Tailoring C─N containing compounds into carbon nanomaterials with tunable morphologies for electrocatalytic applications

Carbon materials with unique sp2-hybridization are extensively researched for catalytic applications due to their excellent conductivity and tunable physicochemical properties. However, the development of economic approaches to tailoring carbon materials into desired morphologies remains a challenge. Herein, a convenient “bottom-up” strategy by pyrolysis of graphitic carbon nitride (g-C3N4) (or other carbon/nitrogen (C, N)-enriched compounds) together with selected metal salts and molecules is reported for the construction of different carbon-based catalysts with tunable morphologies, including carbon nano-balls, carbon nanotubes, nitrogen/sulfur (S, N) doped-carbon nanosheets, and single-atom catalysts, supported by carbon layers. The catalysts are systematically investigated through various microscopic, spectroscopic, and diffraction methods and they demonstrate promising and broad applications in electrocatalysis such as in the oxygen reduction reaction and water splitting. Mechanistic monitoring of the synthesis process through online thermogravimetric-gas chromatography-mass spectrometry measurements indicates that the release of C─N-related moieties, such as dicyan, plays a key role in the growth of carbon products. This enables to successfully predict other widely available precursor compounds beyond g-C3N4 such as caffeine, melamine, and urea. This work develops a novel and economic strategy to generate morphologically diverse carbon-based catalysts and provides new, essential insights into the growth mechanism of carbon nanomaterials syntheses

Tailoring C─N Containing Compounds into Carbon Nanomaterials with Tunable Morphologies for Electrocatalytic Applications

Carbon materials with unique sp2-hybridization are extensively researched for catalytic applications due to their excellent conductivity and tunable physicochemical properties. However, the development of economic approaches to tailoring carbon materials into desired morphologies remains a challenge. Herein, a convenient “bottom-up” strategy by pyrolysis of graphitic carbon nitride (g-C3N4) (or other carbon/nitrogen (C, N)-enriched compounds) together with selected metal salts and molecules is reported for the construction of different carbon-based catalysts with tunable morphologies, including carbon nano-balls, carbon nanotubes, nitrogen/sulfur (S, N) doped-carbon nanosheets, and single-atom catalysts, supported by carbon layers. The catalysts are systematically investigated through various microscopic, spectroscopic, and diffraction methods and they demonstrate promising and broad applications in electrocatalysis such as in the oxygen reduction reaction and water splitting. Mechanistic monitoring of the synthesis process through online thermogravimetric-gas chromatography-mass spectrometry measurements indicates that the release of C─N-related moieties, such as dicyan, plays a key role in the growth of carbon products. This enables to successfully predict other widely available precursor compounds beyond g-C3N4 such as caffeine, melamine, and urea. This work develops a novel and economic strategy to generate morphologically diverse carbon-based catalysts and provides new, essential insights into the growth mechanism of carbon nanomaterials synthese

Rapid Single-Step Induction of Functional Neurons from Human Pluripotent Stem Cells

SummaryAvailable methods for differentiating human embryonic stem cells (ESCs) and induced pluripotent cells (iPSCs) into neurons are often cumbersome, slow, and variable. Alternatively, human fibroblasts can be directly converted into induced neuronal (iN) cells. However, with present techniques conversion is inefficient, synapse formation is limited, and only small amounts of neurons can be generated. Here, we show that human ESCs and iPSCs can be converted into functional iN cells with nearly 100% yield and purity in less than 2 weeks by forced expression of a single transcription factor. The resulting ES-iN or iPS-iN cells exhibit quantitatively reproducible properties independent of the cell line of origin, form mature pre- and postsynaptic specializations, and integrate into existing synaptic networks when transplanted into mouse brain. As illustrated by selected examples, our approach enables large-scale studies of human neurons for questions such as analyses of human diseases, examination of human-specific genes, and drug screening

a homophilic and heterophilic cell adhesion molecule

Der Coxsackievirus- und Adenovirus-Rezeptor (CAR), ein Transmembranprotein der Immunglobulinsuperfamilie mit zwei extrazellulären Ig-Domänen (D1 und D2), wird stark im embryonalen Zentralnervensystem exprimiert. Neben seiner Rolle als Virusrezeptor ist die zellbiologische Funktion im Nervensystem weitestgehend ungeklärt. Aufgrund seiner Lokalisation könnte CAR an der Synaptogenese und dem axonalen Wachstum beteiligt sein. So blockieren Antikörper gegen CAR in vitro die Adhäsion von Neuronen an Glycoproteinen der extrazellulären Matrix (ECM) oder inhibieren das Neuritenwachstum auf Basal- Lamina-Präparationen. In dieser Arbeit konnte gezeigt werden, dass CAR durch direkte Interaktionen seiner extrazellulären Domänen mit ECM-Glycoproteinen wie Fibronektin (FN), Laminin-1, Fibulin-1, Tenascin-R und Agrin die zelluläre Adhäsion und die Ausbildung von Neuriten fördert. Am Beispiel von FN konnte eine Bindung der zweiten Ig-Domäne vom CAR (D2) an das die zweite Heparinbindungsdomäne von FN umfassende Fragment (FN-40-kDa) nachgewiesen werden. Dieses Fragment enthält nicht die Integrinbindungsstelle der sogenannten Zelladhäsionsdomäne von FN. In Zellkulturversuchen zeigte sich, dass es eine Neuriten-fördernde Aktivität besitzt, die verloren geht, sobald CAR-defiziente Neuronen verwendet werden oder neuraler CAR durch anti-CAR- Antikörper blockiert wird. Neben dieser heterophilen Bindungsaktivität ist CAR in der Lage, homophil zu binden. So ist die homotypische Aggregation der CAR- defizienten Neuronen auf FN-40-kDa verringert. CAR-transfizierte NIH 3T3 und CHO Zellen aggregieren stärker als parentale Zellen. Aus Bindungsversuchen ergibt sich, dass CAR über seine extrazelluläre Region direkt an sich selbst bindet, wie es auch bei anderen IgSF-Mitgliedern der Fall ist. Diese Selbstassoziation vom CAR wird durch N-Glycosylierung begünstigt, obwohl auch bakteriell hergestellter extrazellulärer CAR bei hohen Konzentrationen Dimere bildet, wie aus der Kristallstrukturaufklärung hervorgeht. Weitere Bindungsstudien legen nahe, dass es neben einer bereits beschriebenen D1-D1-Wechselwirkung auch zu einer 20mal affineren D1-D2-Wechselwirkung kommt, die eine trans-Homodimerisierung möglich macht. Das zytoplasmatische Segment vom CAR bindet an die Aktin-assoziierten Proteine α Actinin und Profilin-1. Wie Integrine oder Syndecane stellt CAR somit eine Verbindung zwischen der ECM oder CAR benachbarter Zellen und dem Aktin-Zytoskelett her.The coxsackievirus-adenovirus receptor (CAR), a transmembrane protein of the Immunoglobulin superfamily (IgSF) composed of two extracellular Ig domains (D1 and D2), is strongly expressed in the developing central nervous system. Based on its localization it is possibly involved in the formation of synapses or axonal outgrowth. Beside its role as a cellular virus receptor the cell biological function in the nervous system remains to be revealed. Consistently, antibodies to CAR block the attachment of neurons on glycoproteins of the extracellular matrix (ECM) or disturb neurite extension on basal laminae preparations in vitro. In this thesis binding studies showed that fibronectin (FN), laminin-1, fibulin-1, tenascin-R and agrin are extracellular interaction partners of CAR. Most likely through these interactions CAR stimulates processes like cell-adhesion and neurite extension. Concerning FN the interaction could be mapped to a fragment bearing the second heparin-binding-domain (FN-40-kDa), which is different from the main integrin binding segment, and to the second Ig domain (D2) of CAR. This FN-fragment has a neurite-stimulating activity in cell-culture which is abolished on neurons from CAR-deficient mice or when CAR is blocked by antibodies. Beside this heterophilic binding CAR reveals homophilic binding as well. For example, the homotypic interaction of CAR-deficient neurons on FN-40-kDa is disturbed. Furthermore, the aggregation of CAR transfected NIH 3T3 and CHO cells is stimulated compared to their parental cells. As known for several IgSF-members the extracellular part of CAR binds to itself which is favored when it is N-glycosylated. However, high concentrations of bacterially expressed extracellular CAR form also dimers, which is obeserved in the cristallographic structure, where a D1 D1 interaction is visible. Again through binding studies, evidence is given that alternatively to the already described D1 D1 interaction a trans D1 D2 interaction takes place with a 20-fold increased affinity. The intracellular segment of CAR is found to bind to the actin-cytoskeleton by interacting directly with α-actinin and profilin-1. It can be concluded that CAR acts, like integrins and syndecans, as a linker between the ECM or itself on adjacent cells and the actin- cytoskeleton

Thermodynamics of paired charge-compensating doped ceria with superior redox performance for solar thermochemical splitting of H2O and CO2

Paired charge-compensating doped ceria (PCCD) using trivalent and pentavalent cations are evaluated as redox materials for the thermochemical splitting of H2O and CO2. The oxygen nonstoichiometries of PCCD materials with formulas of Ce0.9A0.05Nb0.05O2 (A = Y, La, Sc) and CexLa(1−x)/2Nb(1−x)/2O2 (x = 0.75, 0.95) were measured in a thermogravimetric analyzer over a range of temperatures (T = 1173–1773 K) and oxygen partial pressures (pO2 = 10−15–10−1 atm). Undoped and single element doped ceria (Ce0.9B0.1O2 where B = Y, La, Nb, Hf) served as a reference. At any given set of T and pO2, the relative reduction extent follows Ce0.9Hf0.1O2 > Ce0.9Sc0.05Nb0.05O2 > Ce0.9Y0.05Nb0.05O2 > CexLa(1−x)/2Nb(1−x)/2O2 > CeO2 > solely trivalent or pentavalent doped ceria. The partial molar reduction enthalpies were determined using Van't Hoff analysis coupled to defect modeling and range from 360 to 410 kJ mol−1. A system efficiency model predicts that these PCCD materials have the potential of achieving high solar-to-fuel energy conversion efficiencies because of their balanced reduction and oxidation properties. Ce0.9Y0.05Nb0.05O2 in particular can outperform undoped ceria and reach efficiency values of 31% and 28% for H2 and CO production, respectively

Bifunctional single atom electrocatalysts: coordination–performance correlations and reaction pathways

Single atom catalysts (SACs) are ideal model systems in catalysis research. Here we employ SACs to address the fundamental catalytic challenge of generating well-defined active metal centers to elucidate their interactions with coordinating atoms, which define their catalytic performance. We introduce a soft-landing molecular strategy for tailored SACs based on metal phthalocyanines (MPcs, M = Ni, Co, Fe) on graphene oxide (GO) layers to generate well-defined model targets for mechanistic studies. The formation of electronic channels through π-π conjugation with the graphene sheets enhances the MPc-GO performance in both oxygen evolution and reduction reactions (OER and ORR). Density functional theory (DFT) calculations unravel that the outstanding ORR activity of FePc-GO among the series is due to the high affinity of Fe atoms toward O2 species. Operando X-ray absorption spectroscopy and DFT studies demonstrate that the OER performance of the catalysts relates to thermodynamic or kinetic control at low- or high-potential ranges, respectively. We furthermore provide evidence that the participation of ligating N and C atoms around the metal centers provides a wider selection of active OER sites for both NiPc-GO and CoPc-GO. Our strategy promotes the understanding of coordination-activity relationships of high-performance SACs and their optimization for different processes through tailored combinations of metal centers and suitable ligand environments

Thermodynamics of paired charge-compensating doped ceria with superior redox performance for solar thermochemical splitting of H2O and CO2

ISSN:2050-7488ISSN:2050-749

GluD1 is a signal transduction device disguised as an ionotropic receptor

Ionotropic glutamate delta receptors 1 (GluD1) and 2 (GluD2) exhibit the molecular architecture of postsynaptic ionotropic glutamate receptors, but assemble into trans-synaptic adhesion complexes by binding to secreted cerebellins that in turn interact with presynaptic neurexins1-4. It is unclear whether neurexin-cerebellin-GluD1/2 assemblies serve an adhesive synapse-formation function or mediate trans-synaptic signalling. Here we show in hippocampal synapses, that binding of presynaptic neurexin-cerebellin complexes to postsynaptic GluD1 controls glutamate receptor activity without affecting synapse numbers. Specifically, neurexin-1-cerebellin-2 and neurexin-3-cerebellin-2 complexes differentially regulate NMDA (N-methyl-D-aspartate) receptors and AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid) receptors by activating distinct postsynaptic GluD1 effector signals. Of note, minimal GluD1 and GluD2 constructs containing only their N-terminal cerebellin-binding and C-terminal cytoplasmic domains, joined by an unrelated transmembrane region, fully control the levels of NMDA and AMPA receptors. The distinct signalling specificity of presynaptic neurexin-1 and neurexin-35,6 is encoded by their alternatively spliced splice site 4 sequences, whereas the regulatory functions of postsynaptic GluD1 are mediated by conserved cytoplasmic sequence motifs spanning 5-13 residues. Thus, GluDs are signalling molecules that regulate NMDA and AMPA receptors by an unexpected transduction mechanism that bypasses their ionotropic receptor architecture and directly converts extracellular neurexin-cerebellin signals into postsynaptic receptor responses.</p

Mechanistic insight into the active centers of single/dual-atom Ni/Fe-based oxygen electrocatalysts

Single-atom catalysts with maximum metal utilization efficiency show great potential for sustainable catalytic applications and fundamental mechanistic studies. We here provide a convenient molecular tailoring strategy based on graphitic carbon nitride as support for the rational design of single-site and dual-site single-atom catalysts. Catalysts with single Fe sites exhibit impressive oxygen reduction reaction activity with a half-wave potential of 0.89 V vs. RHE. We find that the single Ni sites are favorable to promote the key structural reconstruction into bridging Ni-O-Fe bonds in dual-site NiFe SAC. Meanwhile, the newly formed Ni-O-Fe bonds create spin channels for electron transfer, resulting in a significant improvement of the oxygen evolution reaction activity with an overpotential of 270 mV at 10 mA cm−2. We further reveal that the water oxidation reaction follows a dual-site pathway through the deprotonation of *OH at both Ni and Fe sites, leading to the formation of bridging O2 atop the Ni-O-Fe sites