UC Santa Barbara

The robust, versatile attachment of mussels in the intertidal zone has motivated a large effort to create adhesives, coatings and energy dispersive materials based on the design principles of these marine organisms. Much progress has been made, but these materials frequently run up against two challenges related to the promiscuous reactivity of the catechol moiety. The first is the inability of reductionist constructs to incorporate the chemical nuances which modulate and optimize the performance of catechols. The second is the great propensity of catechols to oxidize and oligomerize under relatively benign conditions. Addressing these challenges will allow broader control and enhanced performance of catecholic moieties in synthetic systems. Two different strategies were employed to address these challenges: modulating the chemical nature of catechols, and utilizing stimuli-responsive protection chemistries.

First, the effect of local environment on the adhesive, adsorptive, and metal binding behavior of catechols was investigated for both native proteins and synthetic polymeric analogues. The presence of charged cofunctionality is able to modulate the binding properties of catechols by tuning their proton affinity. This effect can be re-created by chemically modifying catechols to create electron-deficient analogues with greater acidity and a lower susceptibility to oxidation. A simple metal coordination crosslinked hydrogel model system and an interpenetrating network hydrogel were used to demonstrate that these analogues possessed clear advantages in the construction of mechanically active structures. Finally, photo-mediated patterning and deprotection strategies were used to exert spatiotemporal control over the reactivity of catechols. By selectively activating catechols, binding can be controlled and catechols protected from premature oxidation. Taken together, these strategies show that controlled catecholic reactivity can be achieved by fusing biological design principles with designed materials engineering. Furthermore, this work identifies the 3-hydroxy-4-pyridinone moiety as an especially promising functionality for metal coordination bonding in supramolecular materials.