Campus Units

Chemistry

Document Type

Article

Publication Version

Published Version

Publication Date

6-2009

Journal or Book Title

Journal of Physical Chemistry B

Volume

113

Issue

25

First Page

8657

Last Page

8669

DOI

10.1021/jp901459y

Abstract

An ab initio study of the addition of successive water molecules to the amino acid l-alanine in both the nonionized (N) and zwitterionic (Z) forms are presented. The main focus is the number of waters needed to stabilize the Z form and how the solvent affects conformational preference. The solvent is modeled by ab initio electronic structure theory, the EFP (effective fragment potential) model, and the isotropic dielectric PCM (polarizable continuum method) bulk solvation techniques. The EFP discrete solvation model is used with a Monte Carlo algorithm to sample the configuration space to find the global minimum. Bridging structures are predicted to be the lowest energy Z minima after 3−5 discrete waters are included in the calculations, depending on the level of theory. Second-order perturbation theory and PCM stabilize the Z structures by ∼3−6 and 7 kcal/mol, respectively, relative to the N global minimum through the addition of up to 8 waters. Subsequently, the contributions of each are ∼1 kcal/mol relative to the N global minimum. The presence of 32 waters appears to be close to converging the N−Z enthalpy difference, ΔHN−Z.

Comments

Reprinted (adapted) with permission from Journal of Physical Chemistry B 113 (2009): 8657, doi:10.1021/jp901459y. Copyright 2009 American Chemical Society.

Copyright Owner

American Chemical Society

Language

en

File Format

application/pdf

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