Radiation-induced crosslinking and grafting of two polyphosphazene elastomers

The radiation-induced crosslinking and grafting of two aryloxy-substituted elastomeric polyphosphazenes have been carried out by both gamma and electron beam irradiation. The classic Charlesby–Pinner [1] plus a simpler approach were used to determine the G(X) values for the crosslinked elastomeric polymers. The apparent G(X) value for the same polymer depended on whether the gamma-ray or the E-beam results were used. The presence of 8.5% repeat units with allylic groups in the side chain increased the G(X) value by an order of magnitude when the irradiation was performed under vacuum with the gamma source. The extent of acrylic acid grafting was also higher for the polymer containing the allylic group. Nearly all the grafted polyphosphazene films were insoluble in THF, a good solvent for the ungrafted samples.     

A [2]rotaxane capped by a cyclodextrin and a guest: formation of supramolecular [2]rotaxane polymer

A [2]rotaxane capped by a beta-cyclodextrin and a 2,4,6-trinitrophenyl group has been prepared by dissolving 6-aminocinnamoyl beta-cyclodextrin in water with 1-adamantane carboxylic acid and complexation with alpha-cyclodextrin followed by the reaction with 2,4,6-trinitrobenzene sulfonic acid sodium salt. The [2]rotaxane has been found to form supramolecular polymers by host-guest interactions.     

Hexakis(2-pyridyl)- and hexakis(3-pyridyl)[3]radialene: novel,water-soluble [3]radialenes with potential utility for supramolecular chemistry

The titled [3]radialenes are the first, water-soluble hexaaryl[3]radialenes with considerably high electron affinity, their alkali metal reduction giving rise to anion-radicals and dianions stepwise as fairly stable species in degassed tetrahydrofuran.     

Aggregated structure analysis of polymer-protected platinum/ruthenium colloidal dispersions using EXAFS, HRTEM, and electron diffraction measurements

Polymer-protected platinum/ruthenium colloidal dispersions were prepared by refluxing mixed solutions of hexachloroplatinic(IV) acid and ruthenium(III) chloride in a mixture of ethanol/water (1/1 v/v) in the presence of poly(N-vinyl-2-pyrrolidone). The electronic spectra and transmission electron micrographs suggested that the colloidal dispersions are almost composed of the mixture of the small monometallic Pt and Ru clusters over all the ratio of Pt/Ru compositions. Extended X-ray absorption fine structure analyses and high resolution electron microprobe analyses indicated that no Pt/Ru alloy clusters exist in the dispersions, and the aggregation occurs between small monometallic Pt clusters (diameter ca. 15 A) and partially oxidized Ru microclusters (diameter less than 10 A). Electron diffraction measurements also suggested that the diffraction pattern of aggregated Pt/Ru cluster particles prepared by the simultaneous reduction of Pt and Ru ions is the same as that of the physical mixture of the small monometallic Pt and Ru clusters separately prepared. Therefore, it can be concluded that the aggregated Pt/Ru cluster particles, with 10 to 60 A in diameter, are built up by small monometallic Pt clusters and partially oxidized Ru microclusters, and that Pt/Ru alloy clusters are not formed.     

On the selection of the optimal plasticizer for calix[n]arene-based ion-selective electrodes: Possible correlation between the ion selectivity and the ‘softness’ of the plasticizer

A criterion for the selection of a suitable plasticizer for calix[n]arene-based ion-selective electrodes is discussed. The cation selectivity of plasticized membranes without the ligand was first measured as a reference. The membranes can be roughly classified into two groups. The first group shows cation selectivity in the order Cs⁺+>K⁺>Na⁺>Li⁺. The membranes in the second group are made of phosphorus plasticizers, which show a selectivity in the reverse order. The plasticizers in the first group featured a linear relationship between the dipole moment of the plasticizer (calculated by a PM3 method) and the ratio of cesium selectivity to lithium selectivity. The linear relationship supports the view that the polar membrane which includes a soft plasticizer with a large dipole moment shows selectivity for Cs⁺, whereas the nonpolar membrane including the soft plasticizer with the small dipole moment shows much lower selectivity for Cs⁺. Next, 2-fluorphenyl-2-nitrophenyl ether (FPNPE) which showed the highest Cs⁺ selectivity and tris(2-ethylhexyl)phosphate (TEHP) which showed the highest Li⁺ selectivity were mixed in an appropriate ratio to make membranes with a different affinity for hard ions. The metal selectivities of several crown-based and calixarene-based ionophores were examined in these membranes. Although a few exceptions exist, the polar soft membrane is favorable when the interfering metal ion is hard, whereas the hard membrane is favorable when the interfering metal ion is soft.     

Effect of mono-CDNP substitution of lysine residues on the redox reaction of cytochrome c electrostatically adsorbed on a mercaptoheptanoic acid modified Au(111) surface

The effect of charge-inverting modification of single surface lysine residue on the electron transfer (ET) reaction of horse heart cytochrome c (cyt c) is examined for 12 different types of mono-4-chloro-2,5-dinitrobenzoic acid substituted cyt c (mCDNPc) adsorbed on a Au(111) electrode modified with a self-assembled monolayer (SAM) of 7-mercapto-heptanoic acid (MHA). A negative shift in the redox potential by 10-35 mV as compared to that of native cyt c and a monolayer coverage in the range of 13-17 pmol cm(-2) are observed for electroactive mCDNPc's. The magnitude of the decrease in the ET rate constant (k(et)) of mCDNPc's compared with that of native cyt c depends on the position of the CDNP substitution. For mCDNPc's in which the modified lysine residue is outside of the interaction domain of cyt c with the SAM, the ratio of the k(et) of mCDNPc to that of native cyt c is correlated to the change in the dipole moment vector of cyt c due to the CDNP modification. This correlation suggests that the dipole moment of cyt c determines its orientation of adsorption on the SAM of MHA and significantly affects the rate of the ET. The CDNP modification of lysine residues at the interaction domain significantly decreases the rate, demonstrating the importance of the local charge environment in determining the rate of ET.     

Improvement of chemical analysis of antibiotics. X. Determination of eight tetracyclines using thin-layer and high-performance liquid chromatography

Analytical methods for eight tetracyclines (TCs) were established using silica gel high-performance thin-layer chromatography (HPTLC), reversed-phase thin-layer chromatography (RP-TLC) and high-performance liquid chromatography (HPLC). Good separations of eight TCs were obtained using chloroform-methanol-5% disodium ethylenediaminetetraacetate solution (65:20:5) (lower layer) and methanol acetonitrile 0.5 M oxalic acid solution (1:1:4) (pH 3.0) on silica gel HPTLC and C8 TLC plates, respectively. A combination of HPTLC and RP-TLC made possible the identification of the eight TCs. Each calibration graph was linear between 0.1 and 1.0 microgram using UV densitometry except for rolitetracycline. For detection reagents, the diazonium salts including Fast Violet B gave variously coloured spots with the eight TCs and good sensitivities were obtained except with minocycline. In HPLC, the simultaneous analysis of the eight TCs on a C8 column was possible using methanol-acetonitrile-0.01 M oxalic acid solution (1:1.5:7) adjusted to pH 3.0 as the mobile phase. A linear relationship was obtained between 1.0 and 10 ng using the usual sample preparation except for rolitetracycline. The direct determination of rolitetracycline was possible using tetrahydrofuran, dimethyl sulphoxide and the mobile phase as solvents for preparation of the sample. For the determination of residual rolitetracycline, it was effective to measure the amount of rolitetracycline as tetracycline by HPLC, HPTLC and RP-TLC after conversion of rolitetracycline to tetracycline by incubating for 5 min in methanol at 50 degrees C.     

Formation of Supramolecular Polymers Constructed by Cyclodextrins with Cinnamamide

-Cyclodextrin having cinnamamide at 6- or 3-positions (6-CiNH--CD, 3-CiNH--CD) and -cyclodextrin with cinnamamide on 6-position (6-CiNH--CD) have been prepared. Supramolecular structures were formed in the solid state or aqueous solutions and characterized by measurements of NMR and vapor pressure osmometry (VPO). The results indicate that 6-CiNH--CD formed insoluble supramolecular polymers in the solid state, while 6-CiNH--CD and 3-CiNH--CD formed supramolecular complexes in aqueous solutions. 6-CiNH--CD was found to form a dimer in an aqueous solution. 3-CiNH--CD formed intermolecular complexes to give supramolecular polymers. The differences of the position of guest part on cyclodextrins caused to give a variety of supramolecular structures in aqueous solutions.     

Ca0.8Y2.4Sn0.8O6, a quaternary oxide with mixed occupations of Ca/Y and Y/Sn

A new quaternary oxide, calcium yttrium stannate, Ca_0.8Y_2.4Sn_0.8O₆, is isostructural with Mg₃TeO₆ (trigonal, R). The empirical formula can be expressed as (Ca_0.2667Y_0.7333)₆(Y_0.4Sn_0.6)SnO₁₂. The Ca/Y site has a distorted coordination octa­hedron of O atoms, with Ca/Y—O distances ranging from 2.227 (3) to 2.350 (3) Å, while the octa­hedra of O atoms that coordinate to the Sn and Y/Sn sites are nearly regular, with an Sn—O distance of 2.066 (2) Å and a Y/Sn—O distance of 2.147 (3) Å.