Investigations of Diatomic Heme Ligands. Part I: Nuclear Resonance Vibrational Spectroscopy of Nitrosyl Iron Porphyrinates. Part II: The Characterization of Hydrosulfido Heme Models

PART I: The underlying biological phenomena for this work is small molecule signaling in heme-protein systems. A new method for single crystal Nuclear Resonance Vibrational Spectroscopy (NRVS) of heme-diatomic model complexes is presented. Prior related single-crystal NRVS was conducted in two porphyrin defined directions, parallel to the porphyrin plane (in-plane but non-specific axis) and perpendicular to the porphyrin plane (out-of-plane or z-direction). A varied angle single-crystal in-plane NRVS is introduced and its complex implementation and revealing results are detailed. Crystals of [Fe(OEP)(NO)] and [Fe(DPIX-DME)(NO)] were analyzed by NRVS along specific in-plane axes, along (x-direction) or normal to (y-direction) the Fe-N-O defined direction. For both, iron motion was found to be highly influenced by the bound NO ligand; either parallel or normal to the Fe-N-O direction. The x-y or 'special in-plane' NRVS (SIP) is also used to judge the purity of out-of-plane modes as prior in-plane analyses could, by chance, fail to fully observe in-plane components to iron motion. Similar results were observed from the SIP of the [Fe(TpFPP)(NO)(1-MeIm)]. Comparisons to DFT calculated directional spectra are made.

PART II: The potential for hydrosulfide-heme based signaling is evaluated. Structures of two hydrosulfido iron(II) porphyrinates are reported and compared to other like porphyrin complexes. Further characterization included far-IR, Mossbauer spectroscopy and mass spectrometry. Porphyrin core deformations are determined and analyzed in conjunction with Mossbauer data. Solution studies were used to determine spectral maxima frequencies and absorption coefficients and indicated the formation of bis-HS and (HS)-Fe-(1-MeIm) porphyrin complexes.