Active transition metal oxo and hydroxo moieties in nature's redox, enzymes and their synthetic models: Structure and reactivity relationships

The high oxidation state transition metal oxo moieties in redox enzymes and their models are generally recognized to serve as the key active intermediates in a series of hydrogen abstraction, oxygen transfer, and electron transfer processes. New evidence suggests that certain transition metal hydroxo moieties also play key roles in oxidative processes in biological and chemical systems. Clarifying the structure and reactivity similarities and differences between the metal oxo functionality and its corresponding metal hydroxo form will help promote understanding of their complementary roles in oxidation processes and aid in the rational design of selective oxidation catalysts to match different requirements. This review summarizes the structure and reactivity similarities and differences of the reported redox enzymes and their models in which the metal oxo and/or corresponding metal hydroxo moieties have demonstrated their activity in oxidation processes. Those enzymes include heme enzymes, lipoxygenases, sulfite oxidases and xanthine oxidases, because the heme enzymes and lipoxygenases would provide the platform to compare the iron oxo with its corresponding hydroxo species, and the sulfite oxidases and xanthine oxidases provide the platform for molybdenum oxo and hydroxo species.