Determination of uranium at ultratrace levels by time-resolved laser fluorimetry

Uranium at ultratrace levels in the pelleted cake from a NaF/Na₂CO₃/K₂CO₃ (10:45:45) fusion is determined by laser fluorimetry. Light scattering and fluorescence from impurities are greatly reduced by time-resolved fluorimetry. The optimum excitation wavelength is shown to be 360 nm from the signal-to-background ratio spectrum; emission is measured at 555 nm. The detection limit is 9 ng kg^?1 for a standard uranium sample. Relative standard deviations in the determination of ca. 50 ng kg^?1 uranium in silica samples are about 10%.     

Lens Design: Global Optimization with Escape Function

The technique of using the ‘escape function’ for global optimization in lens design is described. This includes how to identify two solutions as independent; the threshold value for this criterion can be chosen to determine how to explore local solutions—rough or fine. Choice of appropriate values for two parameters in the escape function is most important, since this will affect the efficiency of the automatic global optimization process. There are two problems, i.e. giving default values at the beginning of the design, and determining a default rule to change them when the escape is unsuccessful. The latter was solved by assuming a ‘saddle path’ as the best route to escape. An exact solution for the former was not found, but a hint for finding a second best solution is shown based on the statistical study of local minima.     

Preparation of polypseudorotaxane consisting of fluorescent molecule-modified β-cyclodextrins and biotin-terminated poly(propylene glycol) with high yield

A polypseudorotaxane was prepared using 4-(N,N-dimethylamino) benzoyl modified β-cyclodextrin (DMAB-β-CD) and biotin-terminated poly(propylene glycol) (biotin-terminated PPG) in water for 7 days. When the biotin-terminated PPG was added to a saturated solution of DMAB-β-CD at room temperature, the polypseudorotaxane was not obtained. However, with increasing temperature to 60 °C, precipitation was observed. The ¹H-NMR spectrum indicated that the obtained precipitate was the polypseudorotaxane. The final yield was 54%, which was higher than that previously reported for polypseudorotaxane formation using chemically modified β-CD. The polypseudorotaxane can be useful to make a polyrotaxane via avidin–biotin molecular recognition using the terminal biotin group.     

Adsorption states of dialkyl ditelluride autooxidized monolayers on Au(111)

Organic ditellurides (R2Te2 where R = n-butyl (C4), n-octyl (C8), and n-cetyl (C16)) were synthesized, and their adsorption states after oxidation on Au(111) surfaces were studied by X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), theoretical analyses, near-edge X-ray absorption fine structure (NEXAFS) measurements, contact angle measurements, and atomic force microscopy (AFM). The obtained results show that dialkyl ditellurides form autooxidized monolayers (AMs) on the surfaces under ambient conditions and that the oxidation process is accelerated by ambient light. XPS, UPS, and theoretical analyses suggest that the autooxidized ditelluride species consist of polymers or oligomers with Te-O-Te-O network structures stabilized by oxygen bridges between tellurium molecules following the cleavage of tellurium-gold bonds. NEXAFS and contact angle measurements indicate that the average tilt angles of the alkyl chains from the surface normal are smaller for the AMs of dialkyl ditellurides having longer alkyl chains. AFM measurements show defects and roughness features around a few angstroms in height on the surfaces of the dialkyl ditelluride AMs.     

Interaction of crosslinked polyethylenimine with a homologous series of methyl orange derivatives in aqueous solution

Polyethylenimine (PEI) was crosslinked with dichloroethane, glyoxal, or glutaraldehyde and polymers of various degrees of crosslinkage were made. The insoluble polymers obtained were examined for their ability to bind methyl orange and its homologs, methyl, ethyl, propyl, and butyl orange at 5, 15, 25, and 35°C, respectively, in an aqueous solution. PEI crosslinked with glutaraldehyde showed markedly increased binding affinity toward these cosolutes compared with the polymers crosslinked with dichloroethane or glyoxal. The extent of the binding increased with an increase in the degree of crosslinkage. These results suggest that the enhancement of the binding by the crosslinking is due mainly to a dual effect, introduction of hydrophobic moieties and proximity of neighboring polymer chains. The first binding constants and the thermodynamic parameters that accompanied the binding were calculated. The thermodynamic data show that the binding process is athermal and is stabilized entirely by the entropy term. Water-soluble PEI exhibited stronger cooperative interactions than the crosslinked polymer because the mobilities of the chains of the former are greater than those of the latter.     

Thermal lensing spectrophotometric analysis with ion-pair solvent extraction

Thermal lensing spectrophotometry is applied to the determination of iron(II) with 4,7-diphenyl-1,10-phenanthroline disulfonic acid in aqueous solution, and in chloroform by ion-pair extraction with trioctylmethylammonium chloride. A phase-sensitive detection system with digital processing was used, the optimum modulation frequency being 5–10 Hz. A baseline drift of 0–03% was achieved. In water, the enhancement factor (sensitivity relative to conventional spectrophotometry) was 70 at an exciting power of 800 mW, and 2 × 10^-9 M iron(II) was determined. In chloroform 2 × 10^-10 M iron(II)—complex could be detected, the enhancement factor being 1200.     

Effect of the concentrations of triphenyltin chloride and anion exchanger on the anion selectivity of a plasticized PVC membrane electrode

 Potentiometric selectivities of a plasticized poly(vinyl chloride) (PVC) membrane containing a hydrophobic quaternary ammonium salt and triphenyltin chloride (TPTCl) for several inorganic anions were evaluated by measurements of the membrane potential of a bi-ionic system (the so-called bi-ionic membrane potential). The addition of TPTCl to the plasticized PVC membrane containing a quaternary ammonium salt gave rise to selectivity patterns different from the Hofmeister anion series, which is observed for a membrane containing only the quaternary ammonium salt. The change in the selectivity pattern from the Hofmeister to the non-Hofmeister was observed under conditions where the TPTCl concentration was higher than the quaternary ammonium salt in the membrane. Response mechanisms and the selectivity of the TPTCl-based electrode are discussed with respect to the concentration dependence of TPTCl and quaternary ammonium salt in the membrane. Received: 6 July 1995/Revised: 2 February 1996/Accepted: 6 February 1996     

pH- and thermosensitive supramolecular assembling system: rapidly responsive properties of beta-cyclodextrin-conjugated poly(epsilon-lysine)

beta-Cyclodextrin-conjugated poly(epsilon-lysine) (beta-CDPL) was synthesized as a novel polymeric host for constructing a smart supramolecular assembling system. Systematic studies on the inclusion complexation between the polymeric host with an alpha- or beta-CD cavity and a model guest molecule provided evidence that dual cooperative interactions, specific host-guest interaction and intermolecular ionic interaction, played a dominant role in leading to a fast aggregation phenomenon. In addition, a rapid phase transition induced by the supramolecular assembly was observed reversibly in response to a small change in pH or temperature.