Sustainable UV filters production through laccase assisted oxidative polymerization

Sunscreens are used to absorb, reflect, or scatter UV radiation preventing and reducing the negative effects of UV light, such as, sunburns and precancerous lesions. Organic UV filters, currently used as photoprotective ingredients in sun-cream and cosmetic formulations, have been associated with negative impacts on marine ecosystems. These compounds pollute the coastal waters, directly as a consequence of washing off from swimmers and indirectly from contaminated effluents, where induce coral bleaching and bioaccumulate in marine biota impairing growth and reproduction.

In recent years, the concern about marine environmental impact of UV filters has increased the demand for more sustainable sunscreens. The OXIPRO project aims to establish the enzymatic synthesis of melanin-like polymers as a green alternative to chemical UV filters. Melanin, a family of heterogeneous polymeric pigments present in all life forms, are able to absorb UV radiation and scavenge active oxygen species, thereby reducing the UV damage associated to sun exposure. In animals, the melanin biosynthetic pathway is based on the enzymatic oxidation and polymerization of tyrosine.

In the present work, within the OXIPRO project, we focus on the use of laccases due to their ability to catalyse oxidative polymerizations. Moreover, these enzymes can be used in combination with redox mediators to achieve the oxidation of larger substrates which otherwise cannot enter the laccase active site. In this context, two strategies have been carried out i) the oxidative polymerization of phenolic building blocks, to mimic the melanin biosynthetic pathway and ii) laccase-assisted phenolation of lignin, where this phenolic biopolymer acts as a starting scaffold that is functionalized with phenolic molecules to increase its UV absorbing properties. In both strategies natural-derived phenolic compounds such as, L-DOPA, ferulic acid and octyl ferulate are oxidized by laccase (+ mediator) to trigger crosslinking reactions between them or the lignin, when present. The resulting phenolic polymers will represent not only an environmentally safe UV-filter for sunscreens but also a bio-based alternative to the currently used petroleum-based photoprotective compounds.