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采用B3LYP/6-31++G(d,p)和M06/6-31++G(d,p)方法研究了Cu2+诱导丙氨酸质子迁移机理,两种方法均得到8个稳定构型(1个两性的和7个中性的)和7个过渡态,构型转化途径一致。两种方法对构型结构的计算结果非常接近,都确认两性构型最稳定,但是认为7个中性构型稳定性的次序不同。采用CCSD/6-31++G(d,p)方法进行了能量校正,表明最稳定的是中性构型,结合能为-217.14kcal/mol,两性构型是次稳定结构;中性构型稳定次序与M06方法的一致,并表明M06方法的能量比B3LYP的好。C—O键和C—C键的旋转(能垒范围分别是2.31~17.49 kcal/mol和4.89~8.95 kcal/mol)以及质子在羧基O原子间的迁移(正逆反应能垒分别为54.99和31.06kcal/mol)导致中性构型间的转化;质子从羧基迁移到氨基导致中性构型变为两性构型(能垒为20.71 kcal/mol)。Cu2+使丙氨酸的电子云向Cu2+偏移,导致N6原子负电荷减少,降低了N6原子对H8原子的库仑作用,钝化了共价键B(O4—H8),动力学上不利于H8质子迁移。
The mechanism of Cu2 + -induced alanine proton transfer was studied by B3LYP / 6-31 ++ G (d, p) and M06 / 6-31 ++ G (d, p) (One amphipathic and seven neutral) and seven transitional states, with the same conformational transitional pathway. The two methods are very close to the calculated results of the configurational structure, confirming the most stable amphiphilic configuration, but the order of the stability of the seven neutral configurations is considered to be different. The energy calibration was performed using the CCSD / 6-31 ++ G (d, p) method, indicating that the most stable is the neutral configuration with a binding energy of -217.14 kcal / mol and the amphoteric configuration is a sub-stable structure. The neutral configuration The type stability order is consistent with the M06 method and shows that the energy of the M06 method is better than that of B3LYP. The rotation of the C-O bond and the C-C bond (energy barriers range from 2.31 to 17.49 kcal / mol and 4.89 to 8.95 kcal / mol, respectively) and proton transfer between carboxyl O atoms (positive and negative energy barriers of 54.99 and 31.06, respectively kcal / mol) resulted in the conversion of the neutral configuration. The migration of protons from carboxyl to amino led to the conversion of the neutral configuration to an amphiphilic configuration (energy barrier of 20.71 kcal / mol). Cu2 + shifts the electron cloud of alanine to Cu2 +, resulting in the decrease of the negative charge of N6 atom, reducing the coulombic effect of N6 atom on H8 atom, inactivating the covalent bond B (O4-H8) and kinetically detrimental to H8 Proton migration.