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Conformational isomerism

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


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TL;DR: A variable-temperature, -pressure, and -ionic strength (1)H NMR study of the DOTA complexes of different trivalent cations yielded data that are in contradiction with the hitherto used model of only two enantiomeric pairs of diastereoisomers that differ in the ligand conformations.
Abstract: A variable-temperature, -pressure, and -ionic strength (1)H NMR study of the DOTA complexes of different trivalent cations (Sc, Y, La, Ce --> Lu) (DOTA = 1,4,7,10-tetraaza-1,4,7,10-tetrakis(carboxymethyl)cyclododecane) yielded data that are in contradiction with the hitherto used model of only two enantiomeric pairs of diastereoisomers that differ in the ligand conformations. A two-isomer equilibrium cannot explain the newly observed apparent reversal of the isomer ratio at the end of the series. As both conformers may lose their inner sphere water molecule, a coordination equilibrium may be superimposed on this conformational equilibrium, as shown by large positive reaction volumes for the isomerization of [Ln(DOTA)(H(2)O)(x)()](-) (Ln = Yb, Lu; x = 1, 0). The isomerization of [Nd(DOTA)(H(2)O)](-) and [Eu(DOTA)(H(2)O)](-) is purely conformational, as shown by near-zero reaction volumes. The measured isomerization enthalpies and entropies agree with this model. The shift of the isomerization equilibria by a variety of non-coordinative salts depends on the ligand conformation rather than the presence or absence of the inner sphere water molecule. This results from weak ion binding and water solvent stabilization of one ligand conformation, rather than the decrease of the activity of the bulk water in the solution, as shown by UV-vis measurements of the coordination number sensitive transition (5)F(0) --> (7)D(0) of Eu(III) as a function of ionic strength. Fluoride ions replace a water molecule in the inner coordination sphere, preferentially for one of the conformational isomers, as proven by (19)F-NMR shifts and the appearance of a third set of resonances corresponding to [Eu(DOTA)F](2)(-) in the (1)H-NMR spectrum of [Eu(DOTA)(H(2)O)](-).

311 citations

Journal ArticleDOI
TL;DR: The phi,psi backbone angle distribution of small homopolymeric model peptides is investigated by a joint molecular dynamics simulation and heteronuclear NMR study and the thermal populations of the peptide conformational states are determined with an uncertainty of <5 %.
Abstract: The φ,ψ backbone angle distribution of small homopolymeric model peptides is investigated by a joint molecular dynamics (MD) simulation and heteronuclear NMR study. Combining the accuracy of the measured scalar coupling constants and the atomistic detail of the all-atom MD simulations with explicit solvent, the thermal populations of the peptide conformational states are determined with an uncertainty of <5 %. Trialanine samples mainly (∼90%) a poly-l-proline II helix-like structure, some (∼10%) β extended structure, but no αR helical conformations. No significant change in the distribution of conformers is observed with increasing chain length (Ala3 to Ala7). Trivaline samples all three major conformations significantly. Tryglycine samples the four corner regions of the Ramachandran space and exists in a slow conformational equilibrium between the cis and trans conformation of peptide bonds. The backbone angle distribution was also studied for the segment Ala3 surrounded by either three or eight amino ac...

308 citations

Journal ArticleDOI
TL;DR: The structural and dynamic properties of protein ions in vacuo have been probed by hydrogen-deuterium exchange in a Fourier-transform mass spectrometer to provide further insight into the role of solvent in protein conformer stabilization.
Abstract: For further insight into the role of solvent in protein conformer stabilization, the structural and dynamic properties of protein ions in vacuo have been probed by hydrogen-deuterium exchange in a Fourier-transform mass spectrometer. Multiply charged ions generated by electrospray ionization of five proteins show exchange reactions with 2H2O at 10(-7) torr (1 torr = 133.3 Pa) exhibiting pseudo-first-order kinetics. Gas-phase compactness of the S-S cross-linked RNase A relative to denatured S-derivatized RNase A is indicated by exchange of 35 and 135 hydrogen atoms, respectively. For pure cytochrome c ions, the existence of at least three distinct gaseous conformers is indicated by the substantially different values--52, 113, and 74--of reactive H atoms; the observation of these same values for ions of a number--2, 7, and 5, respectively--of different charge states indicates conformational insensitivity to coulombic forces. For each of these conformers, the compactness in vacuo indicated by these values corresponds directly to that of a known conformer structure in the solution from which the conformer ions are produced by electrospray. S-derivatized RNase A ions also exist as at least two gaseous conformers exchanging 50-140 H atoms. Gaseous conformer ions are isometrically stable for hours; removal of solvent greatly increases conformational rigidity. More specific ion-molecule reactions could provide further details of conformer structures.

307 citations

Journal ArticleDOI
TL;DR: In this article, the IR spectra of nonionized glycine and its deuterated derivatives isolated in the low-temperature argon matrices have been measured, and for the first time the infrared spectral characteristics of the three most stable conformers have been determined and assigned.
Abstract: The IR spectra of nonionized glycine and its deuterated derivatives isolated in the low-temperature argon matrices have been measured, and for the first time the infrared spectral characteristics of the three most stable conformers have been determined and assigned. Correlated level ab initio and density functional theory (DFT) calculations of IR frequencies and intensities with extended basis sets were performed and their results were employed to separate the bands of the glycine conformers in the experimental spectra and to assist the assignment. The intramolecular interconversion, conformer III ⇒ conformer I, which is observed in the matrices at temperatures higher than 13 K, was found to cause a significant decrease of the band intensities of conformer III in the spectra. This phenomenon was used to distinguish the vibrational bands of this conformer from the bands of the other conformers. The reliability of the Moller−Plesset second-order perturbation theory (MP2) method and the DFT method with the t...

293 citations

Journal ArticleDOI
TL;DR: This tutorial review provides first a brief discussion of the main principles of ECD spectroscopy and related methods for interpretation of spectra, with special reference to conformational aspects, and presents the relatively less common but very interesting application of E CDs for conformational analyses of organic compounds.
Abstract: The electronic circular dichroism (ECD) spectra of flexible molecules include the contributions of all conformers populated at the working temperature. ECD spectra of chiral substrates depend on their stereochemistry in terms of both absolute configuration, as reflected in the sign of the spectrum, and molecular conformation, which dictates the overall spectral shape (possibly including the sign) in a very sensitive manner. The unique high sensitivity of ECD towards conformation, as well as of other chiroptical spectroscopies, renders these techniques a useful alternative or complement to standard spectroscopic tools for conformational investigations, such as NMR. This tutorial review provides first a brief discussion of the main principles of ECD spectroscopy and related methods for interpretation of spectra, with special reference to conformational aspects. The review focuses on the common problems encountered in the application of ECD for assignments of absolute configuration of flexible molecules. These problems can be handled either by taking into account the whole conformational ensemble or by considering rigid derivatives prepared ad hoc. Finally, the review presents the relatively less common but very interesting application of ECD spectroscopy for conformational analyses of organic compounds.

292 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023303
2022618
2021217
2020219
2019228
2018268