Green synthesis of water splitting electrocatalysts: IrO2 nanocages via Pearson's chemistry

Highly porous iridium oxide structures are particularly well-suited for the preparation of porous catalyst layers needed in proton exchange membrane water electrolyzers. Herein, we report the formation of iridium oxide nanostructured cages, via a water-based process performed at room temperature, using cheap Cu₂O cubes as the template. In this synthetic approach, based on Pearson''s hard and soft acid–base theory, the replacement of the Cu₂O core by an iridium shell is permitted by the difference in hardness/softness of cations and anions of the two reactants Cu₂O and IrCl₃. Calcination followed by acid leaching allow the removal of residual copper oxide cores and leave IrO₂ hierarchical porous structures with outstanding activity toward the oxygen evolution reaction. Fundamental understanding of the reaction steps and identification of the intermediates are permitted by coupling a set of ex situ and in situ techniques including operando time-resolved X-ray absorption spectroscopy during the synthesis.

Hierarchical IrO₂ nanocages, easily synthesized in water at room temperature, are extremely active towards the oxygen evolution reaction. The formation mechanism is based on the difference in softness/hardness of the ions involved in the reaction.     

Calculation of densities of aqueous electrolyte solutions at subzero temperatures

We developed a FORTRAN program based on the Pitzer equations to calculate densities of electrolyte solutions at subzero temperatures. Data from the published literature collected at -28.9, -17.8, -12.2, -6.7, 0, and 25°C were used to calculate the Pitzer-equation parameters and to evaluate model performance. Three approaches to estimating the molar volume of the solute at infinite dilution were evaluated: (1) extrapolation of apparent molar volumes to zero square-root ionic strength; (2) calculation with the Tanger and Helgeson model; and (3) global fit of the data in which the molar volume of the solute at infinite dilution was estimated along with the Pitzer-equation parameters. The last approach gave parameter estimates that reproduced the experimental data most accurately. The parameterized model predicted accurately densities of single-electrolyte and multielectrolyte solutions at -28.9, -17.8, -12.2, -6.7, 0, and 25°C. Available experimental data are generally quite poor. Accordingly, Pitzer-equation parameters estimated for subzero temperatures should be viewed as conditional until improved measurements of single-electrolyte solution densities at subzero temperatures are made.     

Characterization of long time fluctuations of forces exerted on an oscillating circular cylinder at KC=10

Flow dynamics, in-line and transverse forces exerted on an oscillating circular cylinder in a fluid initially at rest are studied by numerical resolution of the two-dimensional Navier-Stokes equations. The Keulegan-Carpenter number is held constant at KC=10 and Re is increased from 40 to 500. For the different flow regimes, links between flow spatio-temporal symmetries and force histories are established. Besides simulations of long duration show that in two ranges of Re, forces exhibit low frequency fluctuations compared to the cylinder oscillation frequency. Such observations have been only mentioned in the literature and are more deeply examined here. In both ranges, force fluctuations correspond to oscillations of the front and rear stagnation points on the cylinder surface. However, they occur in flow regimes whose basic patterns (V-shaped mode or diagonal mode) have different symmetry features, inducing two distinct behaviors. For 80≤Re≤100, fluctuations are related to a spectral broadening of the harmonics and to a permutation between three vortex patterns (V-shaped, transverse and oblique modes). In the second range 150≤Re≤280, amplitude fluctuations are correlated to the appearance of low frequency peaks interacting with harmonics of the cylinder frequency. Fluctuations are then a combination of a wavy fluctuation and an amplitude modulation. The carrier frequency corresponding to the wavy fluctuation depends on Re and is related to a fluid characteristic time; the modulation frequency is independent of Re and equal to 1/4 of the cylinder oscillation frequency.     

Design and Synthesis of (13S)‐Methyl‐Substituted Arachidonic Acid Analogues: Templates for Novel Endocannabinoids

Two novel methyl‐substituted arachidonic acid derivatives were prepared in an enantioselective manner from commercially available chiral building blocks, and were found to be excellent templates for the development of (13S)‐methyl‐substituted anandamide analogues. One of the compounds synthesized, namely, (13S,5Z,8Z,11Z,14Z)‐13‐methyl‐eicosa‐5,8,11,14‐tetraenoic acid N‐(2‐hydroxyethyl)amide, is an endocannabinoid analogue with remarkably high affinity for the CB1 cannabinoid receptor.     

p1,n1 salts: Self-assembled supramolecular structures sequestering racemates. Diastereomeric separation and enantiomeric enrichment of trans-chrysanthemic acid

The occurrence of p1,n1 salts can be exploited to sequester racemates; an application to technical mixtures of chrysanthemic acids (ChA) allowed the separation of trans- and cis-ChA and the recovery of the excess enantiomer of trans-ChA.     

Rational design of a beta-lactamase inhibitor achieved via stabilization of the trans-enamine intermediate: 1.28 A crystal structure of wt SHV-1 complex with a penam sulfone

beta-Lactamases are one of the major causes of antibiotic resistance in Gram negative bacteria. The continuing evolution of beta-lactamases that are capable of hydrolyzing our most potent beta-lactams presents a vexing clinical problem, in particular since a number of them are resistant to inhibitors. The efficient inhibition of these enzymes is therefore of great clinical importance. Building upon our previous structural studies that examined tazobactam trapped as a trans-enamine intermediate in a deacylation deficient SHV variant, we designed a novel penam sulfone derivative that forms a more stable trans-enamine intermediate. We report here the 1.28 A resolution crystal structure of wt SHV-1 in complex with a rationally designed penam sulfone, SA2-13. The compound is covalently bound to the active site of wt SHV-1 similar to tazobactam yet forms an additional salt-bridge with K234 and hydrogen bonds with S130 and T235 to stabilize the trans-enamine intermediate. Kinetic measurements show that SA2-13, once reacted with SHV-1 beta-lactamase, is about 10-fold slower at being released from the enzyme compared to tazobactam. Stabilizing the trans-enamine intermediate represents a novel strategy for the rational design of mechanism-based class A beta-lactamase inhibitors.     

A validated method for the determination of traces of UV filters in fish using LC–MS/MS

An analytical method for the determination of UV filter substances in fish tissue has been developed and validated using benzophenone-3, 3-(4-methylbenzylidene)-camphor, 2-ethylhexyl-2-cyano-3,3-diphenyl-2-propenoate and 2-ethylhexyl 3-(methoxyphenyl)-2-propenoate as target analytes. The fish fillets were homogenised and extracted by Soxhlet extraction. The extracts were run through a clean-up process including gel permeation chromatography followed by solid-phase extraction. Quantification of the compounds was performed using liquid chromatography with tandem mass spectrometric detection. Blank fish as well as spiked blank fish were analysed to validate the analytical method. The analytical method developed has the multiple advantages of enabling separation, simultaneous identification and quantification of each of the four selected compounds in a single run. Contamination of blank samples and abnormally high concentrations in spiked samples were avoided by taking extensive precautions during the fish preparation procedure. The method was validated in accordance with internationally accepted criteria, such as specificity, accuracy and repeatability. The combination of LC with tandem mass spectrometry ensures a high level of specificity. The accuracy of the method was reported as the mean recovery rate for the analytes in the sample matrix. Mean recoveries were in the range 86–108%. The precision is expressed as the relative standard deviation, and in all but one of the cases was 20% or below. The accuracy of the method allows residue analyses to be performed on biological matrices at ng/g levels. The determined limit of quantification for each analyte was 8 ng/g fish. For all spiking levels ≥8 ng/g, relative standard deviations were ≤ 20%.