Premium
The conformational characteristics in solution of the synthetic cyclic hexapeptide
Author(s) -
Tonelli Alan E.,
Brewster A. I. Richard
Publication year - 1973
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.1973.360120118
Subject(s) - chemistry , intramolecular force , amide , hydrogen bond , deuterium , peptide bond , coupling constant , glycosidic bond , solvent , chemical shift , vicinal , crystallography , cyclic peptide , nuclear magnetic resonance spectroscopy , residue (chemistry) , stereochemistry , molecule , peptide , organic chemistry , biochemistry , physics , particle physics , quantum mechanics , enzyme
An attempt to elucidate the solution conformation(s) of the synthetic cyclic hexapeptide 5 L ‐ala·D‐ala is described. Nuclear magnetic resonance (nmr) spectra are recorded for the purpose of measuring the vicinal coupling constant between the amide and α‐protons in each residue and to observe the deuterium exchange rate and temperature dependence of the chemical shift of each amide proton. Low‐energy cyclic conformations, whose individual residues are in conformations consistent with the observed amide to α‐proton coupling constant, are searched for in an approximate theoretical treatment. The two lowest energy, all trans peptide bond conformations generated are distinguishable by the presence or absence of a single intramolecular hydrogen bond. The observed temperature independence of the chemical shift of one of the amide protons is consistent with the presence of a single intramolecular hydrogen bond, while the observation of similar deuterium exchange rates for each of the amide protons indicates their comparable availability to solvent. Consequently, it is concluded that 5 L ‐ala·D‐ala is in rapid equilibrium between conformations with and without a single internal hydrogen bond and possesses considerable conformational flexibility in solution.