Probing One-Electron Transfer in Selected Trace Elements

Electron transfer is a key process in many biological redox reactions like photosynthesis, respiration and peroxidases. Several of these processes are mediated by trace elements like transition metals and chalcogens. Although the overall redox reaction often involves the transfer of multiple electrons, it may happen in several steps of single electron transfer processes. Understanding and probing such one-electron processes is necessary to optimize the energy channeling in the mimetic redox biology. However, monitoring such reactions requires advanced spectroscopic tools. In transition metals, due to the availability of stable oxidation states, one-electron transfer can be monitored by steady-state techniques, like cyclic voltammetry and NMR spectroscopy. But such process involving p-block chalcogen elements like oxygen, sulfur, and selenium requires real-time measurements due to the involvement of short-lived (nano to micro seconds) free radical species. Our group has contributed significantly to the study of one-electron transfer reactions in these systems using a nanosecond pulse radiolysis facility with transient absorption detection and identified crucial steps involved in redox processes in enzyme mimicking reactions. Examples include superoxide dismutase activity of copper-curcumin complexes and glutathione peroxidase activity of small organoselenium compounds; salient features pertaining to electron transfer are discussed in this article.