Champ de force de valence et modes normaux de vibration de la glycylglycine et du monochlorhydrate monohydrate de glycylglycine

Abstract

The valence force field and normal modes of vibration of α-glycylglycine have been calculated using the vibrational spectra of ten isotopic derivatives, selectively labeled with deuterium or nitrogen-15. It is shown that this force field permits the determination of the frequencies of glycylglycine-hydrochloride in the solid state, despite a structure very different from that of the zwitterion. The agreement is particularly satisfying for those modes of vibration most sensitive to molecular conformation. It is thus possible to use this type of calculation to determine the conformation of an oligopeptide.

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

“…4) with an average frequency of 2443 cm À1 , also quite close to the 2434 cm À1 observed in ref. 22. The origin of the observed multiple splitting cannot be unequivocally interpreted, but it might be due to a simultaneous occurrence of crystal and Fermi resonance splittings.…”

“…1 hydrogen atoms can only be clearly seen at low temperature and are not discussed in ref. 22 at all. In the spectra at high temperatures, the bands due to these vibrations extensively overlap and produce the broad, almost structureless, band absorbing in the range 3100-2600 cm À1 .…”

“…Comparison of the spectra of di-, tri-and tetra-glycines shows that the intensity of the bands appearing at this frequency increases with the number of peptide bonds, as expected, and close to peak position of 3288 cm À1 observed in ref. 22. The cooling leads to the splitting of the band in two components (at 3284 and 3278 cm À1 ) which can be either due to Fermi resonance with the antisymmetric stretching vibration of the carboxylate group (COO À ), which strongly absorbs around 1650 cm À1 , or crystal splitting effects (due to presence of two slightly different crystal sites).…”

Ab Initio Studies of Solvent Effects on Molecular Conformation and Vibrational Spectra of Diglycine Zwitterion

“…The ground-state structure of Gly-Gly has been experimentally characterized by a variety of techniques. − The X-ray and neutron diffraction studies of the structure of α, β, and γ conformers of diglycine zwitterion have been reported. − The α form of diglycine zwitterion is the most stable one among the α, β, and γ forms and in the α form, the dihedral angle between the plane of the amide group and that of the carboxylate COO - group is 22.4°, whereas the β and γ forms have coplanar amide and COO - groups. Nonplanarity of diglycine zwitterion permits better molecular packing with stronger hydrogen bonds and van der Waals interactions.…”

“…The 13 C NMR spectra of the α form showed that diglycine zwitterion crystallized from aqueous solution possesses the δ form and on dehydration it changes over to the α form . Infrared, Raman, and INS spectra of diglycine zwitterion and its N-deuterated analogue have been reported. ,, The infrared spectra of α-glycylglycine zwitterion and its nine differently labeled N, C-, C- and N-deuterated and 15 N isotopic species have been investigated by Destrade et al, and the assignments for α-glycylglycine zwitterion have been made on the basis of a normal coordinate analysis employing a valence force field. The Raman and infrared spectra of glycylglycine zwitterion and its N-deuterated analogue have also been investigated by Lagant et al They have carried out a normal coordinate analysis for the α-crystalline form using a modified Urey−Bradley force field.…”