Analytical-Bioinorganic Chemistry

Vibrational spectroscopy; resonance Raman effect; structure functions and role of metal sites in biological molecules; coordination compounds and intermediates of biological interests; developing of spectroscopic techniques for probing metalloproteins; metalloporphyrins and oxidized metalloporphyrins; surface adsorbed species; Raman spectroelectro-chemistry and surface enhanced Raman scattering.

The focus of our research is aimed at exploring fundamental questions of structure-function correlations for metal sites of biological systems by exploiting the capabilities of resonance Raman (RR) spectroscopy as a structure probe. The unique ability of RR spectroscopy to study the coordination environment of transition metals in proteins derives from its sensitivity and electronic selectivity conferred by resonance enhancement. Raman excitation within charge-transfer and/or –* electronic transitions of the metalloprotein gives selective enhancement of internal ligand and metal-ligand vibrations, whose frequencies are sensitive to the molecular structure and chemical states of the chromophore, i.e. the metal ions at the active protein site. One such example is illustrated on this page.

The general approach is to compare RR spectra of proteins in their functional states with properly chosen model complexes, with the aim of determining the unique features of biomolecular structure, and of establishing the observed RR bands as markers for structural changes associated with chemistry of the active site. The choice of target metalloproteins is dictated by their intrinsic biochemical interest and by the likelihood of obtaining meaningful RR spectra, and our current efforts focus on the iron-sulfur and blue copper proteins and on the manganese- and vanadium containing proteins and enzymes. This research involves a multifaceted program ranging from exploration of protein sites with excitations from visible and UV laser sources to normal mode computer calculations on the vibrations of inorganic analogues, whose structures have been precisely determined. Another area of work is the resonance Raman investigation of high-valent oxometalloporphyrins, the bio-mimetic model systems of various heme proteins, of high-valent nitridometallo-porphyrins, potential nitrogen transfer catalysts, and of geoporphyrins, the biological markers of fossil fuels.