The quantitative analysis of 1-alpha-acetylmethadol and its principal metabolites in biological specimens by gas chromatography-chemical ionization-multiple ion monitoring mass spectrometry.

1-alpha-acetylmethadol (LAAM) is a new drug under development for the treatment of heroin dependence. A new analytical method applicable to the accurate biodispositional study of the drug and its metabolities is described and critically discussed in this report. The procedure involves sample preparation and direct organic solvent extraction using eta-butyl chloride, amide derivatization by molecular rearrangement, and gas chromatography-chemical ionization mass spectrometry-selected ion monitoring, with methane as the carrier and ammonia as reagent gases. Deuterated (d3 stable isotopes of LAAM and its metabolites are used as internal standards. The method is free from qualitative interferences and has quantitative sensitivity to 5 ng/ml for 2.0 ml samples with 10-15% accuracy and precision in the range 5-100 ng/ml; and 2-5% at concentrations up to 750 ng/ml. Specimens of plasma, whole blood, urine, bile, brain, liver, and other visceral samples have been successfully analyzed, as well as in vitro preparations such as hepatic microsomes. By appropriate data processing, the method lends itself to routine analysis and high volume work; even manually the method is capable of at least 50 samples per week. A simplified procedure for the analysis of LAAM and its metabolites in urine only is also presented and discuet up and use the methods.     

A Subpixel Image Restoration Algorithm

Abstract

In statistical image reconstruction, data are often recorded on a regular grid of squares, known as pixels, and the reconstructed image is defined on the same pixel grid. Thus, the reconstruction of a continuous planar image is piecewise constant on pixels, and boundaries in the image consist of horizontal and vertical edges lying between pixels. This approximation to the true boundary can result in a loss of information that may be quite noticeable for small objects, only a few pixels in size. Increasing the resolution of the sensor may not be a practical alternative. If some prior assumptions are made about the true image, however, reconstruction to a greater accuracy than that of the recording sensor's pixel grid is possible. We adopt a Bayesian approach, incorporating prior information about the true image in a stochastic model that attaches higher probability to images with shorter total edge length. In reconstructions, pixels may be of a single color or split between two colors. The model is illustrated using both real and simulated data.     

The calculation of molecular and cluster auger spectra

The work of Asaad and Burhop and of Shirley on atoms is Shown to form the basis of a useful theory for the analysis of molecular core-valence-valence Auger spectra. If the static relaxation term of Shirley is neglected, the theory requires only a single SCF calculation on the neutral molecule. Since this approximation seems justified for the class of itinerant holes, the theory not only pemits the interpretation of the spectra of molecules considerably larger than previously analyzed, but potentially the spectra of chemisorbed molecules from cluster calculations. Theory and experiment are compared for the carbon KW spectra ofCH₄, C₂H₂, C₂H₄ and CH₃OH.     

An asymmetric sigmatropic rearrangement

Catalysis of the isomerization of the symmetrical adduct 1 by (+)-camphor-10-sulfonic acid in chloroform gave (?)-2, which was enriched by fractional crystallization techniques and purified by column chromatography. Values for the optical purity of this sample were obtained both by conversion into diastereomers and by the isotopic dilution method, and were in fair agreement with one another. They corresponded to an enantiomeric excess of 1·34% in the original synthesis.In benzene as solvent the (+)-enantiomer was preferentially formed.     

DIET in the bulk: evidence for hot electron cleavage of Si---H bonds in SiO2 films

The observed increase in leakage current through SiO₂ films after hot electron exposure is ascribed to dissociation induced by electronic transitions (“DIET”) of bulk Si---H bonds, producing mobile hydrogen. We use ab initio supercell bandstructure calculations at the local density functional level to locate features produced by hydrogen-containing defects in -SiO₂. The edge of the Si---H σ* resonance is found to be about 2.7 eV above the conduction band rise, in good agreement with the observed threshold for hot electron induced damage in amorphous SiO₂ films grown on Si substrates. The O---H σ* resonance is almost 4 eV higher. Removing H from O---H in the supercell does not affect the gap region (---O⁻ forms); however, removing H from Si---H produces a mid-gap state, suggesting leakage current by hopping conductivity between Si dangling bonds. A Morse potential model is used to explore the dynamics of bond scission by short-lived (<1 fs) hot electron σ* capture. Supercell calculations on interstitial atomic hydrogen indicate the energy cost to break an embedded Si---H bond is about 0.6 eV less than in the gas phase. The DIET yield is substantially increased by reducing both ground and electron-attached state binding by this amount. While uncertainty over the displaced equilibrium in the electron-attached excited state remains, the computed DIET cross-section for reasonable parameters is ≈10⁻¹⁸ cm², and is in agreement with the semi-empirically derived value for trap creation. Comparisons are made to surface DIET processes involving Si---H bonds.     

The reduction of chromium(V) in non-aqueous media: The preparation of mixed ligand complexes of chromium(III) from [bipyH2][CrOCl5] (bipy = 2,2′-bipyridyl)

Summary The chromium(V) complex [bipyH₂][CrOCl₅] reacts with MeCN to yield the octahedral chromium(III) complex [CrCl₃(bipy)(NCMe)], the nitrile ligand of which can be replaced by other ligands to give [CrCl₃(bipy)L] complexes (L = py, pyO, and Ph₃PO). However, reactions of [bipyH₂]-[CrOCl₅] with higher nitriles RCN (R = Et, n-Pr, Ph, or PhCH₂) or with MeNO₂ all lead to the isolation of [CrCl₃(bipy)]_n (n most probably being 2), which may also be prepared by thermal decomposition of [CrCl₃(bipy)(NCMe)].