Model studies of azide binding to functional analogues of CcO.

N3- binding to a functional model of CcO is investigated in its Fe3+, Fe3+Cu+, and Fe3+Cu2+ forms. A combination of EPR and FTIR indicates that N3- binds in a bridging mode in the bimetallic sites and signature N3- bands are identified for several forms of N3- binding to the site. The presence of the distal metal increases the binding affinity of N3-. This bridging enables antiferromagnetic interaction between the two metal centers in the Fe3+Cu2+ state, which results in an EPR-silent ground state.