Understanding the Structural and Vibrational Features of Heme Diatomics

This dissertation concerns itself with the interaction of diatomic molecules with heme. More specifically, five- and six-coordinate low-spin iron(II) porphyrinates will be considered. Complexes of the form [Fe(Porph)(XO)(L)] (X = N or C and L = 1-MeIm, 1,2-DiMeIm, 2-MeHIm, 4-MePip, CO, or no ligand) have been synthesized. These systems have been extensively studied using X-ray crystallography, Mössbauer spectroscopy, infrared absorption spectroscopy, resonance Raman spectroscopy, and Nuclear Resonance Vibrational Spectroscopy (NRVS), thereby providing new information regarding structural and vibrational characteristics of hemes coordinated with diatomic molecules. The first structural characterization of a 5-coordinate heme-CO, bis-carbonyl ligated heme, and completely ordered six-coordinate heme-NO are reported. Temperature-dependent information has also been acquired. This information reveals the temperature dependence of the structural and vibrational parameters of heme complexes, especially the biologically relevant Fe-His bond, and relates them to thermal expansion and contraction in the solid state. Finally, the NRVS technique is used extensively to reveal the Fe vibrational dynamics of heme coordinated by diatomic molecules. These studies reveal several reactive vibrational modes associated with ligand ejection and activation which have not previously been described.