The goal of the proposed research program is the complete characterisation of synthetic compounds which are models for the oxygen carrying hemoproteins. This program of research will elucidate the redox reactivity of deoxyhemoglobin and deoxymyoglobin model compounds possessing central metal ions which remain five coordinate upon electron transfer. The desired coordination geometry of the central metal ions will be controlled via steric encumberance synthetically built onto only one side of the porphyrin. These model compounds will then be reacted with CO, CS, CSe (the later two created in situ) to form six coordinate metalloporphyrins in which the diatomic ligand resides in a hydrophobic cavity. The redox reactivity of these compounds will be characterized by careful voltammetric and spectroelectrochemical experiments.