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首页> 外文期刊>Chemistry: A European journal >Kinetics of Dissociative Electron Transfer to Ascaridole and Dihydroascaridole-Model Bicyclic Endoperoxides of Biological Relevance
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Kinetics of Dissociative Electron Transfer to Ascaridole and Dihydroascaridole-Model Bicyclic Endoperoxides of Biological Relevance

机译：离解性电子转移至生物相关的hydro啶和二氢a啶模型双环内过氧化物的动力学。

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摘要

The homogeneous and heterogeneous electron transfer(ET) reduction of ascaridole (ASC) and dihydroascaridole(DASC), two bicyclic endoper-oxides, chosen as convenient models of the bridged bicyclic endoperoxides found in biologically relevant systems, were studied in aprotic media by using electrochemical methods. ET is shown to follow a concerted dissociative mechanism that leads to the distonic radical anion, which is itself reduced in a second step by an overall two-electron process. The kinetics of homogeneous ET to these endoperoxides from an extensive series of radical anion electron donors were measured as a function of the driving force of electron transfer (triangle openG_(ET)deg ). The kinetics of heterogeneous ET were also studied by convolution analysis. Together, the heterogeneous and homogeneous ET kinetic data provide the best example of the parabolic nature of the activation-driving force relationship for a concerted dissociative ET described by Saveant; the data is particularly illustrative due to the low bond-dissociation enthalpy (BDE) of the O-O bond and hence small intrinsic barriers. Analysis of the data allowed the dissociative reduction potentials (E)(DISS)~deg) to be determined as -1.2 and -1.1 V against SCE for ASC and DASC, respectively. Unusually low pre-exponential factors measured in temperature-dependent kinetic studies suggest that ET to these O-O bonded systems is nonadiabatic. Analysis of ET kinetics for ASC and DASC by the Saveant model with a modification for nonadiabaticity allowed the intrinsic free energy for ET to be determined. The use of this approach and estimates for the BDE provide approximations of the reorganization energies. We suggest the methodology described herein can be used to evaluate the extent of ET to other endoperoxides of biological relevance and to provide thrmochemical data not otherwise available.
机译：在非质子介质中，通过电化学方法研究了a啶（ASC）和二氢a啶（DASC）的均相和异相电子转移（ET）还原，这两种双环内过氧化物被选为生物学相关系统中桥接的双环内过氧化物的便捷模型方法。已证明ET遵循一种协同的解离机理，该机理导致了二阶自由基阴离子，该阴离子本身在第二步中通过整个双电子过程被还原。从大量的自由基阴离子电子给体到这些内过氧化物的均相ET动力学是作为电子转移驱动力的函数（三角形openG_（ET）deg）进行测量的。还通过卷积分析研究了异质ET的动力学。总而言之，异质和均匀的ET动力学数据提供了Saveant描述的协同解离ET的激活驱动力关系的抛物线性质的最佳示例。由于O-O键的键解离焓（BDE）低，因此固有的壁垒较小，因此该数据特别具有说明性。数据分析使得对于ASC和DASC，相对于SCE的解离还原电位（E）（DISS）-deg被确定为-1.2和-1.1V。在与温度有关的动力学研究中测得的异常低的指数前因子表明，这些O-O键合系统的ET是非绝热的。通过Saveant模型对非绝热性的修正，分析了ASC和DASC的ET动力学，从而可以确定ET的内在自由能。这种方法的使用和对BDE的估计提供了重组能量的近似值。我们建议本文描述的方法可用于评估ET与其他内过氧化物具有生物学相关性的程度，并提供原本无法获得的血栓化学数据。

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