Determination of GABA, glutamate and carbamathione in brain microdialysis samples by capillary electrophoresis with fluorescence detection

Disulfiram has been used as a deterrent in the treatment of alcohol abuse for almost 60 years. Our laboratory has shown that a disulfiram metabolite, S‐(N,N‐diethylcarbamoyl) glutathione (carbamathione), is formed from disulfiram and appears in the brain after the administration of disulfiram. Carbamathione does not inhibit aldehyde dehydrogenase but has been shown to be a partial non‐competitive inhibitor of the N‐methyl‐D ‐aspartic acid glutamate (Glu) receptor. In light of disulfiram's apparent clinical effectiveness in cocaine dependence, and carbamathione's effect on the N‐methyl‐D ‐aspartic acid receptor, the effect of carbamathione on brain Glu and γ‐aminobutyric acid (GABA) needs to be further examined. A CE‐LIF method based on derivatization with napthalene‐2,3‐dicarboxyaldehyde to simultaneously detect both neurotransmitter amino acids and carbamathione in brain microdialysis samples is described. The separation of Glu, GABA and carbamathione was carried out using a 50 mmol/L boric acid buffer (pH 9.6) on a 75 cm×50 μm id fused‐silica capillary (60 cm effective) at +27.5 kV voltage with a run time of 11 min. The detection limits for Glu, GABA and carbamathione were 6, 10 and 15 nmol/L, respectively. This method was used to monitor carbamathione and the amino acid neurotransmitters in brain microdialysis samples from the nucleus accumbens after the administration of an intravenous dose of the drug (200 mg/kg) and revealed a carbamathione‐induced change in GABA and Glu levels. This method demonstrates a simple, rapid and accurate measurement of two amino acid neurotransmitters and carbamathione for in vivo monitoring in the brain using microdialysis sampling.     

Mass spectrometric investigation of vaporization in the Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> system

The thermodynamics of vaporization in the Bi₂O₃-Fe₂O₃ quasibinary system was studied by high-temperature mass-spectrometry. The partial pressures of the constituents of a saturated vapor over the system at 1100 K were determined. Based on the experimental data, the following parameters were calculated: the activities of the components of the Bi₂O₃-Fe₂O₃ system condensed phase, the standard enthalpies of some heterogeneous reactions, and standard enthalpies of formation and enthalpies of formation for crystalline BiFeO₃ and Bi₂Fe₄O₉ from individual oxides. An optimal temperature for the solid-phase synthesis of bismuth ferrites from simple oxides is recommended.     

Competition between hydrogen bonding and dispersion interactions in the indole···pyridine dimer and (indole)2···pyridine trimer studied in a supersonic jet

Structures of the indole···pyridine dimer and (indole)2···pyridine trimer have been investigated in a supersonic jet using resonant two-photon ionization (R2PI) and IR-UV double resonance spectroscopic techniques combined with quantum chemistry calculations. R2PI spectra of the dimer and the trimer recorded by electronic excitation of the indole moiety show that the red-shift in the band origin of the dimer with respect to the 0(0)(0) band of the monomer is larger compared to that of the trimer. The presence of only one conformer in the case of both the dimer and the trimer has been confirmed from IR-UV hole-burning spectroscopy. The structures of the dimer and the trimer have been determined from resonant ion dip infrared (RIDIR) spectra combined with ab initio as well as DFT/M05-2X and DFT/M06-2X calculations. It has been found that the dimer, observed in the experiment, has a V-shaped geometry stabilized by N–H···N and C–H···N hydrogen bonding interactions, as well as C–H···π and π···π dispersion interactions. The geometry of the trimer has been found to be a cyclic one stabilized by N–H···N, N–H···π, C–H···π, and C–H···N interactions. The most important finding of this current study is the observation of the mixed dimer and trimer, which are stabilized by hydrogen bonding as well as dispersion interactions.     

The impact of the natural sciences on archaeology

This article reviews some of the applications of physics to the solution of archaeological problems. The use of magnetic, resistivity and electromagnetic surveying techniques for the location of buried features is described. Various methods of age determination are outlined while the problems associated with radiocarbon dating of organic material and thermoluminescent dating of pottery are discussed in detail. The techniques, including petrological examination, chemical analysis and isotopic analysis, employed in the physical examination of archaeological artefacts are described. Examples of the application of these techniques in establishing the source of the raw materials used in pottery, metal and stone implements and in elucidating the techniques of manufacture of pottery and metal objects are also given.     

Magnetostructural phase separation and giant isotope effect in R<Subscript>0.5</Subscript>Sr<Subscript>0.5</Subscript>MnO<Subscript>3</Subscript>

Results of neutron diffraction studies of R_0.5Sr_0.5MnO₃ manganites (R = Sm, Nd_0.772Tb_0.228, and Nd_0.544Tb_0.456) performed to reveal the microscopic origins of the giant oxygen isotope effect recently discovered in Sm_0.5Sr_0.5MnO₃ are presented. It is shown that two crystalline phases differing in the type of Jahn-Teller distortions of oxygen octahedra and in the type of magnetic ordering coexist at low temperatures in all the studied compositions. A scenario for the observed phase transitions is suggested based on the diffraction data. It is found that the percolation transition from the metallic to insulating state in compositions with Sm upon substitution of ¹⁸O for ¹⁶O is associated with a sharp (from 65 to 13%) decrease in the volume of the ferromagnetic metallic phase.     

Detection and identification of individual antigen molecules in human serum with pulsed semiconductor lasers

-11 M without separation steps. Received: 25 July 1997     

Positive pion photoproduction from hydrogen at photon energies between 500 MeV and 1,400 MeV in forward direction

The differential cross section of the reactionγ+p→π ⁺ was measured at pion CM-angles of 20° and 30° for photon energies between 500 MeV and 1,400 MeV. The pions were detected in a magnetic spectrometer. By measuring each pion trajectory and by offline calculation of the initial pion parameters an energy resolution of about 2.5% FWHM was achieved. The results complete a set of data which were measured in recent years at the Bonn 2.5 GeV synchrotron. In comparison to photoproduction analyses two effects were revealed: The η cusp appears in the energy dependence of the cross section as a sharp drop atK _γ=710 MeV. In the region of the third resonance the data show a greater enhancement than predicted by most of the analyses.