Vibrational spectra and crystal structure of the di-amino acid peptide cyclo(L-Met-L-Met): comparison of experimental data and DFT calculations

Andrew P. Mendham, Brian S. Potter, Rex A. Palmer, Trevor J. Dines, John C. Mitchell, Robert Withnall, Babur Z. Chowdhry

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    Abstract

    Experimental Raman and FT-IR spectra of solid-state non-deuterated and N-deuterated samples of cyclo(L-Met-L-Met) are reported and discussed. The Raman and FT-IR results show characteristic amide I vibrations (Raman: 1649 cm(-1), infrared: 1675 cm(-1)) for molecules exhibiting a cis amide conformation. A Raman band, assigned to the cis amide 11 vibrational mode, is observed at similar to 1493 cm(-1) but no IR band is observed in this region. Cyclo(L-Met-L-Met) crystallises in the triclinic space group P1 with one molecule per unit cell. The overall shape of the diketopiperazine (DKP) ring displays a (slightly distorted) boat conformation. The crystal packing employs two strong hydrogen bonds, which traverse the entire crystal via translational repeats. B3-LYP/cc-pVDZ calculations of the structure of the molecule predict a boat conformation for the DKP ring, in agreement with the experimentally determined X-ray structure. Copyright (C) 2009 John Wiley & Sons, Ltd.

    Original languageEnglish
    Pages (from-to)148-159
    Number of pages12
    JournalJournal of Raman Spectroscopy
    Volume41
    Issue number2
    DOIs
    Publication statusPublished - Feb 2010

    Keywords

    • cyclic di-amino acid peptides
    • X-ray structure
    • X-ray crystallography
    • ab initio calculations
    • vibrational spectra
    • X-RAY-DIFFRACTION
    • ALANYL-L-ALANYL
    • CYCLIC DIPEPTIDES
    • DIKETOPIPERAZINES
    • IDENTIFICATION
    • HYDROGEN
    • DENSITY
    • BRAIN

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