Transfer assessment of fipronil residues from feed to cow milk

Fipronil, a phenylpyrazole insecticide introduced for pest control on a broad range of crops, can also affect non-target insects such as honeybees. More widely, non-target environment such as milk produced by dairy cows fed with maize silage from treated seeds (=silage T) can be affected. To assess the potential transfer of fipronil residues (sulfone, sulfide, fipronil, desulfinyl and amide), a methodology including gas chromatography coupled with tandem mass spectrometry (GC-MS/MS) analysis was developed and validated according to the 2002/657/EC decision, in order to reach a level of quantification below 0.1 μg L⁻¹ in milk and 0.1 μg kg⁻¹ in plants. Twelve dairy cows were fed with silage T during 4 months. Concentration of fipronil in treated seeds was estimated at 1 g kg⁻¹, whereas silage from these seeds contained 0.30 ± 0.05 μg kg⁻¹ of dry material of fipronil, 0.13 ± 0.03 μg kg⁻¹ of dry material of sulfone. Sulfide residues were below the limit of quantification. Silage from untreated seeds (=silage U) presented traces of fipronil and sulfone, respectively at 0.04 ± 0.06 and 0.02 ± 0.03 μg kg⁻¹ of dry material. Contribution of fipronil residues from supplies was insignificant. During administration of silage T, only sulfone residues were quantified in milk. The average concentration was 0.14 ± 0.05 μg L⁻¹. Before and after administration, sulfone residues were detected but not quantifiable (<0.025 μg L⁻¹). Our results suggest a transfer of fipronil from feed to milk under its sulfone form. Moreover, traces of fipronil residues in maize U, soya, wheat and straw show a diffuse contamination of this pesticide in the environment.     

Transient absorption spectra of 2-hydroxybenzophenone photostabilizers

Transient absorption spectra (400–600 nm) of 2-hydroxybenzophenone and the methyl methacrylate copolymer of 2-hydroxy, 3-allyl, 4,4'-dimethoxybenzophenone following 355 nm excitation (7–480 ps delay) are reported. A short-lived, 435 nm transient (τ ≈ 10 ps in CH₂Cl₂) for both molecules is assigned to the lowest excited singlet before internal proton transfer. Weaker, broad T-T absorption is observed after 480 ps.     

Charge injection and photooxidation of single conjugated polymer molecules

The complex, coupled mechanisms of charge transfer and oxidative damage in organic electronic devices (such as organic light-emitting diodes (OLED), solar cells, etc.) have been elucidated by a new technique that combines single-molecule spectroscopy with charge injection from a metal electrode. The experiments employed a sandwich device architecture (Au/TPD/MEH-PPV:PMMA/SiO2/ITO), essentially a modified OLED with a charge-blocking layer (SiO2) to suppress charge injection at the ITO electrode. The fluorescence (photoluminescence) of isolated MEH-PPV conjugated polymer molecules imbedded in the device was observed to exhibit diverse time- and electrical bias-dependent effects. These include: (i) fluorescence quenching due to interactions between MEH-PPV and holes in the TPD hole-transport layer; (ii) fluorescence quenching, or "photobleaching", due to chemical defects at MEH-PPV generated by photooxidation; and (iii) a novel process, reductive "repair" of the oxidative chemical defects by externally injected carriers. These results demonstrate a very different mechanism for photobleaching of organic conjugated materials than is generally assumed to operate and, furthermore, suggest an intimate relationship among photobleaching, charge transport, and persistent photoconductivity in organic materials.     

Effect of pendent group structures on the chemical selectivity and performance of sulfonated copolymers as novel pseudophases in electrokinetic chromatography

Amphiphilic copolymers of 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS) with dihydrocholesteryl acrylate (pDHCHAt) or tert-octyl acrylamide (ptOAm) as comonomers were synthesized, characterized and used as new polymeric pseudostationary phases in electrokinetic chromatography. High-efficiency separations with theoretical plates around 500,000 to 870,000/m were achieved. Linear solvation energy relationships analysis of 20 solutes was performed to investigate the retention mechanism. Polycyclic aromatic hydrocarbons (PAHs) were separated under 30% v/v acetonitrile. The separation of nine aromatic model solutes by pDHCHAt showed significantly different selectivity from that of sodium dodecyl sulfate. Although only minor difference in selectivity was found for small aromatic compounds on pDHCHAt and poly(AMPS-lauryl acrylate), significantly different retention mechanism was found for PAHs and n-dodecanophenone comparing both copolymers. Significant chemical selectivity difference was found for selected small aromatic compounds on ptOAm and poly(AMPS-stearyl acrylamide).     

Conformational effects on the performance and selectivity of a polymeric pseudostationary phase in electrokinetic chromatography

The effect of the conformation of a polymeric pseudostationary phase on performance and selectivity in electrokinetic chromatography was studied using an amphiphilic pH-responsive polymer that forms compact intramolecular aggregates (unimer micelles) at low pH and a more open conformation at high pH. The change in conformation was found to affect the electrophoretic mobility, retention, selectivity, and separation efficiency. The low-pH conformer has higher electrophoretic mobility and greater affinity for most solutes. The unimer micelle conformation was also found to provide a solvation environment more like that of micelles and other amphiphilic self-associative polymers studied previously. It was not possible to fully characterize the effect of conformation on efficiency, but very hydrophobic solutes with long alkyl chains appeared to migrate with better efficiency when the unimer micelle conformation was employed. The results imply that polymers with a carefully optimized lipophilic-hydrophilic balance that allow self-association will perform better as pseudostationary phases. In addition, the results show that electrokinetic chromatography is a useful method for determining the changes in solvation environment provided by stimuli-responsive polymers with changes in the conditions.     

Pseudo cage effect in double energy transfer

In some systems, the donor of a triplet—triplet energy transfer can be sensitized in its singlet state through a singlet—singlet energy transfer (Dexter mechanism), where the donor is the acceptor of the triplet transfer itself. As a consequence an extra acceptor molecule in the triplet energy transfer is present in the vicinity of the donor, thus enhancing the efficiency of the transfer process. Experiments show clearly this effect and a diffusional model gives semi-quantitative agreement with the experimental data.     

Substitution Reactions of cis- and/or trans-Bromomesitylbis(triethylphosphine) Platinum (II) with Thiourea in Ethanol,Dimethylsulfoxide, and Acetone

The pressure and/or temperature dependencies of the rates of substitution of thiourea in cis- and/or trans-[PtBr(2, 4, 6-Me₃Ph)(Et₃P)₂] were studied in ethanol, DMSO, and acetone. The rate constants for both the nucleophile independent and nucleophile dependent reactions were measured. The rate and activation parameters are discussed in reference to data reported earlier for these reactions in methanol.     

The diazo route to diazonamide A: studies on the tyrosine-derived fragment

Various approaches to the tyrosine-derived fragment of the marine secondary metabolite diazonamide A are described. Initial efforts were focused on the originally proposed structure of the natural product, and a feasibility study established that a model 4-aryltryptamine could be readily prepared. Protected 4-bromotryptamine underwent Pd0-catalyzed coupling with the boronic acid derived from 2-bromophenyl allyl ether by Claisen rearrangement, O-methylation and lithiation-boration. The resulting biaryl was elaborated into an alpha-diazo-beta-ketoester, dirhodium(II)-catalyzed reaction of which with N-Z-valinamide gave the desired tryptamine-oxazole following cyclodehydration of the intermediate ketoamide. A potential precursor to the benzofuran ring of the original structure of diazonamide A was prepared in eight steps from N-Z-tyrosine tert-butyl ester. Iodination, O-protection and Stille coupling gave the cinnamyl alcohol 25, converted via the bromide into the allyl aryl ether 27. Subsequent Claisen rearrangement and oxidative cleavage of the alkene gave the lactol 29, converted into the desired benzofuranone 31. The revision in the structure of diazonamide A to 2 resulted in the targeting of an alternative tyrosine-derived model benzofuranone 41 synthesized in four steps from N-Z-tyrosine methyl ester 36 by a route involving Claisen rearrangement of cinnamyl ether 37. Poor yields in this sequence prompted an investigation into the intramolecular Heck reaction as a route to benzofuranone 50. Coupling of 3-iodotyrosine 44 with 2-phenylbutenoic acid 48 gave ester 49 that readily underwent intramolecular Heck reaction to give benzofuranone 50, albeit with poor stereocontrol.     

Participation of Bao2* in chemiluminescence from low-pressure Ba(g) + O2 flames

New spectioscopic and vibronic population data support the essential correctness of BaO₂^* as the nascent polyatomic emitter and as the precursor to BaO (A ¹Σ⁺ → X¹Σ⁺) and (A' ¹Π → X¹Σ⁺) visible chemiluminescence from metal-rich Ba(g) + O₂ (+ Ar) diffusion flames at 2–350 mTorr- Absolute visible photon yields are reported over this pressure regime.     

Mean configurational distribution function for the steady state and stern-volmer representation

A slight discrepancy appears between the treatment of the steady state of diffusion controlled bimolecular quenching of excited species either by the pair model or by the continuum model. A simplifying assumption is pointed out which helps to solve the steady state case but which is responsible for the discrepancy. The error involved is of small importance considering the experimental accuracy.

---

- , . , , . , .