Electrostatic interactions in peptides.: Polarisation effects due to an α-helix

A quantum mechanical/molecular mechanical study of a dodecapeptide made of 11 alanine and one asparagine residues in a helical conformation is carried out by means of the local self-consistent field/molecular mechanical and integrated molecular orbital and molecular mechanics computational schemes. The electronic properties of the asparagine side chain are analysed to extract the influence of electrostatic and induction interaction. One finds that induction may play an important role in the energetic and structural features of the systems modelled with mixed methods. The importance of performing quantum computations which explicitly take account of the electrostatic interactions is pointed out.