STEADY STATE SPECTRA PROPERTIES OF RUBIADIN ISOLATED FROM MORINDA LUCIDA BENTH

Abstract

Rubiadin a dihydroxyantraquinone isolated from morinda lucida benth has antioxidant, antimalarial, antidiabetic, anticonvulsant, anxiolytic and anti-tumour activities but most obstacles faced in extraction of anthraquinione in pharmaceuticals and nutraceuticals are their low solubility and oral bioavailabilty Understanding this interaction of a molecule (especially drug molecule) with its microenvironment are very important in physics, biochemistry, biology, pharmacy and medicine. The stem barks were purchased at a local market and dried at room temperature. The stem barks of M. lucida (100 g) were macerated with agitation at room temperature for 72 hours and extraction was done successfully using rotary evaporation, the effect of various organic solvents on the solvation properties and antioxidant activities of rubiadin under physiological conditions was monitored using UV-Visible and steady state fluorescence spectroscopy. The radical scavenging ability was studied using the DPPH and ABTS assay method. Rubiadin has a highest scavenging activity in diethyl ether and lowest in distilled water. The steady-state absorption (250nm-450nm) and fluorescence spectral (400nm-750nm) of the compound in various solvents were analyzed using a multiparameter correlation equations based on solvatochromic measurements (proposed by Kamlet Taft approach). The results obtained indicate that both non-specific and specific solute-solvent interactions play roles in solvatochromism of rubiadin molecule. In the protic, aprotic and non-polar solvents the spectroscopic studies indicate also that the nature of the absorbing and emitting states are different. There was a positive/bathochromic shifts which indicated that the basic contributor to the bathochromic shift is the hydrogen bonding acidity of the solvents rather than the polarizability with increasing solvent polarity π-π* transition electronic transition due to the hydroxyl group of the rubiadin structure. The Calculated dipole moment of the excited state (Ue) which gave 2.68 x 10-22 Cm. It was 1.03 x 10-22 Cm at ground state (Ug). This indicated that rubiadin is more stable at the excited state than the ground state in the best solvent. The exciton splitting theory calculation als confirmed the result. In summary, diethyl ether and ethanol are the best solvatochromic solvents for rubiadin than water. The study affirmed that the interactions of a rubiadin with its micro environment is basically due to its electronic and optical properties,