REDOX CHEMISTRY OF VITAMIN B12 DERIVATIVES

该研究项目的目标是将电化学 本文介绍了钴类化合物的体外研究方法， 了解酶促反应中Co-C键的活化。 我们的长期目标之一是研究氧化还原化学 维生素B12的种类，以了解他们的参与 在生物化学过程中。 为了实现这一目标，我们计划研究两个 机理方案：（i）有机-B12物质的还原裂解， (ii)B12催化还原反应。 第一个项目，（i）将是 对烷基钴，烷基钴酰胺， 并使用电化学技术建立系统模型， 详细讨论了碳-钴的还原裂解机理， 键通过电子转移反应断裂。 我们的目标是获得 关于取代基结构如何影响（a）还原的信息 有机-B12物种的电势和（B）电子的速率常数 转移和Co-C键裂变。 这些结果可能有助于 了解Co-C键如何在酶促反应中被激活。 在 在大多数情况下，Co-C键断裂是异常快， 转移事件和用于跟踪这种转移事件的电化学技术 在微秒和纳秒时间域的反应已经开发 来研究这些过程。 研究溶剂、pH、 反应步骤的温度依赖性也是必要的 一个完整的图片的机制。 待研究的第二类电化学过程（ii）是 维生素B12催化还原，例如，氧还原好氧 系统. 该反应需要形成还原型维生素B12 物种，Co（II），B12 r，或Co（I），B12 s，其然后可以反应 快速与氧气或其他基质反应。 在这里，率和产品的 该过程将通过伏安法和光谱电化学进行研究 在不同的电极上。 我们还计划使用表面增强拉曼 利用表面增强拉曼光谱（Sers）来阐明这些化合物中B12中间体的性质。 反应.

The goals of this research project are to apply electrochemical techniques to the study of the Co corrinoid compounds in vitro in order to understand the activation of the Co-C bond in enzymatic reactions. One of our long term objectives has been the study of the redox chemistry of vitamin B12 species with a view toward understanding their involvement in biochemical processes. With this goal in mind, we plan to study two mechanistic schemes: (i) the reductive cleavage of organo-B12 species and (ii) B12 catalyzed reduction reactions. The first project, (i) will be a study of the reduction process of alkylcobalamins, alkylcobinamides, and model systems using electrochemical techniques in order to understand in detail the reductive cleavage mechanism in which the carbon-cobalt bond is cleaved by an electron transfer reaction. Our aim is to obtain information on how substituent group structure affects (a) the reduction potentials of organo-B12 species and (b) the rate constants for electron transfer and for Co-C bond fission. These results could help in understanding how the Co-C bond is activated in enzymatic reactions. In most cases, Co-C bond breaking is exceptional fast following an electron transfer event and electrochemical techniques for following such reactions in the musecond and nanosecond time domain have been developed to study these processes. Experiments to investigate the solvent, pH, and temperature dependence of the reaction steps are also necessary for a complete picture of the mechanisms. The second type electrochemical process to be investigated, (ii), is vitamin B12 catalyzed reductions, e.g., oxygen reduction for aerobic systems. This reaction requires the formation of a reduced vitamin B12 species, the Co(II), B12r, or the Co(I), B12s, which then can react rapidly with oxygen or other substrates. Here the rate and products of the process will be studied by voltammetry and spectroelectrochemistry at various electrodes. We also plan to use surface enhanced Raman spectroscopy (SERS) to elucidate the nature of B12 intermediates in these reactions.