用3种参数分析关于有选择性的化学反应的溶剂效应

根据Curtin-Hammett原理, 反应产物的选择性与迁移状态的自由能稳定性的不同或者是决定选择性阶段的结构有关，因此溶剂分子对酶反应的影响可以认为是由于其在迁移状态时引起了酶的构型的改变.由于酶与溶剂的相互作用（例如静电力、氢键、粘结压力和疏水作用等）会引起酶蛋白质的构型改变，所以文章从溶剂极性、粘结压力、疏水性3个方面选出了3种参数来描述溶剂效应，分别是表示溶剂极性的介电常数的柯克伍德参数［(-1)/(2+1)］、表示溶剂粘结压力的溶度常数的平方，和表示溶剂的疏水作用的分配系数log P.通过3参数线性回归法，得出了经验式ln =a［(-1)/(2+1)］+b2+clog P+d，这里表示产物间的比值.这个经验公式被应用到了一些关于有选择性的酶催化反应和有机化学反应中，得到了相关系数高达0925～0998线性拟和.因此，该经验式可以成为研究有选择性的非极性有机反应和酶催化反应的溶剂效应的有效工具.

Three-Parameter Analysis of Solvent Effects on Selectivity in Chemical Reactions

According to the Curtin-Hammett principle, the selectivity of reaction products relates to the free energy difference of stability at the transition state or structure in the selectivity-determining step. Therefore, it is a reasonable assumption that the solvent molecules in enzymatic reaction influence mainly the difference of conformational change of enzyme at the transition state. The conformational change (fluctuation) of enzyme protein arises from various interactions between enzyme and solvent such as electrostatics, hydrogen-bonding, cohesive pressure, hydrophobic interactions, etc. In this paper, a three-parameter treatment was proposed as a linear function of three complementary parameters describing the polarity, cohesive pressure, and hydrophobic factors of the given solvent. In this case, the Kirkwood parameter ［(-1)(2+1)］ was chosen as the polar factor, the square of solubility parameter 2 as the cohesive factor, and log P as the hydrophobic factor. According to the model, the logarithm of the product ratio (ln ) can be described in terms of equation ln =a［(-1)/(2+1)］+b2+clog P+d. This three-parameter equation has been applied to estimate the solvent effect on the selectivity of various enzymatic and organic reactions, and presents a high linearity with correlation coefficients in the range from 0925 to 0998. The proposed three-parameter analysis can be an extremely useful tool for the investigation of solvent effects on the selectivity in non-polar concerted organic reactions as well as enzymatic reactions.