Predicting properties of species derived from n-(1h-indol-3-ylmethyl)-n,n-dimethylamine, gramine, a indol alkaloid

Hybrid B3LYP/6-31G* calculations were employed to study the structural, electronic, topological and vibrational properties of free base, cationic and hydrochloride species of indol alkaloid, N-(1H-indol-3-ylmethyl)-N,N-dimethylamine known as gramine. The experimental available IR, Raman, 1H- and 13C-NMR spectra were compared with the corresponding predicted showing reasonable concordance among them. In solution, the properties were studies with the polarized continuum (PCM) and the universal solvation model. The cationic species of gramine presents a corrected solvation energy of -261.58 kJ/mol slightly higher than the corresponding to cocaine (-255.24 kJ/mol). NBO and AIM studies have evidenced higher stabilities for free base and hydrochloride species while the comparisons of N-CH3 distances obtained for three species of gramine with similar compounds have evidenced that the hydrochloride species of gramine in solution presents practically the same value than the corresponding species of heroin. The frontier orbitals studies suggest higher reactivities for the hydrochloride species in both media due to its low gap values while on the contrary are observed for the cationic species in both media. Furthermore, the cationic species of gramine shows global nucleophilicity and electrophilicity indexes closer to cocaine. Probably, these results could justify why the corrected solvation energy value observed for the cationic species is approximately closer to the value corresponding to cocaine. The harmonic force fields, force constants and the complete vibrational assignments for the 75, 78 and 81 normal vibration modes of free base, cationic and hydrochloride species are reported for first time.