Investigation of solvent effects on the stability and 15N NMR shielding of hallucinogenic harmine using the PCM model and NBO interpretation

Abstract

Density functional theory (DFT) and Tomasi’s polarized continuum model (PCM) are applied for the investigation of the solvent structure and its dielectric constant effects on the relative stability and nuclear magnetic resonance (NMR) tensors of hallucinogenic harmine. All of the used computational methods indicate that the structural stability in protic polar solvents is higher than that in aprotic polar and nonpolar solvents, and the most stable structure was observed in methanol. Also, the natural bond orbital (NBO) interpretation demonstrates that with an increase in the solvent dielectric constant the resonance energy for LP(N9) → σ* and π* interactions of the strutural pyrrole ring increases while the LP (N9) occupancy decreases, and the highest resonance energy and the lowest occupancy are observed in water and methanol. On the other hand, NMR calculations show that there are the lowest values of Δσdir in water and methanol media for both nitrogen nuclei of the harmine structure.