中文摘要：

通过高精度量子化学理论计算的方法研究了分子间弱的非键相互作用对胸腺嘧啶、尿嘧啶、胞嘧啶和鸟嘌呤四种核酸碱基中~（17）O核的屏蔽张量（σO）和四极耦合常数（QCC）的影响.计算结果表明分子间强的氢键作用以及弱的范德华（vd W）相互作用都对~（17）O核的化学位移（δO）具有较大的影响.随着分子间氢键作用的逐渐增强,δO逐渐减小,当采用包含所有弱相互作用的周期性模型进行计算时,理论结果与实验值吻合.进一步的电荷分析显示,~（17）O核化学位移的减小主要是由于分子间氢键作用强度增加导致~（17）O原子的负电荷密度逐渐增加.此外,计算结果表明碱基中分子间氢键网络和弱的范德华作用对碱基~（17）O QCC也具有显著的影响.周期性模型下,碱基上氧原子的局域结构环境得到平衡,~（17）O QCC达到最小值,与实验结果最为接近.以核酸碱基为例,说明了分子间的氢键网络以及分子间弱的相互作用对于准确计算生物样品的核磁共振（NMR）参数非常重要,以小的团簇模型来计算生物体系的核磁参数将会产生较大的偏差.

英文摘要：

Abstract： The influence of hydrogen bonding on the shielding tensors and quadrupolecoupling constant （QCC） of oxygen atoms in [17O-2] thymine, [17O-4] thymine, [17O-2]uracil, [17O-4] uracil, [17O-2] cytosine, and [17O-6] guanine monohydrate has been studiedby high quality quantum chemical calculations with different cluster models. The resultsshowed that both hydrogen bonding and van der Waals （vdW） interactions are crucial foraccurate prediction of isotropic 17O chemical shifts （δO）. In addition, experimentallymeasured 17O chemical shifts in these bases decrease with the increase of intermolecularhydrogen bonding interactions, and such interactions need to be accounted for in thetheoretical models in order to obtain satisfactory calculated results. Relative to that of δO,the calculation of 17O shielding tensors （δ11, δ22 and δ33） are even more model-dependent.NMR parameters calculated by periodic structure models taking all hydrogen bondinginteractions and non-bonding vdW interactions into account were found to be in goodagreement with the experimental results. Further analysis revealed that intermolecularhydrogen bonding-induced decrease of δO is mainly due to the increase of 17O negativecharge density coming from the carboxyl （C=O） carbon. Furthermore, it was found thathydrogen bonding and weak interaction have remarkable effects on calculated 17Oquadrupole coupling constant （QCC） as well. In conclusion, it is essential to takeintermolecular hydrogen bonding and weak interactions into accounts in theoreticalcalculations in order to predict NMR parameters of biological samples correctly.