Probing molecular interactions, electronic properties, and reactivity of monoamine neurotransmitters in different protonation states via quantum chemical investigation

Abstract
Amphetamine, dopamine, norepinephrine, serotonin, and tryptamine are a group of monoamine neurotransmitters that regulate diverse brain functions. This work examined these compounds’ neutral, protonated, and deprotonated, structural, energetic, and optical properties using quantum chemistry methods. Noncovalent interactions (NCI) and reduced density gradient (RDG) investigations revealed weak intermolecular forces and electron density distribution. The RDG values were observed to span from 0.12 to 0.43, indicating varying degrees of repulsion or attraction. The hydrogen bonding patterns and their strength and nature were also investigated using the Atoms in Molecules (AIM) and B3LYP methods. The quantification was done using —^2 r(r), H(r), and energy density values, which showed a variation from -0.014 to 0.026 Hartree/Bohr3, reflecting covalent or electrostatic interactions. A comparison was made between the compounds based on their physical and chemical attributes, such as polar surface area (ranging from 41.81 to 86.71 Ų), rotatable bonds (which were identical), and proton affinity (a measure of stability). Lewis structures and natural bond orbital (NBO) analysis showed resonance and electron delocalization. The study also examined their molecular orbitals (MOs) and found that protonation and deprotonation could significantly change their electronic characteristics, including the energies of the highest occupied (HOMO) and lowest unoccupied (LUMO), the energy gap, and the shape and size of their lobes. The nonlinear optical properties were also assessed, affected by polarizability and hyperpolarizability indices, ranging from 2.267 a.u. (Dopamine) to 7.891 a.u. (Protonated Serotonin). These properties pointed to the applications of these compounds in optical devices.

Author
Rebaz Anwar OMER

DOI
https://doi.org/10.17308/kcmf.2024.26/12214

ISSN
2687-0711

Publish Date: 2024-10-02