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.

Enthalpy of Transfer of Amino Acids from Water to Aqueous Solu-tions of Urea

Enthalpy of solution of glycine, L-alanine, L-serine in water and aqueous solutions of urea was measured at 298.15 K with an RD496-III microcalorimeter. Enthalpy of transfer of amino acids from water o aqueous solutions of urea was derived and interpreted qualitatively with structural hydration model. The esults show that the process of transfer is governed by the electrostatic interaction and structure interaction etween urea and the zwitterionic group of amino acids with a negative enthalpy, while that with the side hain gives a positive or negative contribution depending on its hydrophobicity or hydrophilicity. In the sol- ent composition range studied, the enthalpy of transfer of amino acids in general decreased with the in- reasing concentration of urea, with the relative order of L-serine