Conformational analysis of Gly–Ala–NHMe in D2O and DMSO solutions: a two-dimensional infrared spectroscopy study

Marco Candelaresi, Elena Ragnoni, Chiara Cappelli, Alessandro Corozzi, Manuela Lima, Susanna Monti, Benedetta Mennucci, Francesca Nuti, Anna Maria Papini, Paolo Foggi

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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 midinfrared 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 beta-like polar conformers in both water and DMSO solvents.

Original languageEnglish
Pages (from-to)14226-14237
Number of pages12
JournalJournal of Physical Chemistry B
Volume117
Issue number46
DOIs
Publication statusPublished - 21 Nov 2013

Keywords

  • POLYPROLINE-II STRUCTURE
  • MOLECULAR-DYNAMICS SIMULATIONS
  • POLARIZABLE CONTINUUM MODEL
  • VIBRATIONAL SPECTROSCOPY
  • ALANINE DIPEPTIDE
  • N-METHYLACETAMIDE
  • AQUEOUS-SOLUTION
  • LIQUID WATER
  • ANISOTROPIC DIELECTRICS
  • NONLINEAR SPECTROSCOPY

Cite this

Candelaresi, M., Ragnoni, E., Cappelli, C., Corozzi, A., Lima, M., Monti, S., Mennucci, B., Nuti, F., Papini, A. M., & Foggi, P. (2013). Conformational analysis of Gly–Ala–NHMe in D2O and DMSO solutions: a two-dimensional infrared spectroscopy study. Journal of Physical Chemistry B, 117(46), 14226-14237. https://doi.org/10.1021/jp406139t