Determination of avoparcin in animal tissues and milk using LC‐ESI‐MS/MS and tandem‐SPE

A highly sensitive and selective method using LC‐ESI‐MS/MS and tandem‐SPE was developed to detect trace amounts of avoparcin (AV) antibiotics in animal tissues and milk. Data acquisition using MS/MS was achieved by applying multiple reaction monitoring of the product ions of [M + 3H]³⁺ and the major product ions of AV‐α and ‐β at m/z 637 → 86/113/130 and m/z 649 → 86/113/130 in ESI(+) mode. The calculated instrumental LODs were 3 ng/mL. The sample preparation was described that the extraction using 5% TFA and the tandem‐SPE with an ion‐exchange (SAX) and InertSep C18‐A cartridge clean‐up enable us to determine AV in samples. Ion suppression was decreased by concentration rates of each sample solution. These SPE concentration levels could be used to detect quantities of 5 ppb (milk), 10 ppb (beef), and 25 ppb (chicken muscle and liver). The matrix matching calibration graphs obtained for both AV‐α (r >0.996) and ‐β (r >0.998) from animal tissues and milk were linear over the calibration ranges. AV recovery from samples was higher than 73.3% and the RSD was less than 12.0% (n = 5).     

Time-resolved EPR investigation on the photoreactions of vitamin K with antioxidant vitamins in micelle systems

The photochemical reactions of vitamin K (VK) with antioxidant vitamins (vitamin E (VE) and vitamin C (VC)) in aqueous hexadecyltrimethylammonium chloride (CTAC), sodium dodecyl sulfate (SDS), and Triton X-100 micelle systems, and in an aerosol OT (AOT) reversed micelle system were investigated by a time-resolved EPR (TR-EPR). The photolysis of VK with VE in the aqueous micelle solutions gave the TR-EPR spectra having strong intensity and net emissive polarization, suggesting that the excited triplet state of VK (³VK^*) was rapidly quenched by VE coexisting inside the micelle. On the other hand, the photolysis of VK with VC in the aqueous SDS and CTAC micelle systems gave the spectra having weak intensity, showing that the reaction between ³VK^* and VC was inefficient in these micelle systems, probably because ³VK^* scarcely diffused out from the micelle. The photolysis of VK with VC in the AOT reversed micelle solution gave the spin-correlated radical pair CIDEP spectrum. The result suggests that the long-lived radical pair was generated from the reaction between ³VK^* and VC in the water/oil interface region of the AOT micelle, although one of the reactants dissolved in the oil phase and another did in the separated water phase.     

Two new dimeric coumarins isolated from Murraya exotica

Bismurrangatin and murramarin A, two new coumarins, were isolated from the vegetative branches of Murraya exotica. Murramarin A is a rare type of bicoumarin that connects two coumarin moieties by orthoester structure. The structures were elucidated based on spectroscopic methods, especially by 2D-NMR experiments.     

Photosensitivity of polyvinylesters of substituted cinnamylideneacetic acids

Several polyvinylesters of substituted cinnamylideneacetic acids were synthesized and their photosensitivities were investigated. It was found that polyvinylesters of planar acids reacted photochemically effectively and were spectrally sensitized by usual triplet sensitizer. On the other hand, polyvinylesters of twisted acids exhibited poor photosensitive properties. Poly(vinyl α-cyanocinnamylideneacetate) (PV-V) was found to be an excellent photosensitive polymer with respect to both photosensitivity and thermal stability (or storage stability).     

Determination of arsenic in sediments by chloride formation and d.c. plasma arc emission spectrometry

The sediment sample is heated in an induction furnace in hydrogen chloride—argon; arsenic trichloride evolved is trapped and then swept into a d.c. plasma arc. Calcium sulfate addition enhances the signals and suppresses interference from organic matter. The limit of detection is 15 ng As; the relative standard deviation is 3.4% (n = 10) for 1.5μg As₂0₃.     

Lyman-α excitation spectra in the photodissociation of the doubly excited states of H2

A Lyman-α excitation spectrum has been observed using synchrotron radiation in the energy region corresponding to the double electron excitation of H₂. There exist in the spectrum three thresholds at 26.6±0.5 eV, 29.2±0.7 eV and 30.9±0.6 eV, and a dip at 34.1±0.5 eV. A Lyman-α excitation spectrum in the energy region corresponding to the single electron excitation has been also observed using a detection system which works as a band pass filter for detecting of Lyman-α fluorescence. The cross section of Lyman-α fluorescence in the photodissociation of the doubly excited states is very small, e.g., in the order of 10^?20 cm² at 30 eV, in comparison with that from the single electron excitation.     

Influence of conformational changes of co(III)–poly-N-vinyl-2-methylimidazole complexes on electron-transfer reactions of the complexes

In order to study the effect of conformational changes in electron-transfer reactions of Co(III)–polymer complexes, cis-[Co(III)(en)₂LCl]Cl₂, where the ligand L is PVI(poly-N-vinyl-2-methylimidazole) or NEI (N-ethylimidazole), was prepared. Electrontransfer reactions with ferrous sulfate or FeEDTA^2? were examined mainly with respect to the effects of the degree of coordination, ionic strength, composition of reaction solvent, in relation to the conformational changes. In the reduction by FeEDTA^2?, an increase in the degree of coordination of Co(III)–PVI brought about an extreme increase in its reactivity, while it was almost unity in the reduction by ferrous sulfate. With an increase in the ionic strength, the reactivity decreased due to the electrostatic shielding in the reduction by FeEDTA^2?. It was noticed that the reaction of Co(III)–PVI was much more enthalpically disadvantageous due to the shrinkage of the polymer chain than that of Co(III)–NEI, when neutral salts were added. In an aqueous alcoholic solvent, an increase in the alcohol concentration accelerated the reaction with FeEDTA^2?, and especially in the reaction of Co(III)-PVI, the maximum and minimum points of the reactivity were observed. On increasing the reaction temperature, the maximum and minimum points shifted to lower alcohol concentration. These phenomena are discussed in regard to the conformational changes of Co(III)–PVI.     

Pressure effects on cation migration in 2,5‐di‐tert‐butyl‐1,4‐benzoquinone radical anion

Pressure effects on the two‐site jumping of sodium and potassium cations in a 2,5‐di‐tert‐butyl‐1,4‐benzoquinone ion pair have been studied using a high‐pressure EPR technique. The rate constants of the intramolecular and intermolecular migrations for Na⁺ and K⁺ were determined from an EPR spectral simulation. The migration rates were found to be accelerated by increasing the external pressure. Using the pressure dependence of the migration rates, we estimated the activation volumes of the intramolecular (ΔV₁^?) and intermolecular (ΔV₂^?) processes for the Na⁺ and K⁺ migrations: ΔV₁^? = ?5.3 cm³ mol^?1 and ΔV₂^? = ?29 cm³ mol^?1 for Na⁺, and ΔV₁^? = ?8.3 cm³ mol^?1 and ΔV₂^? = ?0.85 cm³ mol^?1 for K⁺. Based on the results, the mechanisms for the two‐site jumping of Na⁺ and K⁺ are discussed in terms of volume. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 397–401, 2001     

Reversible Coordination of Molecular Nitrogen to Polymeric Benzenecarbonylchromium Complexes

Polymeric benzenetricarbonylchromium complexes were synthesized by radical copolymerization of benzyl acrylatetricarbonylchromium with styrene and by reaction of (dimethylaminobenzene)tricarbonylchromium with poly(styrene-co-acrylic acid). The polymeric chromium complexes give transparent films and on UV irradiation under nitrogen lead to dinitrogen complexes of the corresponding polymeric dicarbonylchromium. The reversible coordination of dinitrogen was confirmed by IR and visible absorption spectroscopy. A predominant feature of the polymeric dinitrogen complexes is their extraordinarily high stability in air compared with the corresponding low molecular analogs. The effect of polymer matrices on dinitrogen coordination is discussed.