Generalised Weyl–Heisenberg frame operators

We seek to characterise, in simple and unsophisticated terms, frame operators of Weyl–Heisenberg frames. We succeed only partially, using the newly introduced concepts of window operators and tile vertices. However, we are able to completely characterise the frame operator in each of two newly introduced classes: window Weyl–Heisenberg frames (a special class of Weyl–Heisenberg frames) and generalised Weyl–Heisenberg frames (a class more general than Weyl–Heisenberg frames).     

Near-oscillatory relaxation behavior of levitation force in infiltration and growth processed bulk YBCO/Ag superconducting composites

Time relaxation behavior of levitation force has been studied in IGP bulk YBCO/Ag superconductor using levitation force measurements as these measurements throw light on the magnetic relaxation in superconductors and the underlying vortex dynamics, pinning mechanisms and the nature of pinning forces. The measurements have revealed a hitherto unknown near-oscillatory relaxation of the levitation force with varying magnetic field. This kind of behavior is found to be more pronounced at smaller gap distances between the permanent magnet and the superconductor. A switch-type polarity bistable equilibrium model for the supercurrent structure has been proposed based on the understanding that even the permanent magnet gets magnetized in the presence of the superconductor, which has also been verified and reported here. This model satisfactorily explains the observed oscillatory behavior of relaxation rates.     

Allylic carbon-carbon double bond directed Pd-catalyzed oxidative ortho-olefination of arenes

Pd-catalyzed selective ortho-olefination of arenes assisted by an allylic C-C double bond at room temperature using O(2) as a terminal oxidant is described. A possible mechanism involving the initial coordination of allylic C═C bond to Pd followed by selective o-C-H bond metalation is proposed.     

Isolation, enzyme-bound structure, and activity of platensimycin A1 from Streptomyces platensis

Inhibition of fatty acid synthesis is emerging as a valuable target for antibacterial agents. Platensimycin and platencin are novel natural products that were reported recently to inhibit the FabF and FabF/FabH condensing enzymes, respectively, present in the fatty acid biosynthetic pathway. Selective inhibition of these enzymes by platensimycin and platencin accounts for their potent antibiotic activity. We have continued our quest to find additional members of this class of compounds leading to discovery of platensimycin A₁, a hydroxylated congener. We report herein the isolation, structure, antibacterial and enzymatic activities, and co-crystal structure bound to Escherichia coli FabF. The lower activity of platensimycin A₁ suggests that substitution at C-14 is detrimental for the activity.     

Cadmium bioavailability and speciation using the permeation liquid membrane

The permeation liquid membrane (PLM) technique was used to evaluate cadmium speciation in media resembling natural freshwaters. A planar sheet PLM system was characterized by measuring Cd fluxes in the absence and presence of complexing agents such as citrate, malonate, nitrilotriacetate and the Suwannee River standard humic acid. Comparison with theoretical speciation calculations and the results of a Cd²⁺ selective electrode, showed that free Cd was correctly measured using the planar sheet PLM within the studied concentration range, i.e. 10⁻⁸ to 10⁻⁴ M. The effect of pH and potentially co-transported ions on Cd transport through the PLM was also studied. An example of the ability of the hollow-fiber PLM (HFPLM) to measure free Cd in the nM range is also presented. In order to evaluate the usefulness of the technique as a predictor of bioavailability, Cd PLM measurements (fluxes) were compared to Cd biouptake (internalization flux) for a freshwater alga, Chlorella kesslerii, in the absence and presence of SRHA. The use of PLM measurements is shown to be an attractive tool to better understand Cd biouptake.     

Facile synthesis, fluorescence, and photochromism of novel helical pyrones and chromenes

[reaction: see text] Aryl coumaryl ethylenes undergo oxidative photocyclization readily to yield helical pyrone-annulated condensed aromatics. The pyrones are conveniently converted to the corresponding photochromic diphenylpyrans/chromenes. Both pyrones and chromenes exhibit helicity-dependent fluorescence efficiency and persistence, respectively.     

3-(1-Chloro­vinyl)-2,4,6-tri­methoxy­benz­aldehyde

The title compound, C₁₂H₁₃ClO₄, was prepared from the Vilsmeier–Haack reaction on phloroaceto­phenone. The chloro­vinyl and one of the methoxy substituents are twisted through about 75° with respect to the aromatic plane, whilst the other substituents are almost coplanar with the ring. Intermolecular hydrogen bonding involving C—H⃛O interactions generates one-dimensional chains in the direction of the a axis.