Christian Destrade

Utilisation du calcul des modes normaux de vibration pour la détermination de la conformation de la glycylglycine et de la triglycine en solution aqueuse

Abstract The valence force field of α-glycylglycine was applied to different G matrices calculated for several values of the dihedral angles ψ 1 , φ 2 and ψ 2 . The relations v i = ƒ(ψ i ,φ i ) obtained for different isotopic species were compared with the experimental frequencies of the aqueous solution thereby giving the absolute value of the angles. A complementary study by means of depolarised light scattering led to the determination of their sign. These relations were then used in the conformational analysis of triglycine in aqueous solution. The conformation of glycylglycine differs strongly in aqueous solution from that in the solid state, especially concerning the relative positions of the peptide and carboxylic group (φ 2 = −70° and −160°). For triglycine, we showed the existence of a chelated ring “C 7 ” similar to that observed for the acetylated dipeptides.