Faraday Discussions最新文献

A novel dinucleating bis(pyrazolyl)methane ligand was developed for tyrosinase model systems. After ligand synthesis, the corresponding Cu(I) complex was synthesized and upon oxygenation, formation of a µ-η²:η² peroxido complex could be observed and monitored using UV/Vis-spectroscopy. Due to the high stability of this species even at room temperature, a molecular structure of the complex could be characterized via single-crystal XRD. Additional to its promising stability, the peroxido complex showed catalytic tyrosinase activity which was investigated via UV/Vis-spectroscopy. Products of the catalytic conversion could be isolated and characterized and the ligand could be successfully recycled after catalysis experiments. Furthermore, the peroxido complex was reduced by reductants with different reduction potentials. The characteristics of the electron transfer reactions were investigated with the help of the Marcus relation. The combination of the high stability and catalytic activity of the peroxido complex with the new dinucleating ligand, enables the shift of oxygenation reactions for selected substrates towards green chemistry, which is furthered by the efficient ligand recycling capability.

Nickel (Ni) metal has long been considered to be far less active for catalytic ammonia synthesis as compared to iron, cobalt, and ruthenium. Herein, we show that Ni metal synergized with barium hydride (BaH₂) can catalyse ammonia synthesis with an activity comparable to that of an active Cs–Ru/MgO catalyst typically below 300 °C. Kinetic analyses show that the addition of BaH₂ makes the apparent activation energy for the Ni catalyst decrease dramatically from 150 kJ mol^?1 to 87 kJ mol^?1. This result together with N₂-TPR experiments suggests a strong synergistic effect between Ni and BaH₂ for promoting N₂ activation and hydrogenation to NH₃. It is suggested that an intermediate [N–H] species is generated upon N₂ fixation and then is hydrogenated to NH₃ with the regeneration of hydride species, forming a catalytic cycle.

Knowing the nature and strength of noncovalent interactions is key to enhancing the synthetic methods and catalytic processes in which they are involved. We present herein the synthesis and characterization of a novel aluminium sodium oximate compound, followed by a comprehensive computational study of the sodium⋯methyl interaction that appears in its crystal structure. Our experimental results have been compared to a large set of structural data retrieved from the Cambridge Structural Database in order to assess the main geometrical preferences of these interactions. Moreover, representative model systems have been studied at the DFT level and the topology of their electron density analysed by means of QTAIM. Although alkali metal⋯methyl short contacts have been traditionally considered as agostic interactions, we have demonstrated here that the physical origin of the attraction relies on the electron-rich carbon atom bound to aluminium and its interaction with the cation.

Electrochemical reduction of nitrate (NO₃RR) has drawn significant attention in the scientific community as an attractive route for ammonia synthesis as well as alleviating environmental concerns for nitrate pollution. To improve the efficiency of this process, the development of catalyst materials that exhibit high activity and selectivity is of paramount importance. Copper and copper-based catalysts have been widely investigated as potential catalyst materials for this reaction both computationally and experimentally. However, less attention has been paid to understanding the reasons behind such high activity and selectivity. Herein, we use Density Functional Theory (DFT) to identify reactivity descriptors guiding the identification of active catalysts for the NO₃RR, establish trends in activity, and explain why copper is the most active and selective transition metal for the NO₃RR to ammonia among ten different transition metals, namely Au, Ag, Cu, Pt, Pd, Ni, Ir, Rh, Ru, and Co. Furthermore, we assess NO₃RR selectivity by taking into account the competition between the NO₃RR and the hydrogen evolution reaction. Finally, we propose various approaches for developing highly active catalyst materials for the NO₃RR.

Noble metal elements are focal catalytic candidates for many chemical processes, but have received little attention in the field of nitrogen fixation except ruthenium and osmium. Iridium (Ir), as a representative, has been shown to be catalytically inactive for ammonia synthesis because of its weak nitrogen adsorption and severe competitive adsorption of H over N that strongly inhibits the activation of N₂ molecules. Here we show that, upon compositing with lithium hydride (LiH), iridium can catalyze ammonia formation at much enhanced reaction rates. The catalytic performance of the LiH–Ir composite can be further improved by dispersion on a MgO support with a high specific surface area. At 400 °C and 10 bar, the MgO-supported LiH–Ir (LiH–Ir/MgO) catalyst shows a ca. 100-fold increase in activity compared to the bulk LiH–Ir composite and the MgO-supported Ir metal catalyst (Ir/MgO). The formation of a lithium–iridium complex hydride phase was identified and characterized, and this phase may be responsible for the activation and hydrogenation of N₂ to NH₃.

Interactions between the protein Hen Egg White Lysozyme (HEWL) and three different hybrid Anderson–Evans polyoxometalate clusters – AE-NH₂ (δ-[MnMo₆O₁₈{(OCH₂)₃CNH₂}₂]³⁻), AE-CH₃ (δ-[MnMo₆O₁₈{(OCH₂)₃CCH₃}₂]³⁻) and AE-Biot (δ-[MnMo₆O₁₈{(OCH₂)₃CNHCOC₉H₁₅N₂OS}₂]³⁻) – were studied via tryptophan fluorescence spectroscopy and single crystal X-ray diffraction. Quenching of tryptophan fluorescence was observed in the presence of all three hybrid polyoxometalate clusters (HPOMs), but the extent of quenching and the binding affinity were greatly dependent on the nature of the organic groups attached to the cluster. Control experiments further revealed the synergistic effect of the anionic polyoxometalate core and organic ligands towards enhanced protein interactions. Furthermore, the protein was co-crystallised with each of the three HPOMs, resulting in four different crystal structures, thus allowing for the binding modes of HPOM–protein interactions to be investigated with near-atomic precision. All crystal structures displayed a unique mode of binding of the HPOMs to the protein, with both functionalisation and the pH of the crystallisation conditions influencing the interactions. From the crystal structures, it was determined that HPOM–protein non-covalent complexes formed through a combination of electrostatic attraction between the polyoxometalate cluster and positively charged surface regions of HEWL, and direct and water-mediated hydrogen bonds with both the metal-oxo inorganic core and the functional groups of the ligand, where possible. Hence, functionalisation of metal-oxo clusters shows great potential in tuning their interactions with proteins, which is of interest for several biomedical applications.

The paper presents a view on the achievements, challenges and prospects of mechanochemistry. The extensive reference list can serve as a good entry point to a plethora of mechanochemical literature.