A Facile Route to Bio‐Inspired Supramolecular Oligo(Ethylene Glycol) Catecholates

Abstract

A particularly facile synthetic route to mussel‐inspired oligo(ethylene glycol) catecholates is described, yielding high purity materials with minimal purification. The oligocatecholates show remarkable thermal and rheological properties for their actual chain length, suggesting the operation of non‐covalent interactions between their l‐DOPA‐bearing chain ends. This end‐group effect is more pronounced in the shorter oligomers (M n of ethylene glycol chain of 200 and 400 Da), where the end‐group density is higher. Various surfaces (glass, stainless steel) are modified with the oligocatecholates, using a dip‐coating approach from dilute aqueous solutions. Water contact angle measurements and X‐ray photoelectron spectroscopy confirm the presence of a hydrophilic surface coating layer. The potential of these materials for application as antifouling coatings and viscosity modifiers is highlighted.

Recent Advances in Mussel-Inspired Synthetic Polymers as Marine Antifouling Coatings

“…For example, Lee et al [93] used p-nitrophenyl chloroformate to react with a pendant sec-OH group in their PEG backbone to produce a p-nitrophenyl ester and then couple with dopamine to yield a catechol side-chain. In our related previous work [75], we synthesised a range of oligomeric PEG-DOPAs (linear and trifunctional) by direct condensation reaction with l-DOPA [75,95] and studied their adsorption on various substrates by contact angle and XPS measurements, confirming the presence of a PEGylated surface and suggesting the occurrence of intermolecular interactions between the catechol-bearing end-groups. As the diversity of accessible/commercially available PEG variants continues to grow, further relevant modification and coupling chemistries will continue to appear (e.g., click-type chemistry using PEG-N 3 [94]).…”

“…Apart from hydrogen bonding with appropriate oxygen or nitrogen moieties which can contribute towards enhanced surface adhesion on glasses and other polar/hydrophilic substrates, catecholic hydroxyl groups have been suggested to engage in hydrogen bonding with another catechol-bearing molecule [74,75] and provide an alternative metal-free self-healing pathway [74]. Waite and Israelachvili and co-workers [74] have demonstrated this neatly in catechol-bearing methacrylate and methyl methacrylate polymers, in which the catechol hydroxyls were initially protected with triethylsilyl groups.…”

“…PEGs have been extensively utilised by the Messersmith group and others, and a range of catechol/L-DOPA modified PEGs have been reported [61,64,75,[89][90][91][92][93][94]. PEGs are highly versatile polymers in terms of available molecular weight ranges (from ethylene glycol and oligomers of a few repeat units to 10 6 Da molecular weights for poly(ethylene oxide), PEO, materials), morphology (linear, branched, star, dendritic and hyperbranched), functionality (mono-and bifunctional, tri-and tetra-functional, polyfunctional) and end-group chemistry (traditional hydroxyl-terminated; other terminal functionalities such as methoxy, amine, thiol, acrylate, carboxy; homofunctional or heterofunctional) and hence provide a platform of options in order to produce a plethora of catecholdecorated variants.…”

“…A number of further mussel-inspired PEG modification strategies and approaches have been reported [75,93,94], utilizing either chemistries on the hydroxyl end or pendant groups, or using PEGs modified with different functionalities and yielding various polymer morphologies and their corresponding coatings and gels. For example, Lee et al [93] used p-nitrophenyl chloroformate to react with a pendant sec-OH group in their PEG backbone to produce a p-nitrophenyl ester and then couple with dopamine to yield a catechol side-chain.…”

“…Post-synthesis mussel-inspired chemical modification of high polymers, either in the form of end-group chemistries (see paragraphs on PEGs [61,64,75,[89][90][91][92][93][94][96][97][98][99][100][101]) or via reactions to create catechol-bearing pendant groups (see paragraphs on chain-growth polymers [110][111][112] and step-growth polymer end-capping [115]), has been a very popular and successful approach to impart mussel-like adhesion or self-healing to known polymers with useful properties. Apart from the examples presented previously, mussel-inspired derivatives of various biopolymers [116] have attracted attention for their potential as multifunctional materials.…”