对乙酰氨基酚-水复合物中氢键作用的理论研究

Theoretical study on the role of hydrogen bonds in acetaminophen-water complexes

为了解对乙酰氨基酚(AP)在水溶液中的构象,在MP2/6-311++G(d,p)水平上研究了AP与水分子通过不同种氢键作用形成的6种AP-H2O复合物.首先分析这些复合物的几何结构、能量和振动频率,然后运用分子中原子的量子理论(QTAIM)、自然键轨道理论(NBO)和定域分子轨道-能量分解分析(LMO-EDA)等理论和方法对AP-H_2O复合物中的氢键相互作用进行定性和定量分析.研究结果表明:(1)AP分子中的—CH基团与羰基氧原子之间形成的C8H8A···O2A分子内氢键在多数AP-H_2O复合物中被保留下来;(2)AW1和AW6中的分子间氢键强于其他氢键;(3)AP的羰基氧原子是最有可能与H_2O分子形成氢键的位点,第2个最有可能与H_2O分子形成氢键的位点是AP的酚羟基,前者中H_2O是质子供体,而后者中H_2O则是质子受体;(4)AP-H_2O的形成过程中,氢键作用与结构畸变都会在一定程度上决定AP-H_2O复合物的相对稳定性,但前者的作用更大.

To learn the conformation of acetaminophen in water, six acetaminophen-water （AP-H_20） complexes formed by various types of hydrogen bonds（H-bonds） were characterized by geometries, energies, vibrational frequencies at the MP2/ 6-311＋＋G （d,p） level. Natural bond orbital （NBO）, quantum theory of atoms in molecules （QTAIM） analyses and the localized molecular orbital energy decomposition analysis （LMO-EDA） were performed to explore the nature of the hydrogen bonds in these complexes. The results showed that： （ 1 ） The intramolecular H-bond C8H8^A…O2^A formed between the -CH and carbonyl oxygen atom of AP is retained in most of complexes; （2） The intermolecular H-bonds in AWl and AW6 are stronger than the other intermoleeular H-bonds ; （ 3 ） The carbonyl oxygen atom of AP is the most likely site which can form H-bond with H_20 molecule, and the second most likely site forming H-bond with H2O is the phenolic hydroxyl group of AP. Moreover, in the former case H-bonds are formed by the donation of proton from H_2O to AP, while H_2O acts as proton acceptor to form H-bond in the latter; （4） Both the hydrogen bonding interaction and structural deformation can determine the relative stabilities of AP-H_2O complexes in some degrees, but the former had more important roles than the latter.