Evaluation of the International Organization for Standardization-International Dairy Federation (ISO-IDF) draft standard method for detection of Enterobacter sakazakii in powdered infant food formulas

As a result of the growing recognition of Enterobacter sakazakii as an emergent pathogen, the International Dairy Federation (IDF) and the International Organization for Standardization (ISO) have standardized a reference method for the detection of E. sakazakii in milk powder products and powdered infant food formulas (IFF). The objectives of this study were to assess the applicability of the ISO-IDF draft standard, and to compare several chromogenic selective media for E. sakazakii [ready-to-use ESIATM, homemade E. sakazakii isolation agar, and Druggan-Forsythe-lversen (DFI) agar], and a selective media for Enterobacteriaceae Violet Red Bile Glucose (VRBG). We found that the method is sensitive, selective, and applicable to the analysis of powdered IFF, provided that some modifications are added. In particular, definition of typical colonies on chromogenic media should be less restrictive, and the possibility of using chromogenic media other than ESIA should be introduced. Any of the chromogenic media tested here could be used initially, since their performances were similar. In these media, alpha-glucosidase-positive but non-yellow-pigmented isolates should be also considered. Consequently, the yellow pigmentation test should be abandoned, or completed with another test in order to select colonies to confirm. Although the specificity of VRBG was relatively poor, it could be used as a second nonchromogenic medium.     

Laser ablation and secondary ion mass spectrometry of inorganic transition-metal compounds. Part I: comparison between static ToF-SIMS and LA-FTICRMS

Most of the first-row transition-metal oxides, M(A)O(B) (M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn) were examined by static secondary ion mass spectrometry (s-SIMS) and laser ablation/ionization Fourier transform ion cyclotron resonance mass spectrometry (LA-FTICRMS). Positive and negative ions show strong correlation between the studied oxide and the detected cluster ions. Specific M(x)O(y) (+/-) species were systematically observed with both MS techniques for each investigated M(A)O(B) transition-metal oxide. Moreover, the ion composition and ion distribution are greatly dependent on the ionization technique. Laser ablation (LA)/ionization leads to larger cluster ions (ionic species with nearly hundred atoms were in particular detected for Sc2O3 and Y2O3 oxides), whereas hydrogenated, dihydrogenated, and sometimes trihydrogenated species were observed in s-SIMS. However, the ion distribution for a given M(x)O(y) (+/-) ion series (i.e. ions including the same number of metal atoms M) generally presented important similarities in both techniques.Finally, it was demonstrated that the chemical state of metal atoms in the observed ionic species is closely dependent on the metal electronic valence shell. High valence states (+III, +IV, +V, and +VI) are favored for metals with a less-than-half full valence shell configuration, whereas for other first-row transition metals (manganese, iron, cobalt, nickel, copper and zinc) lower metal valence states (0, +I or, +II) are involved.     

Conformation study of HA(306-318) antigenic peptide of the haemagglutinin influenza virus protein

Several HLA-DR alleles present the immunodominant HA(306-318) peptide of haemagglutinin of the influenza virus to T cells. NMR data of the peptide in various water solutions exclude any alpha-helix or turn conformations. Circular dichroism and Fourier transform infrared spectroscopies indicate an estimated beta-extended structure in water of 31% and 28%, respectively, with spectra shape similar to the ones observed for beta-sheet containing proteins. The H/D amide exchange suggests a stable length-dependent interchain hydrogen-bonding. The partially beta-extended conformation of HA(306-318) in solution might be close to the one found in HA(306-318)-HLA-DR1 complex. These results suggest different interconverting extended conformations of HA(306-318), depending on the microenvironment of the solution medium. This flexibility emphasizes the ability of some peptides to fit more easily the binding site of several HLA-DR molecules. Similar results were obtained on the HIV P25(263-277) peptide which has been previously shown to be a good DR1 binder. From a vibrational point of view, infrared Amide I frequencies of secondary structures in peptides were ascertained. As previously demonstrated for proteins in solution, Fourier transform infrared and circular dichroism spectroscopies appear to be valuable tools for conformational properties of peptides. Their use may contribute to the detection of peptide conformation-binding relationship which has to be further tested by biochemical and biological studies.     

Understanding gold-thiolate cluster emission from self-assembled monolayers upon kiloelectronvolt ion bombardment

This article focuses on the emission of organometallic clusters upon kiloelectronvolt ion bombardment of self-assembled monolayers. It is particularly relevant for the elucidation of the physical processes underlying secondary ion mass spectrometry (SIMS). The experimental system, an overlayer of octanethiols on gold, was modeled by classical molecular dynamics, using a hydrocarbon potential involving bonding and nonbonding interactions (AIREBO). To validate the model, the calculated mass and energy distributions of sputtered atoms and molecules were compared to experimental data. Our key finding concerns the emission mechanism of large clusters of the form MxAuy up to M6Au5 (where M is the thiolate molecule), which were not observed under sub-kiloelectronvolt projectile bombardment. Statistically, they are predominantly formed in high-yield events, where many atoms, fragments, and (supra)molecular species are desorbed from the surface. From the microscopic viewpoint, these high-yield events mostly stem from the confinement of the projectile and recoil atom energies in a finite microvolume of the sample surface. As a result of the high local energy density, molecular aggregates desorb from an overheated liquidlike region surrounding the impact point of the projectile.     

Stabilization effect of single-walled carbon nanotubes on the functioning of photosynthetic reaction centers

The interaction between single-walled carbon nanotubes and photosynthetic reaction centers purified from purple bacterium Rhodobacter sphaeroides R-26 has been investigated. Atomic force microscopy studies provide evidence that reaction center protein can be attached effectively to the nanotubes. The typical diameter of the nanotube is 1-4 nm and 15 +/- 2 nm without and with the reaction centers, respectively. Light-induced absorption change measurements indicate the stabilization of the P+(Q(A)Q(B))- charge pair, which is formed after single saturating light excitation after the attachment to nanotubes. The separation of light-induced charges is followed by slow reorganization of the protein structure. The stabilization effect of light-initiated charges by the carbon nanotubes opens a possible direction of several applications, the most promising being in energy conversion and storage devices.     

A Cationic Gold(I) Complex as a General Catalyst for the Intermolecular Hydroamination of Alkynes: Application to the One‐Pot Synthesis of Allenes from Two Alkynes and a Sacrificial Amine

Two very distinct chemical reactions, yet a single catalyst : A gold complex promotes the formation of tertiary enamines from a variety of terminal and internal alkynes. Subsequent addition of a terminal alkyne to the reaction mixture affords allenes (see scheme).

     

Synthesis of Allenylidene Lithium and Silver Complexes,and Subsequent Transmetalation Reactions

Alpha, beta, gamma! Amino substituents in alpha and beta positions allow the isolation of free carbenes, but even in the gamma position, their strong π‐electron‐donating properties permit the synthesis of allenylidene lithium adducts and silver complexes (see picture), which are ideal precursors for the preparation of various transition‐metal–allenylidene complexes.

     

Reactivity of Cyclic (Alkyl)(amino)carbenes (CAACs) and Bis(amino)cyclopropenylidenes (BACs) with Heteroallenes: Comparisons with their N‐Heterocyclic Carbene (NHCs) Counterparts

Similarly to NHCs, CAAC_a and BAC_a react with CO₂ to give the corresponding betaines. Based on the carbonyl stretching frequencies of cis‐[RhCl(CO)₂(L)] complexes, the order of electron donor ability was predicted to be CAAC_a≈BAC_a>NHCs. When the betaines ν_asym(CO₂) values are used, the apparent ordering is BAC_a>NHCs≈CAAC_a that indicates a limitation for the use of IR spectroscopy in the ranking of ligand σ‐donating ability. Although all carbenes react with carbon disulfide to give the corresponding betaines, a second equivalent of CS₂ reacts with the BAC‐CS₂ leading to a bicyclic thieno[2,3‐diamino]‐1,3‐dithiole‐2‐thione, which results from a novel ring expansion process. Surprisingly, in contrast to NHCs, CAAC _a does not react with carbodiimide, whereas BAC_a exclusively gives a ring expanded product, analogous to that obtained with CS₂. The intermediate amidinate can be trapped, using the lithium tetrafluoroborate adduct of BAC_b as a carbene surrogate.