Effect of low-temperature argon matrices on IR spectra and structure of flexible N-acetylglycine molecules

The influence of the matrix environment on structure and IR spectra of the N-acetylglycine conformers was studied. Based on the FTIR spectra of N-acetylglycine isolated in low temperature argon matrices we determined its conformational composition. The spectra bands of main and two minor conformers of N-acetylglycine were identified in the FTIR spectra. The structure of the observed conformers was stabilized by different intramolecular hydrogen bonds. The Gibbs free energies of the conformers (CCSD(T)/CBS method) were performed and population of the conformers at 360 K were determined. They were 85.3% for the main conformer and 9.6 and 5.1% for the minor N-acetylglycine conformers. We also determined size and shape of the cavities which were formed by embedding of the N-acetylglycine conformers in argon matrices during deposition. It was found that for the planar main conformer the most energetically preferred cavity was formed by substituting of 7 argon atoms. At the same time, bulky minor conformers were embedded in a cavity formed by substituting of 8 argon atoms. Complexation energies as well as the deformation energies of the argon crystal and conformers of N-acetylglycine were calculated. Also we determined values of the matrix shifts of vibrational frequencies of N-acetylglycine conformers.