X-Ray and Chemical Studies of Metalloporphyrins

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DESCRIPTION (provided by applicant): The synthesis and characterization of a variety of new metalloporphyrin compounds is proposed. The work will emphasize, but will not be limited to, iron porphyrinate derivatives. Most classes of compounds proposed for study are related to hemoprotein derivatives, which carry out a wide range of biological functions including oxygen utilization, storage and transport, NO-based signaling, electron transport, drug metabolism and other enzymatic processes. The methods of three-dimensional X-ray crystal structure determination will be applied to define molecular structures and various detailed aspects of metalloporphyrin stereochemistry. The new technique of nuclear resonance vibrational spectroscopy (NRVS) is being used to define iron dynamics in biomolecules. The NRVS method allows the observation of all vibrational models in which there is movement of the iron. NRVS has already yielded interesting vibrational data not available by any other technique including the detection of the Fe-Im mode in six-coordinate imidazole-ligated CO derivatives. It will allow an understanding of how the protein environment can change iron dynamics and hence reactivity patterns. Other methodologies to be applied, as appropriate, include characterization of magnetic properties by bulk temperature-dependent susceptibility and electron paramagnetic resonance (EPR) measurements, Mossbauer, vibrational and UV-vis spectroscopy, and electrochemical properties. The research objectives, stated in the broadest terms, are to achieve a synthesis of the structural and physical properties of metalloporphyrins, particularly as these relationships pertain to an understanding of hemoprotein-based biological processes. Iron porphyrinates to be studied include a number of six-coordinate derivatives, [Fe(Por)(XO)(Im)] (XO = O2, CO, NO), in order to examine changes in the Fe-Im vibrations as the opposite ligand is changed, important for understanding issues in hemoglobin oxygen-binding cooperativity. Other projects include detailed study of structure and electronic structure of high-spin five coordinate iron(II) species, additional nitrosyl complexes, synthetic analogues of cytochromes b and c to show how axial ligand orientation affects their electronic structure and oxidation-reduction properties.