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

    Mendham, A.P. and Palmer, R.A. and Potter, B.S. and Dines, T.J. and Snowden, M.J. and Withnall, R. and Chowdhry, Babur Z. (2010) 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.

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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[DOUBLE BOND]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.

    Metadata

    Item Type: Article
    Keyword(s) / Subject(s): cyclic di-amino acid peptides, X-ray crystallography, ab initio calculations, vibrational spectra
    School: Birkbeck Schools and Departments > School of Science > Biological Sciences
    Depositing User: Administrator
    Date Deposited: 11 Dec 2014 17:35
    Last Modified: 11 Dec 2014 17:35
    URI: http://eprints.bbk.ac.uk/id/eprint/11295

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