Ni^(2+)催化甘氨酸质子迁移机理的理论研究

The Mechanisms of Proton Transfer of Glycine Induced by Ni^(2+)

采用B3LYP/6-31++G(d,p)方法研究Ni^(2+)催化甘氨酸质子迁移机理.优化得到了7个中性配合物和1个两性配合物;两性的最稳定,结合能为-927.3 k J/mol.分子内单键旋转和羧基H在2个羧基O原子间的迁移导致中性构型转化,C-C键旋转的能垒低于21.9 k J/mol,C-O键旋转的能垒在23.1-46.4 k J/mol范围内,羧基H在O原子间迁移的正逆反应能垒分别为175.0和108.3 k J/mol.羧基H迁移到氨基生成两性构型,能垒为19.3k J/mol.Ni^(2+)导致氨基N原子负电荷减少0.48,削弱了N原子对羧基H原子的库仑吸引,钝化了共价键B_(O3–H6),动力学上不利于羧基H迁移;但是羧基H迁移后,形成的两性构型却是热力学最稳定体系.最稳定中性构型N1转化为最稳定两性构型Z1的路径为:N1→N1-N7→N7→N3-N7→N3→N3-N5→N5→N5-Z1→Z1,该路径的最高能垒为124.8 k J/mol.

B3LYP/6-31＋＋G（d,p） method was applied to investigate the proton transfer mechanism of glycine catalyzed by Ni2＋. 8 complexes were obtained, 7 of them are neutral and the other is zwitterionic,the most stable structure is the zwitterion with bonding energy-927.3 k J/mol. The neutral complexes can transform mutually via the rotation of single bond and pronton transfing between the two carboxyl O atoms, The energy barrier range of the single bond rotation of C-C and C-O is separately 5.5-21.9 and23.1-46.4 k J/mol, the positive and negative energy barrier of pronton transfing reaction is separate 175.0and 108.3 k J/mol. The neutral complex turn into zwitterionic complex by the pronton transfing from carboxy to amino group with 19.3 k J/mol energy barrier. With the effect of Ni2＋the negative charge on atom N decreased 0.48, which indicated that the Coulomb attraction between amino N and carboxyl H has been reduced and it is not prone to transferring of carboxyl H kinetically. But, via the transfer of carboxyl H,the resulted zwitterionic complex is the most stable thermodynamics structure. The path from the most stable neutral structure to the most stable zwitterionic structure is N1→N1-N7→N7→N3-N7→N3→N3-N5→N5→N5-Z1→Z1, and the highest energy barrier of this path is 124.8 k J/mol.