Mendham, Andrew P., Dines, Trevor J., Snowden, Martin J. ORCID: 0000-0002-1087-2692, Chowdhry, Babur Z. and Withnall, Robert (2009) Vibrational spectroscopy and DFT calculations of di-amino acid cyclic peptides. Part I: cyclo(Gly-Gly), cyclo(L-Ala-L-Ala) and cyclo(L-Ala-Gly) in the solid state and in aqueous solution. Journal of Raman Spectroscopy, 40 (11). pp. 1478-1497. ISSN 0377-0486 (Print), 1097-4555 (Online) (doi:https://doi.org/10.1002/jrs.2293)

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Abstract

Investigations of the vibrational spectra of cyclo(Gly-Gly), cyclo(L-Ala-L-Ala) and cyclo(t-Ala-Gly) are reported. Raman scattering and Fourier transform infrared (FTIR) spectra of solid-state and aqueous protonated samples, as well as their corresponding N-deuterated isotopomers, have been examined. In addition, density functional theory (DFT) (B3-LYP/cc-pVDZ) calculations of molecular structures and their associated vibrational modes were carried out. In each case, the calculated structures of lowest energy for the isolated gas-phase molecules have boat conformations. Assignments have been made for the observed Raman and FTIR vibrational bands of the cyclic di-amino acid peptides (CDAPs) examined. Raman polarization studies of aqueous phase samples are consistent with C-2 and C-1 symmetries for the six-membered rings of cyclo(L-Ala-L-Ala) and cydo(L-Ala-Gly), respectively. There is a good correlation between experimental and calculated vibrational bands for the three CDAPs. These data are in keeping with boat conformations for cydo(L-Ala-L-Ala) and cyclo(L-Ala-Gly) molecules, predicted by the ab initio calculations, in both the solid and aqueous solution states. However, Raman spectroscopic results might infer that cyclo(L-AlaGly) deviates only slightly from planarity in the solid state. The potential energy distributions of the amide I and II modes of a cis-peptide linkage are shown to be significantly different from those of the trans-peptides. For example, deuterium shifts have shown that the cis-amide I vibrations found in cyclo(Gly-Gly), cyclo(L-Ala-L-Ala), and cyclo(L-Ala-Gly) have larger N-H contributions compared to their trans-amide counterparts. Compared to trans-amide II vibrations, cis-amide II vibrations show a considerable decrease in N-H character.

Item Type:	Article
Uncontrolled Keywords:	Raman spectroscopy, FTIR spectroscopy, deuterated isotopomers, spectral assignments, cis-/trans-conformation, ab initio calculations
Subjects:	Q Science > QD Chemistry R Medicine > RM Therapeutics. Pharmacology Q Science > QC Physics
Faculty / School / Research Centre / Research Group:	Faculty of Engineering & Science Faculty of Education, Health & Human Sciences > School of Human Sciences (HUM)
Related URLs:	Publisher
Last Modified:	09 Oct 2021 04:46
URI:	http://gala.gre.ac.uk/id/eprint/2075

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