The goal of the proposed research is to further develop fundamental aspects of copper coordination chemistry relevant to its essential role in the biochemical processing of dioxygen (O2) and nitrogen oxides (NOx). Many questions remain concerning copper(I)/O2 interactions, formation of adducts, derived structures and their associated spectrocopy, O-O bond cleavage, and substrate oxidation chemistries. These may also be relevant to situations of oxidative stress, e.g., in neurological disorders such as Alzheimer's or prion diseases. Copper-NOx investigations are relevant to the active site chemistry in nitrous oxide reductase, and the possibly crucial role of copper ion in nitric oxide (.NO) biochemistry, including (cysteine) thiol nitrosylation chemistry, or mediation of nitroxyl (NO-) chemistry and peroxynitrite oxidative stress. The research methods break down into sub-projects, directed along various themes, questions or chemical systems. These include, (1) amplification of basic Cu/O2 chemistry: study sub-millisecond CuI/O2 interactions by Cu(I)/carbon monoxide photochemical triggering, and ligand electronic effects on Cu/O2 binding and hydroxylation, (2) study of Cu-superoxides, (3) mechanistic investigation of Cun/O2 mediated substrate oxidations, including probing dicopper side-on peroxo vs. bis-mu-oxo interconversion, and protonation-reduction of Cu(III)2(O)2 moieties, (4) generation of relevant chemistry with methionine (thioether) type ligands, and O-O cleavage chemistry with Cu(n)-OOR species, (5) modeling of amino-acid modified Cu-protein active-site cofactors, their biogenesis and chemistry, (6) elucidation of copper ion chemistry with .NO, NO-, peroxynitrite, their relationship to Cu/O2 derived species, and study of Cu mediated dentirosylation, i.e., Cu(I) + RSNO, (7) development of O2-chemistry with tricopper Cu3-cluster complexes relevant to copper oxidases, and (8) elaboration of new Cu-sulfide chemistry and N2O reactivity relevant to nitrous oxide reductase. The proposed studies contribute to a broader understanding of copper biochemistry, to protein activation/reduction of O2 and/or NOx, as applied to other metals (i.e., heme or non-heme iron) and disease states. Potential applications include development of enzyme inhibitors and relevant disease therapeutic strategies.