Conformational Study and Vibrational Spectroscopic (FT-IR and FT-Raman) Analysis of an Alkaloid-Borreverine Derivative.

In the present work, structural and spectroscopic investigations were carried out on a borreverine derivative. Borreverine is a class of alkaloid as well a natural antimalarial drug extracted from Borreria verticillata. With the aim of finding possible conformers, a detailed conformational analysis of a borreverine derivative was conducted utilizing density functional theory employing the B3LYP/6-31G(d,p) method. The crystallographic geometry was used for full geometry optimization, followed by a conformational analysis. The conformational investigation predicted the most stable conformer (conformer I), which was further compared with the initial crystallographic geometry (conformer V). The geometry optimization, vibrational frequency, and intensity of these two conformers (I and V) were calculated in the ground state using density functional theory with the B3LYP functional and 6-31G(d,p) basis set. The spectroscopic investigation was conducted using Fourier transform infrared (FT-IR) and Fourier transform Raman (FT-Raman) techniques. Tentative vibrational assignments of some selective modes were presented utilizing the observed FT-IR, FT-Raman, and calculated spectra. The scaled and observed wavenumbers were found to be in good agreement. The molecular electrostatic potential was computed and plotted so as to elucidate the reactive sites of the molecule. Natural bond orbital studies were performed to investigate the intramolecular charge transfer that results in molecular stability.