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Vibrational spectroscopic studies of the structure of di-amino acid peptides. Part II: cyclo(L-Asp-L-Asp) in the solid state and in aqueous solution

Vibrational spectroscopic studies of the structure of di-amino acid peptides. Part II: cyclo(L-Asp-L-Asp) in the solid state and in aqueous solution

Mendham, Andrew P., Dines, Trevor J., Withnall, Robert, Mitchell, John C. and Chowdhry, Babur Z. (2009) Vibrational spectroscopic studies of the structure of di-amino acid peptides. Part II: cyclo(L-Asp-L-Asp) in the solid state and in aqueous solution. Journal of Raman Spectroscopy, 40 (11). pp. 1498-1507. ISSN 0377-0486 (Print), 1097-4555 (Online) (doi:10.1002/jrs.2307)

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Abstract

Solid-state protonated and N,O-deuterated Fourier transform infrared (IR) and Raman scattering spectra together with the protonated and deuterated Raman spectra in aqueous solution of the cyclic di-amino acid peptide cyclo(L-Asp-L-Asp) are reported. Vibrational band assignments have been made on the basis of comparisons with previously cited literature values for diketopiperazine (DKP) derivatives and normal coordinate analyses for both the protonated and deuterated species based upon DFT calculations at the B3-LYP/cc-pVDZ level of the isolated molecule in the gas phase. The calculated minimum energy structure for cyclo(L-Asp-L-Asp), assuming C-2 symmetry, predicts a boat conformation for the DKP ring with both the two L-aspartyl side chains being folded slightly above the ring. The C=O stretching vibrations have been assigned for the side-chain carboxylic acid group (e.g. at 1693 and 1670 cm(-1) in the Raman spectrum) and the cis amide I bands (e.g. at 1660 cm(-1) in the Raman spectrum). The presence of two bands for the carboxylic acid C=O stretching modes in the solid-state Raman spectrum can be accounted for by factor group splitting of the two nonequivalent molecules in a crystallographic unit cell. The cis amide II band is observed at 1489 cm(-1) in the solid-state Raman spectrum, which is in agreement with results for cyclic di-amino acid peptide molecules examined previously in the solid state, where the DKP ring adopts a boat conformation. Additionally, it also appears that as the molecular mass of the substituent on the C-alpha atom is increased, the amide II band wavenumber decreases to below 1500 cm(-1); this may be a consequence of increased strain on the DKP ring. The cis amide II Raman band is characterized by its relatively small deuterium shift (29 cm(-1)), which indicates that this band has a smaller N-H bending contribution than the trans amide II vibrational band observed for linear peptides.

Item Type: Article
Additional Information: [1] Article first published online: 27 May 2009. [2] First published in print: November 2009. [3] Published as: Journal of Raman Spectroscopy, Volume 40, Issue 11, pages 1498–1507, November 2009. [4] Supporting information may be found in the online version of this article - http://onlinelibrary.wiley.com/doi/10.1002/jrs.2307/suppinfo [5] The definitive version is available at www3.interscience.wiley.com.
Uncontrolled Keywords: cyclic di-amino acid peptides, X-ray crystallography, ab initio calculations, vibrational spectra
Subjects: Q Science > QC Physics
Q Science > QD Chemistry
T Technology > TP Chemical technology
Faculty / Department / Research Group: Faculty of Engineering & Science > Department of Life & Sports Sciences
Faculty of Engineering & Science > Department of Pharmaceutical, Chemical & Environmental Sciences
Related URLs:
Last Modified: 05 Dec 2016 14:39
Selected for GREAT 2016: None
Selected for GREAT 2017: None
Selected for GREAT 2018: None
URI: http://gala.gre.ac.uk/id/eprint/2076

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