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Nanocrystalline Pb films prepared by reducing PbO 2 precursors have up to 700-fold lower H + reduction activity than polycrystalline Pb foil electrodes but maintain the ability to reduce CO 2 . As a result, these "oxide-derived" Pb (OD−Pb) electrodes have higher Faradaic efficiency for CO 2 reduction to HCO 2 − in aqueous solutions with almost no competitive H + reduction. Even with very low CO 2 concentrations in N 2 -saturated NaHCO 3 solution, OD−Pb converts CO 2 derived from HCO 3 − decomposition to HCO 2 − with almost quantitative Faradaic efficiency while Pb foil has less than 10% efficiency. Electrokinetic data suggest that the difference in selectivity between the two electrodes is caused by a difference in the coverage of a surface layerlikely a metastable Pb oxidethat is passivating for H + reduction but active for CO 2 reduction. ■ INTRODUCTIONThe use of renewable electricity to power the conversion of CO 2 and H 2 O into valuable chemicals could reduce net CO 2 emissions. 1−5 The success of this strategy hinges on the development of efficient electroreduction catalysts that selectively and efficiently reduce CO 2 at high rates using H 2 O as a H + source. One of the fundamental challenges in catalyst development is to suppress H + reduction to H 2 without compromising CO 2 reduction. Most materials have a strong preference for H + reduction over CO 2 reduction in aqueous electrolytes unless extreme overpotentials are applied, which compromises energetic efficiency. 6 We have recently explored the use of metal oxides as catalyst precursors and metastable catalytic species to address the challenge of CO 2 versus H + reduction selectivity in aqueous electrolytes. In the case of Sn electrodes, we showed that CO 2 reduction requires metastable surface Sn oxides and that enhancing the oxide content of electrodes improves selectivity. 7 For Au and Cu electrodes, oxide layers are not stable under CO 2 reduction conditions. However, Au and Cu electrodes prepared by reducing Au oxide and Cu oxide precursors "oxide-derived" metalshave very different catalytic properties than bulk materials or nanoparticles. 8−11 Oxide-derived Cu (OD−Cu) and oxide-derived Au (OD−Au) are composed of thin films of interconnected nanocrystallites with 10−100 nm dimensions. In CO 2 reductions, these electrodes have higher selectivity for CO 2 reduction versus H 2 evolution at low overpotential compared to their bulk or nanoparticle counterparts. For OD−Au, this difference is the result of its higher specific (i.e., surface-area-normalized) activity for CO 2 reduction. 9 For OD−Cu, the difference is primarily the result of its lower specific H + reduction activity. 8 These studies demonstrate that the microstructure and morphology that result from metal oxide reduction alter the catalytic properties of these metals.This study examines the factors that control the selectivity for H + versus CO 2 reduction on Pb electrodes by comparing Pb foil to oxide-derived Pb (OD−Pb). Several previous studies have evaluated the CO 2 reduction pr...

A cobalt(II) hangman porphyrin with a xanthene backbone and a carboxylic acid hanging group catalyzes the electrochemical production of hydrogen from benzoic and tosic acid in acetonitrile solutions. We show that Co(II)H is exclusively involved in the generation of H(2) from weak acids. In a stronger acid, a Co(III)H species is observed electrochemically, but it still needs to be further reduced to Co(II)H before H(2) generation occurs. Overpotentials for H(2) generation are lowered as a result of the hangman effect.

The hangman motif provides mechanistic insights into the role of pendant proton relays in governing proton-coupled electron transfer (PCET) involved in the hydrogen evolution reaction (HER). We now show improved HER activity of Ni compared with Co hangman porphyrins. Cyclic voltammogram data and simulations, together with computational studies using density functional theory, implicate a shift in electrokinetic zone between Co and Ni hangman porphyrins due to a change in the PCET mechanism. Unlike the Co hangman porphyrin, the Ni hangman porphyrin does not require reduction to the formally metal(0) species before protonation by weak acids in acetonitrile. We conclude that protonation likely occurs at the Ni(I) state followed by reduction, in a stepwise proton transfer-electron transfer pathway. Spectroelectrochemical and computational studies reveal that upon reduction of the Ni(II) compound, the first electron is transferred to a metal-based orbital, whereas the second electron is transferred to a molecular orbital on the porphyrin ring.renewable | solar fuels | electrocatalysis S olar-to-fuels conversions provide a path to harnessing the ubiquitous albeit intermittent renewable energy resource offered by the sun (1-6). Efficient catalysis of transformations of energy consequence (7-13) mandates the coupling of electron transfer (ET) to proton transfer (PT) in proton-coupled electron transfer (PCET) reactions (14)(15)(16)(17)(18)(19)(20). In the absence of PCET, intermediates possessing equilibrium potentials that are prohibitively large depreciate the storage capacity offered by the solarto-fuels conversion process. The coupling of protons to changes in electron equivalency offers the possibility of restricting the equilibrium potentials of the redox steps to a more narrow potential range, thereby minimizing the overpotential required to sustain catalysis at a desired turnover rate. Thus, the exploitation of PCET pathways to permit potential-leveling effects is a crucial prerequisite for the efficient catalytic conversion reactions of energy relevant molecules.PCET reactions may be classified into stepwise and concerted pathways (14,16,20,21). Stepwise PCET may involve ET first followed by PT (ETPT), or PT followed by ET (PTET). In concerted proton-electron transfers (CPET), the proton and electron traverse a common transition state. Whereas concerted pathways avoid the formation of thermodynamically costly intermediates, CPET reactions may incur kinetic penalties associated with the requirements for proton tunneling (19,20,22). The competition between these dynamics during catalysis determines the most efficient route of reaction. Studies that explore the interplay between these factors are crucial to designing catalytic reactions of high efficiency. Along these lines, the incorporation of proton relays in the second coordination sphere of molecular catalysts has emerged as a useful tool in optimizing PCET transformations (23-29). We have focused on the synthesis and mechanistic investigation of a class of me...

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IFN regulatory factor (IRF)-8 is a transcription factor important for the development and function of macrophages. It plays a critical role in the induction of cytokine genes, including IL-12p40. Immunopurification and mass spectrometry analysis found that IRF-8 interacted with Ro52 in murine macrophages upon IFN-γ and TLR stimulation. Ro52 is an IFN-inducible protein of the tripartite motif (TRIM) family and is an autoantigen present in patients with Sjögren’s syndrome and systemic lupus erythematosus. Ro52 has a RING motif and is capable of ubiquitinating itself. We show that IRF-8 is ubiquitinated by Ro52 both in vivo and in vitro. Ectopic expression of Ro52 enhanced IL-12p40 expression in IFN-γ/TLR-stimulated macrophages in an IRF-8-dependent manner. Together, Ro52 is an E3 ligase for IRF-8 that acts in a non-degradation pathway of ubiquitination, and contributes to the elicitation of innate immunity in macrophages.

A hybrid hydrogel composed of gelatin and gold nanoparticles (GNPs) was designed to evaluate the effect of new bone formation and proves itself to be useful as an implant material for treating defected bone tissues.

Interferon (IFN) consensus sequence-binding protein/IFN regulatory factor 8 (IRF8) is a transcription factor that regulates the differentiation and function of macrophages, granulocytes, and dendritic cells through activation or repression of target genes. Although IRF8 is also expressed in lymphocytes, its roles in B cell and T cell maturation or function are ill defined, and few transcriptional targets are known. Gene expression profiling of human tonsillar B cells and mouse B cell lymphomas showed that IRF8 transcripts were expressed at highest levels in centroblasts, either from secondary lymphoid tissue or transformed cells. In addition, staining for IRF8 was most intense in tonsillar germinal center (GC) dark-zone centroblasts. To discover B cell genes regulated by IRF8, we transfected purified primary tonsillar B cells with enhanced green fluorescent protein–tagged IRF8, generated small interfering RNA knockdowns of IRF8 expression in a mouse B cell lymphoma cell line, and examined the effects of a null mutation of IRF8 on B cells. Each approach identified activation-induced cytidine deaminase (AICDA) and BCL6 as targets of transcriptional activation. Chromatin immunoprecipitation studies demonstrated in vivo occupancy of 5′ sequences of both genes by IRF8 protein. These results suggest previously unappreciated roles for IRF8 in the transcriptional regulation of B cell GC reactions that include direct regulation of AICDA and BCL6.