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A theoretical study of alanine dipeptide and analogs
Author(s) -
HeadGordon Teresa,
HeadGordon Martin,
Frisch Michael J.,
Brooks Charles,
Pople John
Publication year - 2009
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.560360725
Subject(s) - dipeptide , alanine , chemistry , computational chemistry , stereochemistry , amino acid , biochemistry
We present a preliminary report on the conformational and energetic analysis of the molecule ( S )‐2‐acetylamino‐ N ‐methylpropanamide (alanine dipeptide) and an analog molecule, ( S )‐α‐formylamino‐propanamide, using high‐quality ab initio methods. Alanine dipeptide and its analogs are of interest since they incorporate many of the structural features found in proteins, such as intramolecular hydrogen bonds, conformational flexibility, and a variety of chemical functionality. One purpose of this study is to provide a useful benchmark calculation, MP2/6‐31 + G**//HF/6‐31 + G*, for a number of conformations of the alanine system. Based on the comparison of these benchmark calculations with lower‐level basis sets, HF/3‐21G was chosen to generate a fully relaxed φ, ψ dihedral map. These calculations are the first of their kind on systems of this size. Features of the φ, ψ alanine dipeptide map that are discussed include the energetically accessible conformations and possible pathways for their intercon‐version. In addition, we illustrate the importance of fully optimized geometries and the proper evaluation of correlation energies.