Reactivity in the gas phase. Behaviour of isoxazoles under negative ion chemical ionization conditions

[M ? H⁺]^? ions of isoxazole (la), 3-methylisoxazole (1b), 5-methylisoxazole (1c), 5-phenylisoxazole (1d) and benzoylacetonitrile (2a) are generated using NICI/OH^? or NICI/NH₂^? techniques. Their fragmentation pathways are rationalized on the basis of collision-induced dissociation and mass-analysed ion kinetic energy spectra and by deuterium labelling studies. 5-Substituted isoxazoles 1c and 1d, after selective deprotonation at position 3, mainly undergo N ? O bond cleavage to the stable α-cyanoenolate NC ? CH ? CR ? O^? (R = Me, Ph) that fragments by loss of R? CN, or R? H, or H₂O. The same α-cyanoenolate anion (R = Ph) is obtained from 2a with OH^?, or NH₂^?, confirming the structure assigned to the [M ? H⁺]^? ion of 1d, On the contrary, 1b is deprotonated mainly at position 5 leading, via N? O and C(3)? C(4) bond cleavages, to H? C ≡ C? O ^? and CH₃CN. Isoxazole (1a) undergoes deprotonation at either position and subsequent fragmentations. Deuterium labelling revealed an extensive exchange between the hydrogen atoms in the ortho position of the phenyl group and the deuterium atom in the α-cyanenolate NC ? CD = CPh ? O^?.     

Rapid quantitation of globotriaosylceramide in human plasma and urine: a potential application for monitoring enzyme replacement therapy in Anderson-Fabry disease

A method for measuring globotriaosylceramide (Gb3, or GL3) levels in plasma and urine of humans affected by Anderson-Fabry disease has been developed. The analyses are performed using flow injection analysis-electrospray ionization-tandem mass spectrometry (FIA-ESI-MS/MS). The method is rapid, sensitive and hence suitable for high-throughput analyses, requiring only a simple 50-fold dilution for the preparation of plasma and urine samples. The detection of the analytes of interest was achieved using a triple quadrupole instrument operating in the multiple reaction monitoring mode. The linearity of the calibration standard responses, the intra- and inter-assay precision, the accuracy and the detection limit of the method were evaluated. The proposed method allows a rapid and accurate assessment of globotriaosylceramide in biological samples. Data obtained from healthy volunteers and Anderson-Fabry affected subjects suggest a potential role for this technique in monitoring the effectiveness of Anderson-Fabry disease therapy. The results obtained in two actual cases treated with enzyme replacement therapy are reported and discussed.     

First search for the flavor changing neutral current decay D0-->gammagamma

Using 13.8 fb(-1) of data collected at or just below the Upsilon(4S) with the CLEO detector, we report the result of a search for the flavor changing neutral current process D0-->gammagamma. We observe no significant signal for this decay mode and determine 90% confidence level upper limits on the branching fractions B(D0-->gammagamma)/B(D0-->pi(0)pi(0))<0.033 and B(D0-->gammagamma)<2.9 x 10(-5).     

Direct photon production from pions and protons at 200 GeV/c

Direct photon production has been studied by an experiment performed with the NA3 spectrometer at CERN, using incident negative and positive beams at 200 GeV/c interacting with an isoscalar Carbon target. Two different triggers have been used; one of them requires the photon conversion. The experiment is sensitive to direct photons produced with 3.0≦P _T ≦6 GeV/c and center-of-mass rapidity ?0.4≦y ^*≦1.2. Inclusive cross sections are given for incident π^± and protons, and compared with second order QCD predictions; finally an estimation of the gluon structure function of the nucleon is given.     

Quantitative analysis of the molecular species of monosialogangliosides by continuous-flow fast-atom bombardment mass spectrometry.

Negative-ion continuous-flow fast-atom bombardment mass spectrometry was evaluated as a means for the quantitative analysis of N-acetylneuraminyl-galactosyl-glucosyl-ceramide (NeuAc-GM3) and N-acetylgalactosaminyl-(N-acetylneuraminyl)galactosyl-glucosyl-ceramide (NeuAc-GM2). This study was carried out on a 7070-EQ mass spectrometer (VG Analytical, Manchester, UK) using a home-made continuous-flow fast-atom bombardment probe with a mixture of methanol + water + triethanolamine (70:27:3, v/v/v) as the mobile phase. Utilizing 100 ng of acetyl-lysogalactosyl-N-acetylgalactosaminyl-(N-acetylneuraminyl)g alactosyl-glucosyl-ceramide (acetyl-lysoGM1) as an internal standard, standard curves for NeuAc-GM3 d18:1-16:0, NeuAc-GM3 d18:1-18:0 and Neuac-GM2 d18:1-18:0 were found to be linear over the range 5-250 ng, with associated correlation coefficients of 0.990-0.997. The lower limit of detection was found to be 2.5 ng. Satisfactory results could also be obtained when the calibration curves were derived from the deprotonated molecular ions of a mixture of the NeuAc-GM2 and NeuAc-GM3 classes. Using this approach, quantitative determination of NeuAc-GM3 d18:1-16:0 from rat adrenal gland was performed using N-acetylneuraminic acid assay as a test control. We found 278 +/- 36 ng of this species in 1 mg of tissue (three replicate experiments). The procedure represents a sensitive method for the quantitation of monosialogangliosides and its capability to give molecular species information.