Kojic acid

In this study, gold nanoparticles (AuNPs) were bio-fabricated using the water extract of marine brown seaweed Hizikia fusiformis (Hfs), commonly eaten as food in Southeast Asia, Korea, China, and Japan, and in other parts of the world. This process offers massive potential for the manufacture of new-generation nanomaterials utilizing sustainable seaweed components and explores its biological (tyrosinase, antidiabetic, antioxidant) and environmental (photocatalytic degradation of toxic industrial dyes) applications. Different spectroscopic approaches were employed to characterize and confirm the fabrication of Hfs-AuNPs. UV-Vis spectroscopy displayed the Hfs-AuNP's surface plasmon resonance at 534 nm. The XRD result revealed the crystalline nature of the nanoparticle. According to FT-IR analysis, various phytoconstituents like polyphenols and polysaccharides from the Hfs extract contributed to the reduction and stabilization of Hfs-AuNPs. Hfs-AuNPs displayed a spherical form with a zeta potential of -18.6 mV. Notably, Hfs-AuNPs exhibited encouraging tyrosinase inhibition (31.74 % inhibition while kojic acid showed 52.40 % inhibition at 100 µg/ml), antidiabetic effect (56.38 % α-amylase activity while acarbose exhibited 61.19 % activity at 100 µg/ml), and antioxidant properties (82.89 % of DPPH scavenging while 60.04 % scavenging by BHT and 63.73 SOD effect while 61.77 % scavenging by BHT at 100 µg/ml). Besides, Hfs-AuNPs also displayed positive photocatalytic degradation of toxic industrial dyes like methylene blue (29.20 % degradation at 5 h) and methyl orange (21.26 % degradation at 3 h). The above eco-friendly, cost-effective, and sustainable synthesis method can be explored further for large-scale production and future substantial applications in therapeutic and industrial needs.

Tyrosinase is the rate-limiting enzyme in enzymatic browning, and its activity is closely related to copper ions at the active site. We hypothesized that 1,2,4-oxadiazole derivatives could chelate copper ions at the active site of tyrosinase, thereby inhibiting its activity. Fourteen 1,3,4-oxadiazole-2-thiols were developed to evaluate Cu²⁺-chelating and anti-tyrosinase effects. Compound 2f (IC₅₀ = 17.7 ± 0.21 μM) had stronger activity than kojic acid (IC₅₀ = 47.7 ± 0.49 μM) as a mixed-type inhibitor. HPLC revealed that 2f inhibited dopaquinone formation, whereas UV/CD spectroscopy showed that 2f induced tyrosinase conformational changes. Fluorescence quenching, Cu²⁺ chelation, and molecular docking analyses confirmed the direct Cu²⁺-binding ability of 2f. In addition, 2f had low cytotoxicity and effectively prevented browning in fresh-cut potatoes. These results confirm our hypothesis that thiol-containing 1,3,4-oxadiazole derivatives inhibit tyrosinase for Cu²⁺ chelation and hydrophobic interactions. The results support their potential as safe, efficient anti-browning agents for fresh-cut produce preservation, addressing industry needs for practical enzymatic browning control.