Biotransformation of the triketone herbicide mesotrione by a Bacillus strain. Metabolite profiling using liquid chromatography/electrospray ionization quadrupole time-of-flight mass spectrometry

The metabolic pathway involved in the biotransformation of the herbicide mesotrione by the bacterial strain Bacillus sp. 3B6 was investigated by a reliable liquid chromatography/electrospray ionization quadrupole time-of-flight mass spectrometry (LC/ESI-QTOF-MS) method. The LC/ESI-MS method, both in positive and negative mode, with the assistance of MS(2) fragments and isotopic pattern analyses, allowed us to identify five metabolites. This work constitutes the first complete monitoring of mesotrione degradation kinetics. Among the transformation products found by both techniques, one was formed by intramolecular cyclization between a hydroxylamine and a keto function, which is quite a rare biological reactivity process. For each identified metabolite, a fragmentation pathway is proposed for negative and positive mode.     

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.     

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.     

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.

     

Evaluation of antiangiogenic treatment effects on tumors' microcirculation by Bayesian physiological pharmacokinetic modeling and magnetic resonance imaging

A physiological pharmacokinetic (PBPK) model was used to estimate tumor microcirculation in nude mice with a grafted tumor. The kinetics of a rapid clearance blood pool agent, Vistarem, were investigated by dynamic MRI after bolus administration. Signal enhancements were recorded in arterial blood and in tumor tissue. To analyze these data, we developed a whole-body mathematical model of the agent's biodistribution using physiological parameters. The model included six compartments: arterial and venous plasma, tumor (split into capillaries and interstitium), and the rest of the body (also split into capillaries and interstitium). As an application, changes in tumor microcirculation parameters were evaluated in mice receiving either an antiangiogenic treatment (ZD4190) or a placebo. The analysis was performed in a Bayesian framework, and the model was fitted to experimental data using Markov Chain Monte Carlo techniques. Results showed a significant difference in tumor microcirculation between the two groups of mice when the microcirculation parameters are considered together. This whole-body physiological model enables to analyze jointly data in tumor tissue and in arterial blood. This leads to accurate estimates of microcirculation parameters and the evaluation of their uncertainty.