An understanding of biological oxidations is fundamental to an understanding of heart functions. The energy produced in biological oxidations is used to drive the synthesis of adenosine triphosphate (ATP), which is the major energy source for heart muscle contraction and active ion transport. The objective of this research is to discern the significance of sulfur chemistry in biological oxidation. The oxidation of divalent sulfides is surprisingly facile in the presence of suitable neighboring groups, such as those commonly found in proteins. Neighboring group interaction depends markedly on geometry. Simple rigid systems are studied to discern the basis for the interactions. A series of physical organic, electrochemical, spectroscopic (IR, UV, ESR and PE), X- ray crystallographic and pulse radiolysis techniques are used to study electron deficient sulfide intermediates. Such interactions may be important in a number of redox proteins, e.g. cytochrome c. In cytochrome c the thioether of cys-17 which is covalently attached to the heme side-chain has been suggested to mediate electron-transfer at the heme crevice. The role of the "intervening matter" between redox-centers in redox enzymes will be investigated. The rate of electron-transfer between two redox centers coordinated to carefully designed and conformationally constrained ligands will be studied. These methods may provide the key to understanding specificity and control of electron- transfer in redox proteins.