Determination of individual microsphere properties by capillary electrophoresis with laser-induced fluorescence detection

Capillary electrophoresis with postcolumn laser-induced fluorescence detection was used to individually detect 6.0, 1.0, 0.5, and 0.2 num diameter polystyrene microspheres and individually measure their electrophoretic mobility. The analysis of a nanoliter-size volume from a microsphere suspension results in an electropherogram characterized by several narrow spikes in a well-defined migration time window. Each spike is associated with one microsphere because, when one single microsphere is introduced into the capillary by micromanipulation, the electropherogram has only one spike in the same migration time window. The distributions of individual measurements resulting from an electropherogram were used to evaluate the reproducibility from run to run, observe the effect of sodium dodecyl sulfate (SDS) added to the running buffer, and to investigate the origin of electrophoretic dispersion. As expected from the interactions between microspheres and SDS, the addition of this surfactant to the running buffer narrowed the range and shifted the average electrophoretic mobility to more negative values. After evaluating common sources of broadening in capillary electrophoresis, electrophoretic dispersion was attributed to microsphere heterogeneity. Unlike electropherograms displaying Gaussian-like profiles, the two-dimensional representations of the individual measurements provide a new alternative to evaluate and study electrophoretic-related properties of microspheres.     

Orbital Isomerism in the 1.3-Dphosphacyclobutane-2.4-Diyl,Quantum Chemical Investigations at MCSCF Level

Abstract

Quantum chemical calculations at open shell level (MCSCF, MP2, CISD) indicate the strong biradical nature of the title compound which is isoelectronic to the well known S₂N₂.     

Theoretical design of the biradical character in 1,3-diphosphacyclobutanediyl and homologous structures

The electronic nature of 1,3-diphosphacyclobutane-2,4-diyl is explored with wavefunction based and density functional methods. According to MCSCF calculations the singlet state of the title compound is a biradicaloid with closed shell character, the number of unpaired electrons, assigned upon the analysis of the natural orbitals, is close to one. The participation of closed shell contributions in the overall wavefunction arises from a strong mixing of canonical structures, which emphasizes (a) the phosphorane type of bonding as well as (b) π-delocalization within the ring system. The bonding situation changes when σ-attracting substituents, e.g. amino groups, are attached to the phosphorus atoms. They inhibit possible cyclic π-delocalization and enhance the biradical character within the ring system.     

Anion-promoted cation motion and conduction in zeolites

The motion of sodium cations in sodalite and cancrinite has been investigated by force field calculations, solid-state NMR, and impedance spectroscopy. Special emphasis is dedicated to the influence of anions on sodium mobilities. Local cation motion is promoted when they interact with anions. However, not all systems with high local mobilities exhibit good ion conductivities, as cooperativity of the motion appears to be an important factor, as well. The activation barrier for local sodium motion (calculations) and long-range transport (dc conductivities) is lowered in sodalite when halogenide anions, Cl(-), Br(-), or I(-), are present. The activation barriers increase with increasing size of the anion and decreasing coordination in the transition state. On the basis of (23)Na solid-state NMR data, all the sodium ions in the dense sodalite structure are rather rigid up to 470 K. All the cations in chromate sodalite, and Na(+) in the small cancrinite epsilon-cages without anion interactions, show a restricted local motion at higher temperatures. There is a selective high local motion of Na(+) in the neighborhood of chromate anions in the more open channel system of cancrinite. These results suggest that sodium migration can be enhanced, at least locally, in open channel systems by anion interactions. A dynamics coupling between anion reorientation and cation mobility was not observed.     

N-methylpyrrolidine-based precursors for chemical vapor deposition of GaNx particles

An attempt to prepare a metalorganic precursor of gallium with reactivity at low temperature in chemical vapor deposition (CVD) systems was done by reacting N-methylpyrrolidine with metal gallium or gallium nitrate under mild conditions. The precursors were bubbled into a CVD assemblage and then reacted with ammonia at temperatures between 400 and 700 °C. The depositions onto silicon substrates were pyramidal particles of 100 nm width at the base and up to 55 nm in height. The rise in growth temperature increased particle density from 0.9 to 27.1 particles per square micron, but reduced the height from 50 to 10 or 2 nm. XPS spectra showed the presence of gallium and nitrogen. The intensity of the gallium spectrum decreased as the process temperature increased indicating that GaN_x particles were deposited rather than the stoichiometric gallium nitride (GaN). An additional N1s band of impurities appeared whose intensity increases with the reaction temperature. The lower impurity content corresponded to the sample prepared with Ga(NO₃)₃ at 400 °C.     

Integrated-optic ammonia sensor

Fibre coupled optical sensors for chemical and biologial species are important for process control, environmental control and pollution detection. An integrated optic ammonia sensor is described here; this is based on evanescent field absorption. The sensitive element of this sensor is a strip waveguide, fabricated by field assisted ion exchange, coated with a immobilized indicator dye. The sensor has a short response time and a long lifetime. An experimental arrangement is shown which has been built up for the characterization of different integrated optic sensor elements. Spectral response characteristics, response times and the generation of reference signals are reported in detail. The simple temperature dependence, the humidity independence and the very low cross sensitivity of this ammonia sensor is illustrated.     

Stereospezifische Synthese einer neuen Morphin-Teilstruktur

We describe here a synthesis of the morphine partial structures 28 and 36 , and of their enantiomers, which uses 7-methoxy-benzofurancarboxylic acid as starting material. A key intermediate in this scheme is compound 15 , which is converted, via 1,2-ketone shift, into 22 . This latter is stereospecifically reduced to the alcohol 24 and converted to the amide 25 . The diastereomer of 25 is afforded by stereospecific introduction of a ethoxycarbonyl group in 15 to yield the β-ketoester 31 , followed by Curtius degradation of the acid 32 to the acylamine 34 . An efficient method for removal of the methoxy group in methoxy-dihydro-benzofurans is presented (Scheme 9), as is the functionalization of the N-atom in 27 with concurrent complex formation between the free hydroxy group and boric-acid. The aromatization of the furan ring (Scheme 10) with DDQ gave the expected benzofuran derivative 30 .     

Injective Envelopes and (Gorenstein) Flat Covers

We characterize left Noetherian rings in terms of the duality property of injective preenvelopes and flat precovers. For a left and right Noetherian ring R, we prove that the flat dimension of the injective envelope of any (Gorenstein) flat left R-module is at most the flat dimension of the injective envelope of _R R. Then we get that the injective envelope of _R R is (Gorenstein) flat if and only if the injective envelope of every Gorenstein flat left R-module is (Gorenstein) flat, if and only if the injective envelope of every flat left R-module is (Gorenstein) flat, if and only if the (Gorenstein) flat cover of every injective left R-module is injective, and if and only if the opposite version of one of these conditions is satisfied.     

Letter: Four-dimensional Tensor Identities of Low Order for the Weyl and Ricci Tensors

It is shown that the new tensor identityrecently discovered by Bonanos, and some other tensoridentities recently investigated, are consequences of avery simple and mathematically trivial (but subtle) identity highlighted some years ago byLovelock. Lovelock's identity gives a tensor identity offirst order in Weyl-like tensors, and a tensor identityof second order in Ricci-like tensors, from which higher order identities, such as those recentlystudied, can easily be constructed.