Ruffling deformations of Nickel(II) and Zinc(II) hydroporphyrin and chlorophin complexes:: Implications for F430, the nickel tetrapyrrole cofactor of methylcoenzyme M reductase

Nonlocal DFT provides an excellent description of the structural and conformational properties of metallohydroporphyrins and related complexes. The Ni(II) complexes are found to be strongly ruffled and the zn(II) complexes planar, consistent with experimental results. The increased flexibility of the novel chlorophin, bacteriophin, and isobacteriophin ligands, relative to hydroporphyrins, appears to result from a widening of the C-alpha-N-C-alpha angle at the imine nitrogen. A key finding relevant to understanding the chemistry of cofactor F-430 is that seemingly innocent substituents such as methyl and phenyl groups can exert a dramatic impact on the metal coordination geometry and macrocycle conformation of Ni(II) hydroporphyrins and related complexes, shrinking Ni-N bond distances and leading to significantly greater ruffling.