Conformational isomerism

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

Proton-Linked Protein Conformational Switching: Definition of the Alkaline Conformational Transition of Yeast Iso-1-ferricytochrome c‡

Abstract: The alkaline conformation (state IV) of yeast iso-1-ferricytochrome c and variants in which selected lysyl residues were replaced with alanyl residues has been studied by 1H NMR spectroscopy, electronic spectroscopy, EPR spectroscopy, direct electrochemistry, pH-jump kinetics, and temperature-dependent circular dichroism spectroscopy. On the basis of the NMR studies, Lys73 and Lys79 are shown to replace Met80 as the axial ligand in the two conformers of state IV that were detected in previous studies (Hong, X. L.; Dixon, D. W. FEBS Lett. 1989, 246, 105−108; Ferrer, J. C.; Guillemette, J. G.; Bogumil, R.; Inglis, S. C.; Smith, M.; Mauk, A. G. J. Am. Chem. Soc. 1993, 115, 7507−7508). The pKa for the conformational equilibrium between state III (native conformation) and state IV of the wild-type protein (8.70(2)) is found to be intermediate between that of the Lys73 bound conformer (8.44(1)) and that of the Lys79 bound conformer (8.82(2)) (0.1 M NaCl, 25 °C) as are the kinetic parameters for the conversion o...

Bilirubin conformational analysis and circular dichroism

Abstract: Typical linear and porphyrin-like structure representations of bilirubin give an incorrect impression of its actual shape and expected solution properties. Conformational alnalysis of bilirubin, assisted by molecular dynamics computations, indicates that (i) nonbonded intramolecular steric interactions are minimized in a ridge-tile shape conformation lying at a global energy minimum on the conformational energy map and (ii) considerable additional stabilization is achieved though a network of intramolecular hydrogen bonds. The linear and porphyrin-like conformations are computed to lie some 37-48 kcal/mol above the isoenergetic global minimum energy conformations, which correspond to superimposable (identical) or to nonsuperimposable (enantiomeric) mirror image intramolecularly hydrogen-bonded ridge-tile conformers

Molecular Basis for Water-Promoted Supramolecular Chirality Inversion in Helical Rosette Nanotubes

Abstract: Helical rosette nanotubes (RNTs) are obtained through the self-assembly of the GwedgeC motif, a self-complementary DNA base analogue featuring the complementary hydrogen bonding arrays of both guanine and cytosine. The first step of this process is the formation of a 6-membered supermacrocycle (rosette) maintained by 18 hydrogen bonds, which then self-organizes into a helical stack defining a supramolecular sextuple helix whose chirality and three-dimensional organization arise from the chirality, chemical structure, and conformational organization of the GwedgeC motif. Because a chiral GwedgeC motif is predisposed to express itself asymmetrically upon self-assembly, there is a natural tendency for it to form one chiral RNT over its mirror image. Here we describe the synthesis and characterization of a chiral GwedgeC motif that self-assembles into helical RNTs in methanol, but undergoes mirror image supramolecular chirality inversion upon the addition of very small amounts of water (<1% v/v). Extensive physical and computational studies established that the mirror-image RNTs obtained, referred to as chiromers, result from thermodynamic (in water) and kinetic (in methanol) self-assembly processes involving two conformational isomers of the parent GwedgeC motif. Although derived from conformational states, the chiromers are thermodynamically stable supramolecular species, they display dominant/recessive behavior, they memorize and amplify their chirality in an achiral environment, they change their chirality in response to solvent and temperature, and they catalytically transfer their chirality. On the basis of these studies, a detailed mechanism for supramolecular chirality inversion triggered by specific molecular interactions between water molecules and the GwedgeC motif is proposed.

The gas-phase structure of alanine.

Abstract: The jet-cooled rotational spectrum of neutral alanine has been studied using laser-ablation molecular-beam Fourier transform microwave spectroscopy (LA-MB-FTMW). The spectra of the two most stable forms were observed in the frequency range 6-18 GHz for the parent, (15)N alanine, three single (13)C species, and four single D species. The (14)N nuclear quadrupole coupling hyperfine structures have been resolved, and their comparison with those calculated theoretically confirms unambiguously the conformer assignments. The independent structures of both conformers have been determined experimentally for the first time using r(s) and r(0) procedures. In both cases, the amino acid backbone is nonplanar. For the most stable conformer I, the COOH group adopts a cis configuration and an asymmetric bifurcated hydrogen bond is formed between the amino group and carbonyl oxygen (r(N-H(a)...O=C) = 2.70(2) A and r(N-H(b)...O=C) = 2.88(2) A). For conformer IIa, the COOH group adopts a trans configuration and is stabilized by a O-H...N hydrogen bond (r(O-H...N) = 1.96(2) A). The relative conformer abundances in the supersonic expansion have also been investigated.

Conformational Behavior of α-Alanine. Matrix-Isolation Infrared and Theoretical DFT and ab Initio Study

Abstract: Two conformers of the nonionized α-alanine and its isotopomer N,N,O-d3-alanine have been observed in low-temperature Ar matrixes Their infrared spectra have been analyzed and assigned using DFT/B3LYP/aug-cc-pVDZ and MP2/aug-cc-pVDZ geometry and frequency theoretical calculations Two different intramolecular H-bonds, bifurcated NH2···OC and N···H−O, were found in the observed α-alanine conformers, I and IIa We found that the DFT/B3LYP/aug-cc-pVDZ method yields vibrational frequencies of the α-alanine conformers in excellent agreement with the experimental data