Intramolecular interactions (O-H•••O, C-H•••N, N-H•••π) in isomers of neutral, cation, and anion dopamine molecules: A DFT study on the influence of solvents (water and ethanol)

ContextDopamine (DA) is one of the most important neurotransmitters associated with numerous neural disorders. This investigation reports the intramolecular interactions present in the isomers of neutral (DA(0)), anionic (DA(-)), and cationic (DA(+)) dopamine isomers in gas, water, and ethanol mediums. Neutral and anion isomers have O-H center dot center dot center dot O, C-H center dot center dot center dot N intramolecular hydrogen bonds and N-H center dot center dot center dot pi interactions. All the interactions are electrostatic in nature. Isomers of cation dopamine show no intramolecular interactions in the solvent. Natural charges from natural bond orbital (NBO) analysis show that O-H center dot center dot center dot O bonds and the N-H center dot center dot center dot pi interactions are the most and least polar, respectively. H-1 NMR study reveals the inverse linear correlation between shielding constant and electron density in a solvent medium. HOMO-LUMO energy gap indicates higher stability for neutral and cationic forms of dopamine isomers in water and ethanol medium.MethodsWe have optimized all the structural forms of dopamine molecule using the Becke three hybrid exchange and Lee-Yang-Parr correlation functional with Grimme's dispersion correction, B3LYP-D3(BJ), and aug-cc-pVTZ basis set using the Gaussian16 software. Vibrational frequency analysis with no imaginary frequencies confirms the nature of global minima. The solvent studies (water and ethanol) were carried out using the SCRF keyword and the polarisable continuum model (PCM) of Miertus and Tomasi. NBO analysis and NMR studies were also performed for all conformers. Topology analysis was explored using the software Multiwfn.

Automated summary

This investigation explores the intramolecular interactions in different forms of dopamine molecules in gas and different solvent mediums. The interactions are found to be electrostatic in nature, and the stability of different forms is assessed using NBO analysis and HOMO-LUMO energy gap. The study also reveals the relationship between shielding constant and electron density in a solvent medium through H-1 NMR analysis.