Chemistry methods : new approaches to solving problems in chemistry最新文献

The accurate measurement of redox potentials of small molecules is a relatively straightforward task using electrochemical methods such as cyclic voltammetry. However, proteins, in most cases, are not amenable to the same approach due to slow heterogeneous electron transfer and the possibility of denaturing at the electrode surface. This necessitates the use of small molecular weight redox mediators to facilitate electron transfer. This leads to spectroelectrochemical techniques where the applied electrochemical potential is coupled to a spectroscopic signal of the protein. Traditionally this is done at different applied (fixed) potentials akin to an electrochemical titration, but the time required for electrochemical equilibrium to be established, and its consistent application, are major sources of experimental error. Here we have utilised a continuously scanning potential synchronised with time-resolved UV-vis spectroscopy to provide an automated approach that can be used to measure protein redox potentials accurately in an expedient manner. The test cases are the heme proteins cytochrome c and myoglobin. The scope and limitations of the method are discussed.

In operando powder diffraction remains one of the most powerful tools for non-destructive investigation of battery electrode materials. While in operando X-ray, especially synchrotron radiation, powder diffraction is by now a routine experimental technique, in operando neutron powder diffraction is still less established. We present a new electrochemical cell for in operando neutron powder diffraction, which is, first and foremost, easy to use, but can also cycle electrode materials under electrochemical conditions close to those achieved using standard laboratory cells. The cell has been designed in multiple sizes, and high-quality electrochemical and neutron powder diffraction data is presented for sample sizes as low as 48 mg total active material. The cell handles lithium-ion and sodium-ion materials equally well, with no difference in how the cell is prepared and assembled. The cell is intended to be used as sample environment at powder diffractometers at the neutron facilities MLZ, ORNL and ACNS.

The Front Cover shows a sketch of the formation process of metal oxide nanoparticles, where nanocrystalline oxides form from fragments of polyoxometalates. In situ X-ray total scattering studies with Pair Distribution Function analysis can give new insights into the formation process, as it provides structural information on all stages of the reaction – from precursor ions in solution, over amorphous or nanostructured intermediates to the final crystalline material. Here, we show how the analysis of such data can be automated using structure mining and simple computational tools. More information can be found in the Research Article by EmilT. S. Kjær0000et al..

Invited for this month's cover are the groups of Kirsten M. Ø. Jensen at the University of Copenhagen (Denmark) and Simon J. L. Billinge at Columbia University (US). The cover picture shows a sketch of the formation process of metal oxide nanoparticles, where nanocrystalline oxides form from fragments of e.g., polyoxometalates. In situ X-ray total scattering studies with Pair Distribution Function analysis can give new insights into the formation process, as it provides structural information on all stages of the reaction – from precursor ions in solution, over amorphous or nanostructured intermediates to the final crystalline material. Here, it is show how the analysis of such data can be automated using structure mining and simple computational tools. Read the full text of their Research Article at 10.1002/cmtd.202200034.

The electron-donating and -accepting power of organic substituents is an important parameter affecting many properties of parent molecules, most notably their reactivity and pK_a of ionisable groups. These substituent properties are described by Hammett σ constants obtained by measuring ionization constants of substituted benzoic acids. Although values of the Hammett σ constants have been measured for the most common functional groups, data for many important substituents are not available. In the present study, a method to calculate substituent descriptors compatible with the Hammett σ constants using quantum-chemically derived parameters is described. On this basis, a free web tool allowing to calculate electronic and hydrophobic substituent descriptors is made available at https://bitly.com/getsigmas.

Different molecular balances were designed previously to compare noncovalent interactions. However, some balances are difficult to synthesise and there is a need for developing a computational approach. In this work, we probe noncovalent interactions of π systems using DFT methods to assess their reliability in reproducing experimentally measured conformer populations. Based on our results, the PW6B95D3 functional performed best, followed by M11L and ωB97XD. Additionally, the simulation of the rotation of the hydroxyl group revealed stabilising OH⋯Alkyne and OH⋯Nitrile interactions that are difficult to identify experimentally. These methods were then applied to compare the strengths of sulfur⋯π interactions in molecules which have not been explored experimentally. Compared to the hydroxyl counterpart, the simulation of the thiol group rotation showed that the geometry of the conformer with the two sulfur lone pairs oriented towards the aromatic ring or the double bond is stabilised, suggesting that S(LP)⋯π interactions can be attractive in nature. The ability of sulfur to rearrange its electronic surrounding to form an attractive interaction with π systems, including those with either electron-donating or withdrawing groups, was also confirmed. Overall, the results show a promising future for both qualitative and quantitative assessments of the strengths of noncovalent interactions using selected DFT techniques.

We demonstrate a method for in situ monitoring of the crystallisation of basic magnesium chlorides using a laboratory-based SAXS (small angle X-ray scattering)/ WAXS (wide angle X-ray scattering) instrument. By simultaneous acquisition of SAXS/WAXS, time-resolved particle size and phase evolution information was obtained from room temperature to 120 °C. The WAXS data were analysed using two-phase Rietveld refinements, to produce crystallisation curves. From Avrami-type kinetic analysis two competing mechanistic processes were proposed for the formation of Mg₃Cl(OH)₅ ⋅ 4 H₂O with a nucleation-type mechanism extending further into the reaction with increased temperature. When comparing SAXS and WAXS, an offset between the consumption of MgO and the reduction of the sphere contribution to the SAXS scattering is observed. This is rationalised by the formation of an amorphous Mg(OH)₂ layer on the MgO particle surface. Although laboratory-based SAXS/WAXS instruments have limitations compared to synchrotron-based sources, we have demonstrated how they can provide new insights into the formation of materials.

Understanding how the microstructure of the active Cu⁰ component in the commercially applicable Cu/ZnO/Al₂O₃(−Cs₂O) low-temperature water-gas shift catalyst evolves under various H₂ partial pressures in the presence/absence of a Cs promoter during thermal activation has been investigated. Time-resolved XRD and spatially-resolved XRD-CT data were measured as a function of H₂ concentration along a packed bed reactor to elucidate the importance of the zincite support and the effect of the promoter on Cu sintering mechanisms, dislocation character and stacking fault probability. The rate of Cu reduction showed a dependency on [Cs], [H₂] and bed height; lower [Cs] and higher [H₂] led to a greater rate of metallic copper nanoparticle formation. A deeper analysis of the XRD line profiles allowed for determining a greater edge character to the dislocations and subsequent stacking fault probability was also observed to depend on higher [H₂], smaller Cu⁰ (and ZnO) crystallite sizes, increased [ZnO] (30 wt.%, sCZA) and lower temperature. The intrinsic activity of Cu/ZnO/Al₂O₃ methanol synthesis catalysts has been intimately linked to the anisotropic behaviour of copper, and thus the presence of lattice defects; to the best knowledge of the authors, this study is the first instance in which this type of analysis has been applied to LT-WGS catalysts.

Using Pair Distribution Function (PDF) analysis of in situ total scattering data, we investigate the formation of tungsten and niobium oxides in a simple solvothermal synthesis. We use Pearson Correlation Coefficient (PCC) analysis of the time resolved PDFs to both map the structural changes taking place throughout the synthesis and identify structural models for precursor and product through PCC-based structure mining. Our analysis first shows that ultra-small tungsten and niobium oxide nanoparticles form instantaneously upon heating, with sizes between 1.5 and 2 nm. We show that the main structural motifs in the nanoparticles can be described with structures containing pentagonal columns, which is characteristic for many bulk tungsten and niobium oxides. We furthermore elucidate the structure of the precursor complex as clusters of octahedra with O- and Cl-ligands. The PCC based methodology automates the structure characterization and proves useful for analysis of large datasets of for example, time resolved X-ray scattering studies. The PCC is implemented in ‘PDF in the cloud’, a web platform for PDF analysis.

The Front Cover shows a versatile flow synthesis strategy for continuous manufacturing of single- and mixed-metal oxide particles with a high degree of size monodispersity. The flow-focusing microreactor equipped with an online photo-crosslinking module enables facile production of a broad range of monodispersed metal oxide particles (ZnO, SnO2, CeO2, LaPrO3) using metal organic precursors beyond metal alkoxides. More information can be found in the Research Article by Zachary S. Campbell et al..