Selective separation of Am(III) from lanthanides(III) by solvent extraction with hydrophobic field of "superweak" anion

The weakly coordinating hydrophobic anion TFPB-, whose surface is covered with a hydrophobic field, gives rise to a selective separation of Am(III) from lanthanides(III) in their solvent extraction even with a hard-donor extractant that shows no selectivity for Am(III) in traditional solvent extraction.     

Hair analysis of nicotine and cotinine for evaluating tobacco smoke exposure by liquid chromatography-mass spectrometry

A simple liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS) method for the determination of nicotine and cotinine in human hair was established. In the procedure, a hair sample (10 mg) was washed with dichloromethane and digested in 2.5 M sodium hydroxide. The digest was extracted with dichloromethane and then 25 mM hydrochloric acid in methanol was added to the extract, to prevent loss of analytes. The solution was evaporated and redissolved in the mobile phase, methanol/10 mM ammonium acetate (30/70, v/v). A 20 microL aliquot of redissolved solution was subjected to analysis. Nicotine and cotinine in human hair were quantified by using deuterated analytes as internal standards. The quantification limits were 8 microg/L for nicotine and 0.9 microg/L for cotinine. The proposed method was applied to measure the concentrations of nicotine and cotinine in hair of smokers and non-smokers to evaluate their self-reported smoking and exposure to environmental tobacco smoke. In both cases, the method provided good selectivity, accuracy and precision.     

Direct observation of the multistep helix formation of poly-L-glutamic acids

The helix formation dynamics of poly-L-glutamic acids (PGAs) were observed by the microsecond-resolved Fourier transform infrared (FTIR) and circular dichroism (CD) spectroscopies. The helix formation of 34-residue PGA from random coil at pH (or pD for FTIR) 8.0 was initiated by a pH jump to 4.9 using the rapid solution mixer whose mixing dead time is 50 micros. The amide I' line in the time-resolved FTIR spectra exhibited the fast (<100 micros) increase of the total helical content. The time-resolved CD spectra of the same process also showed the fast (<150 micros) formation of short helical segments (5 +/- 1 residues), which was followed by the slower (<1 ms) elongation of the short helices to longer helices (>10 residues). Similar dynamics were observed for the same pH jump of approximately 190-residue PGA, although there were additional steps that made the helix formation of approximately 190-residue PGA more complex. The observed multistep helix formation is likely caused by the strong hydrogen-bonding interactions between the protonated side chains of PGAs.     

Pyrolytic synthesis and Eu→Eu reduction process of blue-emitting perovskite-type BaLiF3:Eu thin films

Perovskite-type barium lithium fluoride (BaLiF₃) was synthesized by pyrolysis of metal trifluoroacetates. The reaction temperature necessary for producing a single-phase material was found to be 600°C, which was lower than that for a conventional solid-state reaction or a melting method. Eu-doped BaLiF₃ was also prepared and characterized to examine the suitability of trifluoroacetates for precursors in synthesizing homogeneous complex metal fluoride materials. It was demonstrated that trivalent Eu³⁺, which was used as acetate for a starting material, was reduced to divalent Eu²⁺ in the pyrolysis process of BaLiF₃, as indicated by a broad blue emission due to an allowed 4f⁶5d→4f⁷ transition at 408 nm with a ultraviolet excitation at 254 nm. The concentration quenching of the blue emission occurred at 5 at% of Eu in BaLiF₃, indicating that Eu was homogeneously dispersed in the BaLiF₃ host lattice. Mechanisms of the formation and reduction process of BaLiF₃ were discussed based on pertinent chemical reactions.     

The effects of epimerization at the 3(1)-position of bacteriochlorophylls c on their aggregation in chlorosomes of green sulfur bacteria. Control of the ratio of 3(1) epimers by light intensity

R- and S-epimerization at the 3(1) position of bacteriochlorophyll (BChl) c and the formation of rod-like aggregates in chlorosomes of green sulfur bacteria were markedly affected in Chlorobium (Cb.) tepidum and Cb. limicola by cultivation under various light intensities (photon fluence rate). The stronger the light, the higher the ratio of the S-epimer to the R-epimer for each homolog of BChl c in the bacteria. S[P,E] BChl cF and S[I,E] BChl cF were found to be the major S-epimers in Cb. tepidum and Cb. limicola, respectively. R[P,E] BChl cF decreased markedly compared to R[E,E] BChl cF in Cb. tepidum, whereas no observable change in the ratio of R[P,E]/R[E,E] was detected for Cb. limicola. With increase in light intensity the Qy absorption maximum of the bacteria shifted to shorter wavelengths. In vitro spectroscopic studies of the aggregates showed a marked difference in the formation of aggregates from R- and S-epimers of BChl c; the S-epimers formed aggregates much more slowly than did the R-epimers. These results suggest that the ratio of the epimers of BChl c might significantly affect the aggregation of BChl in the chlorosome. We propose different roles for the R- and S-epimers in chlorosomes of Cb. limicola and Cb. tepidum.     

An approach to analysis of pigment release from microcapsules with size distribution

We have studied the release curve for microcapsules with size distribution. On the basis of an analogy to the relaxation phenomena with multiple characteristic times, we propose a stretched exponential release curve for the system with size distribution and relate the release curve to the size distribution function of the microcapsule. This method was successfully applied to the transfer of azo-pigments from inner medium of dioctyl phthalate to dispersing medium of methanol through poly(ureaurethane) microcapsule membrane.     

Investigation into new materials for optical devices: the miscibility and solvent effects of azobenzene derivative blends

With the increasing demand for novel devices with optical applications the search for new materials to data store and process becomes a priority. By introducing blends, tailor made properties and low cost give added advantage. Miscibility is an essential requirement for a new material, this research thus involves miscibility studies of poly(4‐(N‐(2‐methacryloyloxyethyl)‐N‐ethylamino)‐4′‐nitroazobenzene)₉₀‐co‐(methyl methacrylate)₁₀, (azobenzene derivative) with polymethyl‐methacrylate (PMMA), polyvinylacetate (PVAc) and polyvinylchloride (PVC) prepared in tetrahydrofuran (THF), and/or dimethylformamide (DMF) and/or dichloromethane (CH₂Cl₂). The glass transitions, solvent and varying molecular weight effect were investigated, since these all primarily influence the miscibility. THF was found to encourage miscibility at specific compositions of PVAc and PVC blends. However, with CH₂Cl₂ and DMF immiscibility is encouraged. The Fox–Flory equation was applied to the blends analyzing the PVC blends in DMF as deviations from ideality. Different molecular weights of PMMA were identified as immiscible regardless of solvent. PMMA's lower solubility in THF and CH₂Cl₂ compared to the azobenzene derivative, displayed the existence of PMMA islands. In all blends the favorable and unfavorable interactions between polymer–solvent–polymer systems are considered. Furthermore, the miscibility effect on increasing the MMA content of the azobenzene derivative was also investigated. Copyright © 2002 John Wiley & Sons, Ltd.     

Photoelectron spectra and angular distribution in reson three-photon ionization of atomic iron: J dependence

Kenetic energies and angular distributions of photoelectrons emitted by three-photon ionization fo atomic iron through two-photon resonant state e⁷D_J and e⁵ D_J, were measured, by using visible lasers. J-resolved photoelectron bands attributab to the a⁶D_J and a⁴F_j ionic states are reported.