  Purpose Study on curcumin dissolved in natural deep eutectic solvents (NADES)
was aimed at exploiting their beneficial properties as drug carriers. Methods
The concentration of dissolved curcumin in NADES was measured. Simulated
gastrointestinal fluids were used to determine the concentration of curcumin
and quantum chemistry computations were performed for clarifying the origin of
curcumin solubility enhancement in NADES. Results NADES comprising choline
chloride and glycerol had the highest potential for curcumin dissolution. This
system was also successfully applied as an extraction medium for obtaining
curcuminoids from natural sources, as well as an effective stabilizer
preventing curcumin degradation from sunlight. The solubility of curcumin in
simulated gastrointestinal fluids revealed that the significant increase of
bioavailability takes place in the small intestinal fluid. Conclusions
Suspension of curcumin in NADES offers beneficial properties of this new liquid
drug formulation starting from excreting from natural sources, through safe
storage and ending on the final administration route. Therefore, there is a
possibility of using a one-step process with this medium. The performed quantum
chemistry computations clearly indicated the origin of the enhanced solubility
of curcumin in NADES in the presence of intestinal fluids. Direct
intermolecular contacts leading to hetero-molecular pairs with choline chloride
and glycerol are responsible for elevating the bulk concentration of curcumin.
Choline chloride plays a dominant role in the system and the complexes formed
with curcumin are the most stable among all possible homo- and hetero-molecular
pairs that can be found in NADES-curcumin systems.
