title: Vibrational spectroscopy and DFT calculations of the di-amino acid peptide L-aspartyl-L-glutamic acid in the zwitterionic state.
abstract: Solid state IR and Raman as well as aqueous solution state Raman spectra are reported for the linear di-amino acid peptide L-aspartyl-L-glutamic acid (L-Asp-L-Glu); the solution state Raman spectrum has also been obtained for the N,O-deuterated derivative. SCF-DFT calculations at the B3-LYP/cc-pVDZ level established that the structure and vibrational spectra of L-Asp-L-Glu can be interpreted using a model of the peptide with ten hydrogen-bonded water molecules, in conjunction with the conductor-like polarizable continuum solvation method. The DFT calculations resulted in the computation of a stable zwitterionic structure, which displays trans-amide conformation. The vibrational spectra were computed at the optimised molecular geometry, enabling normal coordinate analysis, which yielded satisfactory agreement with the experimental IR and Raman data. Computed potential energy distributions of the normal modes provided detailed vibrational assignments.
authors.affiliation: School of Science, University of Greenwich at Medway, Central Avenue, Chatham Maritime, Kent, UK.
authors.forename: Nighat
authors.initials: N
authors.lastname: Kausar
authors.forename: Trevor J
authors.initials: TJ
authors.lastname: Dines
authors.forename: Babur Z
authors.initials: BZ
authors.lastname: Chowdhry
authors.forename: Bruce D
authors.initials: BD
authors.lastname: Alexander
mesh_terms: D000577:Amides / Q000737:chemistry; D000596:Amino Acids / Q000737:chemistry*; D001224:Aspartic Acid / Q000737:chemistry*; D002627:Chemistry, Physical / Q000379:methods; D018698:Glutamic Acid / Q000737:chemistry*; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry / Q000379:methods; D008968:Molecular Conformation; D010455:Peptides / Q000737:chemistry; D012997:Solvents / Q000737:chemistry; D013055:Spectrophotometry, Infrared / Q000379:methods*; D017550:Spectroscopy, Fourier Transform Infrared; D013059:Spectrum Analysis, Raman / Q000379:methods*; D014732:Vibration
chemical_list: D000577:Amides; D000596:Amino Acids; D010455:Peptides; D012997:Solvents; D001224:Aspartic Acid; D018698:Glutamic Acid