Standardization in allergen determination

An overview is given of sensitization and allergic reaction on food, along with minimal eliciting doses for selected allergens (milk, egg, peanut), followed by the legislative situation in the European Community, the USA, Canada, Australia/New Zealand and Japan. The main focus of the paper discusses methods for food allergen determination (chromatography, DNA-based, antibody-based) and their limitations. Special emphasis is given on antibody-based systems, which are at the moment the most advanced and validated methods available. Examples are given of the current status of standardization for egg, milk, nuts, prolamins, glutelins and for clinical validated reference samples from the EU project EuroPrevall. Recommendations for ongoing activities are also included.     

Immunoaffinity screening with capillary electrochromatography

Highly efficient capillary electrochromatographic separations of cardiac glycosides and other steroids are presented. Employing butyl-derivatized silica particles as stationary phase resulted in a nearly three times faster electroosmotic flow (EOF) compared to capillary electrochromatography (CEC) with octadecyl silica particles. On-column focusing with a preconcentration factor of 180 was performed and separation efficiencies of up to 240,000 plates per meter were obtained. Using label-free standard UV absorbance, detection limits of 10-80 nM were reached for all steroids tested. For screening of cardiac glycosides, e.g., digoxin and digitoxin in mixtures of steroids, CEC was combined with immunoaffinity extraction using immobilized polyclonal anti-digoxigenin antibodies and F(ab) fragments. Simply adding small amounts of antibody carrying particles to the samples and comparing chromatograms before and after antibody addition allowed screening for high affinity antigens in mixtures with moderate numbers of compounds. Under conditions of competing antigens, affinity fingerprints of immobilized anti-digoxigenin and anti-digitoxin antibodies were obtained, reflecting the cross-reactivity of eleven steroids. The method provides high selectivity due to the combination of bioaffinity interaction with highly efficient CEC separation and UV detection at several wavelengths in parallel. This selectivity was exploited for the detection of four cardiac glycosides in submicromolar concentrations in an untreated urine sample.     

The quenching of CdSe quantum dots photoluminescence by gold nanoparticles in solution

The photoluminescence (PL) of CdSe quantum dots (QD) in aqueous media has been studied in the presence of gold nanoparticles (NP) with different shapes. The steady state PL intensity of CdSe QD (1.5-2 nm in size) is quenched in the presence of gold NP. Picosecond bleach recovery and nanosecond time-resolved luminescence measurements show a faster bleach recovery and decrease in the lifetime of the emitting states of CdSe QD in the presence of quenchers. Surfactant-capped gold nanorods (NR) with aspect ratio of 3 and surfactant-capped and citrate-capped nanospheres (NS) of 12 nm diameter were used as quenchers in order to study the effect of shape and surface charge on the quenching rates. The Stern-Volmer kinetics model is used to examine the observed quenching behavior as a function of the quencher concentration. It was found that the quenching rate of NR is more than 1000 times stronger than that of NS with the same capping material. We also found that the quenching rate decreases as the length of the NR decreases, although the overlap between the CdSe emission and the NR absorption increases. This suggests that the quenching is a result of electron transfer rather than long-range (Forster-type) energy transfer processes. The quenching was attributed to the transfer of electron with energies below the Fermi level of gold to the trap holes of CdSe QD. The observed large difference between NR and NS quenching efficiencies was attributed to the presence of the [110] facets only in the NR, which have higher surface energy.     

Allylic Peroxidations with Bis(2‐pyridylimino)isoindolato‐Cobalt and ‐Iron Complexes

Several novel substituted bis(2‐pyridylimino)isoindolato (BPI) cobalt(II) and iron(II) complexes [M(BPI)(OAc)(H₂O)] (M = Co: 1 ‐ 6, Fe: 7) have been synthesized by reaction of bis(2‐pyridylimino)isoindole derivatives with the corresponding metal(II) acetates. Reaction of 1‐6 with 1.5 ‐ 2 molar equivalents of t‐BuOOH gave the corresponding alkylperoxocobalt(III) complexes [Co(BPI)(OAc)(OOtBu)] (10 ‐ 15). Using an aqueous solution of t‐BuOOH (70 %), cyclohexene was selectively catalytically oxidized to the dialkylperoxide cyclohex‐2‐ene‐1‐t‐butylperoxide.     

Synthesen und Kristallstrukturen neuer selenidoverbrückter Ruthenium-Clusterverbindungen

Syntheses and Crystal Structures of New Selenido-bridged Ruthenium Clusters The reaction of Se(SiMe₃)₂ with [RuCl₂(PPh₃)₃], or a mixture of [RuCl₂(PPh₃)₃] and alkylphosphines leads to the formation of selenido-bridged ruthenium clusters. In this publication the compounds [Ru₆Se₈(PPh₃)₆] ( 1 ), [Ru₆Se₈(PEt₃)₆] ( 2 ) und[Ru₆Se₈(PⁿPr₃)₆] ( 3 ) are described.The compounds 1-3 contain Ru₆¹⁶⁺ cluster cores with Ru²⁺ and Ru³⁺ centers. The structures of these compounds were elucidated by single crystal X-ray structural analyses.     

High-performance liquid chromatographic determination of xanthohumol in rat plasma, urine, and fecal samples

Xanthohumol (XN) is the major prenylated flavonoid in hop plants and as such a constituent of beer. Pharmacological studies have shown that XN possesses marked antioxidant and antiproliferative effects. In order to study the resorption and metabolism of this compound, reversed-phase high-performance liquid chromatography is used for the determination of XN in rat plasma, urine, and feces. In session one, rats receive either oral or intravenous (iv) administration (20 mg/kg body weight) of XN. In session two, rats receive oral administration of 50, 100, 200, 400, and 500 mg/kg body weight XN for bioavailability studies at various dose levels. Plasma, urine, and feces are collected at varying time points and assayed for their XN content. Plasma levels of XN fell rapidly within 60 min after iv administration; no XN is detected in plasma after oral administration in either session. XN and its metabolites are excreted mainly in feces within 24 h of administration. The method is a reliable tool for performing studies of XN in different biological material.     

Small-angle neutron scattering study of structural changes in temperature sensitive microgel colloids

The structure of temperature-sensitive poly(N-isopropylacrylamide) microgels in dilute suspension was investigated by means of small-angle neutron scattering. A direct modeling expression for the scattering intensity distribution was derived which describes very well the experimental data at all temperatures over an extensive q range. The overall particle form as well as the internal structure of the microgel network is described by the model. The influence of temperature, cross-linking density, and particle size on the structure was revealed by radial density profiles and clearly showed that the segment density in the swollen state is not homogeneous, but gradually decays at the surface. The density profile reveals a box profile only when the particles are collapsed at elevated temperatures. An increase of the cross-linking density resulted in both an increase of the polymer volume fraction in the inner region of the particle and a reduction of the smearing of the surface. The polymer volume fraction inside the colloid decreased with increasing particle size. The structural changes are in good agreement with the kinetics of the emulsion copolymerization used to prepare the microgel colloids.