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Vibrational spectroscopy and crystal structure analysis of two polymorphs of the di-amino acid peptide cyclo(L-Glu-L-Glu)

Vibrational spectroscopy and crystal structure analysis of two polymorphs of the di-amino acid peptide cyclo(L-Glu-L-Glu)

Mendham, Andrew P., Palmer, Rex A., Potter, Brian S., Dines, Trevor J., Snowden, Martin J., 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:
Last Modified: 14 Oct 2016 09:05
Selected for GREAT 2016: None
Selected for GREAT 2017: None
Selected for GREAT 2018: None
URI: http://gala.gre.ac.uk/id/eprint/2079

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