Premium
Conformational transitions and geometry differences between low‐energy conformers of N ‐acetyl‐ N ′‐methyl alanineamide: An ab initio study at the 4‐21G level with gradient relaxed geometries
Author(s) -
Schäfer Lothar,
Klimkowski V. J.,
Momany Frank A.,
Chuman H.,
Van Alsenoy C.
Publication year - 1984
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.360231115
Subject(s) - dihedral angle , conformational isomerism , chemistry , ab initio , molecular geometry , energy minimization , bond length , geometry , crystallography , ab initio quantum chemistry methods , computational chemistry , hydrogen bond , molecule , crystal structure , mathematics , organic chemistry
Energy pathways between the α R , β′, C 7 eq , and β‐regions of the conformational energy surface of N ‐acetyl‐ N ′‐methylalanyl amide were obtained by SCF ab initio calculations on the 4‐21G level, with gradient geometry optimization at each point. The calculations indicate that no barrier exists at this computational level between α R and β′. The variation of geometry (bond distances and bond angles) with conformation is analyzed in detail, and the most important geometrical parameters that should be treated as variables in both empirical energy calculations and in the fitting of polypeptide chains in proteins by x‐ray methods are identified. In addition to the ϕ,ψ correlation discussed previously for the helical state, a correlation of these dihedral angles in the β‐region is described.