中文摘要：

采用从头算（HF与MP2）和密度泛函理论（DFT）方法,在3-21G 和6-31＋G？水平上研究了尼克酰胺核苷（NR）的构象.分别探讨了在气相及液相（水和氯仿）中 NR 分子和一水合物异构体的相对稳定性,分析了溶剂分子的参与对NR异构体的相对稳定性和几何结构参数的影响.结果表明：孤立的NR分子在气相中存在36种稳定构象,其中最稳定的为南式构象NR-S,而最稳定的北式构象为NR-K’,能量比前者高出10.6 kJ/mol （ΔG298K）.NR 分子中酰胺基团优势构象为反式,ω,P 或γ参数的改变可以为 NR 分子提供大约8.4~23.7 kJ/mol（ΔG298K ）稳定化能.不管是南式还是北式褶皱,最稳定 NR 分子构象中都存在多根分子内氢键,且5’-OH 基团都为顺式构象（γ≈-63°）.溶剂效应使一部分NR分子构象相对稳定性降低,而一部分则升高,改变了NR分子各构象的相对稳定性顺序.水分子的加入与酰胺基团结合形成氢键,对NR分子的构型影响较大,而与糖环上羟基结合形成氢键,则影响较小.

英文摘要：

A conformation analysis on the nicotinamide riboside（NR）in gas phase and in water as well as chloroform was performed by ab initio（HF and MP2）and density functional theory（DFT）methods at 3-2 1 G and 6-3 1＋G？ level.The effects of one-water molecule on relative stabilities,conformational pa-rameters of NR were analyzed.The results indicate that there are 3 6 stable conformers for NR in the gas phase.The south conformer NR-S is the most stable form of all conformations in the gas phase.The most stable north puckering is the conformer NAR-K’,which is about 10.6 kJ/mol （ΔG298K）above the globle minimain NAR-S.The carboxamide group of the NR is preferred in an anti configuration.Varies of the key geometrical parametersω,P orγprovide about 8.4~23.7 kJ/mol（ΔG298K）relative stabilities for NR.The most stable conformer of NR both for south and north puckering adopts a syn configuration withγabout-63°and by doing so,forms stronger intramolecular hydrogen bond interactions.Solvent＆amp;nbsp;effects both in water and chloroform change the order of the relative stability of NR,by decreasing or in-creasing the relative stabilities of NR molecules.The addition of one-water molecule will influence great-ly the conformational parameters of NR due to the stronger hydrogen bond interactions with carboxam-ide group of NR,while this influence will be negligible if the hydrogen bonds formed between water molecule and hydroxy groups of furanose ring.