Quantitative Determination of Ala-Ala Conformer Ratios
in Solution by Decomposition of Raman Optical Activity Spectra
Jakub Jungwirth
Jaroslav Šebestík
Martin Šafařík
Josef Kapitán
Petr Bouř
10.1021/acs.jpcb.7b07154.s001
https://acs.figshare.com/articles/journal_contribution/Quantitative_Determination_of_Ala-Ala_Conformer_Ratios_in_Solution_by_Decomposition_of_Raman_Optical_Activity_Spectra/5415010
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 <i>d</i><sub>2</sub>- and <i>d</i><sub>8</sub>-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.
2017-08-30 00:00:00
Amber force field
baseline subtraction
ROA experiment
Ala-Ala Conformer Ratios
ROA results
Conformer ratios
conformation
MD
Quantitative Determination
Ala-Ala dipeptide
chiral molecules
precision
ROA analysis
spectroscopy
quantum-chemical simulations
Raman ones
protonated dipeptide
Molecular dynamics
conformer populations
deprotonated dipeptide forms
Multiple experiments
Raman Optical Activity Spectra Raman