Conformational study on dipeptides containing phenylalanine: A DFT approach

DFT calculations has been done applying 6-31G∗ basis set on a series of dipeptides where the N-terminus position is fixed with phenylalanine and the C-terminus is varied with eight different amino acids. Different geometrical parameters (bond angle, bond length, geometry around α-carbon atom) are thoroughly investigated to study the effect of amino acid sequence on dipeptide. Dihedral angle data analysis shows the deviation of amide plane from planarity, which is due to the combined effect of the steric hindrance of -R group and hydrogen bonding. The λmax value for phenylalanine has been calculated, which shows good agreement with the experimental value. A rigid potential energy scan is performed on phenylalanine by rotating -CH2Ph, -COOH and -NH2 groups separately to get some idea about the conformational stability.