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  • Title: Spectroscopic properties of ferrous heme complexes of sterically hindered ligands.
    Author: Wagner GC, Kassner RJ.
    Journal: Biochim Biophys Acta; 1975 Jun 12; 392(2):319-27. PubMed ID: 165836.
    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.
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