尿素与丙氨酸二肽相互作用的量子化学研究

Studies of the interactions between urea and alanine dipeptide by quantum chemical calculations

应用量子化学方法研究尿素与丙氨酸二肽形成复合物[urea-(Ala)_2]的稳定结构、氢键、电荷分布以及相对稳定性.采用B3LYP/6-311++G(d,p)方法进行结构优化和频率计算,对获得的28种稳定结构进一步采用MP2/6-311++G(d,p)方法计算结合能,并进行基组重叠误差校正.结果表明:在urea-(Ala)2中主要存在着3种类型的氢键:其中,N_U—H_U…O_A型是最主要的氢键类型,N_U—H_U…O_A型和N_A—H_A…O_U型氢键较强,对应的复合物结合能也较大,而C_A—H_A…O_U型氢键较弱.通过Mulliken布局分析,发现复合物中参与形成氢键的原子所带电荷变化明显,而没有参与形成氢键的原子电荷几乎不变;而且复合物结合能的大小与形成氢键的原子之间的电荷转移量密切相关,电荷转移量越大,复合物的结合能越大.

The structures,hydrogen bond,charge distributions and relative stability of the complexes formed by urea and alanine dipeptide[urea-（Ala）2]were studied by quantum chemical calculations.The B3 LYP/6-311＋ ＋G（d,p）method was employed to optimize the structures and calculate frequencies,and the binding energies of 28 stable structures were calculated at MP2/6-311＋＋G（d,p）level with the basis set superposition error correction.Results show that there are mainly 3 types of hydrogen bonds in urea-（Ala）2,of which the NU—HU… OA is the most preferable.The bond strengths of NU—HU…OA and NA—HA…OU are stronger than that of CA—HA…OU,and the corresponding binding energies of the formers are bigger than the later ones.According to the Mulliken population analysis,evident charge transfer is observed between the hydrogen-bonding atoms,while almost no charge transfer between the other atoms.Moreover,the amount of binding energy of the complexes is in accordance with that of the charge transfer between the hydrogen-bonding atoms.