Dative P→Sn interactions in ortho-phenylene phosphine-stannanes

Monophosphine and diphosphine-stannane compounds 1 and 2 are shown spectroscopically, structurally and theoretically to present rare intramolecular P→Sn interactions.     

Archaeological resinous samples from Asian wrecks: Taxonomic characterization by GC-MS

Plant resins, and particularly dammars from the Dipterocarpaceae family, were widely used in the past, notably as part of caulking material. The organic composition of resins, already complicated, is not always preserved over time and can be considerably affected by ageing. Hence, their occurrence in archaeological items leads to the necessity to identify them taxonomically with precision. Resinous organic materials collected near and/or on wrecks discovered in South China Sea, supposed to contain dammar resins because of their geographical excavation context, were investigated by gas chromatography-mass spectrometry (GC-MS), together with freshly collected dammars, to establish taxonomic and alteration parameters allowing to identify dammar even in very altered samples or in mixtures together with other organic materials. This study specially focuses on three samples collected within or close to the M1J wreck, a Portuguese wreck lost in the Straight of Malacca during the 16th century. Our analyses establish that all three are made of dammar, two of them in association with pitch and bitumen. In addition, biodegradation biomarkers were detected in all these three samples, indicating that they were submitted to microbial degradation processes during their ageing.     

Carbon nanotube grease with enhanced thermal and electrical conductivities

A stable and homogeneous grease based on carbon nanotubes (CNTs, single-wall and multi-wall) in polyalphaolefin oil has been produced without using a chemical surfactant. For example, for a 11 wt% (7 vol%) single-wall CNT (diameter 1–2 nm, length 0.5–40 μm) loading, the thermal conductivity (TC) of the grease shows a 60–70% increase compared to that for no nanotube loading. In addition, the grease is electrically conductive, has a high dropping point, good temperature resistance, and does not react with copper at temperatures up to 177 °C. The performance of carbon nanotube grease could be much better with the improvement of nanotube quality and purity. A possible explanation for these results is that of a high loading of CNTs (>10 wt%), they become associated with each other by van der Waals forces in the grease to form three-dimensional percolation networks. Time-dependent magnetic results demonstrate that, even under the influence of a strong outside magnetic field, the TC value remains constant. This phenomenon can be attributed to the existence of networks that makes magnetic alignment of nanotubes impossible.     

Chemoselective α,β‐Dehydrogenation of Saturated Amides

We report a method for the selective α,β‐dehydrogenation of amides in the presence of other carbonyl moieties under mild conditions. Our strategy relies on electrophilic activation coupled to in situ selective selenium‐mediated dehydrogenation. The α,β‐unsaturated products were obtained in moderate to excellent yields, and their synthetic versatility was demonstrated by a range of transformations. Mechanistic experiments suggest formation of an electrophilic Se^IV species.     

Sensory and nonsensory influences on children's performance of dichotic pitch perception tasks

Dichotic pitch perception reflects the auditory system's use of binaural cues to perceptually separate different sound sources and to determine the spatial location of sounds. Several studies were conducted to identify factors that influence children's dichotic pitch perception thresholds. An initial study of school children revealed an age-related improvement in thresholds for lateralizing dichotic pitch tones. In subsequent studies potential sensory and nonsensory limitations on young children's performance of dichotic pitch lateralization tasks were examined. A training study showed that with sufficient practice, young children lateralize dichotic pitch stimuli as well as adults, indicating an age difference in perceptual learning of the lateralization task. Changing the task requirements so that young children made a judgment about the pitch of dichotic pitch tones, rather than the spatial location of the tones, also resulted in significantly better thresholds. These findings indicate that nonsensory factors limit young children's performance of dichotic pitch tasks.     

Explorations in organic chemistry leading to the total synthesis of (+/-)-gelsemine

The total synthesis of (+/-)-gelsemine (1) is described. A defining phase of the effort involved recourse to a strategic oxetane ring (see compound 25). It was constructed anticipating an intramolecular displacement of the carbon (C17)-oxygen (O4) bond (see product 48). A key intermediate in the stereospecific elaboration of the oxetane linkage was enone 22, which was susceptible to two beta-face attacks leading to 24 and, thence, 25. Three sigmatropic rearrangements were employed in building the bridgehead (C20) and the spiroanilide (C7) quaternary centers en route to gelsemine.     

Getting closer to the real bacterial cell wall target: biomolecular interactions of water-soluble lipid II with glycopeptide antibiotics

A novel synthesized water-soluble variant of lipid II (LII) was used to evaluate the noncovalent interactions between a number of glycopeptide antibiotics and their receptor by bioaffinity electrospray ionization mass spectrometry (ESI-MS). The water-soluble variant of lipid II is an improved design, compared to the traditionally used tripeptide N,N'-diacetyl-L-lysyl-D-alanyl-D-alanine (KAA), of the target molecule on the bacterial cell wall. A representative group of glycopeptide antibiotics was selected for this study to evaluate the validity of the novel cell-wall-mimicking target LII. Structure-function relationships of various glycopeptide antibiotics were investigated by means of 1) bioaffinity mass spectrometry to evaluate solution-phase molecular interactions with both LII and KAA, 2) fluorescence leakage experiments to study the interactions with the membrane-embedded lipid II, and 3) minimum inhibitory concentrations against the indicator strain Micrococcus flavus. Our results with the novel LII molecule reveal that some antibiotics interact differently with KAA and LII. Additionally, our data cast doubt on the hypothesis that antibiotic selfdimerization assists in the in-vivo efficacy. Finally, the water-soluble lipid II proved to be a better model of the bacterial cell wall.     

Carbon-13 NMR study of some isomeric n-nitroindazole derivatives

The ¹³C NMR spectra of 1,5- and 2,x-dinitroindazoles “x=4-7” and 3-bromo-1,x-dinitroindazoles are recorded and discussed. The data on he 2,x-dinitroindazoles confirm our previous structurea assignment based on ¹H NMR spectroscopy. The ¹³C NMR spectra established that in the novel 3-bromo-1,x-dinitroindazoles the N-nitro group is attached at N-1.