大蒜素在正戊烷和乙醇中的分解动力学研究

Decomposition Kinetics of Allicin in Pentane and Ethanol

摘要:

研究了大蒜素在正戊烷、乙醇溶剂中的分解动力学过程，拟合得到了动力学参数：大蒜素在正戊烷、乙醇溶剂中的分解活化能分别为56.0、72.0 kJ/mol，指前因子分别为9.2×105、1.5×106。采用B3LYP方法，在6-31+G(d，p)基组下计算了大蒜素与正戊烷、乙醇的相互作用能分别为1.12、31.18 kJ/mol，说明大蒜素与乙醇分子间存在较强的相互作用；采用自然键轨道理论分析了以乙醇为溶剂的体系中电子供体(Donor)轨道、电子受体(Acceptor)轨道以及它们之间相互作用的稳定化能，结果表明大蒜素分子中的氧原子的孤对电子O(13)对乙醇分子的羟基（O(21)-H(20)）的反键轨道稳定化能为45.45 kJ/mol，说明大蒜素与乙醇分子产生较强的氢键作用，分散了大蒜素分子中的氧原子上的负电荷，导致分子内质子转移能量升高，因而大蒜素在乙醇中具有更高热稳定性。

Abstract:

The kinetic parameters for decomposition of allicin in pentane or ethanol were determined. The activation energies and pre-exponential factors were separately 56.0 kJ/mol and 9.2×105 in pentane as well as 72.0 kJ/mol and 1.5×106 in ethanol. The intermolecular interaction energy between allicin and solvent was calculated by density functional theory (DFT) at the B3LYP/6-31+G(d+P) leve1. The results showed that the intermolecular interaction energy between allicin and ethanol (31.18 kJ/mol) was higher than that between allicin and pentane (1.12 kJ/mol). Natural orbital theory (NBO) analysis showed that the anti-bonding orbital stabilization energy between the lone pairs of O (13) in allicin and hydroxyl (O(21)-H(20)) in ethanol molecule was 45.45 kJ/mol, which illustrated that strong hydrogen bonding interaction between them dispersed the negative charges in O atom of allicin. Therefore it became more difficult in the intramolecular to transfer H atom during decomposition of allicin in ethanol.