甘氨酸在尿素、甲脲及二甲脲水溶液中的体积性质

Volumetric Properties of Glycine in Aqueous Urea,Monomethylurea,Dimethylurea Solutions

用精密数字密度计测定了甘氨酸在不同质量分数的尿素、甲脲和二甲脲水溶液中的密度,计算了甘氨酸的极限偏摩尔体积、迁移偏摩尔体积、理论水化数和体积作用系数,讨论了溶剂组成变化对甘氨酸迁移偏摩尔体积和理论水化数的影响.结果表明,甘氨酸与尿素及烷脲分子间的相互作用主要以1:1的形式为主.尿素、甲脲、二甲脲分子与氨基酸荷电中心的直接相互作用,削弱了两性离子带电中心对周围水分子的电致收缩效应,造成了理论水化数随溶液浓度的增加而减小.

Densities of glycine in various aqueous urea,monomethylurea(MMU),dimethylurea (DMU) solutions have been measured at 298.15 K with an Anton Paar Model 55 densimeter.From these densities,apparent molar volumes and limited partial molar volumes have been calculated; transfer volumes from water to aqueous urea,MMU,DMU solutions have also been obtained.Furthermore,the hydration numbers and volumetric interaction coefficients for glycine were evaluated.Solvent effect was discussed in detail.The results show that all of the transfer volumes in different solutions are positive,and increase with increasing the co solutes (urea,MMU,DMU) concentration; the hydration numbers for glycine in three solutions all decrease with increasing the co solutes concentration.It was concluded that interaction between amino acids and urea,MMU,DMU molecule is dominated by 1:1 form from the results of the volumetric interaction coefficients.