Conformational isomerism

About: Conformational isomerism is a research topic. Over the lifetime, 11563 publications have been published within this topic receiving 199312 citations.

Melting of a beta-Hairpin Peptide Using Isotope-Edited 2D IR Spectroscopy and Simulations

Abstract: Isotope-edited two-dimensional infrared spectroscopy has been used to characterize the conformational heterogeneity of the β-hairpin peptide TrpZip2 (TZ2) across its thermal unfolding transition. Four isotopologues were synthesized to probe hydrogen bonding and solvent exposure of the β-turn (K8), the N-terminus (S1), and the midstrand region (T10 and T3T10). Isotope-shifts, 2D lineshapes, and other spectral changes to the amide I 2D IR spectra of labeled TZ2 isotopologues were observed as a function of temperature. Data were interpreted on the basis of structure-based spectroscopic modeling of conformers obtained from extensive molecular dynamics simulations. The K8 spectra reveal two unique turn geometries, the type I′ β-turn observed in the NMR structure, and a less populated disordered or bulged loop. The data indicate that structures at low temperature resemble the folded NMR structure with typical cross-strand hydrogen bonds, although with a subpopulation of misformed turns. As the temperature is ra...

Two rotameric forms of open ring 7-methylguanine are present in alkylated polynucleotides.

Abstract: High performance liquid chromatography analysis of imidazole open ring 7-methylguanine, 2-6 diamino-4-hydroxy-5N-methyl-formamidopyrimidine (rom7G), showed two well-separated peaks (fI and fII) of the same magnitude. Rechromatography of each isolated component indicated that they are slowly interconverted to give a 1:1 mixture. NMR analysis demonstrated that the two species observed on reversed phase HPLC are rotational isomers. Thermodynamic measurements strongly suggested that the equilibrium can be assigned to rotation around the N-methyl formamido bond. The two species, fI and fII, separated by HPLC were identified as rotamers E and Z, respectively. The structures of fI and fII were also determined. A polynucleotide containing rom7G was obtained by alkaline treatment of poly (dGC) containing 7-methylguanine. In order to study its structure within the polynucleotide, rom7G was enzymatically excized by E.coli rom7G-DNA glycosylase. The analysis of the products released by the enzyme showed a 1:4 mixture of the two rotamers favoring the Z form (fII).

Microsolvation of Formamide: A Rotational Study

Abstract: Microsolvated formamide clusters have been generated in a supersonic jet expansion and characterized using Fourier transform microwave spectroscopy. Three conformers of the monohydrated cluster and one of the dihydrated complex have been observed. Seven monosubstituted isotopic species have been measured for the most stable conformer of formamide···H2O, which adopts a closed planar ring structure stabilized by two intermolecular hydrogen bonds (NH···O(H)H···OC). The two higher energy forms of formamide···H2O have been observed for the first time. The second most stable conformer is stabilized by a OH···OC and a weak CH···O hydrogen bond, while, in the less stable form, water accepts a hydrogen bond from the anti hydrogen of the amino group. For formamide···(H2O)2, the parent and nine monosubstituted isotopic species have been observed. In this cluster the two water molecules close a cycle with the amide group through three intermolecular hydrogen bonds (NH···O(H)H···O(H)H···OC), the nonbonded hydrogen ato...

Syntheses and conformational analyses of glutamate analogs: 2-(2-carboxy-3-substituted-cyclopropyl)glycines as useful probes for excitatory amino acid receptors.

Abstract: An hypothesis that each subtype of glutamate receptors requires a specific conformation of l-glutamate for its selective activation was examined using the conformationally constrained analogs of l-glutamate, l-2-(2-carboxycyclopropyl)glycines (CCGs), and l-2-[2-carboxy-3-(methoxymethyl)cyclopropyl]glycines (MCGs). All MCG isomers were newly synthesized in a stereoselective manner via the common synthetic intermediate 5a starting with the oxazolidine aldehyde 1. The synthesis of the four MCG isomers was characterized by a stereoselective inversion of α-cyclopropyl acyl anion (e.g., from 10 to 11). The spectroscopic studies, in particular, pH vs J correlation experiments of CCGs and MCGs using 1H NMR and their molecular mechanics calculations, revealed that these analogs possessed an antiperiplanar conformation regarding the H−C2−C1‘−H bond as a majority among the other possible rotamers in aqueous solution. The fact that each CCG and MCG exhibited potent and selective activities to the distinct types of gl...