title: Conformational analysis of Gly-Ala-NHMe in D(2)O and DMSO solutions: a two-dimensional infrared spectroscopy study.
abstract: A relevant number of experiments on short peptides has been performed in recent years. One of the major problems rises from the simultaneous presence of slightly different conformers at equilibrium in solution. In the present paper, the conformational characteristics of the Gly-l-Ala-Methyl amide dipeptide in D2O and DMSO solutions are investigated by nonlinear IR spectroscopy. The pump-probe scheme with ultrashort mid-infrared pulses, in the Amide I region, is used to determine the mutual orientation of the two C═O bonds and the dynamics due to solute-solvent interactions. The coupling between Amide I modes is evaluated from both linear and 2D spectra. The interconversion between the different conformations occurs on time scales longer than the vibrational lifetime, and the spectral diffusion observed in 2D spectra is attributed to the solvent dynamics. Quantum mechanical calculations and molecular dynamics simulations are performed to identify the most stable geometries. By comparing the experimental and the theoretical data, we establish the prevalence of β-like polar conformers in both water and DMSO solvents.
authors.affiliation: Heriot-Watt University, Edinburgh Campus , Edinburgh, Scotland EH14 4AS.
authors.forename: Marco
authors.initials: M
authors.lastname: Candelaresi
authors.forename: Elena
authors.initials: E
authors.lastname: Ragnoni
authors.forename: Chiara
authors.initials: C
authors.lastname: Cappelli
authors.forename: Alessandro
authors.initials: A
authors.lastname: Corozzi
authors.forename: Manuela
authors.initials: M
authors.lastname: Lima
authors.forename: Susanna
authors.initials: S
authors.lastname: Monti
authors.forename: Benedetta
authors.initials: B
authors.lastname: Mennucci
authors.forename: Francesca
authors.initials: F
authors.lastname: Nuti
authors.forename: Anna Maria
authors.initials: AM
authors.lastname: Papini
authors.forename: Paolo
authors.initials: P
authors.lastname: Foggi
mesh_terms: D017666:Deuterium Oxide / Q000737:chemistry; D004121:Dimethyl Sulfoxide / Q000737:chemistry*; D004151:Dipeptides / Q000138:chemical synthesis / Q000737:chemistry*; D008968:Molecular Conformation; D056004:Molecular Dynamics Simulation; D011789:Quantum Theory; D012996:Solutions / Q000737:chemistry; D013055:Spectrophotometry, Infrared
chemical_list: D004151:Dipeptides; D012996:Solutions; C065992:N-glycylalanine; D017666:Deuterium Oxide; D004121:Dimethyl Sulfoxide