Recognition-induced transformation of microspheres into vesicles: morphology and size control

Polystyrene functionalized with diamidopyridine (DAP) recognition units self-assembles in nonpolar media to form thermally reversible micrometer-scale spherical aggregates. The size and the thermal stability of these microspheres can be controlled by the molecular weight of the polymer. The addition of thymine-functionalized polymer to these self-assembled microspheres converted them into vesicular aggregates with a controlled size. The morphology change was reversible: the addition of DAP-functionalized polymer converted the vesicles back to microspheres.     

Unusual iron(III) ate complexes stabilized by Li-pi interactions

Several iron(III) complexes incorporating diamidoether ligands are described. The reaction between [Li(2)[RN(SiMe(2))](2)O] and FeX(3) (X=Cl or Br; R=2,4,6-Me(3)Ph or 2,6-iPr(2)Ph) form unusual ate complexes, [FeX(2)Li[RN(SiMe(2))](2)O](2) (2, X=Cl, R=2,4,6-Me(3)Ph; 3, X=Br, R=2,4,6-Me(3)Ph; 4, X=Cl, R=2,6-iPr(2)Ph) which are stabilized by Li-pi interactions. These dimeric iron(III)-diamido complexes exhibit magnetic behaviour characteristic of uncoupled high spin (S= 5/2 ) iron(III) centres. They also undergo halide metathesis resulting in reduced iron(II) species. Thus, reaction of 2 with alkyllithium reagents leads to the formation of iron(II) dimer [Fe[Me(3)PhN(SiMe(2))](2)O](2) (6). Similarly, the previously reported iron(III)-diamido complex [FeCl[tBuN(SiMe(2))](2)O](2) (1) reacts with LiPPh(2) to yield the iron(II) dimer [Fe[tBuN(SiMe(2))](2)O](2) but reaction with LiNPh(2) gives the iron(II) product [Fe(2)(NPh(2))(2)[tBuN(SiMe(2))](2)O] (5). Some redox chemistry is also observed as side reactions in the syntheses of 2-4, yielding THF adducts of FeX(2): the one-dimensional chain [FeBr(2)(THF)(2)](n) (7) and the cluster [Fe(4)Cl(8)(THF)(6)]. The X-ray crystal structures of 3, 5 and 7 are described.     

Self-assembly of tetrahedral and trigonal antiprismatic clusters [Fe4(L4)4] and [Fe6(L5)6] on the basis of trigonal tris-bidentate chelators

In a one-pot reaction, the tetranuclear iron chelate complex [Fe4(L4)4] 6 was generated from benzene-1,3,5-tricarboxylic acid trichloride (4), bis-tert-butyl malonate (5a), methyllithium, and iron(II) dichloride under aerobic conditions. Alternatively, hexanuclear iron chelate complex [Fe(L5)6] 7 was formed starting from bis-para-tolyl malonate (5b) by employing identical reaction conditions to those applied for the synthesis of 6. The clusters 6 and 7 are present as racemic mixtures of homoconfigurational (delta,delta,delta,delta)/(lambda,lambda,lambda,lambda)-fac or (delta,delta,delta,delta,delta,delta)/(lambda,lambda,lambda,lambda,lambda,lambda)-fac stereoisomers. The structures of 6 and 7 were unequivocally resolved by single-crystal X-ray analyses. The all-iron(III) character of 6 and 7 was determined by M?ssbauer spectroscopy.     

An investigation of glasses for capillary chromatography

An investigation was conducted of various glasses, other than soda lime or borosilicate, for use in glass capillary gas chromatography. The work has uncovered some unique chromatographic qualities in the use of potash soda lead and fused silica glasses as materials for making glass capillary columns. The fused silica proved to be an ideal material for capillary column construction, being inherently more inert than glass containing metal oxides. It has been shown that through the use of thin wall capillary tubing of high flexibility many of the mechanical problems associated with glass capillary columns, such as fragility and column straightening, can be avoided.     

Influence of load position on the stability of shallow arches

The influence of load position of lhe snap-through instability of shallow, circular, elastic arches is investigated. Results are obtained for pinned, clamped, and clamped-pinned end conditions. The worst load position is seen to depend on the arch rise.

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Zusammenfassung Der Eifluss der Kraftlage auf die Durchschgsinstabilität von flachen, elastischen Kreisbögen wird untersucht. Es sind Ergebnisse erhalten worden für Bögen mit gelenkigen eingespannten, und gelenkig-eingespannten Lagern. Die ungünstigste Kraftlage hängt von der Bogenhöhe ab.

     

Magnetic Effects in Curved Quantum Waveguides

The interplay among the spectrum, geometry and magnetic field in tubular neighbourhoods of curves in Euclidean spaces is investigated in the limit when the cross section shrinks to a point. Proving a norm resolvent convergence, we derive effective, lower-dimensional models which depend on the intensity of the magnetic field and curvatures. The results are used to establish complete asymptotic expansions for eigenvalues. Spectral stability properties based on Hardy-type inequalities induced by magnetic fields are also analysed.     

Alternating and Random Copolymers of Vinyl Acetate and Maleic Anhydride

Alternating copolymers of vinyl acetate (VAc) and maleic anhydride (MA) are produced preferentially when VAc and MA are copolymerized at moderate temperatures while random copolymers are produced at temperatures above 90°C. A charge-transfer complex (CTC) of VAc/MA exists at moderate temperatures but does not exist at temperatures above 90°C.     

Iterative atmospheric correction scheme and the polarization color of alpine snow

Characterization of the Earth's surface is crucial to remote sensing, both to map geomorphological features and because subtracting this signal is essential during retrievals of the atmospheric constituents located between the surface and the sensor. Current operational algorithms model the surface total reflectance through a weighted linear combination of a few geometry-dependent kernels, each devised to describe a particular scattering mechanism. The information content of these measurements is overwhelmed by that of instruments with polarization capabilities: proposed models in this case are based on the Fresnel reflectance of an isotropic distribution of facets. Because of its remarkable lack of spectral contrast, the polarized reflectance of land surfaces in the shortwave infrared spectral region, where atmospheric scattering is minimal, can be used to model the surface also at shorter wavelengths, where aerosol retrievals are attempted based on well-established scattering theories.In radiative transfer simulations, straightforward separation of the surface and atmospheric contributions is not possible without approximations because of the coupling introduced by multiple reflections. Within a general inversion framework, the problem can be eliminated by linearizing the radiative transfer calculation, and making the Jacobian (i.e., the derivative expressing the sensitivity of the reflectance with respect to model parameters) available at output. We present a general methodology based on a Gauss–Newton iterative search, which automates this procedure and eliminates de facto the need of an ad hoc atmospheric correction.In this case study we analyze the color variations in the polarized reflectance measured by the NASA Goddard Institute of Space Studies Research Scanning Polarimeter during a survey of late-season snowfields in the High Sierra. This insofar unique dataset presents challenges linked to the rugged topography associated with the alpine environment and a likely high water content due to melting. The analysis benefits from ancillary information provided by the NASA Langley High Spectral Resolution Lidar deployed on the same aircraft.The results obtained from the iterative scheme are contrasted against the surface polarized reflectance obtained ignoring multiple reflections, via the simplistic subtraction of the atmospheric scattering contribution. Finally, the retrieved reflectance is modeled after the scattering properties of a dense collection of ice crystals at the surface. Confirming that the polarized reflectance of snow is spectrally flat would allow to extend the techniques already in use for polarimetric retrievals of aerosol properties over land to the large portion of snow-covered pixels plaguing orbital and suborbital observations.     

X-ray Measurements of the Bulk Modulus of the Myofilament Liquid Crystal in Striated Muscle

Low-angle X-ray diffraction measurements of the distance between myosin filaments comprising the smectic B₁ liquid crystal found in skinned crayfish striated muscle were made. The interfilament distanceas a function of applied compressive osmotic pressure wasdetermined and the bulk modulus of this myofilament liquid crystal ascertained. Under compression the behavior of this myosin filament lattice is shown to be predicted well by the Murnaghan equation of state. The isothermal bulk modulus, B _o, of this myosin filament liquid crystal is 1.51 × 10⁵ dynes/cm² at 2°C and at 46% actin overlap.