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 x HCl x 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 upsilon1, which can be observed only at low temperature, were used for estimation of the of upsilon1-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 upsilon1 mode bands.

Low-temperature infrared spectra and hydrogen bonding in polycrystalline dl-serine and deuterated derivatives

“…The red shift of n 1 and the blue shift of n 4 bands associated with a given H-bond proton correlate to each other as 10 À4 ½ðn 4 Þ 2 À ðn 0 4 Þ 2 and Dn 1 ¼ n 0 1 À n 1 is the red shift of the n 1 band (both n 1 and n 4 are expressed in cm À1 ) [36]. Taking the as n 0 1 and n 0 4 reference values respectively equal to 3450 and 1000 cm À1 , which correspond to rounded average values for free NH amine stretching and rocking vibrations in amines, amino acids and other compounds bearing amino or protonated amino groups [2,8,35,[37][38][39], the three out-of-plane uncoupled vibrations originated in individual NH protons are predicted to occur at 1131, 1144 and 1149 cm À1 . These frequencies can be associated with the three progressively stronger NHÁ Á ÁO bonds observed in the crystalline phase.…”

“…In the last few years, we have been developing a novel experimental approach for systematic investigation of biologically relevant H-bonded systems in the solid state [1][2][3][4][5][6][7][8], which is based on the study of isotopically doped crystals at low temperature. In this technique, partially deuterated substituted molecules are diluted in crystalline samples of the compound at low 2-10% deuterium content (or unsubstituted molecules are embedded in crystals of the deuterated compound at the same doped concentration), and advantage is taken of working at a temperature of a few degrees Kelvin.…”

“…At low temperature (<30 K), the bandwidth associated with these decoupled vibrations changes typically from hundreds to tens of wavenumbers and, as a result, the spectral resolution of the IR spectra improves significantly, allowing the observation of proton-related bands ascribable to specific Hbonds in the crystal. This approach was previously applied successfully to study of the H-bonding structure in crystalline carbohydrates [12,13], nucleobases (cytosine [4], uracil and thymine [5]), nucleosides (cytidine [6], adenosine and uridine [7]) and several amino acids (glycine, alanine, glutamine, histidine, tyrosine and threonine [2,8]), and led to the establishment of very general correlations between the frequency shifts of the proton vibrations upon hydrogen-bond formation and the corresponding H-bond lengths and energies [1,3,8].…”

“…This is particularly noticeable in the high frequency range (>1800 cm À1 ), since under the experimental conditions used the nO-H and nN-H vibrations give rise to a very broad and extensively structured spectral feature, not allowing direct identification of the bands due to individual modes. On the other hand, recently, we have presented a preliminary report on the infrared spectra of low temperature deuterium-doped crystalline samples of DL-serine [8] where decoupled proton stretching bands were tentatively assigned. However, no detailed discussion of the spectra was given in our previous paper, since the main purpose of that publication was to present a general empirical correlation toolbox to allow for the characterization of H-bonding properties in amino acids and peptides [8].…”

“…On the other hand, recently, we have presented a preliminary report on the infrared spectra of low temperature deuterium-doped crystalline samples of DL-serine [8] where decoupled proton stretching bands were tentatively assigned. However, no detailed discussion of the spectra was given in our previous paper, since the main purpose of that publication was to present a general empirical correlation toolbox to allow for the characterization of H-bonding properties in amino acids and peptides [8].…”