Estudo ab initio das interações por ligações de hidrogênio entre o ácido aspártico, a arginina e a triptamina com moléculas de água.

Abstract

Hydrogen bonds exert fundamental influences on conformational and energetic preferences, as well as on the vibrational, optical, and electronic properties of biomolecules. Among the biomolecules, we can highlight neurotransmitters, as their binding with their protein receptor during the chemical synapse occurs through multiple weak intermolecular interactions, mainly by hydrogen bonds. The objective of this work is to study some structures in the ground state, S0, and in the first excited state, S1, the vertical electronic transitions S1←S0 of aspartic acid, arginine and tryptamine, and their complexes formed by hydrogen bonds with one and two molecules of water in the gaseous state. In order to do this, the DFT and TD-DFT methods were used, with the B3LYP functional, with different basis sets. It was possible to analyze and relate the structural, electronic and stability changes of the complexes in the ground and in the excited states. It was observed that there is a relationship between the electrostatic stabilization (or destabilization) of the excited state compared to the ground state with changes in the UV-Vis absorption band of the complex in relation to the monomer, as well as in the vibrational stretching frequency of the X‒H bond (proton donor). The interactions of water molecules with the HOMO and LUMO orbitals influenced the electrostatic stabilization (or destabilization) of the excited state due to changes in electronic density. However, in some specific cases, opposite behaviors occurred in the values of these parameters due to the small variation in the E of the electronic transition on the complex compared to that transition on the monomer, and the different competitive strengths of hydrogen bonds. In some complexes, it was possible to observe that the charge transfer between the proton donor and recipient are also related to the deviation of the absorption wavelength of the X‒H stretching band. Therefore, the DFT and TD-DFT methods were useful to analyze the preferential interactions between these neurotransmitters and water molecules, and the influences of hydrogen bonds on the properties of these biomolecules in different electronic states.