We report a photomediated disulfide cross-linking strategy for the generation of adaptable hydrogels from telechelic network precursors containing strained cyclic disulfides. Exploiting the intricate stereoelectronic properties of 1,2-dithiolanes arising from the unfavorable four-electron interaction in the disulfide scaffold, amphiphilic poly(ethylene glycol)-1,2-dithiolane conjugates formed free-standing adaptable hydrogels at 10 wt % polymer content upon disulfide photolysis under UV irradiation (λ max = 365 nm). Cross-linking was achieved in less than 10 min with tunable network moduli depending on irradiation time. Investigations into the gelation mechanism suggest the formation of free thiols during light exposure accounting for the dynamic nature of the gels. Furthermore, we successfully expanded this gelation strategy to green light (λ max = 515 nm) by employing the photosensitizer eosin Y, allowing for hydrogel formation open to air.

While certain ternary spinel oxides have been well-explored with colloidal nanochemistry, notably the ferrite spinel family, ternary manganese (Mn)-based spinel oxides have not been tamed. A key composition is cobalt (Co)-Mn oxide (CMO) spinel, Co x Mn3–x O4, that, despite exemplary performance in multiple electrochemical applications, has few reports in the colloidal literature. Of these reports, most show aggregated and polydisperse products. Here, we describe a synthetic method for small, colloidally stable CMO spinel nanocrystals with tunable composition and low dispersity. By reacting 2+ metal-acetylacetonate (M­(acac)2) precursors in an amine solvent under an oxidizing environment, we developed a pathway that avoids the highly reducing conditions of typical colloidal synthesis reactions; these reducing conditions typically push the system toward a monoxide impurity phase. Through surface chemistry studies, we identify organic byproducts and their formation mechanism, enabling us to engineer the surface and obtain colloidally stable nanocrystals with low organic loading. We report a CMO/carbon composite with low organic contents that performs the oxygen reduction reaction (ORR) with a half-wave potential (E 1/2) of 0.87 V vs RHE in 1.0 M potassium hydroxide at 1600 rpm, rivaling previous reports for the highest activity of this material in ORR electrocatalysis. We extend the general applicability of this procedure to other Mn-based spinel nanocrystals such as Zn-Mn-O, Fe-Mn-O, Ni-Mn-O, and Cu-Mn-O. Finally, we show the scalability of this method by producing inorganic nanocrystals at the gram scale.

We report the one-step synthesis of diversely substituted functional 1,2-dithiolanes by reacting readily accessible 1,3-bis-tert-butyl thioethers with bromine.