Mg^(2+)诱导丙氨酸质子迁移机理的理论研究  

Theoretical study on proton transfer mechanism of alanine induced by Mg^(2+)

作　　者：孟祥军[1] 石瑾[1] Meng Xiangjun Shi Jin(Department of Chemistry, Tangshan Normal University, Tangshan, 063000, Chin)

机构地区：[1]唐山师范学院,唐山063000

出　　处：《南京大学学报（自然科学版）》2017年第1期199-207,共9页Journal of Nanjing University（Natural Science）

基　　金：河北省高等学校科学技术研究青年基金(QN2014312)

摘　　要：采用M06/6-31++G**方法研究了Mg^(2+)诱导丙氨酸质子迁移机理,得到8个稳定构型和7个过渡态.最稳定构型Ⅰ是两性的,结合能为-687.0kJ·mol-1;其余7个是中性的.分子内单键旋转和羧基O原子间的质子迁移导致中性构型间的转化.C—C键旋转的能垒低于16.0kJ·mol-1;C—O键旋转的能垒低于60.0kJ·mol-1;质子在羧基O原子间迁移能垒高于105.6kJ·mol-1.质子从羧基迁移到氨基导致中性构型转化为两性构型,能垒为0.2kJ·mol-1.最稳定中性构型Ⅱ转化为两性构型Ⅰ的路径为:Ⅱ→Ⅱ-Ⅲ→Ⅲ→Ⅲ-Ⅶ→Ⅶ→Ⅵ-Ⅶ→Ⅵ→Ⅵ-Ⅷ→Ⅷ→Ⅴ-Ⅷ→Ⅴ→Ⅰ-Ⅴ→Ⅰ.M06/6-31＋＋G＊＊ method was applied to investigate the proton transfer mechanism of[Mg^2＋·Ala].Eight optimized stable configurations are obtained.The most stable configuration I is amphoteric and the rest seven are neutral.The eight stable configurations converts via seven transition states.Mg^2＋coordinates to alanine with bisdentate and mono-dentate coordination modes.The most stable amphoteric configuration I and neutral configuration II adopt bis-dentate mode with binding energies of-687.0and-656.6kJ·mol^-1,respectively.In addition,the rotation of intramolecular single bond leads to the neutral configuration conversion,in which the rotation energy barriers of C—C single bonds are lower than 16.0kJ·mol^-1,and those of C—O single bonds are lower than 60.0kJ·mol^-1.On the other hand,the proton transfers among the carboxylic oxygen atoms can also result in the neutral configuration conversion,whose energy barriers of forward/back reaction are 194.9and 105.6kJ·mol^-1,respectively.In detail,the proton transfers from carboxylic group to amino lead to their configuration conversion from neutral to amphoteric,in which the energy barrier is 0.2kJ·mol^-1.The binding energies of all stable structures seem high（larger than 492.1kJ·mol^-1）,which are much higher than those in the configuration conversions.So,the configuration con-version is thermodynamic control rather than dynamic control.after the Mg^2＋interacts with alanine,the positive charge on Mg^2＋decreases larger than 0.14,suggesting that the electronic cloud tends to the Mg center,and the dipole moments of all the systems increase by over 6.0Debye.The reaction pathway from the most stable neutral structure to the most stable zwitterionic structure isⅡ→Ⅱ-Ⅲ→Ⅲ→Ⅲ-Ⅶ→Ⅶ→Ⅵ-Ⅶ→Ⅵ→Ⅵ-Ⅷ→Ⅷ→Ⅴ-Ⅷ→Ⅴ→Ⅰ-Ⅴ→Ⅰ,and the highest energy barrier of this reaction pathway is 139.9kJ·mol^-1.

关 键 词：配合物 丙氨酸 Mg2+ 质子迁移 过渡态 反应路径 机理 

分 类 号：O641[理学—物理化学]