This broad, long term research plan is designed to obtain the basic understanding of vibrational dynamics required to direct chemical reactions in large condensed phase systems. A causal relationship is postulated to exist between molecular structure and solvent, vibrational flow, and function. Understanding these relationships will promote the use of molecular structure and immediate molecular environment to rationally control chemical reactivity. The proposed research will explore the idea that the events in the first few picoseconds ran be crucial in determining product distributions. Placement and retention of energy in specific coordinate(s) will enhance the quantum yield of the desired product and inhibit the formation of others. A major emphasis of this plan focuses upon biological catalysts.
The Specific Aims of this proposal will explore these issues as they apply to both biologically related model compounds and to protein systems. The primary experimental approach utilizes state-of-the-art ultrafast infrared pump - resonance Raman probe methods. This approach exploits recent exciting technological advances in the generation of ultrashort infrared pulses, coupled with the direct information about vibrational populations provided by the resonance Raman technique. The proposed experiments are conceptually simple: prepare a well defined initial vibronic state in a biologically related molecule in solution, then directly monitor its temporal evolution. IR absorption and stimulated Raman scattering will create the initial vibrational excited state. Vibrational dynamics will be probed using resonance Raman spectroscopy. By using this approach, a map of vibrational dynamics will be determined for the model system Fe octaethylporphyrin 2-methyl imidazole in CH2Cl2 (Specific Aim # 1). The dependence of this map upon solvent and porphyrin structural attributes be assessed (Specific Aim # 2). Vibrational dynamics in native (hemoglobin, myoglobin and cytochrome c) and mutant (deoxymyoglobin) heme proteins will be probed as well (Specific Aim # 3). The role of the specific local protein structure in directing vibrational energy flow at the active site will be learned. Finally, the focus will shift to the functional impact of vibrational energy flow (Specific Aim # 4). Initial studies will focus upon a model system: electron transfer in Zn-tetraphenyl porphyrin with a molybdenum ligand. Vibrational degrees of freedom will be specifically excited and the resulting effects upon electron transfer rate constants and quantum yields measured. The structural and environmental features of the system will then be tuned to direct the flow of vibrational energy within the molecule and by that influence reactivity. The accomplishment of these Specific Aims may contribute significant and unique results to the general understanding of vibrational dynamics and reactivity in biological molecules.
| Peng, Huo-Lei; Payton, John L; Protasiewicz, John D et al. (2009) Twisting the phenyls in aryl diphosphenes (Ar-P=P-Ar). Significant impact upon lowest energy excited states. J Phys Chem A 113:7054-63 |
| Gunaratne, Tissa C; Milliken, Matthew; Challa, J Reddy et al. (2006) Tunable ultrafast infrared/visible laser to probe vibrational dynamics. Appl Opt 45:558-64 |
| Challa, J Reddy; Gunaratne, Tissa C; Simpson, M Cather (2006) State preparation and excited electronic and vibrational behavior in hemes. J Phys Chem B 110:19956-65 |
| Gunaratne, Tissa; Challa, J Reddy; Simpson, M Cather (2005) Energy flow in push-pull chromophores: vibrational dynamics in para-nitroaniline. Chemphyschem 6:1157-63 |
| Shah, S; Simpson, M C; Smith, R C et al. (2001) Three different fates for phosphinidenes generated by photocleavage of phospha-Wittig reagents Arp=PMe3. J Am Chem Soc 123:6925-6 |
