A STUDY ON THE EFFECT OF SOLVENT PROPERTIES ON THE EXTRACTABILITY AND FUNCTIONALITY OF CARMINIC ACID

Abstract

Carminic acid, an anthraquinone, is the main component of cochineal dye, an intensely red substance obtained from the cochineal insect (Dactyloppius coccus Costa) grown on the prickly pear cactus (Nopalea and Opuntia). Carminic acid possesses antioxidant, antibiotic and antitumor properties. This study aimed to explore solvent microscopic environment effect on the bioactivity of carminic acid. The absorption and fluorescence emission spectra of carminic acid were recorded at 25 °C. The effects of methanol, acetone, benzene, acetic acid, diethyl ether, 2-propanol, 1-butanol, dimethylsulfoxide (DMSO), hexane, acetonitrile, chloroform, ethanol and distilled water on carminic acid’s electrooptical properties were studied. These solvents were selected to cover a good range of characteristics including refractive index, polarizability, hydrogen bonding capacity and microscopic polarity. The spectral transitions were assigned and analysed to identify the solute-solvent interaction mechanisms using the quantum approach of computational biochemistry. A net bathochromic shift in the absorption spectra was observed and traced to the phenomenon of prototropic tautomerism. Carminic acid’s red shift was found to increase primarily by the influence of rising hydrogen bond acidity of its microscopic environment. Solvents with higher dipolarisability induced a n-Π* electronic transition, indicated by a blue shift effect. Kamlet-Taft analysis was used to determine that the maximum absorption of carminic acid in gas phase was 271nm. Acetic acid and ethanol showed the greatest effects on the qualitative electrooptical properties of carminic acid with a 2.69% blue shift and a 1.422% red shift, respectively. Distilled water exhibited the least effect on this characteristic with a blue shift of 0.03%. It was determined that the 3’, 5‘, 6’, 8’-Hydroxyl and 7’-glycopyranosyl groups are the main solubilizing agents on the vii carminic acid molecule while 9’, 10’-keto and 2’-carboxylic groups are the main loci of blue-red qualitative electrooptical transformations. Acetic acid stabilised the highest ratios of bioefficient carminic acid tautomers. The dipole moments of the excited states were observed to be higher than those of the ground state using Lippert’s, Bakhshiev’s and Chamma-Viallet’s equations, inferring a substantial redistribution of Π-electron densities of carminic acid. Exciton splitting theory demonstrated that carminic acid aggregates lost their molecular compaction with increasing solvent microscopic polarity. However, 1- butanol and 2-propanol exhibited low molecular distance values suggesting that factors other than solvent polarity influences aggregation in these systems. The combined consideration of results present acetic acid as the prime solvent for the optimization of the bioefficient tautomer ratio of the anthraquinone while distilled water had potential for its optimal solubilisation.