Synthesis of water-soluble violacein nanoparticles and molecular dynamic study

Natural pigment violacein exhibits many pharmaceutical properties which include antimicrobial, anticancer and antioxidant activities. However, limited solubility of violacein in water has restricted its application. Hence, in this study, the violacein nanoparticles were synthesised via sonication technique with the aid of surfactants as dispersing and stabilising agent. Experimentally, the effect of surfactant and violacein concentrations on the production, size and stability of violacein nanoparticles was studied. The location of the violacein in the surfactant micelle was studied using computational study. Violacein nanoparticles were successfully produced at optimized parameters, surfactant concentration of 1 mM, concentration of violacein of 50 µg/mL and sonication time of 10 min. The smallest violacein nanoparticles were 131.5 ± 2.001 nm, with PDI of 0.180 ± 0.018, which indicated a monodispersed violacein nanoparticle distribution. The violacein nanoparticles were stable upon dispersion in water, with a zeta potential of − 49.8 ± 3.49 mV. Violacein was located in the hydrophobic tail region of SDS surfactant micelle after 92 ns. The violet colour of the nanoparticles was maintained at pH from 3 to 11, temperature up to 60 °C and under dark condition, despite its nanoscale size. Higher degradation rate was observed at high temperature and upon light illumination, with k = 6.51 × 10⁻³ h⁻¹, t_1/2 = 106 h and k = 6.75 × 10⁻⁴ h⁻¹, t_1/2 = 1027 h, respectively, following the first-order kinetics. As conclusion, the violacein nanoparticles were able to be produced using water as a medium for green approach, and the nanoparticle colour remained stable at various conditions. This study provides an insight into the molecular mechanism of violacein-surfactant interaction for its solubility and stability in water.