Synthesis, structure, and nonlinear optical properties of cross-conjugated perphenylated iso-polydiacetylenes

Monodisperse, cross-conjugated perphenylated iso-polydiacetylene (iso-PDA) oligomers, ranging from monomer 15 to pentadecamer 25, have been synthesized by using a palladium-catalyzed cross-coupling protocol. Structural characteristics elucidated by X-ray crystallographic analysis demonstrate a non-planar backbone conformation for the oligomers due to the steric interactions between alkylidene phenyl groups. The electronic absorption spectra of the oligomers show a slight red-shift of the maximum absorption wavelength as the chain length increases from dimer 17 b to pentadecamer 25, a trend that has saturated by the stage of nonamer 22. Fluorescence spectroscopy confirms that the pendent phenyl groups present on the oligomer framework enhance emission, and the relative emission intensity consistently increases as a function of chain length n. The molecular third-order nonlinearities, gamma, for this oligomer series have been measured via differential optical Kerr effect (DOKE) detection and show a superlinear increase as a function of the oligomer chain length n. Molecular modeling and spectroscopic studies suggest that iso-PDA oligomers (n>7) adopt a coiled, helical conformation in solution.     

Homoatomic P --> P coordination: a versatile synthetic approach to polyphosphorus dications

Polyphosphorus dications have been synthesised and comprehensively characterised as diphosphine (dppe, dmpe and dpph) linked Ar2P+ Lewis acids (Ar = C6H5); this application of unique homoatomic coordination chemistry provides important building blocks for extended systems.     

Chemicals from forest products by supercritical fluid extraction

Supercritical acetone or methanol extraction of wood gave liquid products with a maximum yield of 74%. Approximately 5% of these complex products was identified as substituted guaiacols and levoglucosan. Acetone extract could substitute for 30% of the phenol in phenolic resins.

Resin and fatty acids were extracted from southern pine and waxes from Douglas-fir bark using supercritical carbon dioxide, nitrous oxide, propane or ethylene. Of these, propane and nitrous oxide gave the best yields.     

Study of cross-conjugated iso-polytriacetylenes and related oligoenynes

Two series of monodisperse cross-conjugated oligomers based on enyne repeat units have been realized. The first class of molecules, iso-polytriacetylenes (iso-PTAs, 2), was divergently synthesized using an iterative sequence of palladium-catalyzed cross-coupling reactions of vinyl triflate 5 with terminal alkynes. The second series of oligoenynes (17-20) are based on an octatetrayne backbone, and result from homocoupling of the differentially protected iso-PTA oligomers 8-11. The longest member of this series, 20, spans ca. 5.6 nm from Si atom to Si atom and is composed of a contiguous sequence of 44 sp and sp(2) carbons. The lowest energy electronic absorption band for iso-PTA dimers in the progression 13 --> 9 --> 16 is consistently red-shifted as a result of extending the cross-conjugated structure. A similar comparison within each series (i.e., 16, 6-7, or 17-20), however, suggests little effect on the electronic characteristics of these molecules as oligomer length is increased. The solid-state properties of one derivative, 17, are also described.     

Copper(II) coordination to ligands immobilized on photoluminescent porous silicon

Increased preorganization can be achieved by immobilizing ligands on solid supports. Photoluminescent porous silicon, which can undergo facile hydrosilylation, was used as a support for open chain neutral N- and O-donor ligands. The abilities of these ligands to bind the divalent metal ions Ni(2+), Cu(2+), Zn(2+), and Pb(2+) are examined. Immobilized ligands selectively complexed Cu(II) over the other metal ions studied. Ligands immobilized on photoluminescent porous silicon also removed a significant amount, up to 98%, of Cu(II) from copper(II)-spiked, organic-rich, seawater samples.     

Ion flotation of zinc using ethylhexadecyldimethylammonium bromide

Zinc ions react with the surfactant ethylhexadecyldimethylammonium bromide (EHDABr) to form a surface active sublate which can be removed from aqueous chloride solutions by ion flotation. A typical ion flotation procedure involves passing air through a 235-ml solution containing 5 ppm Zn²⁺, 2.0 M HCl, and 2.5 × 10^?3M EHDABr at a flow rate of 40 ml/min for 150 min. The procedure is simple and rapid. Cadmium, copper, lead, and nickel ions cause reductions of zinc flotation efficiencies of less than 2.5% under the experimental conditions.     

Determination of the distribution of cannabinoids in cannabis resin from the Lebanon using HPLC. Part III

Samples taken from 61 slabs of cannabis resin originating in The Lebanon were examined by high performance liquid chromatography. The slabs were derived from seizures of cannabis resin made over a three-year period. From a study of 14 of these samples, taken from bags which bore a number of identical stamp marks, it was shown that there was a correlation between the cannabinoid distribution and the marks. The remaining 47 samples of cannabis resin, all of which were from bags with different marks, were each found to have a unique cannabinoid distribution. Such an examination can therefore be used to aid investigations where evidence of a common origin is sought.     

Colorimetric uranium determination with arsenazo

A rapid and sensitive method is described for the quantitative colorimetric determination of uranium(Vl). Masking agents such as EDTA, tartaric acid or thioglycerol make possible the determination of uranium in the presence of many foreign metal ions. If thorium is present, a preliminary extraction of uranium as the diethyldithiocarbamate is required.