Topic
Conformational isomerism
About: Conformational isomerism is a research topic. Over the lifetime, 11563 publications have been published within this topic receiving 199312 citations.
Papers published on a yearly basis
Papers
More filters
TL;DR: In this article, the authors used density functional theory (DFT) based on the B3LYP/m6-31G(d) model without any scaling and manipulation.
89 citations
TL;DR: The results obtained for the relative energies of the three conformers and the conformation of the side groups were affected by the inclusion of the electrostatic term and, in particular, by the charge assigned to the ionic groups of DMIS.
Abstract: Methods of molecular mechanics were applied to investigate the conformation of the (methyl 2-O-sulfate-4-methyl-α-L-idopyranose) uronic acid (DMIS), in order to correlate the peculiar vicinal proton coupling constants observed in polysaccharides containing the iduronate ring to the conformational characteristics of this sugar ring. We found three conformers with comparable energies, namely the two chair forms 1C4 and 4C1 and the skew-boat form 2S0(L); the latter is separated from each chair form by a barrier of about 9 kcal/mol. Along the pseudorotational path three additional minima (3S1, 1S3, and 1S5) were found, yet at least 4 kcal/mol higher than 2S0. The results obtained for the relative energies of the three conformers and the conformation of the side groups were affected by the inclusion of the electrostatic term and, in particular, by the charge assigned to the ionic groups of DMIS. However, the conformational properties of the idopyranosidic ring in DMIS (and in related compounds) should still be interpreted in terms of equilibrium among these three conformers only.
89 citations
TL;DR: The results indicate that the shape of the molecule can have a greater effect on electron capture efficiency than either collisional cross section or charge state alone.
89 citations
TL;DR: NMR structural investigations of equilibrium conformers under pressure provide information about the structures of kinetic intermediates during folding/unfolding reactions, and can also be used to investigate association/dissociation equilibria of oligomeric or aggregated proteins.
89 citations
TL;DR: The conformational properties of the basic pancreatic trypsin-inhibitor have been studied using both physical and chemical techniques and it is indicated that the acidic conformational change I ⇌ II is dependent upon the ionisation of a buried carboxylate which may be the side-chain of Glu7.
Abstract: The conformational properties of the basic pancreatic trypsin-inhibitor have been studied using both physical and chemical techniques.
The structural properties of this mini-protein are quite unusual. The folded conformation remains unaltered at 77 °C and pH 2.1 or in 6 M guanidine-HC] at pH 7.5.
The selective cleavage [22] of the disulfide bridge Cys14-Cys38 reduces considerably the stability of the inhibitor towards heat or guanidine-HCl. A conformational study of the carboxamidomethyl, carboxymethyl, and aminoethyl derivatives of the inhibitor has been carried out after partial reduction and modification of Cys14 and Cys38 by iodoacetamide, iodoacetic acid, and ethyleneimine.
There exist three folded isomeric forms of the inhibitor between pH 1 and 11. Form I is the most stable form; it exists near neutral pH. It is extremely thermostable and remains folded in 6 M guanidine-HCl. Form II is stable below pH 1.5–2; its transition temperature is 81 °C. Form III is predominant at pH 10–11 at 20 °C. A detailed analysis of the conformational isomers I, II and III has been carried out with the carboxamidomethylated inhibitor.
Both physico-chemical and chemical data indicate that the acidic conformational change I ⇌ II is dependent upon the ionisation of a buried carboxylate which may be the side-chain of Glu7.
The alkaline isomerisation I ⇌ III is induced by the unmasking of the α-ammonium of the N-terminal arginine residue. The apparent pK of the group is 9.4 at 25 °C. Acetylation of the α-amino group stabilizes a form very similar to III and prevents the formation of form I at neutral pH.
89 citations