Tunneling and related effects

Of the mechanistic issues dealt with in the full study (including kinetic trade-off s between different Co-+ spin states in the reaction product and the role of solvent and conformational fluctuations of the DBA system), we focus here on the activation parameters and related nuclear tunneling and entropy effects which are crucial for establishing meaningful contact with the Arrhenius parameters obtained from the experimental rate data [158]. The theoretical analysis also led to new insights... 

Z.7 Dynamics, Tunneling and Related Nuclear Quantum Mechanical Effects 11195... 

The only (to the best of our knowledge) theoretical treatment of hydrogen transfer by tunnelling to explicitly recognise the role of protein dynamics, and relate this in turn to the observed kinetic isotope effect, was described by Bruno and Bialek. This approach has been termed vibration-ally enhanced ground state tunnelling theory. A key feature of this theory... 

For further important work on this and related concepts, see Rucker, J. and Kliman, J.P. (1999). Computational study of tunneling and coupled motion in alcohol dehydrogenase-catalyzed reactions Implication for measured hydrogen and carbon isotope effects. J. Am. Chem. Soc. 121, 1997 -2006, and Kohen, A. and Jensen, J.H. (2002). Boundary conditions for the Swain-Schaad relationship as a criterion for hydrogen tunneling. J. Am. Chem. Soc. April 17, 124(15), 3858-3864. 

Mann-Whitney Rank Sum Test, Sigmastat v 2.0 1 PERE = Potential Effluent Related Effect 3 NF (Nearfield) significantly greater than both Tunnel Bay and Santoy Bay reference areas, 4 t-tests, Mann-Whitney U-tests, Mann-Whitney rank sum tests, a = 0.05,5 National EEM database, unpublished data 6 significantly less at Santoy Bay reference area, Significant difference at Tunnel Bay. 

In view of the presently available results it seems that proton tunneling is confined to the top 20 % of the barrier, at most, and that the effects to be attributed to it will be small. The more profound effects to be expected from deep tunneling seem absent in A-SB2 and related reactions. 

The imaging of anodic oxides raises the question about the necessary electron transfer. A thin film of less than 1 nm permits direct tunnelling from the tip to the substrate metal. However, if the film thickness exceeds ca. 1 nm, then tunnelling should not be possible according to relation 35 for the tunnel probability, which contains the energy AE and the width x for the barrier of the tunnel process and the effective mass of the electron m. If the oxide layer is thicker than 1 nm, then the electrons have to... 

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