Lateral phase separation in lipid-coated microbubbles

In the design of lipid-coated microbubble ultrasound contrast agents for molecular imaging and targeted drug delivery, the surface distribution of the shell species is important because it dictates such properties as ligand location, brush coverage, and amount of drug loading. We used a combination of spectroscopy and microscopy techniques to test the prevailing notion that the main phosphatidyl choline (PC) and lipopolymer species are completely miscible within the monolayer shell. NMR spectroscopy showed that the shell composition is roughly equivalent to the bulk lipid ratio. FTIR spectroscopy showed a sharp melting peak corresponding to the main phase-transition temperature of the main PC species, with no observed pretransitions while scanning from room temperature, indicating a single PC-rich ordered phase. Electron and fluorescence microscopy showed a heterogeneous microstructure with dark (ordered) domains and bright (disordered) regions. Domain formation was thermotropic and reversible. Fluorescent labeling of the lipopolymer following shell formation showed that it partitions preferentially into the disordered interdomain regions. The ordered domains, therefore, are composed primarily of PC, and the disordered interdomain regions are enriched in lipopolymer. Phase heterogeneity was observed at all lipopolymer concentrations (0.5 to 20 mol %), and the degree of phase separation increased with lipopolymer content. The composition and temperature dependence of the microstructure indicates that phase separation is driven thermodynamically rather than being a kinetically trapped relic of the shell-formation process. The overall high variation in microstructure, including the existence of anomalous three-phase coexistence, highlights the nonequilibrium (history-dependent) nature of the monolayer shell.     

Asymptotic behavior of self-normalized trimmed sums: Nonnormal limits II

Let {X _j} be independent, identically distributed random variables which are symmetric about the origin and have a continuous nondegenerate distributionF. Let {X _n(1),...,X _n(n)} denote the arrangement of {X ₁,...,X _n} in decreasing order of magnitude, so that with probability one, |X _n(1)|>|X _n(2)|>...> |X _n(n)|. For initegersr _n such thatr _n/n0, define the self-normalized trimmed sumT _n= _i=rn ⁿ X _n(i)/{ _i=rn ⁿ X _n ² (i)}^1/2. Hahn and Weiner⁽⁶⁾ showed that under a probabilistically meaningful analytic condition generalizing the asymptotic normality criterion forT _n, various nonnormal limit laws forT _n arise which are represented by means of infinite random series. The analytic condition is now extended and the previous approach is refined to obtain limits which are mixtures of a normal, a Rademacher, and a law represented by a more general random series. Each such limit law actually arises as can be seen from the construction of a single distribution whose correspondingL(T _n ) generates all of the law along different subsequences, at least if {r _n} grows sufficiency fast. Another example clarifies the limitations of the basic approach.     

Optical properties of certain steroid hormones and related compounds

Summary Optical properties of one adrenal cortex, one corpus luteum, two testes, six gluco corticoid, and three unclassified steroids were determined. These data afford a positive identification of these compounds with only minute amounts of material.

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Zusammenfassung Die optischen Eigenschaften von 13 Steroiden (ein Nebennierenrindensteroid, ein Gelhkörpersteroid, zwei Keimdrüsensteroide, sechs Glucocortieosteroide, drei nicht näher klassifizierte Steroide) wurden bestimmt. Die gefundenen Daten ermöglichen die einwandfreie Identifizierung dieser Verbindungen mit sehr geringem Materialaufwand.

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Résumé On a déterminé les propriétés optiques de 13 stéroïdes (un stéroïde cortico-surrénal, un stéroïde du corps jaune, deux stéroïdes des glandes génitales, six glueocorticostéroïdes, trois stéroïdes n'appartenant pas aux classifications précédentes). Les données trouvées permettent l'identification rigoureuse de ces composés sur très peu de substance.

     

Synthesis of new azido porphyrins and their reactivity in copper(I)-catalyzed Huisgen 1,3-dipolar cycloaddition reaction with alkynes

We report herein the preparation of two novel porphyrins substituted with an azido group born either on the para-position of one phenyl meso-susbtituent of a tetraaryl zinc porphyrin (1) or directly on the meso-position of a trisaryl nickel porphyrin (2). We studied the scope and the limitation the Huisgen cycloaddition reaction of these two porphyrins using different catalytic conditions. We observed that the carbene (SIMes)CuBr in THF/H₂O 3:1 at 45 °C for 60 h gives almost quantitative yields for the reaction between 1 and different alkynes, but significantly lower yields with 2 probably due to its thermal instability.     

Effect of surrounding point charges on the density functional calculations of NixOx clusters (x = 4-12)

Embedded Ni(x)O(x) clusters (x = 4-12) have been studied by the density-functional method using compensating point charges of variable magnitude to calculate the ionic charge, bulk modulus, and lattice binding energy. The computations were found to be strongly dependent on the value of the surrounding point charge array and an optimum value could be found by choosing the point charge to reproduce the experimentally observed Ni--O lattice parameter. This simple, empirical method yields a good match between computed and experimental data, and even small variation from the optimum point charge value produces significant deviation between computed and measured bulk physical parameters. The optimum point charge value depends on the cluster size, but in all cases is significantly less than +/-2.0, the formal oxidation state typically employed in cluster modeling of NiO bulk and surface properties. The electronic structure calculated with the optimized point charge magnitude is in general agreement with literature photoemission and XPS data and agrees with the presently accepted picture of the valence band as containing charge-transfer insulator characteristics. The orbital population near the Fermi level does not depend on the cluster size and is characterized by hybridized Ni 3d and O 2p orbitals with relative oxygen contribution of about 70%.