Cytochrome c oxidase (CcO) is an important enzyme in the respiratory cycle of many life forms. Once in the cell, oxygen binds to the enzyme and is converted to water and energy. A study of the structure of cytochrome c oxidase and similar proteins, like hemoglobin, will allow for a better understanding of the mechanism of oxygen conversion into water and the overall cellular respiration process. Toward achieving this understanding, a series of reduced, heteronuclear heme-copper (Fe II/Cu I) or reduced Fe II-porphyrin complexes that are designed to mimic the active centers of these biological heme-containing enzymes will be synthesized within sol-gel matrices. Reactivity studies will be performed to further elucidate influences of subtle changes in environment upon complex activity toward oxygen binding and subsequent reduction to water. Included amongst these fully-reduced biomimics are carbonmonoxy and isocyanide ligated derivatives of covalently-linked model compounds because these ligands stabilize the reduced states, Fe II and Cu I. Reactivity studies, focusing upon photolytic displacement of these ligands, will be performed to further elucidate influences of subtle changes in ligand coordination environment upon complex reactivity toward 02 binding and ligand recombination. Tethering the heme to the sol-gel matrix will inhibit direct heme-heme reactivity, similar to the protein backbone in natural systems. A ligand bridged Fe-X-Cu center has been implicated in the CcO catalytic cycle. Several "mixed valence" (Fe II/Cu II) tethered heme/copper complexes will be synthesized and characterized to mimic the spectral and reactivity characteristics of the native enzyme. These complexes may have relevance with regard to the energy translocation and storage required for proton pumping across the mitochondrial membrane in CcO. This aspect of the project is designed to answer the questions regarding ligand shuttling after photoinitiated intervalence charge transfer in these novel bimetallic systems.