SCALED QUANTUM-MECHANICAL FORCE-FIELD FOR GLYCINE IN BASIC SOLUTION
SCALED QUANTUM-MECHANICAL FORCE-FIELD FOR GLYCINE IN BASIC SOLUTION
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DOI：
10.1007/bf00681202
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发表时间：
1993-10-01
影响因子：
1.7
通讯作者：
WILLIAMS, RW
中科院分区：
文献类型：
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作者：
LOWREY, AH;KALASINSKY, V;WILLIAMS, RW
我们得到的三个甘氨酸-nH2O从头算力场的比例因子，使用4 - 31G基组，可用于建立一个缩放的量子力学力场丙氨酸，随后，在水溶液中的肽。从充分优化的甘氨酸-nH2O超分子的力常数缩放通过使用实验确定的振动频率的甘氨酸在水中pH 13。对甲胺和乙酸盐进行了类似的计算。乙酸盐的拉伸模式的比例因子在甘氨酸盐的相关比例因子的2%以内。甲胺中NH_2吸收模式的标度因子也与甘氨酸盐的标度因子一致。在甘氨酸盐和乙酸盐之间，作为水合水分子数量的函数的比例因子的变化也是相似的。胺组显示出相对较小的变化。没有水合分子的甘氨酸盐的比例因子从超分子结果外推，因为用4 - 31G基组获得的分离的甘氨酸盐的优化结构产生一个虚频。甘氨酸盐，乙酸盐和甲胺的计算频率和实验频率之间的良好协议，得到了每组比例因子。缩放似乎可以补偿水合作用对力常数的系统影响，从而可以在不诉诸昂贵的超分子计算的情况下获得水中氨基酸的可靠频率预测。
We obtain scale factors for three glycinate-nH2O ab initio force fields, using the 4-31G basis set, that can be used in building a scaled quantum mechanical force field for alanine and, subsequently, for peptides in aqueous solutions. Force constants from the fully optimized glycinate-nH2O supermolecules were scaled by using experimentally determined vibrational frequencies of glycine in water at pH 13. Similar calculations were performed for methylamine and acetate. Scale factors for the stretching modes of acetate are within 2% of the related scale factors for glycinate. The scale factor for the NH2 scissor mode in methylamine is also in agreement with that of glycinate. Changes in the scale factors as a function of the number of hydrating water molecules were also similar between glycinate and acetate. Amine groups showed relatively small changes. Scale factors for glycinate with no hydrating molecules were extrapolated from the supermolecule results, since the optimized structure of isolated glycinate obtained with the 4-31G basis set yielded one imaginary frequency. Good agreements between calculated and experimental frequencies for glycinate, acetate, and methyl amine were obtained for each set of scale factors. Scaling appears to compensate for the systematic effects of hydration on force constants, making it possible to obtain reliable frequency predictions for amino acids in water without resorting to expensive supermolecule calculations.