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Vibrational spectra of alpha-amino acids in the zwitterionic state in aqueous solution and the solid state

Vibrational spectra of alpha-amino acids in the zwitterionic state in aqueous solution and the solid state: DFT calculations and the influence of hydrogen bonding

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Authors

  • Babur Z. Chowdhry
  • Trevor J. Dines
  • Saima Jabeen
  • Robert Withnall

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Original languageEnglish
Pages10333-10347
Number of pages15
JournalJournal of Physical Chemistry A
Journal publication date16 Oct 2008
Volume112
Issue41
DOIs
StatePublished

Abstract

The zwitterionic forms of the two simplest alpha-amino acids, glycine and L-alanine, in aqueous solution and the solid state have been modeled by DFT calculations. Calculations of the structures in the solid state, using PW91 or PBE functionals, are in good agreement with the reported crystal structures, and the vibrational spectra computed at the optimized geometries provide a good fit to the observed IR and Raman spectra in the solid state. DFT calculations of the structures and vibrational spectra of the zwitterions in aqueous solution at the B3-LYP/cc-pVDZ level were found to require both explicit and implicit solvation models. Explicit solvation was modeled by inclusion of five hydrogen-bonded water molecules attached to each of the five possible hydrogen-bonding sites in the zwitterion and the integration equation formalism polarizable continuum model (IEF-PCM) was employed, providing a satisfactory fit to observed IR and Raman spectra. Band assignments are reported in terms of potential-energy distributions, which differ in some respects to those previously reported for glycine and L-alanine.

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