Sulfated phenolic polymers as non-toxic antifouling agents

Nature -inspired highly sulfated bioactive polyphenols are recently emerging as antifouling agents with low or non-toxic effects to the environment representing a valuable alternative to the most used harmful biocides. In this frame, we report herein the preparation of sulfated derivatives of two phenolic polymers of tyrosol and gallic acid previously obtained via a convenient horseradish peroxidase/H2O2-catalyzed oxidation process. A mild sulfation procedure based on the use of sulfur trioxide triethylamine complex under microwave irradiation afforded the corresponding sulfated polymers OligoTyrS and OligoGallS in good yields (90-95 % w/w). Elemental analysis, FT-IR and MALDI-MS investigation provided evidence for an almost complete sulfation of the -OH groups. In line with a high degree of sulfation, OligoTyrS and OligoGallS exhibited lower antioxidant properties compared to the non -sulfated polymers as evaluated by the 2,2-diphenyl-1-picrylhydrazyl and ferric reducing/antioxidant power assays. In contrast to the non -sulfated polymers, OligoTyrS and OligoGallS showed a significant inhibitory effect against the settlement of mussel (Mytilus galloprovincialis) plantigrade without lethality effects and without affecting the selected biofilm-forming organisms like five marine bacteria and a diatom. Both sulfated polymers were also found to be non-toxic to the non -target species Artemia salina. The overall results presented herein put forward the potential of non -natural sulfated phenolic polymers as new nontoxic antifouling agents.