title: Spectroscopic properties of ferrous heme complexes of sterically hindered ligands.
abstract: Mesoheme IX complexes of sterically hindered ligands 2-methylimidazole, tert-butylamine and 2-methylpyridine in aqueous glycerol solutions are characterized by broad visible absorption spectra at ambient temperature exhibiting close similarities to high-spin ferrous hemeproteins. Spectrophotometric titrations of mesoheme IX with these ligands indicate well-defined equilibria for 2-methylimidazole and tert-butylamine corresponding to the formation of penta-coordinate strong-field ligand complexes. Variable temperature spectra of these complexes from ambient to 77 degrees K exhibit a change to hemochrome spectra characteristic of the low-spin unhindered ligand complexes. Corresponding changes in the visible spectra are not observed for the high-spin hemeproteins deoxymyoglobin, horse-radish peroxidase and cytochrome ć. The appropriate utilization of these hindered ligand heme complexes as model systems for high-spin ferrous hemeproteins has been discussed.
mesh_terms: D001665:Binding Sites; D002082:Butylamines; D003574:Cytochrome c Group; D006418:Heme; D007093:Imidazoles; D007501:Iron / Q000032:analysis*; D007700:Kinetics; D008024:Ligands; D008968:Molecular Conformation; D009211:Myoglobin; D010544:Peroxidases; D010944:Plants / Q000201:enzymology; D011485:Protein Binding; D011487:Protein Conformation; D011725:Pyridines; D013053:Spectrophotometry; D013696:Temperature
chemical_list: D002082:Butylamines; D003574:Cytochrome c Group; D007093:Imidazoles; D008024:Ligands; D009211:Myoglobin; D011725:Pyridines; D006418:Heme; D007501:Iron; D010544:Peroxidases