Tunnel effect theory energy transfer

DR. EPHRAIM BUHKS (University of Delaware) I would like to ask your opinion about a possible interpretation of proton transfer in terms of nuclear tunneling effects. Might it be possible that as the energy of the vibrational modes becomes very large, the classical rate theory might not work ... 

Quantum dynamics effects for hydride transfer in enzyme catalysis have been analyzed by Alhambra et. al., 2000. This process is simulated using canonically variational transition-states for overbarrier dynamics and optimized multidimensional paths for tunneling. A system is divided into a primary zone (substrate-enzyme-coenzyme), which is embedded in a secondary zone (substrate-enzyme-coenzyme-solvent). The potential energy surface of the first zone is treated by quantum mechanical electronic structure methods, and protein, coenzyme, and solvent atoms by molecular mechanical force fields. The theory allows the calculation of Schaad-Swain exponents for primary (aprim) and secondary (asec) KIE... 

Kelley and co-workers [70, 71] measured the dynamics of the excited-state intramolecular proton transfer in 3-hydroxyflavone and a series of its derivatives as a function of solvent (Scheme 2.9). The energy changes associated with the processes examined are of the order of 3 kcal/mol or less. The model they employed in the analysis of the reaction dynamics was based upon a tunneling reaction path. Interestingly, they find little or no deuterium kinetic isotope effect, which would appear to be inconsistent with tunneling theories. For 3-hydroxy-flavone, they suggest the lack of an isotope effect is due to a very large... 

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