Proof of Concept of Natural and Synthetic Antifouling Agents in Coatings.

Marine biofouling, caused by the deposition and accumulation of marine organisms on submerged surfaces, represents a huge concern for the maritime industries and also contributes to environmental pollution and health concerns. The most effective way to prevent this phenomenon is the use of biocide-based coatings which have proven to cause serious damage to marine ecosystems. Several research groups have focused on the search for new environmentally friendly antifoulants, including marine and terrestrial natural products and synthetic analogues. Some of these compounds have been incorporated into marine coatings and display interesting antifouling activities caused by the interference with the biofilm-forming species as well as by the inhibition of the settlement of macroorganisms. This review highlights the proof-of-concept studies of emerging natural or synthetic antifouling compounds in coatings, from lab-made to commercial ones, performed between 2019 and 2023 and their results in the field or in in vivo laboratorial tests.

The Role of Natural and Synthetic Flavonoids in the Prevention of Marine Biofouling.

Marine biofouling is a major concern for the maritime industry, environment, and human health. Biocides which are currently used in marine coatings to prevent this phenomenon are toxic to the marine environment, and therefore a search for antifoulants with environmentally safe properties is needed. A large number of scientific papers have been published showing natural and synthetic compounds with potential to prevent the attachment of macro- and microfouling marine organisms on submerged surfaces. Flavonoids are a class of compounds which are highly present in nature, including in marine organisms, and have been found in a wide range of biological activities. Some natural and synthetic flavonoids have been evaluated over the last few years for their potential to prevent the settlement and/or the growth of marine organisms on submerged structures, thereby preventing marine biofouling. This review compiles, for the first-time, natural flavonoids as well as their synthetic analogues with attributed antifouling activity against macrofouling and microfouling marine organisms.

Chalcone derivatives as promising antifoulants: Molecular optimization, bioactivity evaluation and performance in coatings.

Marine biofouling remains a huge concern for maritime industries and for environmental health. Although the current biocide-based antifouling coatings can prevent marine biofouling, their use has been associated with toxicity for the marine environment, being urgent to find sustainable alternatives. Previously, our research group has identified a prenylated chalcone (1) with promising antifouling activity against the settlement of larvae of the macrofouling species Mytilus galloprovincialis (EC50 = 16.48 µM and LC50 > 200 µM) and lower ecotoxicity when compared to Econea®, a commercial antifouling agent in use. Herein, a series of chalcone 1 analogues were designed and synthesized in order to obtain optimized antifouling compounds with improved potency while maintaining low ecotoxicity. Compounds 8, 15, 24, and 27 showed promising antifouling activity against the settlement of M. galloprovincialis larvae, being dihydrochalcone 27 the most potent. The effect of compound 24 was associated with the inhibition of acetylcholinesterase activity. Among the synthesized compounds, compound 24 also showed potent complementary activity against Navicula sp. (EC50 = 4.86 µM), similarly to the lead chalcone 1 (EC50 = 6.75 µM). Regarding the structure-activity relationship, the overall results demonstrate that the substitution of the chalcone of the lead compound 1 by a dihydrochalcone scaffold resulted in an optimized potency against the settlement of mussel larvae. Marine polyurethane (PU)-based coatings containing the best performed compound concerning anti-settlement activity (dihydrochalcone 27) were prepared, and mussel larvae adherence was reduced compared to control PU coatings.

Gallic acid derivatives as inhibitors of mussel (Mytilus galloprovincialis) larval settlement: Lead optimization, biological evaluation and use in antifouling coatings.

The addition of biocides to marine coatings has been the most used solution to avoid marine biofouling, however they are persistent, bioaccumulative, and toxic (PBT) to marine ecosystems. The development of natural products or Nature-inspired synthetic compounds to replace these harmfull biocides has been pursued as one of the most promising antifouling (AF) alternatives. Following a bioprospection strategy, we have previously reported the AF activity of gallic acid persulfate (1) against the settlement of Mytilus galloprovincialis larvae (EC50 = 18 µM and LC50/EC50 = 27) without exhibiting ecotoxicity to Artemia salina. In this work, a lead optimization strategy was applied to compound 1 in order to improve potency while maintaining a low ecotoxicity profile. In this direction, twenty-seven compounds were synthesized, from which eighteen were obtained for the first time. An AF screening was performed against the settlement of mussel M. galloprovincialis larvae and derivative 26, 2-(3,4,5-trihydroxybenzamido)ethan-1-aminium bromide, was found to be more potent (EC50 = 3 µM and LC50/EC50 = 73) than compound 1 and the biocide Econea® (EC50 = 4 µM). The potential impact on neurotransmission, and ecotoxicity against two non-target marine organisms was also evaluated. Marine polyurethane (PU)-based coatings containing compound 26 were prepared and lower adherence of mussel larvae was observed compared to compound 26 free PU-coatings. Studies concerning the leaching of compound 26 from the prepared coating were also conducted, and < 10% of this compound was detected after 45 days of submersion in water. Overall, we have optimized the potency against the settlement of mussels of our initial lead compound, not compromising the toxicity and compatibility with PU-based coatings.

Impact of changing gloves during cesarean section on postoperative infective complications: A systematic review and meta-analysis.

INTRODUCTION: The cesarean section rate around the world, currently estimated at 21.1%, continues to increase. Women who undergo a cesarean section sustain a seven- to ten-fold greater risk of infective morbidity compared with those who deliver vaginally. MATERIAL AND METHODS: We aimed to assess the impact of changing gloves intraoperatively on post-cesarean section infective morbidity (PROSPERO CRD42018110529). MEDLINE, Scopus, Web of Science, CINAHL, WHO Global Index Medicus, and Cochrane Central were searched for randomized controlled trials until June 2020. Published randomized controlled trials that evaluated the effects of glove changing during cesarean section on infective complications were considered eligible for the review. Two reviewers independently selected studies, assessed the risk of bias, and extracted data about interventions and adverse maternal outcomes. Dichotomous variables were presented and included in the meta-analyses as risk ratios (RR) with 95% confidence intervals (CI). The quality of evidence was assessed using the GRADE approach in alignment with the recommendations from the Cochrane Review Group. RESULTS: We identified seven randomized controlled trials reporting data over 1948 women. Changing gloves during a cesarean section was associated with a statistically significantly lower incidence of wound infective complications (RR 0.41, 95% CI 0.26-0.65, p < 0.0001; GRADE moderate quality evidence). This intervention seemed to be effective only if performed after delivery of the placenta. No significant difference was seen in the incidence of endometritis (RR 0.96, 95% CI 0.78-1.20, p = 0.74; GRADE moderate quality evidence) and/or febrile morbidity (RR 0.73, 95% CI 0.30-1.81, p = 0.50; GRADE moderate quality evidence), regardless of the timing of the intervention. CONCLUSIONS: Changing gloves after delivery of the placenta during a cesarean section is associated with a significant reduction in the incidence of post-surgical wound complications compared with keeping the same gloves throughout the whole surgery. However, an adequately powered study to assess the limitations and cost-effectiveness of the intervention is needed before this recommendation can be translated into current clinical practice.

Natural Benzo/Acetophenones as Leads for New Synthetic Acetophenone Hybrids Containing a 1,2,3-Triazole Ring as Potential Antifouling Agents.

Marine biofouling is a natural process that represents major economic, environmental, and health concerns. Some booster biocides have been used in biofouling control, however, they were found to accumulate in environmental compartments, showing negative effects on marine organisms. Therefore, it is urgent to develop new eco-friendly alternatives. Phenyl ketones, such as benzophenones and acetophenones, have been described as modulators of several biological activities, including antifouling activity (AF). In this work, acetophenones were combined with other chemical substrates through a 1,2,3-triazole ring, a strategy commonly used in Medicinal Chemistry. In our approach, a library of 14 new acetophenone-triazole hybrids was obtained through the copper(I)-catalyzed alkyne-azide cycloaddition "click" reaction. All of the synthesized compounds were evaluated against the settlement of a representative macrofouling species, Mytilus galloprovincialis, as well as on biofilm-forming marine microorganisms, including bacteria and fungi. The growth of the microalgae Navicula sp. was also evaluated after exposure to the most promising compounds. While compounds 6a, 7a, and 9a caused significant inhibition of the settlement of mussel larvae, compounds 3b, 4b, and 7b were able to inhibit Roseobacter litoralis bacterial biofilm growth. Interestingly, acetophenone 7a displayed activity against both mussel larvae and the microalgae Navicula sp., suggesting a complementary action of this compound against macro- and microfouling species. The most potent compounds (6a, 7a, and 9a) also showed to be less toxic to the non-target species Artemia salina than the biocide Econea®. Regarding both AF potency and ecotoxicity activity evaluation, acetophenones 7a and 9a were put forward in this work as promising eco-friendly AF agents.

From Natural Xanthones to Synthetic C-1 Aminated 3,4-Dioxygenated Xanthones as Optimized Antifouling Agents.

Biofouling, which occurs when certain marine species attach and accumulate in artificial submerged structures, represents a serious economic and environmental issue worldwide. The discovery of new non-toxic and eco-friendly antifouling systems to control or prevent biofouling is, therefore, a practical and urgent need. In this work, the antifouling activity of a series of 24 xanthones, with chemical similarities to natural products, was exploited. Nine (1, 2, 4, 6, 8, 16, 19, 21, and 23) of the tested xanthones presented highly significant anti-settlement responses at 50 µM against the settlement of mussel Mytilus galloprovincialis larvae and low toxicity to this macrofouling species. Xanthones 21 and 23 emerged as the most effective larval settlement inhibitors (EC50 = 7.28 and 3.57 µM, respectively). Additionally, xanthone 23 exhibited a therapeutic ratio (LC50/EC50) > 15, as required by the US Navy program attesting its suitability as natural antifouling agents. From the nine tested xanthones, none of the compounds were found to significantly inhibit the growth of the marine biofilm-forming bacterial strains tested. Xanthones 4, 6, 8, 16, 19, 21, and 23 were found to be non-toxic to the marine non-target species Artemia salina (<10% mortality at 50 µM). Insights on the antifouling mode of action of the hit xanthones 21 and 23 suggest that these two compounds affected similar molecular targets and cellular processes in mussel larvae, including that related to mussel adhesion capacity. This work exposes for the first time the relevance of C-1 aminated xanthones with a 3,4-dioxygenated pattern of substitution as new non-toxic products to prevent marine biofouling.

Multidimensional characterization of a new antifouling xanthone: Structure-activity relationship, environmental compatibility, and immobilization in marine coatings.

The accumulation of marine biofouling on ship hulls causes material damage, the spread of invasive species, and, indirectly, an increase in full consumption and subsequent pollutant gas emissions. Most efficient antifouling (AF) strategies rely on the conventional release of persistent, bioaccumulative, and toxic biocides incorporated in marine coatings. A simple oxygenated xanthone, 3,4-dihydroxyxanthone (1), was previously reported as a promising AF agent toward the settlement of Mytilus galloprovincialis larvae, with a therapeutic ratio higher than the commercial biocide Econea®. In this work, a structure-AF activity relationship study, an evaluation of environmental fate, and an AF efficiency in marine coatings were performed with compound 1. Hydroxy or methoxy groups at 3 and 4 positions in compound 1 favored AF activity, and groups with higher steric hindrances were detrimental. Compound 1 demonstrated low water-solubility and a short half-life in natural seawater, contrary to Econea®. In silico environmental fate predictions showed that compound 1 does not bioaccumulate in organism tissues, in contrast to other current emerging biocides, has a moderate affinity for sediments and slow migrates to ground water. No toxicity was observed against Vibrio fischeri and Phaeodactylum tricornutum. Polyurethane-based marine coatings containing compound 1 prepared through an innovative non-release-strategy were as efficient as those containing Econea® with low releases to water after 45 days. This proof-of-concept helped to establish compound 1 as a promising eco-friendly AF agent.

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

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 agent capable of improving the antifouling activity of several commercial marine coatings with desirable environmental properties.

Flavonoid Glycosides with a Triazole Moiety for Marine Antifouling Applications: Synthesis and Biological Activity Evaluation.

Over the last decades, antifouling coatings containing biocidal compounds as active ingredients were used to prevent biofouling, and eco-friendly alternatives are needed. Previous research from our group showed that polymethoxylated chalcones and glycosylated flavones obtained by synthesis displayed antifouling activity with low toxicity. In this work, ten new polymethoxylated flavones and chalcones were synthesized for the first time, including eight with a triazole moiety. Eight known flavones and chalcones were also synthesized and tested in order to construct a quantitative structure-activity relationship (QSAR) model for these compounds. Three different antifouling profiles were found: three compounds (1b, 11a and 11b) exhibited anti-settlement activity against a macrofouling species (Mytilus galloprovincialis), two compounds (6a and 6b) exhibited inhibitory activity against the biofilm-forming marine bacteria Roseobacter litoralis and one compound (7b) exhibited activity against both mussel larvae and microalgae Navicula sp. Hydrogen bonding acceptor ability of the molecule was the most significant descriptor contributing positively to the mussel larvae anti-settlement activity and, in fact, the triazolyl glycosylated chalcone 7b was the most potent compound against this species. The most promising compounds were not toxic to Artemia salina, highlighting the importance of pursuing the development of new synthetic antifouling agents as an ecofriendly and sustainable alternative for the marine industry.

The Marine Seagrass Halophila stipulacea as a Source of Bioactive Metabolites against Obesity and Biofouling.

Marine organisms, including seagrasses, are important sources of biologically active molecules for the treatment of human diseases. In this study, organic extracts of the marine seagrass Halophila stipulacea obtained by different polarities from leaves (L) and stems (S) (hexane [HL, HS], ethyl acetate [EL, ES], and methanol [ML, MS]) were tested for different bioactivities. The screening comprehended the cytotoxicity activity against cancer cell lines grown as a monolayer culture or as multicellular spheroids (cancer), glucose uptake in cells (diabetes), reduction of lipid content in fatty acid-overloaded liver cells (steatosis), and lipid-reducing activity in zebrafish larvae (obesity), as well as the antifouling activity against marine bacteria (microfouling) and mussel larval settlement (macrofouling). HL, EL, HS, and ES extracts showed statistically significant cytotoxicity against cancer cell lines. The extracts did not have any significant effect on glucose uptake and on the reduction of lipids in liver cells. The EL and ML extracts reduced neutral lipid contents on the larvae of zebrafish with EC50 values of 2.2 µg/mL for EL and 1.2 µg/mL for ML. For the antifouling activity, the HS and ML extracts showed a significant inhibitory effect (p < 0.05) against the settlement of Mytilus galloprovincialis plantigrade larvae. The metabolite profiling using HR-LC-MS/MS and GNPS (The Global Natural Product Social Molecular Networking) analyses identified a variety of known primary and secondary metabolites in the extracts, along with some unreported molecules. Various compounds were detected with known activities on cancer (polyphenols: Luteolin, apeginin, matairesinol), on metabolic diseases (polyphenols: cirsimarin, spiraeoside, 2,4-dihydroxyheptadec-16-ynyl acetate; amino acids: N-acetyl-L-tyrosine), or on antifouling (fatty acids: 13-decosenamide; cinnamic acids: 3-hydroxy-4-methoxycinnamic acid, alpha-cyano-4-hydroxycinnamic), which could be, in part, responsible for the observed bioactivities. In summary, this study revealed that Halophila stipulacea is a rich source of metabolites with promising activities against obesity and biofouling and suggests that this seagrass could be useful for drug discovery in the future.

Antifouling Napyradiomycins from Marine-Derived Actinomycetes Streptomyces aculeolatus.

The undesired attachment of micro and macroorganisms on water-immersed surfaces, known as marine biofouling, results in severe prevention and maintenance costs (billions €/year) for aquaculture, shipping and other industries that rely on coastal and off-shore infrastructures. To date, there are no sustainable, cost-effective and environmentally safe solutions to address this challenging phenomenon. Therefore, we investigated the antifouling activity of napyradiomycin derivatives that were isolated from actinomycetes from ocean sediments collected off the Madeira Archipelago. Our results revealed that napyradiomycins inhibited ≥80% of the marine biofilm-forming bacteria assayed, as well as the settlement of Mytilus galloprovincialis larvae (EC50 < 5 µg/ml and LC50/EC50 >15), without viability impairment. In silico prediction of toxicity end points are of the same order of magnitude of standard approved drugs and biocides. Altogether, napyradiomycins disclosed bioactivity against marine micro and macrofouling organisms, and non-toxic effects towards the studied species, displaying potential to be used in the development of antifouling products.

Overcoming environmental problems of biocides: Synthetic bile acid derivatives as a sustainable alternative.

Marine biofouling represents a global economic and ecological challenge. Some marine organisms produce bioactive metabolites, such as steroids, that inhibit the settlement and growth of fouling organisms. The aim of this work was to explore bile acids as a new scaffold with antifouling (AF) activity by using chemical synthesis to produce a series of bile acid derivatives with optimized AF performance and understand their structure-activity relationships. Seven bile acid derivatives were successfully synthesized in moderate to high yields, and their structures were elucidated through spectroscopic methods. Their AF activities were tested against both macro- and microfouling communities. The most potent bile acid against the settlement of Mytilus galloprovincialis larvae was the methyl ester derivative of cholic acid (10), which showed an EC50 of 3.7 µM and an LC50/EC50 > 50 (LC50 > 200 µM) in AF effectiveness vs toxicity studies. Two derivatives of deoxycholic acid (5 and 7) potently inhibited the growth of biofilm-forming marine bacteria with EC50 values < 10 µM, and five bile acids (1, 5, and 7-9) potently inhibited the growth of diatoms, showing EC50 values between 3 and 10 µM. Promising AF profiles were achieved with some of the synthesized bile acids by combining antimacrofouling and antimicrofouling activities. Initial studies on the incorporation of one of these promising bile acid derivatives in polymeric coatings, such as a marine paint, demonstrated the ability of these compounds to generate coatings with antimacrofouling activity.

A Multi-Bioassay Integrated Approach to Assess the Antifouling Potential of the Cyanobacterial Metabolites Portoamides.

The cyclic peptides portoamides produced by the cyanobacterium Phormidium sp. LEGE 05292 were previously isolated and their ability to condition microcommunities by allelopathic effect was described. These interesting bioactive properties are, however, still underexplored as their biotechnological applications may be vast. This study aims to investigate the antifouling potential of portoamides, given that a challenge in the search for new environmentally friendly antifouling products is to find non-toxic natural alternatives with the ability to prevent colonization of different biofouling species, from bacteria to macroinvertebrates. A multi-bioassay approach was applied to assess portoamides antifouling properties, marine ecotoxicity and molecular mode of action. Results showed high effectiveness in the prevention of mussel larvae settlement (EC50 = 3.16 µM), and also bioactivity towards growth and biofilm disruption of marine biofouling bacterial strains, while not showing toxicity towards both target and non-target species. Antifouling molecular targets in mussel larvae include energy metabolism modifications (failure in proton-transporting ATPases activity), structural alterations of the gills and protein and gene regulatory mechanisms. Overall, portoamides reveal a broad-spectrum bioactivity towards diverse biofouling species, including a non-toxic and reversible effect towards mussel larvae, showing potential to be incorporated as an active ingredient in antifouling coatings.

Characterization of fungal communities in house dust samples collected from central Portugal-a preliminary survey.

House dust is a repository and concentrator of many chemical and biological agents including fungi. Considering that dust acts as a long-term reservoir of airborne fungi and that cumulative exposure is more relevant to potential health problems than single-day or short-term exposure, characterization of fungal communities in dust samples is of paramount importance. In the present study, the fungal composition of Portuguese house dust samples was determined. A total of 28 samples were obtained from vacuum cleaner deposits from households located in central Portugal. DNA was extracted from dust samples and fungal communities were analyzed using a culture-independent polymerase chain reaction (PCR)- denaturing gradient gel electrophoresis (DGGE) approach. Cultural analyses were also performed in order to identify the viable fungi species present in selected samples. Fungal diversity, reported as the number of operational taxonomic units (OTU), varied between 9 and 56 OTU. This analysis of viable fungi showed that Aspergillus was the most abundant genus, followed by Penicillium, Mucor, and Rhizomucor. Trichoderma, Chrysosporium, Fusarium, Rhizopus, and Stachybotrys were found in a limited number of houses. Our results demonstrated that dust is, in fact, home for a diverse and heterogeneous fungal community and that some of the species found are known allergic agents with severe negative impacts on human health.

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

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.

Linking behavioural alterations with biomarkers responses in the European seabass Dicentrarchus labrax L. exposed to the organophosphate pesticide fenitrothion.

The acute effects of the organophosphate insecticide fenitrothion on Dicentrarchus labrax juveniles were investigated through a bioassay using biomarkers and swimming behaviour as effect criteria. After 96 h of exposure to sub-lethal concentrations of fenitrothion, the swimming velocity and several biomarkers were individually determined, namely: brain acetylcholinesterase (AChE) activity; muscle cholinesterases (ChE), lactate dehydrogenase and isocitrate dehydrogenase activities; liver ethoxyresorufin-O-deethylase (EROD), glutathione S-transferases, glutathione peroxidase, glutathione reductase, catalase and superoxide dismutase (SOD) activities and lipid peroxidation levels (LPO). A significant decrease of the swimming velocity (LOEC = 2 mg l(-1)), an inhibition of both AChE (LOEC = 0.06 mg l(-1)) and ChE activities (LOEC = 0.03 mg l(-1)), and a positive and significant correlation between the swimming velocity and AChE were found in exposed fish, suggesting an influence of the inhibition of these enzymes in the swimming velocity decrease. An increase of EROD activity (LOEC = 1 mg l(-1)), indicating the involvement of this enzyme in fenitrothion biotransformation, and a negative and significant correlation between EROD activity and swimming velocity were also found, suggesting that the two findings may somehow be related. Furthermore, results show a significant induction of SOD (LOEC = 0.13 mg l(-1)) without LPO increase, suggesting that the enzyme is preventing oxidative stress damage. No significant alterations were found in any of the other parameters tested. Thus, exposure of seabass to fenitrothion in the wild at concentrations similar to those tested here may have adverse consequences at population level as neurotransmission and swimming ability are essential for fish performance and survival.

Structure-Antifouling Activity Relationship and Molecular Targets of Bio-Inspired(thio)xanthones.

The development of alternative ecological and effective antifouling technologies is still challenging. Synthesis of nature-inspired compounds has been exploited, given the potential to assure commercial supplies of potential ecofriendly antifouling agents. In this direction, the antifouling activity of a series of nineteen synthetic small molecules, with chemical similarities with natural products, were exploited in this work. Six (4, 5, 7, 10, 15 and 17) of the tested xanthones showed in vivo activity toward the settlement of Mytilus galloprovincialis larvae (EC50: 3.53-28.60 µM) and low toxicity to this macrofouling species (LC50 > 500 µM and LC50/EC50: 17.42-141.64), and two of them (7 and 10) showed no general marine ecotoxicity (<10% of Artemia salina mortality) after 48 h of exposure. Regarding the mechanism of action in mussel larvae, the best performance compounds 4 and 5 might be acting by the inhibition of acetylcholinesterase activity (in vitro and in silico studies), while 7 and 10 showed specific targets (proteomic studies) directly related with the mussel adhesive structure (byssal threads), given by the alterations in the expression of Mytilus collagen proteins (PreCols) and proximal thread proteins (TMPs). A quantitative structure-activity relationship (QSAR) model was built with predictive capacity to enable speeding the design of new potential active compounds.

Antifouling potential of Nature-inspired sulfated compounds.

Natural products with a sulfated scaffold have emerged as antifouling agents with low or nontoxic effects to the environment. In this study 13 sulfated polyphenols were synthesized and tested for antifouling potential using the anti-settlement activity of mussel (Mytilus galloprovincialis) plantigrade post-larvae and bacterial growth inhibition towards four biofilm-forming bacterial strains. Results show that some of these Nature-inspired compounds were bioactive, particularly rutin persulfate (2), 3,6-bis(ß-D-glucopyranosyl) xanthone persulfate (6), and gallic acid persulfate (12) against the settlement of plantigrades. The chemical precursors of sulfated compounds 2 and 12 were also tested for anti-settlement activity and it was possible to conclude that bioactivity is associated with sulfation. While compound 12 showed the most promising anti-settlement activity (EC50 = 8.95 µg.mL-1), compound 2 also caused the higher level of growth inhibition in bacteria Vibrio harveyi (EC20 = 12.5 µg.mL-1). All the three bioactive compounds 2, 6, and 12 were also found to be nontoxic to the non target species Artemia salina (<10% mortality at 250 µM) and Vibrio fischeri (LC50 > 1000 µg.mL-1). This study put forward the relevance of synthesizing non-natural sulfated small molecules to generate new nontoxic antifouling agents.

Natural antifouling compounds: Effectiveness in preventing invertebrate settlement and adhesion.

Biofouling represents a major economic issue regarding maritime industries and also raise important environmental concern. International legislation is restricting the use of biocidal-based antifouling (AF) coatings, and increasing efforts have been applied in the search for environmentally friendly AF agents. A wide diversity of natural AF compounds has been described for their ability to inhibit the settlement of macrofouling species. However poor information on the specific AF targets was available before the application of different molecular approaches both on invertebrate settlement strategies and bioadhesive characterization and also on the mechanistic effects of natural AF compounds. This review focuses on the relevant information about the main invertebrate macrofouler species settlement and bioadhesive mechanisms, which might help in the understanding of the reported effects, attributed to effective and non-toxic natural AF compounds towards this macrofouling species. It also aims to contribute to the elucidation of promising biotechnological strategies in the development of natural effective environmentally friendly AF paints.