Abstract: Bile acids play an important role in the digest process. It was found that various bile acids exhibited different biological and spectroscopic behavior. We supposed the difference may be correlated with the different capability of forming intra-molecular hydrogen bond. So the possibility of forming intramolecular hydrogen bond for various bile acids were investigated by molecular mechanics calculation code MM3. In this paper, we proposed a new pre-optimized calculation method, which was used along with the MM3 molecular mechanics calculation to evaluate the possibility of forming intra-molecular hydrogen bond in various bile acids. The calculation results show that (1) 17R-7α-OH-bile acid is not able to form stable intra-molecular hydrogen bond while the 17S-7α-OH-bile acid can form two stable intramolecular hydrogen bonds. The stability of the conformation is proved by the fact that the conformation has lower steric energy and no negative vibration frequncies. (2) 17S-12α-OH-bile acid can also form intra-molecular hydrogen bond.

Key words: molecular mechanics, bile acid, hydrogen bond

摘要： 胆汁酸是胆汁中的主要成分，不同种类胆汁酸在生理特性和光谱行为方面表现出很大差异，这可能与其形成分子内氢键能力不同有关。用MM3分子力学方法研究了几种胆汁酸形成分子内氢键的可能性，并设计预优化法以配合计算。实践表明,预优化法与分子力学相结合是成功的。结果表明，(1) 17R-7α-OH-胆汁酸的羧基难以与7α位的羟基生成分子内氢键，而17S-7α-OH-胆汁酸的羧基可与7α位的羟基生成两个分子内氢键。立体能比无分子内氢键结构的低且计算出的振动光谱无负频率，这两方面结果说明该结构是稳定的；(2)17S-12α-OH-胆汁酸也可生成分子内氢键。

关键词: 分子力学, 胆汁酸, 氢键