A correlation between the proton stretching vibration red shift and the hydrogen bond length in polycrystalline amino acids and peptides

Abstract

The FTIR spectra of pure and isotopically diluted (H/D and D/H) polycrystalline L-glutamine, L-hystidine, L-tyrosine, DL-serine, L-threonine, di-, tri-glycine and di-glycine·HCl·H2O salt were measured in the range 4000–2000 cm−1 at temperatures from 300 to 10 K. The frequencies of decoupled proton stretching mode bands ν1, which can be observed only at low temperature, were used for estimation of the of ν1-bands red shift, which occurs upon formation of H-bonds involving ionized NH3+ and/or peptide HN–CO groups. The empirical correlation between the red shift and H-bond length, which was found previously for binary gas phase H-bonded complexes, carbohydrates and nucleosides [M. Rozenberg, A. Loewenschuss and Y. Marcus, Phys. Chem. Chem. Phys., 2000, 2, 2699–2702; M. Rozenberg, C. Jung and G. Shoham, Phys. Chem. Chem. Phys., 2003, 5, 1533–1535], was now extended to H-bonded networks in polycrystalline amino acids and peptides. The energies of the different H-bonds present in the crystalline structures could also be successfully estimated from the well-established empirical correlation [A. V. Iogansen, Spectrochim. Acta, 1999, A55, 1585–1612] between this property and the red shifts of the corresponding ν1 mode bands.