1,4-与1,2-二氢NADH模型物反应活性的比较

Comparison of the Reactivity Between 1,4-and 1,2-Dihydro NADH Models

合成了两类NADH模型物:p-G-1,4-2H-PNAH和p-G-1,2-2H-PNAH,测得了它们在不同温度下的乙腈中分别与四氯苯醌及N,N,N′,N′-四甲基对苯二胺自由基正离子(TMPA+.)反应的速率常数及反应的活化参数(ΔH≠,ΔS≠,ΔG≠).动力学研究结果表明:1,2-2H-PNAH和1,4-2H-PNAH的相对反应活性可以通过远位取代基调节;1,2-2H-PNAH和1,4-2H-PNAH与四氯苯醌的反应是决速步骤的熵控反应,而1,2-2H-PNAH和1,4-2H-PNAH与TMPA+.的反应决速步骤则是由焓和熵共同控制的反应;通过lnk2～σ的相关分析可以看出1,2-2H-PNAH和1,4-2H-PNAH与四氯苯醌及TMPA+.反应决速步骤中反应中心是正电荷增加的过程,而且1,2-2H-PNAH的取代基效应大于1,4-2H-PNAH的取代基效应.

Two series of NADH models： p-G-PNAH-1,4-2H and p-G-PNAH-1,2-2H are syntheslzed. The rate constants at different temperatures and the activation parameters for the reaction of two oxidants （p-chloranil and TMPA^＋.） with these NADH models were determined in acetonitrile. The kinetics results reveal that the reactivity of 1,2-2H-isomer and 1,4-2H-isomer can be controlled by the remote substitutions. The reaction between GPNAH and p-chloranil was controlled by entropy while the reaction between GPNAH and TMPA^＋ . was controlled by enthalpy and entropy together. And the substituted effect of 1,2-2H-isomer is bigger than 1,4-2H-isomer .