3,4-Dioxygenated xanthones as antifouling additives for marine coatings: in silico studies, seawater solubility, degradability, leaching, and antifouling performance

Abstract

Marine biofouling pollution is a process that impacts ecosystems and the global economy. On the other hand, traditional antifouling (AF) marine coatings release persistent and toxic biocides that accumulate in sediments and aquatic organisms. To understand the putative impact on marine ecosystems of recently described and patented AF xanthones (xanthones 1 and 2), able to inhibit mussel settlement without acting as biocides, several in silico environmental fate predictions (bioaccumulation, biodegradation, and soil absorption) were calculated in this work. Subsequently, a degradation assay using treated seawater at different temperatures and light exposures was conducted for a period of 2 months to calculate their half-life (DT50). Xanthone 2 was found to be non-persistent (DT50 < 60 days) at 50 μM, contrary to xanthone 1 (DT50 > 60 days). To evaluate the efficacy of both xanthones as AF agents, they were blended into four polymeric-based coating systems: polyurethane- and polydimethylsiloxane (PDMS)-based marine paints, as well as room-temperature-vulcanizing PDMS- and acrylic-based coatings. Despite their low water solubility, xanthones 1 and 2 demonstrated suitable leaching behaviors after 45 days. Overall, the generated xanthone-based coatings were able to decrease the attachment of the Mytilus galloprovincialis larvae after 40 h. This proof-of-concept and environmental impact evaluation will contribute to the search for truly environmental-friendly AF alternatives.

Proof of Concept of Natural and Synthetic Antifouling Agents in Coatings

“…Nevertheless, it was found that, after 45 days of the leaching assays, xanthones 97 and 98 were leached from the PDMS-based marine coatings by approximately 17% and 25%, respectively, whereas the same compounds showed a leaching value lower than 2% from the PU-based coatings, as reported in subsection 3.2. These results may indicate a possible short time effect of these compounds in the PDMS coating [79].…”

“…and the evaluation of the anti-settlement activity against mussel M. galloprovincialis. The PU marine coating containing xanthone 97 was shown to be more effective against the settlement of the mussel larvae after 40 hours of incubation (10% larval settlement) than the control PU marine coating (35% larval settlement) [79]. As expected from the low water solubility, xanthone 97 presented a leaching value lower than 2%, after 45 days in artificial seawater, indicating the potential to generate long-lasting PU-based coatings.…”

“…Moreover, several nature-inspired xanthones obtained by synthesis, such as compounds 97 and 98 (Figure 5), showed effective activity in the inhibition of the settlement of M. galloprovincialis mussel larvae. Later, xanthones 97 and 98 were incorporated in the same commercial AV-based coating [79]. Xanthone 97 was previously dissolved in dichloromethane and further added and blended into the AV coating components in the exact amount to yield a 0.55% of xanthone 97 in the wet formulation system.…”

“…Xanthones 97 and 98 were also incorporated by the same group in PDMS (HEMPASIL X3+87500) and in a non-marine coating system RTV-PDMS [79]. Xanthone 97 was previously dissolved in dichloromethane to provide solutions with compound contents of 12.58 and 6.81 wt.%, which were further added and blended into PDMS and RTV-PDMS coating components, respectively, and in the exact amounts to yield the desired xanthone 97 contents of 0.52-0.53 wt.% in those wet formulation systems.…”

Research Progress of Natural Products and Their Derivatives in Marine Antifouling

“…Over the past decade, various AF agents have been developed, such as copper and copper compounds, zinc, Irgarol 1051 and Sea-Nine 211, since the use of triphenyltin (TBT) system AF coatings have been banned in the worldwide due to their environmental toxicity [ 6 , 7 , 8 ]. However, the release of metals from copper- and zinc-based AF coatings are also deleterious to marine organisms which are widely used in the industry [ 9 , 10 , 11 , 12 ]. Therefore, based on the adverse effects of excessive release of metal ions in the widely used AF coatings on the development of marine ecosystems, it is of great significance to develop environmentally friendly coatings with nontoxic AF agents.…”