Stereocontrolled (E,Z and erythro, threo) synthesis of ⊙-hydroxyallylic sulphides

All four isomers of substituted 3-alkylthio-4-hydroxybutenes have been synthesised: both the geometry of the double bond and the relative stereochemistry of the two chiral centres are controlled.     

A local spectral approach for assessing time series model misspecification

We consider band-limited frequency-domain goodness-of-fit testing for stationary time series, without smoothing or tapering the periodogram, while taking into account the effects of parameter uncertainty (from maximum-likelihood estimation). We are principally interested in modeling short econometric time series, typically with 100 to 150 observations, for which data-driven bandwidth selection procedures for kernel-smoothed spectral density estimates are unlikely to have adequate levels. Our mathematical results take parameter uncertainty directly into account, allowing us to obtain adequate level properties at small sample sizes. The main theorems provide very general results involving joint normality for linear functionals of powers of the periodogram, while accounting for parameter uncertainty, which can be used to determine the level and power of a wide array of statistics. We discuss several applications, such as spectral peak testing and testing for the inclusion of an Unobserved Component, and illustrate our methods on a time series from the Energy Information Administration.     

Analytical applications of bioluminescence

The phenomenon of bioluminescence has, since the time of Sir Robert Boyle, attracted the interest of scientific researchers. The detailed mechanisms of many bioluminescent systems are now well understood and have the potential to form the basis of accurate and sensitive analytical methods.     

A review of recent developments in self-attenuation correction leading to a simple dual energy lump correction model for use in the quantitative gamma assay of plutonium

The application of quantitative high-resolution gamma-ray spectrometry for the non-destructive assay of plutonium bearing items, such as waste drums, is complicated by self-attenuation if the plutonium is present as lumps. By definition, lumps are small compared to the bulk matrix and so are not accounted for in the gross matrix correction yet can exert a significant influence on the assay result. Compared to a calibration using dilute standards, self-attenuation results in an under-reporting of the mass of plutonium present. The availability of representative standards is unrealistic for diverse waste streams and so a means to detect and compensate for the presence of lumps is needed. An experimental approach that can in principle generate an item specific correction factor is to exploit the differential attenuation between a set of gamma-lines of known relative emission intensity. In the case of routine measurements of drummed Pu wastes the choice of lines is often limited, the most appropriate often being those at 129 keV and 414 keV from ²³⁹Pu. This paper discusses the problems and potential of exploiting this pairing in a simple dual energy approach to the long standing and challenging problem of self-attenuation.     

Synthesis of the CD-ring of the anticancer agent streptonigrin: studies of aryl-aryl coupling methodologies

A series of functionalized 4-bromopyridines, representing the C-ring of the anticancer agent streptonigrin have been prepared and their abilities to undergo Pd-catalyzed cross-coupling with streptonigrin D-ring siloxanes were evaluated. The coupling reaction was generally tolerant to the preparation of hindered CD biaryls; however, the electronic effects of both partners play a pivotal role in the success of the coupling process. Analogs of the CD biaryl were prepared by coupling of aryl siloxane derivatives (D-ring component) with highly functionalized 4-bromopyridines (C-ring); however, the CD biaryl of the natural product could not be prepared in high yield by siloxane coupling due to the facile formation of reduced pyridine under the coupling conditions. Alternatively, the fully functionalized CD biaryl of streptonigrin was prepared using a Suzuki coupling of appropriately functionalized C-ring bromide and D-ring aryl boronic acid. The described approach is highly convergent and readily amenable to the synthesis of analogs.     

Siloxane-based cross-coupling of bromopyridine derivatives: studies for the synthesis of streptonigrin and lavendamycin

Highly functionalized 4-bromopyridines were prepared and found to undergo fluoride-promoted, Pd-catalyzed cross-coupling with aryltrialkoxysilanes to give sterically demanding biaryls. The 3-nitro-4-bromopyridine derivative coupled in good yield with TBAT (tetrabutylammonium triphenyldifluorosilicate) to provide a biaryl adduct that serves as a model system for the total synthesis of the antitumor antibiotics streptonigrin and lavendamycin. [reaction: see text]     

Intercomparison of simultaneously obtained infrared (4.8 microm) and visible (515-715 nm) ozone spectra using ACE-FTS and MAESTRO

Laboratory ozone absorption spectra were measured simultaneously in the visible (515-715 nm) and infrared (2070-2140 cm(-1)) spectral regions using SCISAT-1's MAESTRO (Measurement of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation) and ACE-FTS (Atmospheric Chemistry Experiment-Fourier Transform Spectrometer) spectrometers. An intercomparison of these measurements was used to assess the relative accuracy of HITRAN absolute line strengths, for which there was a 4% change between the 2000 and 2004 versions. Results reported here show that Chappuis band cross section strengths are more consistent with the HITRAN 2004 4.8 microm band line strengths than with the 2000 compilation.