We report a method to form multifunctional polymer coatings through simple dip-coating of objects in an aqueous solution of dopamine. Inspired by the composition of adhesive proteins in mussels, we used dopamine self-polymerization to form thin, surface-adherent polydopamine films onto a wide range of inorganic and organic materials, including noble metals, oxides, polymers, semiconductors, and ceramics. Secondary reactions can be used to create a variety of ad-layers, including self-assembled monolayers through deposition of long-chain molecular building blocks, metal films by electroless metallization, and bioinert and bioactive surfaces via grafting of macromolecules.

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Mussel-Inspired Surface Chemistry for Multifunctional Coatings

The major strategies for designing surfaces that prevent fouling due to proteins, bacteria, and marine organisms are reviewed. Biofouling is of great concern in numerous applications ranging from biosensors to biomedical implants and devices, and from food packaging to industrial and marine equipment. The two major approaches to combat surface fouling are based on either preventing biofoulants from attaching or degrading them. One of the key strategies for imparting adhesion resistance involves the functionalization of surfaces with poly(ethylene glycol) (PEG) or oligo(ethylene glycol). Several alternatives to PEG-based coatings have also been designed over the past decade. While protein-resistant coatings may also resist bacterial attachment and subsequent biofilm formation, in order to overcome the fouling-mediated risk of bacterial infection it is highly desirable to design coatings that are bactericidal. Traditional techniques involve the design of coatings that release biocidal agents, including antibiotics, quaternary ammonium salts (QAS), and silver, into the surrounding aqueous environment. However, the emergence of antibiotic- and silver-resistant pathogenic strains has necessitated the development of alternative strategies. Therefore, other techniques based on the use of polycations, enzymes, nanomaterials, and photoactive agents are being investigated. With regard to marine antifouling coatings, restrictions on the use of biocide-releasing coatings have made the generation of nontoxic antifouling surfaces more important. While considerable progress has been made in the design of antifouling coatings, ongoing research in this area should result in the development of even better antifouling materials in the future.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/adma.201001215

Antifouling coatings: recent developments in the design of surfaces that prevent fouling by proteins, bacteria, and marine organisms.

https://www.zora.uzh.ch/id/eprint/44154/1/Rabe1.pdf

Understanding protein adsorption phenomena at solid surfaces

The attachment strategy based on catecholic chemistry has been arousing renewed interest since the work on polymerized catecholic amine (polydopamine) (Messersmith et al., Science, 2007, 318, 426) was published. Catechols and their derived compounds can self-assemble on various inorganic and organic materials, including noble metals, metals, metal oxides, mica, silica, ceramics and even polymers. It opens a new route to the modification of various substrates and the preparation of functional composite materials by simple chemistry. However, there is still not a full review so far about the attachment chemistry despite the dramatically increasing number of publications. This critical review describes the state-of-the-art research in the area: the design and synthesis of catecholic molecules, their adsorption mechanisms and the stability of assemblies in solution, and their applications etc. Some perspectives on future development are raised (195 references).

Bioinspired catecholic chemistry for surface modification.

Advances in the chemistry of tetrahydroquinolines.

Siderophores are natural iron chelators that have been evolutionarily selected to bind to Fe ions with very high binding constants. We utilize these unique properties to bind to metal oxide surfaces using a fragment of the cyanobacterial siderophore anachelin. The resulting poly(ethylene glycol) conjugate forms stable adlayers on TiO2 as has been shown by variable angle spectroscopic ellipsometry and X-ray photoelectron spectroscopy. Moreover, these coated surfaces are highly protein-resistant against the adsorption of full human serum.

Biomimetic Surface Modifications Based on the Cyanobacterial Iron Chelator Anachelin

The first biomimetic total synthesis of the iron chelator anachelin H isolated from the cyanobacterium Anabaena cylindrica is reported. A first generation approach delivered one enantiomeric series of the polyketide fragment. Comparison of the 1H NMR data suggested the relative configuration of this anachelin fragment. The relative and absolute configuration of anachelin H was then established by total synthesis. A second generation approach involved the enzymatic conversion of N,N-dimethyltyramine to the anachelin chromophore. It was demonstrated that the enzyme tyrosinase is activated by the product during this reaction, the anachelin chromophore can serve as a tyrosinase activator. Anachelin H was evaluated against a panel of eleven bacterial and fungal pathogens, and moderate antibiotic activity (32 microg/mL) against Moraxella catarrhalis was found.

Biomimetic total synthesis and antimicrobial evaluation of anachelin H.

Total Synthesis of Anachelin H

A postulated biogenesis forms the basis for a synthetic route to the natural product anachelin H. Key steps include a tellurium-mediated, oxidative aza annulation and a Claisen condensation under mild conditions. Experiments with a model substrate indicate that it is likely that a catechol oxidase-type enzyme is involved in the biosynthesis of the anachelin chromophore.

A biomimetic route to the peptide alkaloid anachelin.

The cyanobacterial metabolite anachelin, postulated to serve as a biological ligand to Fe (siderophore), is composed of a fascinating blend of polyketide, peptide, and alkaloid building blocks. In particular, the latter consists of a N,N-dimethyltetrahydroquinolinium fragment, of which the biosynthesis is unknown. To investigate the role of this permanently positive charged fragment, a synthesis of both the anachelin chromophore and its bis-nor derivative lacking the N,N-di-Me groups was developed starting from suitably protected nitro-DOPA in six and five steps, resp., and in 50-64% overall yield. Both compounds were then compared for their chemical behavior toward oxidation. It was found that the bis-nor-anachelin chromophore is readily oxidized in solution in the presence of air, with a clear dependence of the rate of oxidation on the pH value. In addition, we could demonstrate that the enzyme tyrosinase, postulated to serve as key catechol oxidase in the biosynthesis of anachelin, also oxidized the bis-nor-hydroquinonamine deriv. Last, Fe(III) was shown to be an effective oxidant for the bis-nor-anachelin chromophore, resulting in all cases in the corresponding aminoquinone. In stark contrast, the anachelin chromophore resisted oxidation under various conditions surveyed (i.e., mediated by air, by tyrosinase, and by Fe(III)). In particular, Fe(III) was readily complexed by the anachelin chromophore, and the resulting complexes were characterized. In conclusion, these experiments demonstrate that the bis-nor-anachelin chromophore is unlikely to serve as cyanobacterial ligand, due to its instability toward oxidation. Moreover, the permanent quaternary ammonium group in anachelin renders the alkaloid chromophore much more stable against oxidation and thus results in its use as ligand for Fe (III).

Yann Bethuel

Papers

Biomimetic Surface Modifications Based on the Cyanobacterial Iron Chelator Anachelin

Biomimetic total synthesis and antimicrobial evaluation of anachelin H.

Total Synthesis of Anachelin H

A biomimetic route to the peptide alkaloid anachelin.

Synthesis and evaluation of the bis-nor-anachelin chromophore as potential cyanobacterial ligand.