Ecological implications of hypoxia-triggered shifts in secondary metabolism.

Members of the actinomycete genus Streptomyces are non-motile, filamentous bacteria that are well-known for the production of biomedically relevant secondary metabolites. While considered obligate aerobes, little is known about how these bacteria respond to periods of reduced oxygen availability in their natural habitats, which include soils and ocean sediments. Here, we provide evidence that the marine streptomycete strain CNQ-525 can reduce MnO2 via a diffusible mechanism. We investigated the effects of hypoxia on secondary metabolite production and observed a shift away from the antibiotic napyradiomycin towards 8-amino-flaviolin, an intermediate in the napyradiomycin biosynthetic pathway. We purified 8-amino-flaviolin and demonstrated that it is reversibly redox-active (midpoint potential -474.5 mV), indicating that it has the potential to function as an endogenous extracellular electron shuttle. This study provides evidence that environmentally triggered changes in secondary metabolite production may provide clues to the ecological functions of specific compounds, and that Gram-positive bacteria considered to be obligate aerobes may play previously unrecognized roles in biogeochemical cycling through mechanisms that include extracellular electron shuttling.

Paired Electrolysis in the Simultaneous Production of Synthetic Intermediates and Substrates.

In electrochemical processes, an oxidation half-reaction is always paired with a reduction half-reaction. Although systems for reactions such as the reduction of CO2 can be coupled to water oxidation to produce O2 at the anode, large-scale O2 production is of limited value. One may replace a low-value half-reaction with a compatible half-reaction that can produce a valuable chemical compound and operate at a lower potential. In doing so, both the anodic and cathodic half-reactions yield desirable products with a decreased energy demand. Here we demonstrate a paired electrolysis in the case of the oxidative condensation of syringaldehyde and o-phenylenediamine to give 2-(3,5-dimethoxy-4-hydroxyphenyl)benzimidazole coupled with the reduction of CO2 to CO mediated by molecular electrocatalysts. We also present general principles for evaluating current-voltage characteristics and power demands in paired electrolyzers.

Photochemical and photoelectrochemical reduction of CO2.

The recent literature on photochemical and photoelectrochemical reductions of CO(2) is reviewed. The different methods of achieving light absorption, electron-hole separation, and electrochemical reduction of CO(2) are considered. Energy gap matching for reduction of CO(2) to different products, including CO, formic acid, and methanol, is used to identify the most promising systems. Different approaches to lowering overpotentials and achieving high chemical selectivities by employing catalysts are described and compared.

A facile and patternable method for the surface modification of carbon nanotube forests using perfluoroarylazides.

A facile patterning method for the functionalization of vertically aligned carbon nanotubes is described. Modification of the surface of nanotube forests with hydrophilic, hydrophobic, or polymerizable small molecules was achieved via UV-triggered attachment of perfluoroarylazides. Multiple functionalizations of the tube surface can be achieved. Macro- and micropatterning of forest substrates were demonstrated. Superhydrophobic surfaces containing superhydrophilic regions were prepared.