A matrine-based supramolecular ionic salt that enhances the water solubility, transdermal delivery, and bioactivity of salicylic acid

Salicylic acid (H[Sal]) is an attractive bionic acid that is widely used in cosmetics and drugs for the treatment of skin diseases, owing to its excellent anti-acne, anti-inflammatory, antibacterial, oil-control, stratum-corneum-conditioning, and anti-photoaging abilities. However, H[Sal] is a relatively strong irritant and cannot be used on sensitive skin, and its poor water solubility limits the amounts that can be included in formulas, resulting in poor transdermal efficiency and bioavailability. In this study, we develop matrinium salicylate ([Mat][Sal]), a supramolecular ionic salt that is less cytotoxic and irritates the skin less than H[Sal], while exhibiting enhanced water-solubility, transdermal-delivery, and bioactivity properties. The anticancer, antioxidant, anti-inflammatory, and antibacterial properties of [Mat][Sal] are found to be superior or comparable to those of H[Sal]. The molecular structure of [Mat][Sal] is thoroughly investigated, including through single-crystal structure refinement, to gain an in-depth understanding of its properties. Moreover, in-vitro skin penetration experiments show that forming a salt with matrine increase the transdermal efficiency of H[Sal] while not damaging the skin barrier. The transdermal mechanisms of H[Sal] and [Mat][Sal] are studied both experimentally and using molecular dynamics simulations, which show that, compared to H[Sal], [Mat][Sal] reacts more strongly with the skin, and [Sal] − diffuses more rapidly in the skin owing to its higher water solubility and the ion-pair effect. Furthermore, [Mat][Sal] exhibits satisfactory anti-acne capabilities in a clinical-efficacy trial, highlighting its great potential for use in biomedical and cosmetics applications.