The electrochemical synthesis of ammonia from nitrogen under mild conditions using renewable electricity is an attractive alternative
to the energy-intensive Haber-Bosch process, which dominates ...industrial ammonia production. However, there are considerable scientific and technical challenges
facing the electrochemical alternative, and most experimental studies reported so far have achieved only low selectivities and conversions. The amount of ammonia produced is usually so small that it cannot be firmly attributed to electrochemical nitrogen fixation
rather than contamination from ammonia that is either present in air, human breath or ion-conducting membranes
, or generated from labile nitrogen-containing compounds (for example, nitrates, amines, nitrites and nitrogen oxides) that are typically present in the nitrogen gas stream
, in the atmosphere or even in the catalyst itself. Although these sources of experimental artefacts are beginning to be recognized and managed
, concerted efforts to develop effective electrochemical nitrogen reduction processes would benefit from benchmarking protocols for the reaction and from a standardized set of control experiments designed to identify and then eliminate or quantify the sources of contamination. Here we propose a rigorous procedure using
N
that enables us to reliably detect and quantify the electrochemical reduction of nitrogen to ammonia. We demonstrate experimentally the importance of various sources of contamination, and show how to remove labile nitrogen-containing compounds from the nitrogen gas as well as how to perform quantitative isotope measurements with cycling of
N
gas to reduce both contamination and the cost of isotope measurements. Following this protocol, we find that no ammonia is produced when using the most promising pure-metal catalysts for this reaction in aqueous media, and we successfully confirm and quantify ammonia synthesis using lithium electrodeposition in tetrahydrofuran
. The use of this rigorous protocol should help to prevent false positives from appearing in the literature, thus enabling the field to focus on viable pathways towards the practical electrochemical reduction of nitrogen to ammonia.
► Review of catalysts for photocatalytic proton reduction. ► Review of catalysts for photocatalytic CO2 reduction. ► Comparison of the bridging ligands in supramolecular assemblies.
Molecular ...photocatalysts, combining a light absorber and a catalytic active center via a bridging ligand, have received much attention during the last decade. Therefore, many new types of photocatalysts containing novel bridging ligands are reported. The bridging ligand is expected to play an important role and does not only represent the chemical connection between a photosensitizing unit and a catalytically active center, but can also greatly affect the overall catalytic activity and stability of the photocatalysts. Moreover, a well-chosen combination of the three parts photosensitizer-bridge-catalyst is expected to yield intramolecular photocatalysts superior over intermolecular systems. This review will discuss the coordination, photophysical, electrochemical and photocatalytic properties of multinuclear metal complexes based on a selection of heterocyclic bridging ligands that show significant photocatalytic activity for hydrogen generation or CO2 reduction. Of particular interest in the discussion will be the effect of the bridging ligand on the photocatalytic properties of the compounds. Based on the results obtained, possible design principles for the optimization of the photocatalytic properties of this type of compounds will be suggested.
In the Spring of 2013, NMR spectroscopists convened at the Weizmann Institute in Israel to brainstorm on approaches to improve the sensitivity of NMR experiments, particularly when applied in ...biomolecular settings. This multi‐author interdisciplinary Review presents a state‐of‐the‐art description of the primary approaches that were considered. Topics discussed included the future of ultrahigh‐field NMR systems, emerging NMR detection technologies, new approaches to nuclear hyperpolarization, and progress in sample preparation. All of these are orthogonal efforts, whose gains could multiply and thereby enhance the sensitivity of solid‐ and liquid‐state experiments. While substantial advances have been made in all these areas, numerous challenges remain in the quest of endowing NMR spectroscopy with the sensitivity that has characterized forms of spectroscopies based on electrical or optical measurements. These challenges, and the ways by which scientists and engineers are striving to solve them, are also addressed.
A new spin on bio‐NMR: This Review presents a state‐of‐the‐art description of the leading approaches being considered today to improve the sensitivity of NMR spectroscopy, particularly as applied in biomolecular settings. The focus is on the future of ultrahigh‐field NMR systems, emerging NMR detection technologies, new approaches to nuclear hyperpolarization, and progress in sample preparation.
Electrocatalytic N2 reduction to ammonia has recently attracted a great deal of interest as a possible renewable energy-driven alternative to the Haber–Bosch process. However, the detection of NH3 ...after attempting electrocatalytic reduction of N2 can be hampered by low NH3 yields, ambient NH3 contamination, and the need for multistep chemical separation of NH3 from the electrolyte. Herein, we report a frequency-selective pulse nuclear magnetic resonance (NMR) method and quantify the efficacy of this method to measure the concentration of NH3 (present in the assay as NH4 +) in an electrolyte after electrocatalysis. This NMR method was demonstrated to be effective in a variety of nondeuterated, nonaqueous and aqueous electrolytes, and did not require the separation of NH3 from the electrolyte. NH3 sensitivity down to 1 μM was readily achieved with isotopic and chemical specificity. Compatible electrolytes and solvents included ethanol, tetrahydrofuran, dimethyl sulfoxide, acetonitrile, propylene carbonate, diethyl either, hexanes, and water. The efficacy of the commonly employed Berthelot method was also quantified and compared to the NMR method in a range of nonaqueous and aqueous electrolytes, including ethanol, THF, propylene carbonate, and water.
Reports detailing the prognostic impact of TP53 mutations in medulloblastoma offer conflicting conclusions. We resolve this issue through the inclusion of molecular subgroup profiles.
We determined ...subgroup affiliation, TP53 mutation status, and clinical outcome in a discovery cohort of 397 medulloblastomas. We subsequently validated our results on an independent cohort of 156 medulloblastomas.
TP53 mutations are enriched in wingless (WNT; 16%) and sonic hedgehog (SHH; 21%) medulloblastomas and are virtually absent in subgroups 3 and 4 tumors (P < .001). Patients with SHH/TP53 mutant tumors are almost exclusively between ages 5 and 18 years, dramatically different from the general SHH distribution (P < .001). Children with SHH/TP53 mutant tumors harbor 56% germline TP53 mutations, which are not observed in children with WNT/TP53 mutant tumors. Five-year overall survival (OS; ± SE) was 41% ± 9% and 81% ± 5% for patients with SHH medulloblastomas with and without TP53 mutations, respectively (P < .001). Furthermore, TP53 mutations accounted for 72% of deaths in children older than 5 years with SHH medulloblastomas. In contrast, 5-year OS rates were 90% ± 9% and 97% ± 3% for patients with WNT tumors with and without TP53 mutations (P = .21). Multivariate analysis revealed that TP53 status was the most important risk factor for SHH medulloblastoma. Survival rates in the validation cohort mimicked the discovery results, revealing that poor survival of TP53 mutations is restricted to patients with SHH medulloblastomas (P = .012) and not WNT tumors.
Subgroup-specific analysis reconciles prior conflicting publications and confirms that TP53 mutations are enriched among SHH medulloblastomas, in which they portend poor outcome and account for a large proportion of treatment failures in these patients.
Cytochrome bd-type oxidases play a crucial role for survival of pathogenic bacteria during infection and proliferation. This role and the fact that there are no homologues in the mitochondrial ...respiratory chain qualify cytochrome bd as a potential antimicrobial target. However, few bd oxidase selective inhibitors have been described so far. In this report, inhibitory effects of Aurachin C (AurC-type) and new Aurachin D (AurD-type) derivatives on oxygen reductase activity of isolated terminal bd-I, bd-II and bo
oxidases from Escherichia coli were potentiometrically measured using a Clark-type electrode. We synthesized long- (C10, decyl or longer) and short-chain (C4, butyl to C8, octyl) AurD-type compounds and tested this set of molecules towards their selectivity and potency. We confirmed strong inhibition of all three terminal oxidases for AurC-type compounds, whereas the 4(1H)-quinolone scaffold of AurD-type compounds mainly inhibits bd-type oxidases. We assessed a direct effect of chain length on inhibition activity with highest potency and selectivity observed for heptyl AurD-type derivatives. While Aurachin C and Aurachin D are widely considered as selective inhibitors for terminal oxidases, their structure-activity relationship is incompletely understood. This work fills this gap and illustrates how structural differences of Aurachin derivatives determine inhibitory potency and selectivity for bd-type oxidases of E. coli.
NLRP3 is a receptor important for host responses to infection, yet is also known to contribute to devastating diseases such as Alzheimer's disease, diabetes, atherosclerosis, and others, making ...inhibitors for NLRP3 sought after. One of the inhibitors currently in use is 2-aminoethoxy diphenylborinate (2APB). Unfortunately, in addition to inhibiting NLRP3, 2APB also displays non-selective effects on cellular Ca2+ homeostasis. Here, we use 2APB as a chemical scaffold to build a series of inhibitors, the NBC series, which inhibit the NLRP3 inflammasome in vitro and in vivo without affecting Ca2+ homeostasis. The core chemical insight of this work is that the oxazaborine ring is a critical feature of the NBC series, and the main biological insight the use of NBC inhibitors led to was that NLRP3 inflammasome activation was independent of Ca2+. The NBC compounds represent useful tools to dissect NLRP3 function, and may lead to oxazaborine ring-containing therapeutics.
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•New inhibitors of the NLRP3 inflammasome are described•NLRP3 inflammasome activation is independent of Ca2+•These new inflammasome inhibitors are effective in vivo•The inhibitors described may lead to the development of new drugs
The NLRP3 inflammasome is known to contribute to damaging inflammation during disease. Baldwin et al. describe a new boron-containing series of inflammasome inhibitors, which may lead to the development of new anti-inflammatory molecules and allow further interrogation of inflammatory mechanisms.
The paper focuses on the photogrammetric investigation of geometric models for different types of optical fisheye constructions (equidistant, equisolid-angle, sterographic and orthographic ...projection). These models were implemented and thoroughly tested in a spatial resection and a self-calibrating bundle adjustment. For this purpose, fisheye images were taken with a Nikkor 8 mm fisheye lens on a Kodak DSC 14n Pro digital camera in a hemispherical calibration room. Both, the spatial resection and the bundle adjustment resulted in a standard deviation of unit weight of 1/10 pixel with a suitable set of simultaneous calibration parameters introduced into the camera model. The camera-lens combination was treated with all of the four basic models mentioned above. Using the same set of additional lens distortion parameters, the differences between the models can largely be compensated, delivering almost the same precision parameters. The relative object space precision obtained from the bundle adjustment was ca. 1:10 000 of the object dimensions. This value can be considered as a very satisfying result, as fisheye images generally have a lower geometric resolution as a consequence of their large field of view and also have a inferior imaging quality in comparison to most central perspective lenses.
The construction of a new class of compoundsthe hangman corrolesis provided efficiently by the modification of macrocyclic forming reactions from bilanes. Hangman cobalt corroles are furnished in ...good yields from a one-pot condensation of dipyrromethane with the aldehyde of a xanthene spacer followed by metal insertion using microwave irradiation. In high oxidation states, X-band EPR spectra and DFT calculations of cobalt corrole axially ligated by chloride are consistent with the description of a Co(III) center residing in the one-electron oxidized corrole macrocycle. These high oxidation states are likely accessed in the activation of O−O bonds. Along these lines, we show that the proton-donating group of the hangman platform works in concert with the redox properties of the corrole to enhance the catalytic activity of O−O bond activation. The hangman corroles show enhanced activity for the selective reduction of oxygen to water as compared to their unmodified counterparts. The oxygen adduct, prior to oxygen reduction, is characterized by EPR and absorption spectroscopy.
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