Model Complexes of Cobalt-Substituted Matrix Metalloproteinases: Tools for Inhibitor Design

The tetrahedral cobalt(II) complex [(TpPh,Me)CoCl] (TpPh,Me = hydrotris(3,5-phenylmethylpyrazolyl)borate) was combined
with several hydroxypyridinone, hydroxypyridinethione, pyrone, and thiopyrone ligands to form the corresponding
[(TpPh,Me)Co(L)] complexes. X-ray crystal structures of these complexes were obtained to determine the mode of
binding for each ligand L. The structures show that the [(TpPh,Me)Co(L)] complexes are pentacoordinate complexes,
with a general tendency toward square pyramidal geometry. The electronic, EPR, and paramagnetic NMR
spectroscopy of the [(TpPh,Me)Co(L)] complexes have been examined. The frozen-solution EPR spectra are indicative
of pentacoordination in frozen solution, while the NMR indicates some dynamics in ligand binding. The findings
presented here suggest that [(TpPh,Me)Co(L)] complexes can be used as spectroscopic references for investigating
the mode of inhibitor binding in metalloproteinases of medicinal interest. Potential limitations when using cobalt(II)
model complexes are also discussed.