Novel Palmatine Hydrochloride-Phenolic Acid Cocrystals: Effects of Different Phenolic Acids on Hygroscopicity Improvement and Antibacterial Activity Enhancement

Abstract

To address the problematic hygroscopicity of palmatine chloride (PCl), a pharmaceutically relevant alkaloid, three novel heteromolecular cocrystals of PCl with phenolic acids (ferulic acid [FA], vanillic acid [VA], syringic acid [SA]) were designed and synthesized via solvent evaporation combined with mechanochemical grinding. Our study revealed that different phenolic acids exert varying effects on the properties of the cocrystal active pharmaceutical ingredient (API). Single-crystal X-ray diffraction confirmed these cocrystals (PCl-FA, PCl-VA, PCl-SA) are stabilized by robust hydrogen-bonding networks, where chloride ions, water molecules, and phenolic acid conformers form fundamental motifs, assembling into 2D sheets via van der Waals interactions with palmatine cations constructing a 3D framework. Compared to pristine PCl, all cocrystals showed markedly improved hygroscopic stability, attributed to phenolic acids competitively occupying chloride coordination sites and reducing water binding affinity. Though aqueous solubility decreased moderately, antibacterial efficacy was significantly enhanced: 1.5–2.0-fold larger inhibition zones and 2–4-fold lower MICs against Escherichia coli, Staphylococcus aureus, and Bacillus subtilis than PCl or individual phenolic acids. These findings demonstrate phenolic acid - based cocrystallization as a viable strategy to modulate PCl’s physicochemical and biological properties. Given that palmatine hydrochloride is a natural compound, such results lay a foundation for exploring its potential in pharmaceutical - related material development through cocrystallization - mediated property optimization.