A high resolution 4π alpha spectrometer with silicon surface barrier detectors

An alpha counting system has been designed which gives counting geometry of nearly 4π with resolution capabilities of 25 keV or better. The alpha source is electro-deposited onto a thin gold foil which is sandwiched between two silicon surface barrier detectors. Alpha pulses from the two detectors are amplified, normalized and summed as a single pulse height spectrum. The techniques for the electrodeposition of the alpha activity onto the thin gold foil are described.     

Cavitand boronic acids mediate highly selective fructose transport

The synthesis sugar-transport properties of a family of five cavitand rim-appended boronic acids are reported. These conformationally rigid compounds are not observed to leach out of lipophilic membranes, and they exhibit unprecedented fructose to glucose transport selectivities and give higher fluxes than other neutral boronic acids. These properties make the cavitand boronic acids the best artificial fructose transporters described thus far. [structure: see text]     

269. Steroid total synthesis. 8. (+)-Estr-4-ene-3, 17-dione

A novel synthesis of the title compound, involving the resolution of a Mannichbase derived from racemic 11,11-o-phenylenedioxy-7-hydroxy-1-dodecen-3-one is described. In an alternate approach 2(S)-acetamido-6,6-o-phenylenedioxy-heptanoic acid was used as the optically active starting material. This scheme features the preparation of a chiral 1,2-epoxide and its regiospecific alkylation with lithio-1, 1-diethoxy-2-propyne.     

The preparation of fluorescence-quenched probes for use in the characterization of human factor Xa substrate binding domains

The preparation and characterization by LCMS of a library of 55 fluorescence- quenched peptides is described. The peptides bear a terminal anthranilamide fluorophore and a penultimate 2,4-dinitrophenyl-L-lysine quencher, and will be used to probe the substrate binding domain of the human blood coagulation enzyme, factor Xa.     

Radionuclide dating and trace element analysis by accelerator mass spectrometry

Accelerator Mass Spectcrometry (AMS) is being used for both radionuclide dating and stable isotope trace element determination with limits of high sensitivity. The areas of applications of radionuclide AMS include oceanography, terrestrial studies, glaciology, hydrology, environmental studies, meteorology, archaeology, anthropology, analysis of crude oils, biomedical and materials sciences, etc. The techniques and applications of radionuclide AMS are reviewed. The applications of stable element AMS include the measurements of trace impurities in electronic and other materials. The techniques and applications of stable element AMS are discussed with particular emphasis on electronic materials such as Si, GaAs, and HgCdTe. The design of the University of North Texas stable element AMS facility built in collaboration with Texas Instruments Incorporated is discussed.Work supported in part by the National Science Foundation Grants No. DMR-8812331 and ECD-9003099, the Office of Naval Research Grants No. N00014-89-J-1309, N00014-89-J-1344, N00014-90-J-1691, and N00014-91-J-1785, Texas Instruments Incorporated, Texas Utilities Electric Inc. International Digital Modeling Corp., North Texas Research Institute, Combustion Engineering Inc., LTV Corporation, the State of Texas Higher Education Coordinating Board — Texas Advanced Technology Research Program, the Robert A. Welch Foundation, and the University of North Texas Organized Research Fund.     

Highly fructose selective transport promoted by boronic acids based on a pentaerythritol core

We have designed and synthesized a highly lipophilic boronic acid (11) with a molecular shape that makes it much more effective at carrying sugars through organic membranes than a previously used steroidal boronic acid. The corresponding diboronic acid (12) was also found to transport fructose ahead of glucose with a very high selectivity (7.6:1.0). Modeling suggests that 12 is able to carry two fructose molecules at once in a complex stabilized through hydrogen bonding and ion pairing.     

Thermal desorption characterisation of molecularly imprinted polymers. Part I: a novel study using direct-probe GC-MS analysis

A novel thermal desorption technique using a direct-probe device (Chromatoprobe) attached to a gas chromatograph–mass spectrometer is presented for the thermal pretreatment, characterisation and analysis of molecularly imprinted polymers. The technique is demonstrated as effective for the removal of volatile materials, including template and unreacted monomers, from methacrylic acid–ethylene glycol dimethacrylate copolymers imprinted with 2-aminopyridine. Mass spectrometry is a powerful technique for polymer bleed characterisation. Thermal desorption studies on reloaded template and related compounds are reported as a means of assessing polymer morphology, specific binding by imprinted polymers compared with reference non-imprinted polymers and selective binding by an imprinted polymer for its template. Calibration studies on the thermal desorption technique using an internal standard are presented with R ² > 0.999. The technique provides a novel method for assessment of polymer thermal stability, composition and morphology.