Metalloporphyrins

Metalloporphyrins catalyze a variety of biological reactions, including electron and energy transfer, O2 transport and storage, oxidation reactions, and the conversion of light energy to chemical energy. Technological applications also increasingly exploit the useful properties of porphyrins. These molecules are becoming prevalent as active materials in fuel cells, alkane oxidation processes, chiral synthesis and separation methods, and as the binary switch elements in sensors and molecular memory devices. The structural variability inherent in porphyrin systems allows catalyst specificity, efficiency, and stability to be tuned. These properties give porphyrins the potential to play pivotal roles as future catalysts designed to perform selected tasks.
Vibrational energy dynamics in metalloporphyrins are not well understood. However, nonthermal vibrational energy distributions have been observed in these molecules. Some modes couple quite poorly to the other modes and to the solvent. The energy flow through these degrees of freedom is retarded. Such bottleneck modes can be used to funnel energy into desired reaction coordinates and away from those leading to unwanted products. An understanding of the vibrational behavior in metalloporphyrins will lend insight into the detailed mechanisms that determine catalytic efficiency and specificity in natural systems, and will allow the rational design of porphyrin-based catalysts to carry out particular functions. Selected Publications

"Heme-CO Religation in Photolyzed Hemoglobin: A Time-Resolved Raman
Study of the Fe-CO Stretching Mode," 1993, Biochem., 32, 1318.

"Mode Specific Heme Photodynamics in Deoxyhemoglobin," J. Raman
Spec., 23, 1993, 569.
"Mode Selective Energy Localization in Photoexcited Deoxyhemoglobin
and Heme Model Complexes," Chem. Phys. Lett., 215, 1993, 251.

"Time-Resolved Resonance Raman Spectroscopy," 1994, in Raman
Spectroscopy (J. Laserna, ed.), John Wiley & Sons.
"Transient Resonance Raman Evidence for Structural Reorganizational
Dynamics during Electron Transfer in Ruthenated Yeast Cytochrome c"
J. Am. Chem. Soc., 117, 1995, 3296.
"Ruffling in a Series of Nickel(II) Meso-Tetrasubstituted Porphyrins
as a Model for the Conserved Ruffling of the Heme of Cytochromes c",
J. Am. Chem. Soc., 117, 1995, 11085.
"Transient Raman Observations of Heme Electronic and Vibrational
Photodynamics in DeoxyHemoglobin" J. Am. Chem. Soc., 1996,
(submitted).