Modeling side-on NO coordination to type 2 copper in nitrite reductase: structures, energetics, and bonding

DFT calculations reveal the existence of metastable side-on {CuNO}10 and {CuNO}11 species relevant to the type 2 copper site of nitrite reductase (CuNIR). Side-on NO coordination seems especially favorable in energy terms for the {CuNO}11 species. The {CuNO}11 geometry parameters also seem to be in better agreement with those reported for a crystallographically characterized CuNIR intermediate, relative to the {CuNO}10 parameters.