素分子与二肽分子之间不同的作用方式,为进一步探讨电解质及尿素对蛋白质分子构型的不同作用提供实验依据。 甘氨酰甘氨酸是结构最简单的二肽分子。本论文测定了其在系列浓度的NaX、KCl水溶液中的密度,和在混合溶剂中的溶解焓;系统地研究了甘氨酰甘氨酸从水到相应电解质水溶液中的迁移偏摩尔体积和迁移焓;分析并讨论了离子与甘氨酰甘氨酸分子之间相互作用的规律以及温度对体积性质的影响。结果表明:离子与甘氨酰甘氨酸分子两性离子头部、肽键之间的静电和亲水—亲水相互作用在分子间作用力中占据主导地位,甘氨酰甘氨酸在电解质溶液中溶解为焓驱动过程,温度对其迁移体积性质的影响不大。负离子半径的变化对甘氨酰甘氨酸分子迁移性质的影响中,静电相互作用的差异起了主要作用;而正更多还原

【Abstract】 Proteins are the material base depended by the structures and life activities in biological systems. Because of the structure complexities of proteins, it is extremely difficult to investigate thermodynamics properties directly. It has been common practice to use amino acids and oligopeptides as model compounds since they make up of the protein structures. The features that distinguishes dipeptide model from others reported in the literature are that the compounds chosen as models are themselves portions of proteins, i.e. peptide molecules and that they could solute easily in aqueous solutions. Investigations on the thermodynamic behavior of model compounds in aqueous solution would provide information about mechanism of action of proteins in aqueous solution, however, most proteins exist in the complicated environment containing many organic substances, which leads to significant interests in investigation on the interaction in aqueous solutions between model compounds and organic molecules present in living organisms or possessing functional group identical.The water structure hypothesis predicts that structure-breaking solutes stabilize proteins and that structure-making solutes destabilize proteins. A lot of experiments have proved that electrolytes and urea are the structure-breaker. Electrolytes could stabilize the protein conformation, and urea is the notable denaturant. There were papers reported that the changes of radium of anion and cation had different effect on the thermodynamic properties of peptides. To study systems consist of dipeptides, sodium halide (potassium chloride or urea) and water, we can obtain (i) the information that contributes to the growing body of knowledge about solute solvation and solute interactions in aqueous media, and (ii) a better understanding of their role played in the conformational stability and unfolding behavior of proteins, and then we want to explain the questions above.The configuration of glycylglycine is the simplest in dipeptides. The densities and solution enthalpies of glycylglycine in aqueous sodium halide and potassiumchloride solutions were determined. The transfer Enthalpy and transfer partial molar volume of glycylglycine from water to above mixed solvent were obtained and discussed in terms of solute-solute interaction between dipeptide and ions, which also bring a new insight into the structure of the mixed solvent mentioned above. Using the consphere overlap model explained these tendencies and gained conclusions: Interactions between peptide bond or charged centers of glycylglycine and ions are dominant. The solvation of glycylgycine in electrolyte solution is the enthalpy driven. The transfer volume depend less on temperature. Electrostatic effect is dominating in the transfer properties of glycylglycine arising from the changes of anion radium. Because of breaking the hydrogen bond in the solvation layer ofpeptide bond, the rule of cation is contrary with anion.Hydrophobic interaction plays an important role on stabilizing the configuration of proteins. N-glycyl-DL-alanine and N-glycyl-L-valine were choused as the model compounds because of hydrophobic groups. Their densities and enthalpies of solution in aqueous sodium chloride and urea solutions were determined at 298.15 K. The transfer enthalpy and transfer partial molar volume from water to above mixed solvent were obtained and discussed. Analyzing the results, we gained the conclusions: The transfer of hydrophobic group from water to NaCl solution is the process that is entropy favorable and enthalpy unfavorable. Hydrophobic-hydrophile interaction dominates in enthalpy contribution. Urea could displace water in the solvation shell of nonpolar group accompanying an increase in entropy, and urea also could reduce the energy by forming the hydrogen bond with around water. Urea also could displace water in the solvation shell of peptide bond and form the multiple hydrogen bonds with it, which could reduce the energy more. So the transfer of hydrophobic groups and peptide bond from water to aqueous urea solution is the process that is favorable for entropy and enthalpy.In conclusion, the effect of electrolyte on protein stability might be the model in which nonpolar groups get together avoiding to contact with water, which could reduce the energy. The denaturalization of urea on protein might be the model in which urea denatures protein by diminishing the hydrophobic effect by displacing water molecules from the solvent shell around nonpolar groups and binding directly to amide unite via hydrogen bonds. These models are in good agreement with recentresults of MD simulation.更多还原