Isolation of single crystals of homoleptic UO22+- diglycolamide complex from a room temperature ionic liquid: X-ray crystallography and complexation studies

Complexation and structural investigations of the solid complex of UO22+ ion and N,N,N’,N’-tetramethyl diglycolamide isolated from a room temperature ionic liquid, for the first time, revealed that the nature and...

Strengthening Cellulose Nanopaper via Deep Eutectic Solvent and Ultrasound-Induced Surface Disordering of Nanofibers

The route for the preparation of cellulose nanofiber dispersions from bacterial cellulose using ethylene glycol- or glycerol-based deep eutectic solvents (DES) is demonstrated. Choline chloride was used as a hydrogen bond acceptor and the effect of the combined influence of DES treatment and ultrasound on the thermal and mechanical properties of bacterial cellulose nanofibers (BC-NFs) is demonstrated. It was found that the maximal Young’s modulus (9.2 GPa) is achieved for samples prepared using a combination of ethylene glycol-based DES and ultrasound treatment. Samples prepared with glycerol-based DES combined with ultrasound exhibit the maximal strength (132 MPa). Results on the mechanical properties are discussed based on the structural investigations that were performed using FTIR, Raman, WAXD, SEM and AFM measurements, as well as the determination of the degree of polymerization and the density of BC-NF packing during drying with the formation of paper. We propose that the disordering of the BC-NF surface structure along with the preservation of high crystallinity bulk are the key factors leading to the improved mechanical and thermal characteristics of prepared BC-NF-based papers.

Effect of the reductive treatment on the state and electrocatalytic behavior of Pt in catalysts supported on Ti0.8Mo0.2O2-C composite

Ti(1-x)MoxO2-carbon composites are promising new supports for Pt-based electrocatalysts in polymer electrolyte membrane fuel cells offering exciting catalytic properties and enhanced stability against electrocorrosion. Pt and the mixed oxide form a couple liable for strong metal-support interaction (SMSI) phenomenon, generally manifesting itself in decoration of the metal particles by ultrathin layers of the support material upon annealing under reductive conditions. The aim of this work is to evaluate the SMSI phenomenon as a potential strategy for tailoring the properties of the electrocatalyst. A 20 wt% Pt/50 wt% Ti0.8Mo0.2O2-50 wt% C electrocatalyst prepared on Black Pearls 2000 carbon functionalized with HNO3 and glucose was reduced at 250 °C in H2 in order to induce SMSI. The electrocatalytic properties and the stability of the reduced and the original catalysts were analyzed by cyclic voltammetry and COads stripping voltammetry. Structural investigations as well as X-ray photoelectron spectroscopy (XPS) measurements were performed in order to obtain information about the details of the interaction between the oxide and the Pt particles. The electrochemical experiments pointed out a small loss of the electrochemically active surface area of Pt in the reduced catalyst along with enhanced stability with respect to the original one, while structural studies suggested only a minimal decrease of the Pt dispersion. At the same time, hydrogen exposure experiments combined with XPS demonstrated the presence of Mo species directly adsorbed on the Pt surface. Thus, the properties of the reduced catalyst can be traced to decoration of the surface of Pt by Mo-containing species.

Using cryo-EM to uncover mechanisms of bacterial transcriptional regulation

Transcription is the principal control point for bacterial gene expression, and it enables a global cellular response to an intracellular or environmental trigger. Transcriptional regulation is orchestrated by transcription factors, which activate or repress transcription of target genes by modulating the activity of RNA polymerase. Dissecting the nature and precise choreography of these interactions is essential for developing a molecular understanding of transcriptional regulation. While the contribution of X-ray crystallography has been invaluable, the ‘resolution revolution’ of cryo-electron microscopy has transformed our structural investigations, enabling large, dynamic and often transient transcription complexes to be resolved that in many cases had resisted crystallisation. In this review, we highlight the impact cryo-electron microscopy has had in gaining a deeper understanding of transcriptional regulation in bacteria. We also provide readers working within the field with an overview of the recent innovations available for cryo-electron microscopy sample preparation and image reconstruction of transcription complexes.

Ce-exchange capacity of zeolite L in different cationic forms: a structural investigation

Cerium exchange by microporous materials, such as zeolites, has important applications in different fields, for example, rare earth element recovery from waste or catalytic processes. This work investigated the Ce-exchange capacity of zeolite L in three different cationic forms (the as-synthesized K form and Na- and NH4-exchanged ones) from a highly concentrated solution. Chemical analyses and structural investigations allowed determination of the mechanisms involved in the exchanges and give new insights into the interactions occurring between the cations and the zeolite framework. Different cation sites are involved: (i) K present in the original LTL in the cancrinite cage (site KB) cannot be exchanged; (ii) the cations in KD (in the 12-membered ring channel) are always exchanged; while (iii) site KC (in the eight-membered ring channel) is involved only when K+ is substituted by NH4 +, thus promoting a higher exchange rate for NH4 + → K+ than for Na+ → K+. In the Ce-exchanged samples, a new site occupied by Ce appears in the centre of the main channel, accompanied by an increase in the number of and a rearrangement of H2O molecules. In terms of Ce exchange, the three cationic forms behave similarly, from both the chemical and structural point of view (exchanged Ce ranges from 38 to 42% of the pristine cation amount). Beyond the intrinsic structural properties of the zeolite L framework, the Ce exchange seems thus also governed by the water coordination sphere of the cation. Complete Ce recovery from zeolite pores was achieved.

THERMAL PARAMETERS AND STRUCTURAL INVESTIGATIONS OF Cu-BASED SHAPE MEMORY ALLOYS IRRADIATED WITH Co-60

Gamma radiation is a type of radiation that can change the structural properties of materials. Many physical and structural properties of metals and alloys change due to defects in their crystal structures in response to irradiation. Shape memory alloys (SMAs) are functional materials and are used in mechanical devices for monitoring nuclear facilities. In this study, copper-based SMAs were used. Copper-based SMAs are very sensitive to alloying elements and small changes in element percentages. Cu-11.6Al-0.42Be, Cu-11.8Al-0.47Be, Cu-13Al-4Ni, and Cu-13.5Al-4Ni (wt%) SMA samples were irradiated with a fixed radiation dose of 50 kGy. The effect of irradiation on the thermodynamic parameters and structural properties of copper-based SMAs was investigated. The effects of irradiation on thermodynamic parameters were determined by differential scanning calorimetry (DSC). Structural examinations were made by X-ray diffraction (XRD) and optical microscope observations. Microhardness measurements were taken. The results obtained for Cu-based SMAs were evaluated both as homogeneous and irradiated samples and according to alloying elements.