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.     

The structure of compact disjointness preserving operators on continuous functions

Let T be a compact disjointness preserving linear operator from C₀(X) into C₀(Y), where X and Y are locally compact Hausdorff spaces. We show that T can be represented as a norm convergent countable sum of disjoint rank one operators. More precisely, T = Σ_n δ ?h_n for a (possibly finite) sequence {x_n }_n of distinct points in X and a norm null sequence {h_n }_n of mutually disjoint functions in C₀(Y). Moreover, we develop a graph theoretic method to describe the spectrum of such an operator (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

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.     

Primary and secondary relaxations in supercooled eugenol and isoeugenol at ambient and elevated pressures: dependence on chemical microstructure

Dielectric loss spectra of two glass-forming isomers, eugenol and isoeugenol, measured at ambient and elevated pressures in the normal liquid, supercooled, and glassy states are presented. The isomeric chemical compounds studied differ only by the location of the double bond in the alkyl chain. Above the glass transition temperature T(g), the dielectric loss spectra of both isomers exhibit an excess wing on the high frequency flank of the loss peak of the alpha relaxation and an additional faster gamma process at the megahertz frequency range. By decreasing temperature below T(g) at ambient pressure or by elevating pressure above P(g), the glass transition pressure, at constant temperature, the excess wing of isoeugenol shifts to lower frequencies and is transformed into a secondary beta-loss peak, while in eugenol it becomes a shoulder. These spectral features enable the beta-relaxation time tau(beta) to be determined in the glassy state. These changes indicate that the excess wings in isoeugenol and eugenol are similar and both are secondary beta relaxations that are not resolved in the liquid state. While in both isoeugenol and eugenol the loss peak of the beta relaxation in the glassy state and the corresponding excess wing in the liquid state shifts to lower frequencies on elevating pressure, the locations of their gamma relaxation show little change with increasing pressure. The different pressure sensitivities of the excess wing and gamma relaxation are further demonstrated by the nearly perfect superposition of the alpha-loss peak together with excess wing from the data taken at ambient pressure and at elevated pressure (and higher temperature so as to have the same alpha-peak frequency), but not the gamma-loss peak in both isoeugenol and eugenol. On physical aging isoeugenol, the beta-loss peak shifts to lower frequencies, but not the gamma relaxation. Basing on these experimental facts, the faster gamma relaxation is a local intramolecular process involving a side group and the slower beta relaxation mimics the structural alpha relaxation in behavior, involves the entire molecule and satisfies the criteria for being the Johari-Goldstein beta relaxation. Analysis and interpretation of the spectra utilizing the coupling model further demonstrate that the excess wings seen in the equilibrium liquid states of these two isomers are their genuine Johari-Goldstein beta relaxation.     

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.     

Highly enantioselective direct reductive coupling of conjugated alkynes and alpha-ketoesters via rhodium-catalyzed asymmetric hydrogenation

Catalytic hydrogenation of 1,3-enynes 1a-7a in the presence of ethyl pyruvate and related activated ketones using chirally modified cationic rhodium catalysts results in reductive coupling to afford dienylated alpha-hydroxy esters 1b-7b and 3c-3f with exceptional levels of regio- and enantiocontrol. These studies represent the first highly enantioselective direct catalytic reductive couplings of alkynes to ketones. As illustrated by the conversion of 6b to 6c-6h, the diene containing the side chain of the coupling products is subject to diverse chemo- and regioselective manipulation. Reductive coupling of enyne 6a and ethyl pyruvate using elemental deuterium provides the monodeuterated product deuterio-6b, consistent with a catalytic mechanism involving alkyne-carbonyl oxidative coupling followed by hydrogenolytic cleavage of the resulting oxametallacycle, as corroborated by ESI-MS analysis.