Electron transfer in transition metal-pteridine systems

The combination of a pterin and a transition metal in many enzymes is the motivation for exploring the chemistry of pteridine complexes in detail. Unlike other biological ligands for essential transition metals, pterin is unique in displaying multi-electron redox reactivity, an ability that resembles the redox capabilities of transition metals. It is perhaps because these two partners, metal and pterin, have this chemical similarity that their compounds defy traditional categorization by formal oxidation number. The result challenges the chemist to formulate fresh interpretations of these deceptively ordinary complexes. This review concerns reports of metal-pterin complexes that appeared from the early 1980s through 1996. In a few cases older literature is briefly mentioned to build a context for the newer work. The review comprises four sections. Section 1 introduces the pteridine family and its important contributions to biochemistry. Section 2 is devoted to studies of molybdenum (6+) complexes reacted with reduced pterins. Section 3 describes redox interactions between reduced pterins and the first row metals copper and iron. Finally, Section 4 turns to a discussion of the electronic interactions in flavin complexes of various metals. An Epilogue closes the review.