Nature Materials 12, 1137 (2013). doi:10.1038/nmat3795
Authors: Samira Siahrostami, Arnau Verdaguer-Casadevall, Mohammadreza Karamad, Davide Deiana, Paolo Malacrida, Björn Wickman, María Escudero-Escribano, Elisa A. Paoli, Rasmus Frydendal, Thomas W. Hansen, Ib Chorkendorff, Ifan E. L. Stephens & Jan Rossmeisl
The homogeneous catalysis of water oxidation by transition-metal complexes has experienced spectacular development over the last five years. Practical energy-conversion schemes, however, require robust catalysts with large turnover frequencies. Herein we introduce a new oxidatively rugged and powerful dinuclear water-oxidation catalyst that is generated by self-assembly from a mononuclear catalyst during the catalytic process. Our kinetic and DFT computational analysis shows that two interconnected catalytic cycles coexist while the mononuclear system is slowly and irreversibly converted into the more stable dinuclear system: an extremely robust water-oxidation catalyst that does not decompose over extended periods of time.
Zweifach hält länger: Die Umwandlung eines hoch aktiven einkernigen Aquaruthenium-Wasseroxidationskatalysators in einen zweikernigen Komplex im Verlauf der Sauerstoffentwicklungskatalyse führt zur gemeinsamen Existenz von zwei Katalysezyklen (siehe Bild; Ru rosa, N blau, O rot). Der zweikernige Komplex ist robuster als der einkernige und bleibt daher länger als der aktive Katalysator in der Wasseroxidation bestehen.
The role of graphene in enabling deoxidation of silver nanostructures, thereby contributing to enhance plasmonic properties and to improve the temporal stability of graphene/silver hybrids for both general plasmonic and meta-materials applications, as well as for surface enhanced Raman scattering (SERS) substrates, is demonstrated. The chemical mechanism occurring at the graphene–silver oxide interface is based on the reduction of silver oxide triggered by graphene that acts as a shuttle of electrons and as a kind of catalyst in the deoxidation. A mechanism is formulated, combining elements of electron transfer, role of defects in graphene, and electrochemical potentials of graphene, silver, and oxygen. Therefore, the formulated model represents a step forward from the simple view of graphene as barrier to oxygen diffusion proposed so far in literature. Single layer graphene grown by chemical vapor deposition is transferred onto silver thin films, a periodic silver fishnet structure fabricated by nanoimprint lithography, and onto silver nanoparticle ensembles supporting a localized surface plasmon resonance in the visible range. Through the study of these nanostructured graphene/Ag hybrids, the effectiveness of graphene in preventing and reducing oxidation of silver plasmonic structures, keeping silver in a metallic state over months at air exposure, is demonstrated. The enhanced and stable plasmonic properties of the silver-fishnet/graphene hybrids are evaluated through their SERS response for detecting benzyl mercaptane.
The role of graphene in enabling deoxidation of silver nanostructures, thereby contributing to enhance plasmonic properties and to improve the temporal stability of graphene/silver hybrids for both general plasmonic and meta-materials applications as well as for surface enhanced Raman scattering (SERS) substrates, is demonstrated.
Weißlicht: [{Au(L)}3] (L=3-(2-Thienyl)pyrazolat) zeigt eine duale Emission, zum einen von einem organischen Chromophor, zum anderen durch aurophile Stapelwechselwirkungen. Die resultierenden blau-grünen und orange-roten Emissionen können durch Modulation des Aggregationsverhaltens des Clusters so reguliert werden, dass man weißes Licht erhält.
A high performance laccase-based biofuel cell cathode is developed using carbon nanosheets (CNS) as the catalyst support and buckypaper (BP) as the substrate electrode. Compared to multiwalled carbon nanotube (MWNT)-based electrodes, CNS-based electrodes exhibit better electrochemical properties for the oxygen reduction reaction (ORR) under biologically relevant conditions. It is shown that CNSs are conformally coated on the nanotubule bundles within the BP and that laccase is intimately attached to the CNS-BP. Electrochemical characterization is carried out to derive the kinetic parameters of the ORR at the laccase-CNS-BP cathode. The laccase-CNS-BP exhibits a steep ORR cathodic wave with a Tafel slope of 19 mV decade-1. The onset potential obtained for laccase ORR at CNS-BP is 20 mV higher than that of the MWNT-based electrodes, and the laccase-CNS-BP cathode has a higher current density than MWNT electrodes.
A high performance enzymatic cathode material based on a carbon nanosheet support exhibits high electron transfer properties and good O2 reduction electrocatalysis. The enhanced electron transfer kinetics are made possible by the graphene edge planes and the ability of carbon nanosheets to transfer electrons from the enzyme to the current collector.
Herein we describe the preparation and structure-activity relationship studies on range of stilbene based compounds and their antibacterial activity. Two related compounds, each bearing carboxylic acid moieties, exhibit good activity against several bacterial strains, including methicillin-resistant Staphylococcus aureus MRSA (ATCC 33592 and NCTC 10442). Compound 10 was most active against Moraxella catarrhalis with minimum inhibitory concentrations (MICs) of 0.12–0.25 μg mL−1 and against Staphylococcus spp. with MICs ranging from 2–4 μg mL−1. The derivative 17 showed increased activity with MICs of 0.06–0.25 μg mL−1 against M. catarrhalis and 0.12–1 against Staphylococcus spp. This level of activity is similar to that reported for S. aureus for antibiotics, such as vancomycin, with MICs of ≤2.0 μg mL−1 and clindamycin with MICs of ≤0.5 μg mL−1. As an indicator of toxicity, 17 was tested for its ability to lyse sheep erythrocytes, and showed low haemolytic activity. Such results highlight the value of tris(stilbene) compounds as antibacterial agents providing suitable properties for further development.
Routes to new antibiotics: The preparation of and structure–activity relationship studies on a range of stilbene based compounds revealed two related compounds, each bearing carboxylic acid moieties, exhibiting pronounced activity against several bacterial strains including methicillin-resistant Staphylococcus aureus, MRSA (see scheme, dba = dibenzylidene acetone).
Etwas Luft schadet nicht: Eine sauerstofftolerante Hydrogenase kann in Kombination mit einem Farbstoff zur photokatalytischen H2-Erzeugung eingesetzt werden. Das homogene System bedarf keines Redoxvermittlers und liefert unter Bestrahlung mit sichtbarem Licht auch in Gegenwart von Luft große Mengen an H2.
Frustriert? Lach mal! Frustrierte Lewis-Paare aus einem sperrigen tertiären Phosphan und einem stark Lewis-sauren Ferrocenylboran (FcB(C6F5)2) wurden für den kolorimetrischen/elektrochemischen Nachweis von N2O untersucht. Ein solches System, basierend auf tBu3P/FcB(C6F5)2, zeigt nicht nur die Präsenz von N2O an, sondern hat auch die Fähigkeit, zwischen N2O und O2 zu unterscheiden.
The luminescent properties of a family of lanthanide metal–organic frameworks LnL (Ln=Y, La–Yb, except Pm; L=4,4′-({2-[(4-carboxyphenoxy)methyl]-2-methylpropane-1,3-diyl}bis{oxy})dibenzoic acid) have been explored, and the energy-transfer process in the compounds has been carefully analyzed. The visible-emitting Tb0.08Gd0.92L and the near-infrared (NIR)-luminescent Yb0.10Gd0.90L show excellent optical performances and can be considered as fluorescent probes for acetone sensing based on luminescence quenching effects arising from host–guest interactions. Moreover, GdL exhibits a strong second harmonic generation (SHG) signal 6.1 times that of potassium dihydrogen phosphate (KDP) and an outstanding phase-matchable effect. These lanthanide compounds combining fluorescent and nonlinear optical (NLO) properties could meet further requirements as multifunctional materials.
Lighting up time: A family of LnMOFs has been developed (see figure), the members of which show luminescence from the visible to the near-infrared region. Detailed luminescence studies have revealed a potential application for Tb0.08Gd0.92L and Yb0.10Gd0.90L as new fluorescent probes for acetone sensing.
