Triplet state magnetic resonance and fluorescence spectroscopy of metal-substituted hemoglobins

Abstract

Fluorescence detected magnetic resonance (FDMR) spectra detected at 596 nm of zinc-substituted hemoglobins at 4.2 K show a split D-E transition, which is not observed for zinc protoporphyrins ligated by methylimidazole in glasses. Incorporation of the zinc heme into the globin pocket is also accompanied by a blue shift of the fluorescence of 20 nm at 4.2 K. FDMR spectra recorded at 576 nm do not show the D-E splitting. The D-E splitting and the huge blue shift are not observed for the magnesium-substituted hemoglobins. Fluorescence measurements at 4.2 K and 77 K, and EPR measurements at 110 K, were carried out to obtain information about the ligation states of the zinc and magnesium protoporphyrins in glasses and in hemoglobin. The results are explained by considering ligation effects and distortion of the porphyrin plane.