An electrokinetic/hydrodynamic flow microfluidic CE-ESI-MS interface utilizing a hydrodynamic flow restrictor for delivery of samples under low EOF conditions

A hydrodynamic flow restrictor (HDR) that is used to combine electrokinetic and hydrodynamic flow streams has been fabricated in a microfluidic channel by laser micromachining. Combining electrokinetic and hydrodynamic flow streams is challenging in microfluidic devices, because the hydrodynamic flow often overpowers the electrokinetic flow, making it more difficult to use low electroosmotic flow in the electrokinetic portion of the system. The HDR has been incorporated into a capillary electrophoresis-mass spectrometry interface that provides continuous introduction of a make-up solution and negates the hydrodynamic backpressure in the capillary electrophoresis channel to the extent that low EOF can be utilized. Moreover, the hydrodynamic backpressure is sufficiently minimized to allow coatings that minimize EOF to be used in the electrokinetically driven channel. Such coatings are of great importance for the analysis of proteins and other biomolecules that adsorb to charged surfaces.     

Magnetic field effects on coherent backscattering of light

We have studied the influence of magneto-optical Faraday rotation on coherent backscattering of light experimentally, theoretically and by computer simulations of Monte-Carlo type. The consistency of these three approaches reveals new aspects of the propagation of vector waves in turbid media with and without Faraday rotation. Experimentally, we have demonstrated that the Faraday rotation may almost completely destroy the reciprocity of light paths. However, as shown by the simulations, the cone of coherent backscattering may not only be destroyed but also shifted off the exact backscattering direction, parallel to the magnetic field, as long as the amount of circular polarization is not completely destroyed by the multiple scattering. The relationship between coherent backscattering, depolarization and Faraday rotation are explained by a simple path model of vector waves. This leads to a new characteristic correlation length required to properly describe the influence of Faraday rotation on multiple light scattering. Received 28 January 2000     

Stereoselective total synthesis of (±)-7-deoxy-trans-dihydronarciclasine, a potent antineoplastic phenanthridone alkaloid

A short and efficient stereoselective total synthesis of (±)-7-deoxy-trans-dihydronarciclasine, a highly potent antineoplastic agent and constituent of the Amaryllidaceae alkaloids, is described. Starting from a known arylcyclohexylamine-type precursor 6, the C-ring with the required stereochemistry is constructed using a chemo- and stereoselective enone reduction (NaBH₄/CaCl₂ system) and a Mitsunobu reaction. For the B-ring closure, the Banwell modification of the Bischler-Napieralski reaction was applied.     

Coherent backscattering and localization in a self-attracting random walk model

Intensity propagation of waves in dilute 2D and 3D disordered systems is well described by a random walk path-model. In strongly scattering media, however, this model is not quite correct because of interference effects like coherent backscattering. In this letter, coherent backscattering is taken into account by a modified, self-attracting random walk. Straightforward simulations of this model essentially reproduce the results of current theories on “non-classical” transport behavior, i.e. Anderson localization in 1D and 2D for any amount of disorder and a phase transition from weak to strong localization in 3D. However, in the strongly scattering regime corrections are necessary to account for the finite number of light modes due to their non-vanishing lateral extention. Within our model this correction leads to the observation that strong localization does not take place. Received 17 September 2001     

Record high extreme-ultraviolet efficiency at near-normal incidence from a multilayer-coated polymer-overcoated blazed ion-etched holographic grating

We have measured the extreme-ultraviolet (EUV) efficiency of a polymer-overcoated blazed ion-etched holographic test grating. The grating had a magnetron-sputtered Mo2C/Si multilayer coating matched to the grating blaze angle of 2.78 degrees. At an angle of incidence of 5.6 degrees and a wavelength of 15.79 nm, the measured efficiency peaks in the second outside order at 29.9%. The derived groove efficiency is 53.0%. To the best of our knowledge these are the highest values obtained yet at EUV wavelengths from a holographic ion-etched blazed grating.     

An expedient total synthesis of ent-(−)-7-deoxy-trans-dihydronarciclasine

A short and efficient stereoselective total synthesis of (−)-7-deoxy-trans-dihydronarciclasine, an ent-form of a highly potent antineoplastic agent constituent of the Amaryllidaceae alkaloids, is described. Starting from the enantiopure form of a known arylcyclohexylamine type precursor 6, which was synthesized enantioselectively utilizing a highly enantioselective nitromethane addition, the three hydroxy groups on the C-ring with the required stereochemistry were introduced by a chemo- and stereoselective enone reduction (NaBH₄/CaCl₂ system) followed by a Mitsunobu reaction and subsequent osmylation. The ring closure of the B-ring was accomplished by the Banwell modification of the Bischler-Napieralski reaction.     

In situ thermoset molecular composites

The polymerization of rigid rod polymer precursors in a reactive matrix precursor, which is later cured in the mold, constitutes the in situ process. A poly-azomethine (PAM) was used as the rigid rod molecule. The resin used was an epoxy. We discuss the prediction of mechanical properties using micromechanics equations for chopped fiber composites. The chemistry used to synthesize the rigid rod polymer PAM in the epoxy precursor is reviewed. Approaches to better control the cure of these epoxy systems through cure kinetics and cure rheology studies completes the thermoset in situ molecular composite process. There was a 71% increase in tensile modulus in comparison to that of the neat epoxy resin. Molecular modeling simulations and continuum mechanics are used to help understand these findings. PAM/epoxy systems were used as a matrix material in the fabrication of unidirectional glass fiber/(PAM/epoxy) structural composites. © 1994 John Wiley & Sons, Inc.