Update of CHARMM36's atomic charges for aromatic amino acids in water solution simulations and spectroscopy analysis via sequential molecular dynamics and DFT calculations

Abstract

In this theoretical work we develop simulations of classical molecular dynamics sequentially combined with quantum calculations to obtain an update of the atomic charges of the aromatic amino acids: Phenylalanine, Tryptophan and Tyrosine in water solution. The charge point model was used to describe the solvent medium and obtain new atomic charges as the aromatic amino acids' dipole moment convergence into solution. Additionally, we developed quantum calculations for GIAO-NMR and absorption spectrum (TD-DFT) spectroscopy to verify the influence of electrical distribution adjustment on the spectroscopic properties of these amino acids in water. Our results show that, in fact, a new electronic distribution of the amino acids is obtained and updates the CHARMM36's atomic charges. In this way the solute-solvent interaction is modified and indicates deviations on the magnetic shielding spectroscopy signature up to −6.9 ppm for carbon atoms, −4.4 ppm for nitrogen atoms and −13.4 ppm for oxygen atoms. Electronic absorption spectrum demonstrates a change in the distribution of electronic transitions.