Liquid chromatography-mass spectrometry of spiroketal stereoisomers of pectenotoxins and the analysis of novel pectenotoxin isomers in the toxic dinoflagellate Dinophysis acuta from New Zealand

The acid-catalyzed inter-conversion of spiroketal isomers of pectenotoxins PTX1, PTX6 and PTX2 were studied by liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-MS-MS). Using a C8-silica reversed-phase column and a mobile phase of aqueous acetonitrile containing 2 mM ammonium formate and 50 mM formic acid, the known spiroketal stereoisomers of PTX1 eluted in order of PTX1, PTX4 and PTX8, while those of PTX6 eluted in the order PTX6, PTX7 and PTX9. Acid treatment of PTX2 yielded two novel spiroketal stereoisomers, which have been named PTX2b and PTX2c. LC-MS-MS spectra obtained for the [M+NH4]- ions of PTX2, PTX2b and PTX2c were essentially identical. As an application of the LC-MS-MS methodology, a sample of the toxic dinoflagellate Dinophysis acuta collected from the coast of New Zealand was analyzed for pectenotoxins. PTX2 and a new pectenotoxin, which has been named PTX11, were detected as the most predominant compounds. Novel PTX2 and PTX11 isomers were also found in the D. acuta although the levels of these compounds were low.     

Search for associated production of Upsilon and vector boson in pp collisions at sqrt[s]=1.8 TeV

We present a search for associated production of the Upsilon(1S) and a vector boson in 83 pb(-1) of ppmacr; collisions at sqrt[s]=1.8 TeV collected by the CDF experiment in 1994-1995. We find no evidence of the searched signal in the data, and set upper limits to the production cross sections.     

Search for a W' boson decaying to a top and bottom quark pair in 1.8 TeV pp collisions

We report the results of a search for a W' boson produced in pp; collisions at a center-of-mass energy of 1.8 TeV using a 106 pb(-1) data sample recorded by the Collider Detector at Fermilab. We observe no significant excess of events above background for a W' boson decaying to a top and bottom quark pair. In a model where this boson would mediate interactions involving a massive right-handed neutrino (nu(R)) and have standard model strength couplings, we use these data to exclude a W' boson with mass between 225 and 536 GeV/c(2) at 95% confidence level for M(W')>M(nu(R)) and between 225 and 566 GeV/c(2) at 95% confidence level for M(W')相似文献   

Perturbation results of critical elliptic equations of Caffarelli-Kohn-Nirenberg type

We find for small ε positive solutions to the equation

     

A confinement model calculation of h1(x)

The transverse polarization distribution of quarks h₁(x) is computed in a confinement model, the chiral chromodielectric model. The flavor structure of h₁, its Q² evolution and Soffer's inequality are studied. The Drell-Yan double transverse asymmetry A_TT is evaluated and found to be one order of magnitude smaller than some previous estimates which equated it to the double longitudinal asymmetry.     

REMOVAL OF THYMINE-CONTAINING PYRIMIDINE DIMERS FROM UV LIGHT-IRRADIATED DNA BY S1 ENDONUCLEASE

Abstract— S₁ endonuclease was shown to remove thymine-containing pyrimidine dimers from UV-irradiated human DNA, although efficient removal could be demonstated only by using long digestion times, relatively high enzyme concentrations, and irradiation sufficient to yield dimer substitutions in DNA of 1 per 1W300 (dimers/base pair). Neutral and alkaline sucrose gradient analysis of strand break induction by S, of UV-irradiated DNA suggests that recognition of the dimer by S, is the limiting factor in its removal and dimer removal usually results from attack on the dimer containing DNA strand without the induction of a double-strand break.     

Diffractive production of the charmed baryon Λ+c at the CERN ISR

In a sample of diffractive events of high multiplicity a sharp five standard deviation signal is observed at M = 2255 MeV/c² in the K^?pπ⁺ mass distribution and, although with less statistical strength, at the same mass in the Λ⁰π⁺π⁺π^? channel. These signals are identified as being due to the decay of the charmed baryon Λ⁺_c which is produced with a cross section times branching ratio σ_cB in the range 0.7?1.8 μb for the K^?π⁺p decay and 0.3?0.7 μb for the Λ^-π⁺π⁺ π^? system.     

YBCO/Nb bulk junctions: Observation of the Josephson effect

Summary The fabrication procedure of reliable YBCO-based bulk junctions with a Nb film as a counterelectrode is described. Typical currentvoltage characteristics are presented, clearly showing the presence of the Josephson effect.