A SOLVATOCHROMIC STUDY OF KOLAVIRON: AN EXPERIMENTAL AND THEORETICAL APPROACH

Abstract

Kolaviron, a major bioflavonoid complex of Garcinia bioflavonoid 1 (GB1), Garcinia bioflavonoid 2 (GB2) and kolaflavanone, possesses hepatoprotective, antioxidant, antibacterial, antiviral, antifungal, antidiabetic, antiantherogenic and anticancer properties. The influence of non-specific and specific solute-solvent interactions on this potential drug candidate was studied using steady state spectroscopic techniques combined with quantumchemical modeling. The influence of microenvironment on the spectroscopic properties of the bioflavonoid is important for better understanding of kolaviron – solvent interactions in true biological systems. The steady state electronic absorption and emission spectral of this bioflavonoid were measured in fourteen solvents of different polarity and recorded at 25 °C. The organic solvents are: methanol, acetone, benzene, acetic acid, diethyl ether, 2- propanol, 1-butanol, dimethylsulfoxide (DMSO), hexane, acetonitrile, chloroform, toluene, acetone, ethanol and distilled water. The ground and the excited states dipole moments of the bioflavonoid were estimated from Lippert–Mataga, Bakhshiev, Kawski–Chamma– Viallet and Reichardt equations. The spectral data were analyzed by the Katritzky and Kamlet–Taft multi-parameter scales to understudy the electronic behavior of the drug candidate in different environments. Kolaviron gaseous phase was calculated at 293 nm and exhibited a bathochromic (red) shift in methanol, acetic acid, diethyl ether, 2-propanol, 1-butanol, dimethylsulfoxide (DMSO), acetonitrile, chloroform, ethanol and distilled water, showing π→π* electronic transition characteristics. Diethyl ether had the highest bathochromic effect of 2.81% while hexane caused an insignificant hypsochromic shift (0.0009%). Kamlet-Taft analysis revealed kolaviron qualitative spectra is a function of its microenvironment, solvents hydrogen bond acidity and dipolarisability. Solvents with vii hydrogen bond basicity created hypsochromic effect. This infered that kolaviron is a hydrogen bond acceptor bioflavonoid which uses its keto groups to achieve an excited state and uses it’s highly hydroxylated structure to form dipole interactions with its environment. 1-butanol has the highest stabilization effect on kolaviron-excited state to maximize its solute-solvent bio efficiency. The excited states of the bioflavonoid had higher dipole moment values than the ground states in all solvents used, a phenomenon associated with preferential stabilization of the excited state of the molecule with increasing solvent microscopic polarity. It was deduced that 1-butanol was the best solvent for the bioactivity of kolaviron for drug applications while ethanol and methanol showed the best solvation ability.