Systematic Determination of Distribution Constants in Deep Eutectic Solvent–Organic Solvent Biphasic Systems: A Quantitative Database for the Rational Extraction of Bioactive Compounds

Abstract This work determines distribution constants (P) for 19 bioactive compounds (flavonoids, phenolic acids, alkaloids, and glycosides) in biphasic liquid–liquid systems. The systems comprise a deep eutectic solvent (DES) based on choline chloride with urea, malonic acid, or L-lactic acid as one phase, and ethyl acetate or 1-octanol as the organic phase. Measurements were performed at 25.0 ± 0.1 °C and ambient pressure using HPLC-UV analysis. Apparent distribution constants (logP) range from about −3.4 to +2.8, depending on DES composition, organic solvent, and solute hydrogen-bonding functionality. For most solutes, distribution constants are higher in ethyl acetate/DES than in 1-octanol/DES, with differences from less than 1 order of magnitude to over 2 orders of magnitude. Notable exceptions exist; for example, chlorogenic acid partitions less into ethyl acetate for certain DES compositions, and sinapic acid with ChCl–U gives a higher value in octanol. The P values, expressed on a molality basis, provide a quantitative thermodynamic basis for rational design of selective extraction processes, replacing empirical solvent screening with a predictive, data-driven approach. For quinic acid, ursolic acid, rutin, and apigenin, distribution constants could not be determined in some systems owing to low solubility or undetectable concentrations in one phase.