Preparation,Homogeneity and Stability of Polar Pesticides in Freeze-Dried Water Interlaboratory Exercise

Abstract

An interlaboratory exercise was carried out to improve the state of the art of some polar pesticide determination in water (atrazine, simazine, carbaryl, propanil, linuron, fenamiphos and permethrin). The preparation, the homogeneity and the stability of freeze-dried water samples containing the above pesticides was studied. The final concentration of each pesticide in water was in the 50–80 μg.^?1 range with a salt content of 2.5 g.l^?1 of NaCl. After the lyophilization the residue was reho-mogenised, filled into amber glass bottles and stored at -20 °C and +20 °C. Every three months, one sample was analysed to verify the stability of the residue.

All pesticides were determined by high performance liquid chromatography with diode-array detection (HPLC-DAD) except permethrin which was determined by gas chromatography with electron capture detection (GC-ECD).

The results obtained show that the atrazine, carbaryl, propanil, linuron and fenamiphos samples were homogeneously distributed, whereas simazine and permethrin were not. With respect to the stability over three months, all pesticides were stable at ?20 °C. Atrazine, simazine, carbaryl, propanil and linuron are also stable for the maximum storage time at +20 °C but the concentration of fenamiphos decreased by about 70% after one month.

The results obtained in the interlaboratory study by the participants were in good agreement for many of the pesticides.     

Strain induced nanocavitation and crystallization in natural rubber probed by real time small and wide angle X‐ray scattering

The concomitant appearance of crystallites and nanocavities under uniaxial strain is investigated by X‐ray scattering in a model natural rubber system. The nanocavities appear after crystallization and only when the true stress is above a critical cavitation stress σ_Cav. The presence of crystallites alone does not influence the calculation of the void volume fraction ?_void. The nanocavities formed are 20–50 nm in size with a constant aspect ratio. The presence of filler shifts the critical crystallization extension ratio λ_Cry, λ_Cav, and σ_Cav to lower values. The clear correlation between σ_Cav and the crystallinity at the onset of cavitation χ_C(λ_Cav) implies that the crystallites take most of the mechanical loading thus delaying the cavitation in the amorphous phase. Under cyclic loading, nanocavitation is significant only in the first loading and in the successive loadings if the extension ratio is above its maximum historical value. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1125–1138     

Untersuchung von Milch und Milchprodukte

Ohne Zusammenfassung     

Evolution of NMDA receptor cytoplasmic interaction domains: implications for organisation of synaptic signalling complexes

Background  

Glutamate gated postsynaptic receptors in the central nervous system (CNS) are essential for environmentally stimulated behaviours including learning and memory in both invertebrates and vertebrates. Though their genetics, biochemistry, physiology, and role in behaviour have been intensely studied in vitro and in vivo, their molecular evolution and structural aspects remain poorly understood. To understand how these receptors have evolved different physiological requirements we have investigated the molecular evolution of glutamate gated receptors and ion channels, in particular the N-methyl-D-aspartate (NMDA) receptor, which is essential for higher cognitive function. Studies of rodent NMDA receptors show that the C-terminal intracellular domain forms a signalling complex with enzymes and scaffold proteins, which is important for neuronal and behavioural plasticity     

Two Counter-moving Light Beams

The cylindrically symmetric field of two beamsof light shining in opposite directions is studied. Wepresent four static or stationary exact solutions of thecorresponding field equations and compare their properties.     

Artificial vascular implants from bacterial cellulose: preliminary results of small arterial substitutes

The biomaterial bacterial cellulose (BC) represents an innovative approach for overcoming reconstructive problems associated with extended vascular diseases by providing small caliber vascular grafts (diameter 1.0–3.7, length 5.0–10.0, and wall-thickness 0.7 mm). In a first microsurgical study, the BC implants were attached in an artificial defect of the carotid artery of rats for 1 year. These long term results show the incorporation of the BC under formation of neointima and ingrowth of active fibroblasts. In a second study, the grafts were used to replace the carotid arteries of pigs. After 3 months, these grafts were removed and analyzed both macro- and microscopically. Seven grafts (87.5%) were patent whereas one graft was found occluded. These data indicate that the innovative BC engineering technique results in the production of stable vascular conduits and confirm a highly attractive approach to in vivo tissue engineered blood vessels as part of programs in cardiovascular surgery.     

Optical methods for the study of dynamics in biological membrane models

Membranes are highly complex and heterogeneous interfaces that are the active partition between living cells and the outside world. Many biologically important processes occur at the membrane surface, such as transmembrane transport and signaling. Many of these processes depend on the subtle interactions between the different membrane constituents: lipids, proteins and water. At present, a large body of knowledge exists on the molecular composition and static structure of membranes. However, our understanding of the dynamics of membrane molecules has not yet reached the same level of sophistication. Information on membrane dynamics, such as conformational fluctuations, conformational changes and dynamical interactions between membrane constituents are essential for a full understanding of membrane action. Here, we review a recently developed approach aimed at obtaining such dynamical information. The approach is based on surface-specific femtosecond laser vibrational spectroscopy, and is illustrated for simple membrane model systems.     

Irradiation-dependent equilibrium between open and closed form of UV absorbers of the 2-(2-hydroxyphenyl)-1,3,5-triazine type

2-(2-Hydroxyphenyl)-4,6-diaryl-1,3,5-triazines (HPTs) bearing one or more intramolecular hydrogen bonds (IMHBs) show phosphorescence in polar solvents at 77 K which increases in intensity with UV-irradiation time (λ_irr = 333 nm) until an equilibrium value is reached (phosphorescence evolution). Phosphorescence emission is produced from open conformers of the molecules with intermolecular rather than intramolecular hydrogen bonds, which are formed in polar solvents under the influence of UV radiation. All IMHBs of an individual molecule must be broken to enable triplet state population. Reformation of the closed form is observed for HPTs after dark periods resulting in a lower initial phosphorescence intensity upon renewed irradiation (relaxation). The methoxy derivatives (MPTs), where the OH groups are replaced by methoxy groups, can be employed as spectroscopic models for the open form; they emit phosphorescence independent of irradiation time. For the equilibrium between open and closed form of M-OH-P (2-(2-hydroxy-4-methoxyphenyl)-4,6-diphenyl-1,3,5-triazine) under constant irradiation (λ_irr = 333 nm, 100 W-HBO lamp) a proportion of 5% of open form was evaluated.