甘氨酸和L-丝氨酸在LiNO3,NaNO3和KNO3水溶液中的体积性质

用Anton Paar DMA 55精密数字密度计测定了甘氨酸和L-丝氨酸在LiNO3, NaNO3和KNO3水溶液中的密度, 计算了氨基酸的表观摩尔体积、极限偏摩尔体积、迁移偏摩尔体积、理论水化数和体积作用系数. 根据静电相互作用和结构水合作用模型讨论了氨基酸的侧链和阳离子的性质对迁移偏摩尔体积的影响. 结果表明, 甘氨酸和L-丝氨酸在3种硝酸盐水溶液中的迁移体积均为正值, 并且随着盐溶液浓度的增大而增大. 氨基酸两性离子端基和阴阳离子间的静电作用对迁移体积的贡献是主要的, 静电作用削弱了两性离子带电中心对周围水分子的电致收缩效应, 造成氨基酸的理论水化数随盐溶液浓度的增加而减小. L-丝氨酸的侧链与离子之间的亲水-亲水相互作用对迁移体积有小的正贡献, 使得在同一种盐溶液中L-丝氨酸的迁移体积较甘氨酸的大. 同一种氨基酸在NaNO3和KNO3水溶液中的迁移体积较在LiNO3水溶液中的大, 主要是由于Li＋难以去水化. 在低浓度的盐溶液中氨基酸与盐之间的相互作用以1∶1形式为主, 随着溶液浓度的增大, 1∶2形式的相互作用逐渐增大

Volumetric Properties of Glycine and L-Serine in Aqueous LiNO3, NaNO3 and KNO3 Solutions at 298.15 K

Densities of glycine and L-serine in aqueous LiNO3, NaNO3 and KNO3 solutions have been measured at 298.15 K with an Anton Paar Model 55 densimeter. Apparent molar volumes, limiting partial molar volumes and transfer volumes have been calculated. Hydration numbers and volumetric interaction coefficients for amino acids were evaluated. The influence of side groups of amino acids and the property of cations on transfer volumes has been discussed in terms of electrostatic interaction and structural interaction. All the transfer volumes of glycine and L-serine are positive and increase with increasing the concentration of salts. The contribution of electrostatic interaction to the transfer volumes is predominant. The reduction in the electrostriction with increasing the concentration of salts was confirmed by the decreased hydration number. Hydrophilic-hydrophilic interaction between the side group of L-serine and ions gives a positive contribution to the transfer volume, which makes the transfer volumes of L-serine larger than that of glycine in the same salt solutions. The transfer volumes of each amino acid in NaNO3 and KNO3 solutions are larger than in LiNO3 solutions. The difference is due to the hard dehyration effect of Li＋. At lower concentrations of the salts the interaction between the amino acids and salts is dominated by 1∶1 form, and at higher concentrations the interaction of 1∶2 form increases.