Therapeutic deep eutectic solvents based on natural product matrine and caprylic acid: Physical properties, cytotoxicity and formation of surfactant free microemulsion

Deep eutectic solvents (DESs), as a new type of green solvent, have drawn much attention in various fields. DESs constructed from active pharmaceutical ingredients (APIs), termed as therapeutic deep eutectic solvent (THEDES), have displayed great potential applications in pharmaceutic fields. In this work, a new type of THEDES based on matrine and caprylic acid was prepared. The physical properties like density, viscosity, and electric conductivity of THEDESs were measured at various matrine and caprylic acid ratios in the temperature range from 298.15 K to 333.15 K. Further analysis by Walden plot suggested the "poor ionic liquid" behavior of the THEDESs studied herein. Moreover, it has been shown that these THEDESs displayed slightly higher cytotoxicity than that of matrine. Moreover, surfactant free microemulsions (SFMEs) consisted of 1,2-propanediol (PG), isopropyl myristate (IPM) and THEDESs were constructed and characterized. It was further found that curcumin, a poorly soluble API, displayed much higher solubility and stability in this SFME as compared to these in commonly used solvents.