PH, Viscosity of Hydrophobic Based Natural Deep Eutectic Solvents and the Effect of Curcumin Solubility in it

Abstract

Turmeric contains curcumin as one of the active constituents, which gives yellow color and possesses lots of pharmacological actions. Even though curcumin has lots of pharmacological actions till now, it has not been approved as a medicine due to its low water solubility, permeability, and poor bioavailability. Deep eutectic solvent (DES) can be prepared by simply mixing two or more solid components, [among the two one is hydrogen bond donor (HBD) and another is hydrogen bond acceptor (HBA)] at a definite molar ratio where the solid components by self-association converted into a liquid at room temperature (RT). Natural deep eutectic solvents (NADES) are a specific subgroup of DES containing primary plant-based metabolites such as organic acids, alcohols, amino acids, or sugars. In this work, natural hydrophobic DESs were prepared with Camphor, Menthol, and Thymol. This was prepared from different ratios of Menthol:Thymol 1:1 to 1:5 and 1:1 to 5:1 (MT-DES); Camphor:Thymol 1:1 to 1:5 and 1:1 to 5:1 (CT-NADES); Camphor:Menthol 1:1 to 1:5 and 1:1 to 2:1 (CM-NADES). The pH and viscosity of prepared DESs were determined with the help of a digital pH meter and Brookfield viscometer. The solubility of curcumin in different NADESs was determined at room temperature (RT) to higher temperatures. The formation of different clear DES was obtained with slight heat. There was no difference in pH for the NADESs prepared without and with heat. Regarding the viscosity CM-DES (1:1) showed less viscosity when compared to other NADESs. The solubility of curcumin was found to be nearly double when it was dissolved in NADES for 1 hr at 35-40°C compared to 48 h stirring at 500 rotations per minute (rpm) at RT. Among different NADESs, curcumin solubility was found to be more in CM (1:1) ratio when compared to other NADESs.