Next-generation aqueous flow battery chemistries

The battery industry is seeking solutions for large-scale energy storage that are affordable, durable, and safe. Aqueous redox flow batteries (RFBs) have the inherent properties to meet these requirements. While much has been learned over the past decade on the properties of redox materials, the focus of next-generation systems must be primarily on lowering redox material cost and increasing durability. In this context, in addition to inexpensive materials such as iron salts, redox couples based on small organic molecules have shown significant promise. A considerable level of understanding has been gained on the factors affecting the durability of aqueous RFB systems, specifically relating to molecular stability and crossover. New molecular classes, substituent strategies, and cell configurations have been identified to enhance the durability of systems in the future. Next-generation systems will also need to focus on designing molecules for achieving high energy efficiency and power density as well. Furthermore, the application of computational methods for screening of chemical stability could accelerate discovery of new molecular architectures.     

Unexpected Kinetics in the Polymerization of Ethene by Cp$\rm{ {_{2}^{{\ast}}}}$ZrCl2/MAO

A sterically hindered metallocene catalyst, Cp ZrCl₂ activated with methylaluminoxane (MAO), is found to polymerize ethene at temperatures up to 60° with a good propagation rate constant but low number of active sites, and with negligible β‐hydride elimination or β‐hydride transfer to monomer. Moreover, transmetalation to Al is found to be effectively irreversible for alkyl groups larger than Me. With the major mechanisms for chain transfer and termination suppressed, one might expect a living polymerization. The bulk polymerization of ethene was indeed found to be quasi‐living even when performed at well above room temperature, and furthermore provided rate constants which agreed remarkably well with those from the mass‐spectrometric study.     

Laser-induced structural changes in pure GeO2 glasses

We report on the characterization of structural modifications created by micro-explosions at the beam waist of a tightly focused femtosecond laser pulse inside of GeO₂ glass. Micro-Raman scattering revealed the presence of structurally strongly modified regions at and around the irradiated sites. For separations of 5 μm between adjacent irradiated sites structural modifications due to a pressure increase are observed, whereas smaller spacings of 2 μm lead to thermal effects and crystallization. The mechanisms and the interplay of pressure and temperature effects are discussed.     

Homochiral helices of oligonaphthalenes inducing opposite-handed cholesteric phases

The helical structure of the chiral nematic phases (cholesterics) obtained by doping nematic solvents with chiral non-racemic compounds is a macroscopic proof of the solute chirality. Oligonaphthalene (tetra-, hexa-, octa-) derivatives linked at the 1,4-positions have been used as chiral dopants: When the chirality axes are configurationally homogeneous (that is, all-S), the molecular structures correspond to right-handed helices. Yet, we have found series of derivatives with the surprising property that the handedness of the induced cholesteric phase alternates from positive to negative and to positive again, on passing from tetra- to hexa- and to octanaphthalene. A comparison with oligonapthalene derivatives, which do not exhibit this twisting ability, points to the importance of the substitution pattern. Both the possibility of inducing oppositely-handed cholesteric phases by homochiral helices of different length, and the role played of substituents, are confirmed by calculations performed with the surface chirality model.     

Size and shape of fast-tumbling bicelles as determined by translational diffusion

In this study, the size and shape of an isotropic bicelle have been determined by measuring the translational diffusion as a function of the volume fraction of the lipids. A linear relation between the diffusion coefficients is obtained for both DMPC and DHPC in the bicelles. The slope of this linear function, which is strongly shape-dependent, is found to be different for the two molecules. This difference is direct evidence that the two molecules are not fully mixed in the bicelle. The shape- combined with the size-dependence of the diffusion coefficient allows us to calculate both the size and shape of the bicelle.     

New screening method for basic compounds in urine by on-line extraction-high-performance liquid chromatography with photodiode-array detection

A fully automated, qualitative screening HPLC method for the identification of basic compounds in urine has been developed. A 1-ml volume of urine was extracted by on-line extraction and separated on two coupled strong cation-exchange (SCX) columns (2 x LunaSCX, 150 mm x 4.6 mm, 5 microm) under isocratic conditions. The mobile phase consisted of a mixture of potassium dihydrogenphosphate buffer (pH 2.3) and acetonitrile. The use of photodiode-array detection (DAD, lambda = 190-800 nm) gave access to a library of approximately 2600 toxicologically relevant compounds. The validated method is reliable, simple and in addition successfully proven with the analysis of real biological specimen for the routine use.     

Ion-pair supercritical fluid chromatography of metoprolol and related amino alcohols on diol silica

In this paper, a chromatographic system based on carbon dioxide with methanol as mobile phase, and diol silica as stationary phase has been investigated for metoprolol and related amino alcohols by addition of strong acids to systems with triethylamine base as primary additive. Standard conditions used were 10% of methanol, containing 24 mM of acid and 18 mM of triethylamine, in carbon dioxide with a flow rate of 1.5 ml min(-1). The column dimensions were 125 mm x 4 mm I.D. and kept at 40 degrees C with a back pressure of 150 bar. Effects on selectivity were stronger with trifluoroacetic acid than with ethanesulfonic acid. From a large set of related analytes, it was shown that selectivity changes were significant when the structure close to the nitrogen of the amino alcohol analyte differed. The stability of the column in the short time perspective was examined and it showed negligible changes. For a diastereoisomeric pair, not resolved in a basic system with triethylamine nor by addition of ethanesulfonic acid, resolution improved to about 2.1 with trifluoroacetic acid. The described approach offers a way to tune the selectivity of SFC systems when amines are analyzed without the need to change stationary phase for the chromatographic separation.     

Formation of Dusty Plasma Clouds at Meteoroid Impact on the Surface of the Moon

The nature of two dusty plasma clouds appearing because of the impact of a meteoroid on the surface of the Moon has been discussed. It has been shown that one of the clouds is formed by particles (or fragments) of regolith ejected into free space by a shock wave induced by the meteoroid impact on the surface of the Moon and the second cloud is formed by solidified melt droplets. The main characteristics of these clouds, including the cloud expansion rates, the characteristic sizes of particles in both clouds, and the concentrations and charges of particles, have been calculated. The calculated cloud expansion rates are in qualitative agreement with the observational data.     

Spectroscopic and photophysical properties of dUTP and internally DNA bound fluorophores for optimized signal detection in biological formats

Efficient signal generation in DNA-based assays requires understanding of the influence of fluorophore's interactions on the spectroscopic properties. The resulting changes in fluorescence intensity, quantum yield, emission anisotropy, and fluorescence lifetime provide straightforward tools for the study of molecular dynamics and interaction between labels and nucleic acids. Searching for bright fluorescent reporters for rolling circle amplification (RCA) as efficient signal enhancement strategy for biological formats, we investigated the spectroscopic properties of seven dyes: cyanines, rhodamines, and BODIPYs. They spectrally resemble Cy3, the most frequently used fluorophore in biodetection formats, and are measured in six samples (free dye, dye-dUTP, internally labeled ssDNA and dsDNA-single- and triple-labeled) using steady-state and time-resolved fluorometry. Special emphasis was dedicated to characterizing the nature of the interaction of these fluorophores differing in dye class, charge, and rigidity. Our results suggest dye charge and structure as main factors governing the dye's interactions, with DY-555 and Cy3B presenting the best candidates for our envisaged signal amplification strategy. This label comparison underlines the importance of a proper understanding of structure-property relations and dye-biomolecule interactions for reporter choice and presents a road map towards the design and interpretation of experiments using these labels on DNA of known sequence.