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Quantitative Determination of Ala-Ala Conformer Ratios in Solution by Decomposition of Raman Optical Activity Spectra
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SYSNO ASEP 0480247 Document Type J - Journal Article R&D Document Type Journal Article Subsidiary J Článek ve WOS Title Quantitative Determination of Ala-Ala Conformer Ratios in Solution by Decomposition of Raman Optical Activity Spectra Author(s) Jungwirth, Jakub (UOCHB-X)
Šebestík, Jaroslav (UOCHB-X) RID, ORCID
Šafařík, Martin (UOCHB-X) ORCID
Kapitán, J. (CZ)
Bouř, Petr (UOCHB-X) RID, ORCIDSource Title Journal of Physical Chemistry B. - : American Chemical Society - ISSN 1520-6106
Roč. 121, č. 38 (2017), s. 8956-8964Number of pages 9 s. Language eng - English Country US - United States Keywords density functional theory ; vibrational circular dichroism ; ab initio calculation Subject RIV CF - Physical ; Theoretical Chemistry OECD category Physical chemistry R&D Projects GA16-05935S GA ČR - Czech Science Foundation (CSF) LTC17012 GA MŠMT - Ministry of Education, Youth and Sports (MEYS) Institutional support UOCHB-X - RVO:61388963 UT WOS 000412150700009 EID SCOPUS 85030462605 DOI 10.1021/acs.jpcb.7b07154 Annotation Raman optical activity (ROA) spectroscopy combined with quantum-chemical simulations is a sensitive method to determine the absolute configuration and conformation of chiral molecules in solutions. However, the precision of this approach varies for different systems. In the present study, the reliability and numerical stability of decomposing experimental spectra into calculated subspectra is tested on the Ala-Ala dipeptide. Molecular dynamics (MD) snapshots of Ala-Ala/water clusters are averaged to account for solvent effects and molecular flexibility. Multiple experiments with protonated, zwitterionic, and deprotonated dipeptide forms and natural and d(2)- and d(8)-isotopically labeled dipeptides are used to verify the results and estimate the overall accuracy. Although the precision is still limited by experimental noise and computational error, a very close match between the observed and theoretical spectral shapes has been achieved. This enabled quantitative determination of conformer populations with a typical dispersion of 10%. The spectroscopy also demonstrated how the conformation depends on pH. The ROA results were more consistent than the Raman ones. Typically, the ROA analysis was more resistant to artifacts in the experiment, such as incomplete baseline subtraction. Conformer ratios predicted by MD agree fairly but not fully with the experimental ones. This indicates minor deficiencies in the Amber force field, particularly for the protonated dipeptide. Overall, the combination of ROA experiment and computational chemistry appears to be a robust tool providing deep insight into molecular structure. Workplace Institute of Organic Chemistry and Biochemistry Contact asep@uochb.cas.cz ; Kateřina Šperková, Tel.: 232 002 584 ; Jana Procházková, Tel.: 220 183 418 Year of Publishing 2018
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