Spirobicyclo[2.2.2]octane derivatives: mimetics of baccatin III and paclitaxel (Taxol)

The formylated spirobyclic alcohol was computer modeled to be a mimetic of paclitaxel. In this model, the formyl group was used as a truncated paclitaxel side chain in order to reduce the computational work. Compound , carrying the paclitaxel side chain, was synthesized in six steps from optically active 1,3-diketone . Microtubule stabilization was not observed for , indicating that the model needs to be adjusted.     

A molecular description of profile analysis: decision weights and internal noise

Systematic inefficiencies and internal noise in a spectral profile discrimination task were investigated. Listeners detected a 1000-Hz sinusoid added in-phase to the central component of a complex consisting of 11 equal-intensity sinusoids. Parameters for a channel model that employs decision weights and internal noise were estimated with molecular psychophysical techniques. Maximum likelihood predictions of the model were generally within a few decibels of observed thresholds. The degree to which an assumption of ideal weights leads to overestimation of internal noise was also assessed.     

High speed microtribology with quartz crystal resonators

Quartz resonators in contact with metal-covered spheres have been used to study the tribology of micron-sized metal-metal contacts at high speed (1 m/sec and high frequency (12 MHz), while maintaining a shear amplitude in the nanometer range. The data aquisition is based on ring-down experiments, where the electrical excitation is periodically interrupted and the free decay of the oscillation is analyzed. At contact, an amplitude-dependent frequency and decay rate are found, indicative of an underlying nonlinear equation of motion. Using perturbation theory and the two-timing approximation, a nonlinear spring constant kappa(1)(x) and a nonlinear drag coefficient xi(1)(x) are explicitly derived. We find a local slip-to-stick-transition at a shear amplitude of 0.5 nm. Coating the gold sufaces with a self-assembled thiol monolayer removes the stick.     

Excitation and decay of the isovector giant monopole resonances via the 208Pb(3He,t p) reaction at 410 MeV

The excitation and subsequent proton decay of the isovector spin-flip giant monopole resonance (IVSGMR) is studied via the 208Pb(3He,t) reaction at 410 MeV. In the inclusive spectrum (60+/-5)% of the non-energy-weighted sum-rule strength for this 2 variant Planck's over 2h omega resonance was found in the region 29相似文献   

Comparison of capillary zone electrophoresis performance of powder-blasted and hydrogen fluoride-etched microchannels in glass

The applicability of glass chips with powder-blasted microchannels for electrophoretic separations was examined, and the performance was compared to microchannels etched with hydrogen fluoride (HF), using bicarbonate buffer and rhodamine B and fluorescein as model compounds. The measured electroosmotic mobilities in all chips were comparable, with values of ca. 7 x 10(-4) cm(2) V(-1)s(-1). The effect of electrical field strength and detection length on the separation efficiency was monitored. It was found that the main source of dispersion is of the Taylor-Aris type, which was discussed in relation to channel roughness differences. Although in powder-blasted channels with a separation length of 8.20 cm, 7-9 times lower plate numbers were obtained than in a HF-etched channel with similar dimensions, successful separation of five fluorescein isothiocyanate (FITC)-labeled amino acids was obtained on a powder-blasted chip within 80 s. Efficiencies of up to 360 000 plates/m were demonstrated on this chip, when a higher buffer concentration was used at a field strength of 664 V/cm. It can be concluded that powder-blasted microchannel chips, although they have a lower separation efficiency compared to HF-etched chips, perform well enough for many applications. Powder blasting can therefore be considered a low-cost and efficient alternative to HF etching, in particular because of the possibility to fabricate access holes through the glass with the same process.     

Fluxional behavior of a cadmium zwitterion complex: proton transport and tautomerism in methylene chloride solution

The synthesis and structure of the tautomeric Cd(II) isoindoline zwitterion coordination compound [Cd(4'-MeLH)(NO(3))(2)].CH(3)OH (4'-MeLH = 1,3-bis[2-(4-methylpyridyl)imino]isoindoline) are reported. In methylene chloride solution, tautomer interconversion occurs as the N-H proton moves between the identical imine nitrogen atoms. We report the kinetics of proton transfer as followed by variable temperature (1)H NMR spectroscopy and demonstrate that methanol of solvation and adventitious water facilitate rapid proton transfer.     

Observation of hot-electron pressure in the vibration dynamics of metal nanoparticles

We investigate the vibration dynamics of ellipsoidal silver nanoparticles, using time-resolved optical pump-probe spectroscopy. When excited with femtosecond laser pulses, the particles execute anisotropic shape oscillations. We show that these vibrations are triggered by the thermal expansion of the optically heated particles. The time dependence of the vibrations indicates that this expansion is caused by two mechanisms: The lattice anharmonicity and the extremely large pressure of the hot conduction electrons.     

Gamow-teller strengths of the inverse beta transition 176Yb-->176Lu for spectroscopy of proton-proton and other sub-MeV solar neutrinos

Discrete Gamow-Teller (GT) transitions 176Yb-->176Lu at low excitation energies have been measured via the ( 3He,t) reaction at 450 MeV and at 0 degrees. For 176Yb, two low-lying states are observed, setting low thresholds Q(nu) = 301 and 445 keV for neutrino ( nu) capture. Capture rates estimated from the measured GT strengths, the simple two-state excitation structure, and the low Q(nu) in Yb-Lu indicate that Yb-based nu detectors are well suited for a direct measurement of the sub-MeV solar electron-neutrino ( nu(e)) spectrum including pp neutrinos.     

Electrochemical reduction of oxygen catalyzed by a wide range of bacteria including Gram-positive

Most bacteria known to be electrochemically active have been harvested in the anodic compartments of microbial fuel cells (MFCs) and are able to use electrodes as electron acceptors. The reverse phenomenon, i.e. using solid electrodes as electron donors, is not so widely studied. To our knowledge, most of the electrochemically active bacteria are Gram-negative. The present study implements a transitory electrochemical technique (cyclic voltammetry) to study the microbial catalysis of the electrochemical reduction of oxygen. It is demonstrated that a wide range of aerobic and facultative anaerobic bacteria are able to catalyze oxygen reduction. Among these electroactive bacteria, several were Gram-positive. The transfer of electrons was direct since no activity was obtained with the filtrate. These findings, showing a widespread property among bacteria including Gram-positive ones, open new and interesting routes in the field of electroactive bacteria research.     

Open tubular columns and non-porous packings in copolymer HPLC analysis

Summary The separation of poly(styrene-co-acrylonitrile) is presented in open tubular stainless steel columns and columns packed with non-porous glass beads. Furthermore separation on a short silica packed column proved to be better than on a similar longer column. A definition of the term high performance precipitation liquid chromatography is suggested for gradient elution with sample injection into a starting eluent which is a nonsolvent for the copolymer under investigation. The choice of a suitable solvent-nonsolvent combination is of essential importance.