复杂缔合体系NMA-H2O的^1H NMR研究

1H NMR Studies on Complex NMA-H2O Association System

N 甲基乙酰胺 (NMA)是最简单的肽键模型分子 ,广泛地被用来研究氢键相互作用 .采用外标法测量了不同温度下NMA H2 O缔合体系的1HNMR数据 ,通过磁化率校正得到了混合物的准确化学位移数据 .然后用量子化学计算的结果确定体系的缔合形式 ,运用化学缔合理论建立模型 ,对模型进行降维 ,减少模型参数 ;再采用最小二乘法 ,联合遗传算法 (GA)和Levenberg Marquardt算法对模型参数进行全局寻优 ,求解得到了缔合平衡常数和缔合平衡的ΔH和ΔS .此外 ,还采用密度泛函理论 (DFT)计算了NMA H2 O的几种主要缔合形式在 2 98K的ΔH ,计算结果与化学缔合模型得到的结果和文献吻合较好 .

N-methylacetamide (NMA), one of the simplest model molecules of peptide group, has been extensively studied using a variety of techniques. 1H NMR of NMA-H 2O system was determined by the external reference method in the whole concentration range at different temperatures, and chemical shift data were corrected via the magnetic susceptibilities. The association model was determined by quantum chemical calculation. Dimensionality reduction was also carried out. Based on chemical association theory the association equilibrium constant and the corresponding ΔH and ΔS were obtained by nonlinear least-square fitting. In addition, density functional theory (DFT) was also used to calculate the ΔH of main association forms in NMA-H 2O system. The results calculated by chemical association theory are in good agreement with those calculated by DFT and the literatures.