Zou, Shouzhong and Baskin, J. Spencer and Zewail, Ahmed H. (2002) Molecular recognition of oxygen by protein mimics: Dynamics on the femtosecond to microsecond time scale. Proceedings of the National Academy of Sciences of the United States of America, 99 (15). pp. 9625-9630. ISSN 0027-8424 http://resolver.caltech.edu/CaltechAUTHORS:ZOUpnas02
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Molecular recognition by biological macromolecules involves many elementary steps, usually convoluted by diffusion processes. Here we report studies of the dynamics, from the femtosecond to the microsecond time scale, of the different elementary processes involved in the bimolecular recognition of a protein mimic, cobalt picket-fence porphyrin, with varying oxygen concentration at controlled temperatures. Electron transfer, bond breakage, and thermal "on" (recombination) and "off" (dissociation) reactions are the different processes involved. The reaction on-rate is 30 to 60 times smaller than that calculated from standard Smoluchowski theory. Introducing a two-step recognition model, with reversibility being part of both steps, removes the discrepancy and provides consistency for the reported thermodynamics, kinetics, and dynamics. The transient intermediates are configurations defined by the contact between oxygen (diatomic) and the picket-fence porphyrin (macromolecule). This intermediate is critical in the description of the potential energy landscape but, as shown here, both enthalpic and entropic contributions to the free energy are important. In the recognition process, the net entropy decrease is -33 cal mol-1 K-1; Delta H is -13.4 kcal mol-1.
|Additional Information:||Contributed by Ahmed H. Zewail, June 4, 2002. The research is part of the collaboration with Prof. Fred C. Anson and his group. We acknowledge the help of Dr. Hotae Kim, Prof. M. Than Htun, Mr. Binghai Ling, Dr. Robert Clegg, and Dr. Beat Steiger. This work was supported by the National Science Foundation.|
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|Deposited On:||11 Jul 2005|
|Last Modified:||26 Dec 2012 08:40|
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