Self-assembled thermoreversible gels of nonpolar liquids by racemic propargylic alcohols with fluorinated and nonfluorinated aromatic rings

The synthesis and colloidal study of a new class of low molecular weight organogelators is reported. Racemic propargylic alcohols with perfluoroaryl and nonfluorinated aryl rings are capable of forming gels in alkane liquids and/or silicone oil. A full colloidal characterization of alkane gels prepared from (R/S)-1-pentafluorophenyl-3-phenylprop-2-yn-1-ol [(R/S)- 1] was conducted, including both structural [optical microscopy, scanning electron microscopy (SEM), powder X-ray diffraction (XRD), attenuated total reflectance infrared spectroscopy (ATR-IR)] and thermal stability [differential scanning calorimetry (DSC)] studies. A model of the organization of gelator molecules within gel fibers has been proposed primarily based on the correlation of diffraction data for the powder XRD pattern of a gel and a simulated powder pattern from a sublimed crystal of the gelator. Furthermore, structural requirements for propargylic alcohol gelators were investigated by subjecting derivatives with modified structures to gelation tests. An enantiomerically enriched sample [(R)- 1, 83% ee] fails to entrap the solvent under conditions where the racemate successfully forms a gel. The remaining racemic derivatives (with p-alkoxy or p-alkyl substituents on the nonfluorinated arene) form gels or partial gels in silicone oil and in some alkane preparations.     

Simultaneous determination of metal traces by ICP-MS in environmental waters using SPE preconcentration on different polymeric sorbents

This paper deals with multielement profiling of microlements in the form of their isotopes ⁹Be, ⁵¹V, ⁵⁹Co, ⁶⁰Ni, ⁸⁹Y, ¹¹¹Cd, ²⁰⁸Pb, ²³²Th, and ²³⁸U. After their complexation by 4-(2-pyridylazo)resorcinol (PAR), 3,4-dihydroxy-9,10-dioxo-2-anthracenesulfonic acid sodium salt (ALS), 8-hydroxyquinoline-5-sulphonic acid (8-HQS), and ammonium pyrrolidinedithiocarbamate (APDC), the elements were preconcentrated and separated on Amberlite XAD-16 and Amberlite SDB-L prior to their analysis by inductively coupled plasma mass spectrometry. Various parameters such as pH, eluent type and volume, presence of surfactants and volume, and matrix effects on the retention of analytes were examined. Relative standard deviation and recovery values for four replicate determinations under optimal condition were in the range of 0.2?C3.6 % and 59?C98 %. The proposed method was applied to the determination of elements in lake water sample and industrial water. Recovery experiments with spiked water samples were performed.     

Propagation of mode shape errors in structural identification

It is of interest to the modal testing and health monitoring community to quantify how an error in any identified mode shape propagates to the identified flexibility matrix. Here this problem is investigated in a probabilistic framework. The approach followed involves deriving analytical expressions to track how errors, due to random deviations between identified and “true” mode shapes, propagate to the Modal Assurance Criterion (MAC) and the Coordinate Modal Assurance Criterion (COMAC) values as well as the estimated flexibility matrix. The comparison of the expected values and variances of these errors identifies the inconsistency between the magnitude of errors in the MAC and COMAC values and the identified flexibility matrix. The analytical results are further validated via Monte Carlo simulations. Finally, two mode shape comparison criteria, termed as the Flexibility Proportional Modal Assurance Criterion (FPMAC) and the Flexibility Proportional Coordinate Modal Assurance Criterion (FPCOMAC), are proposed. These new criteria aim to mimic the expected error in the predicted flexibility matrix in a direct comparison of the identified and “true” mode shapes, and hence they can be used to complement MAC and COMAC in interpreting the analysis results.     

A highly catalytic asymmetric conjugate addition: synthesis of the C14-C20 fragment of antibiotic TMC-151A, siphonarienal and siphonarienone

A highly selective and general method for the synthesis of enantiopure deoxypropionates via the iterative application of CuI-Tol-BINAP-catalyzed asymmetric conjugate addition is described. This method gives access to all possible stereoisomers since both syn- and anti-deoxypropionates were obtained in high diastereoselectivities. The usefulness of the method is further exemplified by the preparation of two marine organisms, siphonarienal and siphonarienone, from commercially available trans-2-hexenoate.     

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Stability of Residual Oxides in Oxide‐Derived Copper Catalysts for Electrochemical CO2 Reduction Investigated with 18O Labeling

Oxide‐derived (OD) Cu catalysts have high selectivity towards the formation of multi‐carbon products (C₂/C₃) for aqueous electrochemical CO₂ reduction (CO₂R). It has been proposed that a large fraction of the initial oxide can be surprisingly resistant to reduction, and these residual oxides play a crucial catalytic role. The stability of residual oxides was investigated by synthesizing ¹⁸O‐enriched OD Cu catalysts and testing them for CO₂R. These catalysts maintain a high selectivity towards C₂/C₃ products (ca. 60 %) for up to 5 h in 0.1 m KHCO₃ at ?1.0 V vs. RHE. However, secondary‐ion mass spectrometry measurements show that only a small fraction (<1 %) of the original ¹⁸O content remains, showing that residual oxides are not present in significant amounts during CO₂R. Furthermore, we show that OD Cu can reoxidize rapidly, which could compromise the accuracy of ex situ methods for determining the true oxygen content.     

Interwining Operators for Vertex Representations of Toroidal Lie Algebras

The construction of the vertex representation of the toroidal Lie algebra ^[n] depends on the way of labelling the points in the dual ⁿ of the torus Tⁿ. Thus there is a built-in symmetry of the vertex representation with respect to the symmetry of Zⁿ. In conjunction with this, the energy operator L₀ gives rise to intertwining operators which reflect the symmetry of the vertex representation with respect to S¹ action on .