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Large Tunneling Effect on the Hydrogen Transfer in Bis(μ-oxo)dicopper Enzyme: A Theoretical Study.
MedLine Citation:
PMID:  22276687     Owner:  NLM     Status:  Publisher    
Abstract/OtherAbstract:
Type III copper-containing enzymes have dicopper centers in their active sites and exhibit a novel capacity for activating aliphatic C-H bonds in various substrates by taking molecular oxygen. Dicopper enzyme models developed by Tolman et al. reveal exceptionally large kinetic isotope effects (KIEs) for the hydrogen transfer process, which indicates a significant tunneling effect. In this work, we demonstrate that variational transition state theory allows accurate prediction of the KIE and Arrhenius parameters in such model systems. This includes multidimensional tunneling based on the state-of-the-art quantum mechanical calculations of the minimum energy path (MEP). The computational model of bis(μ-oxo)dicopper enzyme consists of 70 atoms, resulting in a 204 dimensional potential energy surface. The calculated values of the Ea(H) - Ea(D), A(H)/A(D) and KIE at 233 K are -1.86 kcal/mol, 0.51 and 28.1, respectively, for the isopropyl ligand system. These values agree very well with experimental values within the limits of experimental error. For the representative tunneling path (RTP) at 233K, the pre- and post-tunneling configurations are 3.3 kcal/mol below the adiabatic energy maximum, where the hydrogen travels 0.54 Å by tunneling. We found that tunneling is very efficient for hydrogen transfer, and that RTP is very different from the MEP. Heavy atoms move mostly when the reaction changes from the reactant complex to the pre-tunneling configuration, and suddenly the hydrogen hops at that point.
Authors:
Kisoo Park; Youngshang Pak; Yongho Kim
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Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2012-1-24
Journal Detail:
Title:  Journal of the American Chemical Society     Volume:  -     ISSN:  1520-5126     ISO Abbreviation:  -     Publication Date:  2012 Jan 
Date Detail:
Created Date:  2012-1-26     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  7503056     Medline TA:  J Am Chem Soc     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
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