An approach to the synthesis of tricholomalide A: an effective means for achieving homo-Robinson annulation

A procedure has been developed for the construction of 7,5-fused ring systems through the ring expansion of silyl enol ethers. This method has been applied to the synthesis of an intermediate en route to the natural product, tricholomalide A.     

Non-linear acoustic measurements to assess crack density in trabecular bone

Three methods to measure qualitative and quantitative aspects of bone non-linearity were investigated in the context of diagnosis of bone “biomechanical health”: i.e. harmonic generation, parametric emission and parametric reception using phase modulation. Trabecular bone exhibited hysteretic non-linear behavior due to microcracks in bone tissue, and parametric reception using phase modulation seemed to be the best configuration for in vivo application. However, the relationship between level of non-linearity and crack density needs to be validated by histological analysis.     

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Preparation and reactions of N-thioformyl peptides from amino thioacids and isonitriles

The preparation of N-thioformyl peptides from amino thioacids and isonitriles at room temperature is described.     

Elastic modulus of poly(ethylene oxide) determined from the Raman longitudinal acoustic mode

The chain modulus of poly(ethylene oxide) is determined by the Raman longitudinal acoustic mode method with the aid of a normal coordinate analysis and found to be 1.3 × 10¹¹ dyn/cm². Our normal mode calculations provide a clear basis for explaining the discrepancy between chain moduli determined from Raman and x-ray experiments. They show that the uncorrected Raman modulus of helical polymers reflects the presence of interchain interactions and therefore should not be taken as the correct elastic modulus of a single chain.     

Emission spectroscopy of flame fronts in aluminum suspensions

Spatially resolved emission spectra from Bunsen-type flames stabilized in aluminum suspensions in air and oxygen–argon/helium mixtures were obtained using a mechanical-optical scanning system. A low resolution (1.5 nm) spectrometer was used to acquire the broad spectra over the 350–1000 nm range, and a high-resolution (0.04 nm) instrument was used for observation of AlO molecular bands and non-ionized atomic aluminum. The temperature of condensed phase emitters in the flame was derived using polychromatic fitting of the continuum spectra to Planck’s law. AlO temperature was found by fitting of the theoretically calculated shape of the band to experimental data. Peak temperatures of the condensed emitters were found to be approximately 3250 K in aluminum-air flames and approximately 3350 K for oxygen–argon/helium flames. Temperatures derived from AlO spectra coincide with the temperature of the condensed emitters with measurement accuracy and are only 100–200 °C lower than the computed equilibrium flame temperatures. The radial distribution of the temperature profile of the continuous emitters was found via Abel deconvolution and recovered the double-front structure of the Bunsen flame cone, with the outer flame being attributed to a diffusion flame of the fuel-rich products with ambient air. The observation of atomic aluminum lines seen in emission from the outer flame edge and partial self-absorption from the inner flame confirms the structure associated with the double-front structure. The implications of these results for the regime of particle combustion in a dust flame are discussed.     

Sequential intermediates in the base-catalyzed conversion of bis(pi-conjugated propargyl) sulfones to 1,3-dihydrobenzo- and naphtho[c]thiophene-2,2-dioxides

[reaction: see text] In a recent article, we reported on the base-catalyzed rearrangements of dipropargyl selenides, -sulfides, -sulfoxides, and -sulfones that eventually lead to polycyclic aromatic products. In the present work, we report on the first isolation and characterization of the thiophene dioxide intermediates 5b,c from a mild tandem isomerization/cyclization/aromatization of bis(pi-conjugated propargyl) sulfones. Monoallene 2b,c and diallene 3b intermediates were also identified by NMR. A kinetic study of the rearrangement of 1a-c revealed that the unusual facile tandem process is highly dependent on the nature of gamma-substitution.     

Atmospheric pressure MALDI-FTMS of normal and chemically modified RNA

Atmospheric pressure (AP) MALDI has been combined with Fourier transform mass spectrometry (FTMS) to obtain the unambiguous characterization of RNA samples modified by solvent accessibility reagents used in structural studies of RNA and protein-RNA complexes. The formation of cation adducts typical of MS analysis of nucleic acids was effectively reduced by extensive washing of the anionic analytes retained onto the probe surface by strong interactions with a cationic layer of poly(diallyldimethylammonium chloride) (PADMAC). This rapid desalting procedure allowed for the detection of DNA and RNA samples in high femtomole quantities distributed over a 4 x 4 mm sample well. AP MALDI-FTMS was shown to provide high-resolution spectra for analytes as large as approximately 6.4 kDa with little or no evidence of metastable decomposition. The absence of significant metastable decay observed for precursor ions selected for tandem experiments offered a further measure of the low energy content typical of ions generated by AP MALDI. This feature proved to be very beneficial in the characterization of chemically modified RNA samples, which become particularly prone to base losses upon alkylation. The high resolution offered by FTMS enabled the application of a data-reduction algorithm capable of rejecting any signal devoid of plausible isotopic distribution, thus facilitating the analysis of complex analyte mixtures produced by nuclease treatment of RNA substrates. Proper selection of nucleases and digestion conditions can ensure the production of hydrolytic fragments of manageable size, which could extend the range of applicability of this bottom-up strategy to the structural investigation of very large RNA and protein-RNA complexes.     

Amplifying fluorescent polymer sensors for the explosives taggant 2,3-dimethyl-2,3-dinitrobutane (DMNB)

Structural and electronic effects on the efficiency of DMNB detection with fluorescent conjugated polymers are described.