Computational studies of dielectric permittivity effects on chemical shifts of alanine dipeptide

Dielectric permittivity effect on chemical shifts of alanine dipeptide is studied using hybrid density functional theory. The dependence is shown to be highly sensitive to conformation, and, a reasonable explanation is outlined based on the solvent reaction field model. The danger of the observed shape of dependence for the chemical shift evaluations at low dielectric constant environment, as in the case of protein interior, is emphasized. The nuclear shielding sensitivity towards the dielectric permittivity is examined over different ϕ / ψ combinations. Comparison with the experimental data from protein backbone suggests an effective dielectric constant of ≈ 4–5 for protein interior.