In a study of cross sections of the E = f(X1,X2) side-chain conformational potential energy surface of the γL or C7eq backbone conformation of For-L-Phe-NH2, it was found that there are three conformations (g + , a and g -) due to rotation about the Cα X1 Cβ bond. It should be emphasised that the γL backbone conformation is conserved during rotation about X1. However, there is only one unique conformation along the rotation about the Cβ X2 Ph bond. The -CH2-Ph group showed greater stabilisation, with respect to hydrogen (Gly), than the -CH3 (Ala) or -CH2-OH (Ser) substituents. The hydrogen-bonded C=O (amide 1) vibrational frequency is split into two bands due to the coupling of the C=O stretching and -NH2 scissoring modes of motion. The other carbonyl, not involved in hydrogen bonding, has a characteristic single IR band with a relatively high frequency. The orientation of the -Ph group has no appreciable effect on these vibrational frequencies.
- Conformational analysis
- Peptide model
ASJC Scopus subject areas
- Condensed Matter Physics
- Physical and Theoretical Chemistry