Web Release Date: October 19,
Deprotonation of a Histidine Residue in Aqueous Solution Using Constrained Ab Initio Molecular Dynamics
Center for Molecular Modeling and Department of Chemistry, University of Pennsylvania, 231 South 34th Street, Philadelphia, Pennsylvania 19104-6323
Received August 1, 2002
Abstract:
The dissociation of a weak acid - a histidine residue - in water was investigated by means of constrained Car-Parrinello ab initio molecular dynamics. Both linear and coordination constraints were employed, and the structural, electronic, and dynamical transformations along the respective reaction coordinates were analyzed. The calculated potentials of mean force for the dissociation of a hydrogen atom from the N
and N
positions of the imidazole ring reveal that protonated forms are ~9.0-9.5 kcal/mol more stable than the deprotonated. This result seems to agree well with the experimental estimate based on pKa. A possible transition state for the deprotonation has also been identified. Analysis of the electron localization function indicates that the proton transfer along the selected reaction path is not a fully concerted process.
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