It is proposed to apply the synthetic model approach to the oxygen-carying protein, hemocyanin, in order to gain an understanding of the fundamental active site chemistry. The synthetic chemistry involves the preparation of new benzimidazole chelating ligands which can hold copper ions in structures similar to those envisaged for the various states of hemocyanin. Having completed a detailed study of analogues of met-hemocyanin attention will now be focused on the more challenging problem of oxyhemocyanin. Emphasis will be placed on definitive characterization of crystalline materials by x-ray crystallography and spectroscopic methods (IR, ESR, UV-VIS, Resonance Raman). The compounds will provide well-defined systems on which to test the validity of recent electronic, vibrational and EXAFS spectroscopy applications to hemocyanin. The long term goal is to gain an understanding of the chemistry and biochemistry of copper proteins, particularly those having copper/dioxygen interactions. A detailed molecular level undertanding of copper proteins must underlie medical approaches to the therapy of disorders involving copper (e.g., Wilson's disease) or therapies using copper chelates (e.g., antiarthritic, antitumor agents).