Interlaboratory validation of the Vidas SET2 kit for detection of staphylococcal enterotoxins in milk products

An earlier intralaboratory validation study based on the EN ISO 16140 Standard conducted by the Community Reference Laboratory for coagulase-positive staphylococci including Staphylocococcus aureus showed that, after an extraction step using dialysis concentration, the Vidas SET2 detection kit could be used to screen staphylococcal enterotoxins in milk and milk products. In order to fully validate Vidas SET2, an interlaboratory study was organized. Six freeze-dried samples and 3 ready-to-use concentrated extracts were analyzed by 21 laboratories according to the method, including a detection with Vidas SET2. Results did not show false-positive or -negative results. Accordance and concordance parameters were equal to 100%, corresponding to a concordance odds ratio of 1. This interlaboratory study confirmed the satisfactory outcome of the preliminary tests and of the intralaboratory study performed previously. The Vidas SET2 detection kit can be used as a method for the detection of staphylococcal enterotoxins in milk and milk products as well as the Transia Plate SET detection kit in the European screening method for official control purposes, after an extraction step followed by dialysis concentration.     

The sigma-CAM Mechanism: sigma complexes as the basis of sigma-bond metathesis at late-transition-metal centers

Complexes in which a sigma-H--E bond (E=H, B, Si, C) acts as a two-electron donor to the metal center are called sigma complexes. Clues that it is possible to interconvert sigma ligands without a change in oxidation state derive from C--H activation reactions effecting isotope exchange and from dynamic rearrangements of sigma complexes (see Frontispiece). Through these pathways, metathesis of M--E bonds can occur at late transition metals. We call this process sigma-complex-assisted metathesis, or sigma-CAM, which is distinct from the familiar sigma-bond metathesis (typical for d(0) metals and requiring no intermediate) and from oxidative-reductive elimination mechanisms (inherently requiring intermediates with changed oxidation states and sometimes involving sigma complexes). There are examples of sigma-CAM mechanisms in catalysis, especially for alkane borylation and isotope exchange of alkanes. It may also occur in silylation and alkene hydrogenation.     

Congested ferrocenyl polyphosphanes bearing electron-donating or electron-withdrawing phosphanyl groups: assessment of metallocene conformation from NMR spin couplings and use in palladium-catalyzed chloroarenes activation

The synthesis of novel substituted cyclopentadienyl salts that incorporate both a congested branched alkyl group (tert-butyl, (triphenyl)methyl, or tri(4-tert-butyl)phenylmethyl) and a phosphanyl group is reported. The introduction of either electron-withdrawing or electron-donating substituents (furyl, i-propyl, cyclohexyl, tert-butyl) on P atoms was generally achieved in high yield. The modular synthesis of ferrocenyl polyphosphanes from an assembly of these cyclopentadienyl salts was investigated, leading to the formation of new triphosphanes (denoted as 9-12) and diphosphanes (denoted as 14-16). The resulting phosphanes are not sensitive to air or moisture, even when electron-rich substituents are present. This set of polyphosphanes displays varied conformational features, which are discussed in the light of their multinuclear NMR characterization in solution and of the X-ray solid state structure of the representative triphosphane 1,2-bis(diphenylphosphanyl)-1'-(diisopropylphosphanyl)-3'-(triphenyl)methyl-4-tert-butyl ferrocene, 11. In particular, the existence of a range of significantly different nonbonded ("through-space", TS) spin-spin coupling constants between heteroannular P atoms, for the triphosphanes of this class, allowed their preferred conformation in solution to be appraised. The study evidences an unanticipated flexibility of the ferrocene platform, despite the presence of very congested tert-butyl and trityl groups. Herein, we show that, contrary to our first belief, the preferred conformation for the backbone of ferrocenyl polyphosphanes can not only depend on the hindrance of the groups decorating the cyclopentadienyl rings but is also a function of the substituents of the phosphanyl groups. The interest of these robust phosphanes as ligands was illustrated in palladium catalysis for the arylation of n-butyl furan with chloroarenes, using direct C-H activation of the heteroaromatic in the presence of low metal/ligand loadings (0.5-1.0 mol?%). Thus, 4-chlorobenzonitrile, 4-chloronitrobenzene, 4-chloropropiophenone, and 4-(trifluoromethyl)chlorobenzene were efficiently coupled to n-butyl furan, using Pd(OAc)(2) associated to the new diphosphane ligands 1,1'-bis(diisopropylphosphanyl)-3,3'-di(triphenyl)methyl ferrocene (15) or 1,1'-bis(dicyclohexylphosphanyl)-3,3'-di(triphenyl)methylferrocene (16), which respectively hold the electron-rich -Pi-Pr(2) and -PCy(2) groups.     

SAXS investigation of a cubic to a sponge (L3) phase transition in self-assembled lipid nanocarriers

The encapsulation and release of peptides, proteins, nucleic acids, and drugs in nanostructured lipid carriers depend on the type of the self-assembled liquid-crystalline organization and the structural dimensions of the aqueous and membraneous compartments, which can be tuned by the multicomponent composition of the systems. In this work, small-angle X-ray scattering (SAXS) investigation is performed on the 'melting' transition of the bicontinuous double diamond cubic phase, formed by pure glycerol monooleate (MO), upon progressive inclusion of varying fractions of pharmaceutical-grade glycerol monooleate (GO) in the hydrated system. The self-assembled MO/GO mixtures are found to form diamond (Pn3m) inverted cubic, inverted hexagonal (H(II)), and sponge (L(3)) phases at ambient temperature in excess of aqueous medium without heat treatment. Mixing of the inverted-cubic-phase-forming MO and the sponge-phase-forming GO components, in equivalent proportions (50/50 w/w), yields an inverted hexagonal (H(II)) phase nanostructured carrier. Scattering models are applied for fitting of the experimental SAXS patterns and identification of the structural changes in the aqueous and lipid bilayer subcompartments. The possibility of transforming, at ambient temperature (20 °C), the bicontinuous cubic nanostructures into inverted hexagonal (H(II)) or sponge (L(3)) mesophases may facilitate novel biomedical applications of the investigated liquid crystalline self-assemblies.     

Two‐Coordinate Iron(I) Complex [Fe{N(SiMe3)2}2]−: Synthesis,Properties, and Redox Activity

First‐row two‐coordinate complexes are attracting much interest. Herein, we report the high‐yield isolation of the linear two‐coordinate iron(I) complex salt [K(L)][Fe{N(SiMe₃)₂}₂] (L=18‐crown‐6 or crypt‐222) through the reduction of either [Fe{N(SiMe₃)₂}₂] or its three‐coordinate phosphine adduct [Fe{N(SiMe₃)₂}₂(PCy₃)]. Detailed characterization is gained through X‐ray diffraction, variable‐temperature NMR spectroscopy, and magnetic susceptibility studies. One‐ and two‐electron oxidation through reaction with I₂ is further found to afford the corresponding iodo iron(II) and diiodo iron(III) complexes.     

B?H,C?H,and B?C Bond Activation: The Role of Two Adjacent Agostic Interactions

Tuning the nature of the linker in a L∼BHR phosphinoborane compound led to the isolation of a ruthenium complex stabilized by two adjacent, δ‐C H and ε‐B_sp2 H, agostic interactions. Such a unique coordination mode stabilizes a 14‐electron “RuH₂P₂” fragment through connected σ‐bonds of different polarity, and affords selective B H, C H, and B C bond activation as illustrated by reactivity studies with H₂ and boranes.     

Hemoglobin,horseradish peroxidase,and heme-bovine serum albumin as biocatalyst for the oxidation of dibenzothiophene

Hemoglobin, horseradish peroxidase, and bovine serum albumin incubated heme-catalyzed the oxidation of dibenzothiophene into sulfoxide in the presence of hydrogen peroxide. This reaction was carried out in an aqueous buffer containing 25% of water-miscible organic solvents. The observation of this transient state of hemoproteins during sulfoxidation showed heme degradation. None of the compounds usually involved in a classical peroxidative activity mechanism were detected. Furthermore, this activity did not appear to be based on a Fenton-type reaction. The highest degrees of sulfoxidation were obtained with hemoglobin. Under the best conditions of reaction, 100% of dibenzothiophene were converted into dibenzothiophene sulfoxide by hemoglobin. Heat-denatured hemoproteins did keep their sulfoxidation activity. With hemoglobin, a k_cat of 0.22 min^-1 was determined. Nearly the same values were obtained with heat-denatured hemoglobin and bovine serum albumin-adsorbed heme. With horseradish peroxidase, only 4% of conversion was attained. This percentage could be slightly increased by using a less pure peroxidase or heat-denatured peroxidase.     

Generation of superparamagnetic liposomes revealed as highly efficient MRI contrast agents for in vivo imaging

Maghemite (gamma-Fe2O3) nanocrystals stable at neutral pH and in isotonic aqueous media were synthesized and encapsulated within large unilamellar vesicles of egg phosphatidylcholine (EPC) and distearoyl-SN-glycero-3-phosphoethanolamine-N-[methoxy(poly(ethylene glycol))-2000] (DSPE-PEG(2000), 5 mol %), formed by film hydration coupled with sequential extrusion. The nonentrapped particles were removed by flash gel exclusion chromatography. The magnetic-fluid-loaded liposomes (MFLs) were homogeneous in size (195 +/- 33 hydrodynamic diameters from quasi-elastic light scattering). Iron loading was varied from 35 up to 167 Fe(III)/lipid mol %. Physical and superparamagnetic characteristics of the iron oxide particles were preserved after liposome encapsulation as shown by cryogenic transmission electron microscopy and magnetization curve recording. In biological media, MFLs were highly stable and avoided ferrofluid flocculation while being nontoxic toward the J774 macrophage cell line. Moreover, steric stabilization ensured by PEG-surface-grafting significantly reduced liposome association with the macrophages. The ratios of the transversal (r2) and longitudinal (r1) magnetic resonance (MR) relaxivities of water protons in MFL dispersions (6 < r2/r1 < 18) ranked them among the best T2 contrast agents, the higher iron loading the better the T2 contrast enhancement. Magnetophoresis demonstrated the possible guidance of MFLs by applying a magnetic field gradient. Mouse MR imaging assessed MFLs efficiency as contrast agents in vivo: MR angiography performed 24 h after intravenous injection of the contrast agent provided the first direct evidence of the stealthiness of PEG-ylated magnetic-fluid-loaded liposomes.