Marine mussels secrete proteins rich in residues containing catechols and cationic amines that displace hydration layers and adhere to charged surfaces under water via a cooperative binding effect known as catechol-cation synergy. Mussel-inspired adhesives containing paired catechol and cationic functionalities are a promising class of materials for biomedical applications, but few studies address the molecular adhesion mechanism(s) of these materials. To determine whether intramolecular adjacency of these functionalities is necessary for robust adhesion, a suite of siderophore analog surface primers was synthesized with systematic variations in intramolecular spacing between catechol and cationic functionalities. Adhesion measurements conducted with a surface forces apparatus (SFA) allow adhesive failure to be distinguished from cohesive failure and show that the failure mode depends critically on the siderophore analog adsorption density. The adhesion of these molecules to muscovite mica in an aqueous electrolyte solution demonstrates that direct intramolecular adjacency of catechol and cationic functionalities is not necessary for synergistic binding. However, we show that increasing the catechol-cation spacing by incorporating nonbinding domains results in decreased adhesion, which we attribute to a decrease in the density of catechol functionalities. A mechanism for catechol-cation synergy is proposed based on electrostatically driven adsorption and subsequent binding of catechol functionalities. This work should guide the design of new adhesives for binding to charged surfaces in saline environments.

Prodiginines, tripyrrole alkaloids displaying a wide array of bioactivities, occur as linear and cyclic congeners. Identification of an unclustered biosynthetic gene led to the discovery of the enzyme responsible for catalyzing the regiospecific C–H activation and cyclization of prodigiosin to form cycloprodigiosin in Pseudoalteromonas rubra. This enzyme is closely related to alkylglycerol monooxygenase, and unrelated to RedG, the Rieske oxygenase that produces cyclized prodiginines in Streptomyces, implying convergent evolution.

Synthesis and genome mining leverage access to diastereomers of the siderophore cyclic trichrysobactin. Computational modeling and CD spectroscopy address effects that ligand-based stereochemistry exerts on the configuration at Fe(iii).

The Gram-negative bacterium Yersinia ruckeri is the causative agent for enteric red mouth disease in salmonids. The genome of Y. ruckeri YRB contains a biosynthetic gene cluster encoding the biosynthesis of catechol siderophores that are diastereomeric with the known vanchrobactin class of siderophores, (DHB D Arg L Ser) (1−3) . Ruckerbactin (1), produced by Y. ruckeri YRB, was found to be the linear tris-L-serine ester composed of L-arginine and 2,3-dihydroxybenzoic acid, (DHB L Arg L Ser) 3 . The biscatechol, (DHB L Arg L Ser) 2 (2), and monocatechol, DHB L Arg L Ser (3), compounds were also isolated and characterized. The macrolactone of ruckerbactin was not detected. The presence of L Arg in ruckerbactin makes it the diastereomer of trivanchrobactin with D Arg. The electronic circular dichroism spectra of Fe(III)− ruckerbactin and Fe(III)−trivanchrobactin reveal the opposite enantiomeric configurations at the Fe(III) sites. Fe(III)− ruckerbactin adopts the Δ configuration, and Fe(III)−trivanchrobactin adopts the Λ configuration. Y. ruckeri YRB was also found to produce the antimicrobial agent holomycin (4).

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