Elucidating the Reactivity and Mechanism of CO₂ Electroreduction at Highly Dispersed Cobalt Phthalocyanine

Transforming carbon dioxide to carbon monoxide with electrochemical methods allows for small-scale, modular conversion of point sources of carbon dioxide. In this work, through the preparation of a well-dispersed cobalt phthalocyanine model catalyst immobilized on carbon paper, we revealed high turnover frequencies for reducing carbon dioxide at low catalyst loadings, which are obscured at higher loadings due to aggregation. The low catalyst loadings have also enabled mechanistic studies that provide a detailed understanding of the molecular-level picture of how cobalt phthalocyanine facilitates proton and electron transfers in the rate-limiting step. We are able to tune the rate-limiting step from electron transfer to concerted proton–electron transfer, enabling higher rates of carbon dioxide reduction. Our results highlight the significance of dispersion for understanding the intrinsic catalytic performance of metal phthalocyanines for electroreduction of CO₂

Rapid Bioorthogonal Chemistry Turn-on through Enzymatic or Long Wavelength Photocatalytic Activation of Tetrazine Ligation

Rapid bioorthogonal reactivity can be induced by controllable, catalytic stimuli using air as the oxidant. Methylene blue (4 μM) irradiated with red light (660 nm) catalyzes the rapid oxidation of a dihydrotetrazine to a tetrazine thereby turning on reactivity toward <i>trans</i>-cyclooctene dienophiles. Alternately, the aerial oxidation of dihydrotetrazines can be efficiently catalyzed by nanomolar levels of horseradish peroxidase under peroxide-free conditions. Selection of dihydrotetrazine/tetrazine pairs of sufficient kinetic stability in aerobic aqueous solutions is key to the success of these approaches. In this work, polymer fibers carrying latent dihydrotetrazines were catalytically activated and covalently modified by <i>trans</i>-cyclooctene conjugates of small molecules, peptides, and proteins. In addition to visualization with fluorophores, fibers conjugated to a cell adhesive peptide exhibited a dramatically increased ability to mediate contact guidance of cells