摘要
用LKB-2277精密微热量计测定了298.15 K时甘氨酸、L-丙氨酸、L-丝氨酸、L-缬氨酸、L-苏氨酸和L-脯氨酸六种α-氨基酸分别与甲脲分子在水溶液中的混合过程焓变及这些溶质分子在水溶液中的稀释焓.实验数据根据McMillan-Mayer理论进行回归分析，得到各级交叉焓相互作用系数.讨论了不同氨基酸与甲脲分子的相互作用机制.结果表明，氨基酸的两性离子部分、α-碳上的非极性脂肪侧基、极性的羟基侧基和五元吡咯环结构对交叉焓对作用系数h_(xy)具有不同贡献.与尿素相比，甲脲分子中－CH3基团的引入明显增强了分子的疏水性.
The enthalpies of mixing of monomethylurea(MMU) with six kinds of amino acids (glycine, L-alanine, L-serine, L-proline, L-threonine, L-valine) in aqueous solutions have been determined by the LKB-2277 flow microcalorimetric system at 298. 15 K. These results along with enthalpies of dilution of these solutes for the initial solutions were used to determine the enthalpic interaction coefficients (h(xy), h(xxy), etc.) in terms of the McMillan-Mayer theory. The pairwise cross interaction coefficients (h(xy)) of amino acids and MMU have been discussed. The results show that different side-groups of amino acids have different contributions to h(xy). The hydrophobic-hydrophobic interactions of glycine, L-alanine and L-valine with MMU increase with the number of - CH2- groups on alpha -carbon. The hydroxyl group gives a negative contribution to h(xy). The five-membered pyrolidine ring in proline exhibits some hydrophobicity. The introduction of CH3 makes the hydrophobicity of MMU stronger than that of urea.
出处
《物理化学学报》
SCIE
CAS
CSCD
北大核心
2001年第7期645-650,共6页
Acta Physico-Chimica Sinica
基金
国家自然科学基金资助项目(20073039)
