Akanthomycin, a new antibiotic pyridone from the entomopathogenic fungus Akanthomyces gracilis

[structure: see text] Organic extracts of the entomopathogenic fungus Akanthomyces gracilis ARS 2910 contained antibiotics active against Staphylococcus aureus. Bioassay-guided fractionation of the CH2Cl2 extract yielded the antibacterial compound akanthomycin as a mixture of atropisomers along with the closely related compounds 8-methylpyridoxatin and cordypyridone C. Akanthomycin was characterized using X-ray crystallography and NMR.     

Radical C?H Functionalization of Heteroarenes under Electrochemical Control

Electrochemical reactions are shown to be effective for the C H functionalization of a number of heterocyclic substrates that are recalcitrant to conventional peroxide radical initiation conditions. Monitoring reaction progress under electrochemical conditions provides mechanistic insight into the C H functionalization of a series of heterocycles of interest in medicinal chemistry.     

Solution mixing and the emission of light in flow-cells for chemiluminescence detection

Constructing flow-through reactors for chemiluminescence detection by machining channels into polymer disks has enabled the exploration of new configurations and materials that can improve signal intensity beyond that attainable with the traditional coiled-tubing design. Several approaches to merge reactant solutions were examined: an intersection, chamber or deeper well in the centre of a serpentine configuration flow-cell (directly in front of a photomultiplier tube), or a confluence point outside the detection zone. For several analytically useful, rapid chemiluminescence reactions, the single-inlet flow-cell with external Y-piece was most suitable, but for others (such as KMnO(4)/Mn(II) with morphine, and [Ir(f-ppy)(2)BPS](-) with fluoroquinolones) the dual-inlet configuration provided greater signals. The introduction of central mixing zones with larger widths than the channel reduced the chemiluminescence response. The reversing turns of a serpentine channel promote efficient mixing and greater chemiluminescence intensities than a spiral channel, but increasing the sharpness of the turns created areas of poor solution flow and decreased the chemiluminescence response. Teflon disks impregnated with glass microspheres increased the chemiluminescence signals by 13%-17%, due to the greater reflection of stray light towards the photodetector.     

Characterization of an assortment of commercially available multiwalled carbon nanotubes

The objective of this study was to characterize an assortment of as received, commercially available, non-functionalized multiwalled carbon nanotubes (MWCNT) samples (n?=?24) using thermogravimetric analysis, energy dispersive X-ray fluorescence spectrometry, high-resolution transmission electron microscopy and scanning electron microscopy. Each sample was assigned to one of six types based on nominal length and diameter. Some of the samples from the product assortment exhibited significant differences in purity and morphology from their nominal values. Variability in the physicochemical properties of MWCNTs may be a significant factor in why many toxicological investigations have findings that are difficult to reproduce. Therefore, it is strongly recommended that investigators studying these materials present characterization information in addition to providing their source.

High conduction neutron absorber to simulate fast reactor environment in an existing test reactor

A new metal matrix composite material has been developed to serve as a thermal neutron absorber for testing fast reactor fuels and materials in an existing pressurized water reactor. The performance of this material was evaluated by placing neutron fluence monitors within shrouded and unshrouded holders and irradiating for up to four cycles. The monitor wires were analyzed by gamma and X-ray spectrometry to determine the activities of the activation products. Adjusted neutron fluences were calculated and grouped into three bins—thermal, epithermal, and fast—to evaluate the spectral shift created by the new material. A comparison of shrouded and unshrouded fluence monitors shows a thermal fluence decrease of ~11 % for the shielded monitors. Radioisotope activity and mass for each of the major activation products is given to provide insight into the evolution of thermal absorption cross-section during irradiation. The thermal neutron absorption capability of the composite material appears to diminish at total neutron fluence levels of ~8 × 10²⁵ n/m². Calculated values for dpa in excess of 2.0 were obtained for two common structural materials (iron and nickel) of interest for future fast flux experiments.     

Hidden Markov models approach to the analysis of array CGH data

The development of solid tumors is associated with acquisition of complex genetic alterations, indicating that failures in the mechanisms that maintain the integrity of the genome contribute to tumor evolution. Thus, one expects that the particular types of genomic alterations seen in tumors reflect underlying failures in maintenance of genetic stability, as well as selection for changes that provide growth advantage. In order to investigate genomic alterations we are using microarray-based comparative genomic hybridization (array CGH). The computational task is to map and characterize the number and types of copy number alterations present in the tumors, and so define copy number phenotypes and associate them with known biological markers.To utilize the spatial coherence between nearby clones, we use an unsupervised hidden Markov models approach. The clones are partitioned into the states which represent the underlying copy number of the group of clones. The method is demonstrated on the two cell line datasets, one with known copy number alterations. The biological conclusions drawn from the analyses are discussed.     

[PbAsSiiPr3]6 — the First Structurally Characterized Compound with Chemical Bonds between Lead and Arsenic

The compound [PbAsSiiPr₃]₆ ( 1 ) could be obtained by the reaction of PbCl₂ with iPr₃SiAs(SiMe₃)₂ in THF at 0 °C. Central structural motif is a hexagonal prism built by six lead and six arsenic atoms. The average Pb—As bond length is 281 pm. The cluster crystallizes in the monoclinic space group C2/c, the lattice constants are: a = 4460.8(9) b = 2296.6(5), c = 2734.4(6) pm, β = 117.57(3)°. The thermogravimetric analysis in vacuum shows the tendecy of 1 to decompose under formation of elementary lead and volatile arsenic compounds.