title: On the photosensitivity of liganded hemoproteins and their metal-substituted analogues.
abstract: We have examined the photosensitivity of low-spin liganded hemoglobin, myoglobin, and peroxidase, and their metal-substituted analogues, using three different metals (Fe, Mn, Co) in several oxidation states and employing a variety of diatomic or pseudo-diatomic ligands (L). We have discovered a number of photosensitive systems, and present an overall stereo-electronic classification scheme for these photodissociation reactions: Linear, formally d6, metal-ligand fragments [e.g., Fe(II) +/- CO; Mn(II) +/- NO] are relatively photoliable, but systems with a bent fragment, and higher electron occupancy [e.g., Fe(II) +/- O2; Co(II) +/- NO] are relatively photoinert. Photostability appears to correlate with the occurrence of long-wavelength features in the optical absorption spectra, and the classification scheme is explained by considerations of electronic structure. The discussions are further applied to d5 systems and to low-spin d6 metalloporphyrins with nitrogenous bases as axial ligands.
mesh_terms: D002245:Carbon Dioxide; D006420:Hemeproteins; D006454:Hemoglobins; D008024:Ligands; D008670:Metals; D009211:Myoglobin; D009569:Nitric Oxide; D010100:Oxygen; D010544:Peroxidases; D010782:Photolysis
chemical_list: D006420:Hemeproteins; D006454:Hemoglobins; D008024:Ligands; D008670:Metals; D009211:Myoglobin; D002245:Carbon Dioxide; D009569:Nitric Oxide; D010544:Peroxidases; D010100:Oxygen
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