利用半經驗PM3方法與全始算密度泛函數理論之B3LYP/6-311++G**方法，探討七圓環之醣水解酵素抑制劑Trihydroxyazepanes三種異構物之最穩定構形，我們發現由於有分子內氫鍵形成會穩定整個分子結構。在本篇論文研究中，也利用不同計算方法包含HF及密度泛含數理論之B3LYP和OPBE方法，搭配一系列基底函數包含6-311++G**、6-311+G(2d,p)、cc-pVDZ與cc-pVTZ來計算化學位移，所搭配計算化學位移的方法為GIAO。由計算結果發現，以OPBE方法計算所得之化學位移會介於HF和B3LYP之間，而其中搭配cc-pVDZ此基底函數計算所得之化學位移的平均絕對誤差( MAE)會較小，且較接近於實驗值。 PM3 of semiempirical methods and B3LYP/6-311++G** of ab initio methods were used to investigate the most stable conformer of three isomers of trihydroxyazepanes, which are seven-membered-rings glycosidases. According to the calculation results, the stable conformer depend on intramolecular hydrogen bonding. In this study, the physical property( NMR chemical shift ) of the most stable conformers were generated by HF method, B3LYP and OPBE of ab initio( GIAO) methods with a series of basis sets include 6-311++G**, 6-311+G(2d,p), cc-pVDZ and cc-pVTZ . Comparing to the experimental data of 13C NMR for all most stable conformers, we predict the chemical shift which was obtained by OPBE method is between HF and B3LYP methods, and the mean absolute error( MAE ) of cc-pVDZ is close to the experimental data.
