Mendham, Andrew P., Palmer, Rex A., Potter, Brian S., Dines, Trevor J., Snowden, Martin J. ORCID: https://orcid.org/0000-0002-1087-2692, Withnall, Robert and Chowdhry, Babur Z. (2009) Vibrational spectroscopy and crystal structure analysis of two polymorphs of the di-amino acid peptide cyclo(L-Glu-L-Glu). Journal of Raman Spectroscopy, 41 (3). pp. 288-302. ISSN 0377-0486 (Print), 1097-4555 (Online) (doi:10.1002/jrs.2467)

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Abstract

Cyclo(L-Glu-L-Glu) has been crystallised in two different polymorphic forms. Both polymorphs are monoclinic, but form 1 is in space group P21 and form 2 is in space group C2. Raman scattering and FT-IR spectroscopic studies have been conducted for the N,O-protonated and deuterated derivatives. Raman spectra of orientated single crystals, solid-state and aqueous solution samples have also been recorded. The different hydrogen-bonding patterns for the two polymorphs have the greatest effect on vibrational modes with N&bond;H and C&dbond;O stretching character. DFT (B3-LYP/cc-pVDZ) calculations of the isolated cyclo(L-Glu-L-Glu) molecule predict that the minimum energy structure, assuming C2 symmetry, has a boat conformation for the diketopiperazine ring with the two L-Glu side chains being folded above the ring. The calculated geometry is in good agreement with the X-ray crystallographic structures for both polymorphs. Normal coordinate analysis has facilitated the band assignments for the experimental vibrational spectra. Copyright © 2009 John Wiley & Sons, Ltd.

Item Type:	Article
Additional Information:	[1] Article first published online: 6 Oct 2009. [2] First published in print: March 2010. [3] Published in the Journal of Raman Spectroscopy, (2010), Volume 41, Issue 3, pp. 288–302.
Uncontrolled Keywords:	cyclic di-amino acid peptides, X-ray crystallography, ab initio calculations, vibrational spectra
Subjects:	Q Science > QD Chemistry Q Science > QC Physics
Pre-2014 Departments:	School of Science School of Science > Department of Medway Sciences
Related URLs:	Publisher Organisation
Last Modified:	16 Apr 2020 13:26
URI:	http://gala.gre.ac.uk/id/eprint/2079

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