Stability, release, and tyrosinase inhibition behaviors of kojic acid encapsulated in the interlayer space of layered yttrium hydroxide

Kojic acid (KA) is widely utilized in cosmetic formulations for skin brightening and as a food preservative to prevent oxidative browning in fruits and vegetables. However, its effectiveness is compromised by susceptibility to pH and temperature fluctuations, as well as oxidation after exposure to UV light. These limitations highlight the need for improvements to facilitate sustainable applications. In this study, KA was encapsulated within the interlayer space of layered yttrium hydroxide (LYH) through a two-step host-guest reaction involving dodecylsulfate and basic ethoxide anions. Examination of the X-ray diffraction (XRD) pattern of the resulting product (KA-LYH) revealed an expanded interlayer space from approximately 8.4 to 16.7 Å, conducive to a partially interdigitated bilayer arrangement of KA anions within the LYH interlayer. KA-LYH demonstrated significantly improved stability against light, heat, and oxygen compared to free KA, indicating effective confinement and protection of KA from photoreaction and oxidation in the interlayer space of LYH host. Minimal release of KA was observed in saline solution and simulated seawater, while sustained release occurred in a phosphate buffer solution even after 24 h. Notably, the KA released from the LYH interlayer space retained potent tyrosinase inhibition activity, showcasing the sustainable efficacy of KA-LYH under physiological conditions.