Water-soluble caffeic acid-dopamine acid-base complex exhibits enhanced bactericidal, antioxidant, and anticancer properties

Despite the highly potent biological characteristics, the poor water-solubility of caffeic acid (CA) limits its applications in various domains. Here, we present a facile approach, wherein CA has been treated with dopamine hydrochloride (Dopa.HCl) to obtain a water-soluble acid-base complex, which does not possess any covalent bond between the individual components and thus retains their nativity. Simple mixing of CA and Dopa.HCl did not provide water solubility to CA, but the complex became readily soluble in water when the mineral acid was scavenged using sodium bicarbonate. The obtained CA-Dopa complex had been characterized using FT-IR, 1H NMR, 13C NMR, 2D 1H-1H NOESY NMR, XPS, and DSC techniques. The complex was found to exhibit excellent bactericidal, antibiofilm, antioxidant, and anticancer properties in the physiologically relevant pH range of 5.5 to 7.5. The results have revealed the high potential of the simple acid-base complex of CA in diverse domains.