**One Step Forward towards the Development of Eco-Friendly Antifouling Coatings: Immobilization of a Sulfated Marine-Inspired Compound**

**Cátia Vilas-Boas 1,2, Francisca Carvalhal 1,2, Beatriz Pereira 3, Sílvia Carvalho 4, Emília Sousa 1,2, Madalena M. M. Pinto 1,2, Maria José Calhorda 3, Vitor Vasconcelos 2,5, Joana R. Almeida 2, Elisabete R. Silva 3,\* and Marta Correia-da-Silva 1,2,\***


Received: 18 August 2020; Accepted: 23 September 2020; Published: 25 September 2020

**Abstract:** Marine biofouling represents a global economic and ecological challenge and few eco-friendly antifouling agents are available. The aim of this work was to establish the proof of concept that a recently synthesized nature-inspired compound (gallic acid persulfate, GAP) can act as an eco-friendly and effective antifoulant when immobilized in coatings through a non-release strategy, promoting a long-lasting antifouling effect. The synthesis of GAP was optimized to provide quantitative yields. GAP water solubility was assessed, showing values higher than 1000 mg/mL. GAP was found to be stable in sterilized natural seawater with a half-life (DT50) of 7 months. GAP was immobilized into several commercial coatings, exhibiting high compatibility with different polymeric matrices. Leaching assays of polydimethylsiloxane and polyurethane-based marine coatings containing GAP confirmed that the chemical immobilization of GAP was successful, since releases up to fivefold lower than the conventional releasing systems of polyurethane-based marine coatings were observed. Furthermore, coatings containing immobilized GAP exhibited the most auspicious anti-settlement effect against *Mytilus galloprovincialis* larvae for the maximum exposure period (40 h) in laboratory trials. Overall, GAP promises to be an agen<sup>t</sup> capable of improving the antifouling activity of several commercial marine coatings with desirable environmental properties.

**Keywords:** biofouling; marine coatings; anti-settlement; chemical synthesis; sulfated; gallic acid; eco-friendly
