Sedimentation analysis of latex spheres and gold sols

Summary Analytical centrifugation was used for the analysis of latex spheres. It appeared that the latex spheres sedimented according to Stokes' law. Therefore the diameters calculated from the sedimentation coefficients deviated on average less than 5 % from the diameters observed with the electron microscope.Colloidal gold was also investigated and it was shown that the gold sol consisted of particles with discrete sizes. The masses of the particles expressed in the mass of the smallest particles formed the arithmetic series 1, 2, 3, 4...n. The fact that apparently colloidal gold particles cannot exist below a certain definite size was confirmed by gel filtration.It was concluded that analytical centrifugation can be safely used for the determination of the size distribution of relatively large particles, membrane vesicles included.

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Zusammenfassung Die Brauchbarkeit der analytischen Zentrifugation zur Bestimmung der Größenverteilung von relativ großen Partikeln wurde untersucht. Latexkügelchen sedimentierten entsprechend dem Stokes'schen Gesetz. Dementsprechend stimmten die aus den Sedimentationskoeffizienten berechneten Durchmesser binnen 5 % mit den elektronenphonetisch ermittelten Durchmessern überein.Kolloidales Gold ergab eine diskrete Größenverteilung der im Kolloid enthaltenen Goldpartikel. Die Massen der Partikel waren ganzzahlige Vielfache (1, 2, 3, 4...n) der Masse der kleinsten Partikel. Durch Gelfiltration wurde bestätigt, daß die Partikel eines Goldkolloids nicht unter einer bestimmten Mindestgröße vorkommen.Aus den beschriebenen Versuchen wurde abgeleitet, daß die analytische Zentrifugation eine sichere Methode zur Bestimmung der Größenverteilung relativ großer Partikel - Membranbläschen inbegriffen - darstellt.

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With 3 figures and 2 tables     

Integrated Molecular Logic Using a Multistate Electrochromic Platform

Herein, we present an approach that integrates molecular logic functions using surface-confined metallo-organic assemblies. These assemblies are electrochromic and mimic the behaviour of logic elements. The logic elements are addressed individually by electrochemical methods, and their outputs are simultaneously read-out optically by UV/Vis absorption spectroscopy. The versatility of our setup is demonstrated by the integration of two multi-component assemblies; each acting as ternary logic elements. We used also a laminated cell configuration to demonstrate color-to-color and color-to-transparent transitions. This concept offers a route for the future development of devices with multiple logic states.     

Self-propagating assembly of a molecular-based multilayer

Accelerated growth of a molecular-based material that is an active participant in its continuing self-propagated assembly has been demonstrated. This nonlinear growth process involves diffusion of palladium into a network consisting of metal-based chromophores linked via palladium.     

Selective optical recognition and quantification of parts per million levels of Cr(6+) in aqueous and organic media by immobilized polypyridyl complexes on glass

Selective optical sensing of parts per million levels of Cr(6+) in water under acidic conditions with robust, osmium-chromophore-based monolayers is demonstrated. The sensor system can be reset by washing with water at neutral pH and can be readily monitored by UV/vis spectroscopy.     

Monolayer-based selective optical recognition and quantification of FeCl3 via electron transfer

Reagentless optical recognition and parts-per-million (ppm) quantification of FeCl3 in CH3CN was demonstrated using a redox-active Os(II)-chromophore-based monolayer on glass. The Fe3+-induced oxidation of the monolayer is fully reversible and can be monitored optically with a conventional UV/vis spectrophotometer (260-800 nm). The system can be reset with water within <1 min. Selectivity of the sensor toward FeCl3 is not affected by the presence of representative alkali metals, alkaline earth metals, and other transition-metal salts. Sensing of Fe3+ and concurrent generation of Fe2+ can be also observed with the naked eye by adding 2,2'-bipyridyl (bipy) to the solution to generate [Fe(bipy)3]2+. Validation of the analytical performance characteristics of the sensor was performed including reversibility, reproducibility, stability, and the detection range (0.5-162 ppm of FeCl3 in CH3CN, 100-1000 ppm in water). The monolayer is sensitive and specifically responsive to its target ion. In addition, a blind test was conducted to probe the reproducibility and reproducibility variances of the system. The reaction of the monolayer with a CH3CN solution containing 5 ppm of FeCl3 follows pseudo first-order kinetics in the monolayer with DeltaG298K = 21.6 +/- 0.1 kcal/mol, DeltaH = 10.2 +/- 1.5 kcal/mol, DeltaS = -38.3 +/- 4.9 eu.     

The study of the changes in the thermal properties of <Emphasis Type="Italic">Labeo rohita</Emphasis> bones due to arsenic exposure

The paper presents the changes in the thermal properties of control, arsenic exposed and DMSA treated Labeo rohita bones by using thermo analytical techniques. The result shows that the mass loss due to the thermal decomposition occurs in three distinct steps due to loss of water, organic and inorganic materials. The arsenic exposed bones present a different thermal behaviour compared to the control bones. The residue masses are increased due to arsenic exposure, while the DMSA treatment reduces the residue mass level. These thermal characteristics can be used as a qualitative method to check the metal accumulation in samples.     

Strategies for electrooptic film fabrication. Influence of pyrrole-pyridine-based dibranched chromophore architecture on covalent self-assembly, thin-film microstructure, and nonlinear optical response

The new dibranched, heterocyclic "push-pull" chromophores bis{1-(pyridin-4-yl)-2-[2-(N-methylpyrrol-5-yl)]ethane}methane (1), 1-(pyrid-4-yl)-2-(N-methyl-5-formylpyrrol-2-yl)ethylene (2), {1-(N-methylpyridinium-4-yl)-2-[2-(N-methylpyrrol-5-yl)]ethane}{(1-(pyridin-4-yl)-2-[2-(N-methylpyrrol-5-yl)]ethane}methane (3), N-methyl-2-[1-(N-methylpyrid-4-yl)ethen-2-yl]-5-[pyrid-4-yl]ethen-2-yl]pyrrole iodide (4), bis{1-(N-methyl-4-pyridinio)-2-[2-(N-methylpyrrol-5-yl)]ethane}methane iodide (5), and N-methyl-2,5-[1-(N-methylpyrid-4-yl)ethen-2-yl]pyrrole iodide (6) have been synthesized and characterized. The neutral (1 and 2) and monomethyl salts (3 and 4) undergo chemisorptive reaction with iodobenzyl-functionalized surfaces to afford chromophore monolayers SA-1/SA-2 and SA-3/SA-4, respectively. Molecular structures and other physicochemical properties have been defined by (1)H NMR, optical spectroscopy, and XRD. Thin-film characterization by a variety of techniques (optical spectroscopy, specular X-ray reflectivity, atomic force microscopy, X-ray photoelectron spectroscopy, and angle-dependent polarized second harmonic generation) underscore the importance of the chromophore molecular architecture as well as film growth method on film microstructure and optical/electrooptic response.     

Optical sensing of parts per million levels of water in organic solvents using redox-active osmium chromophore-based monolayers

Optical sensing of parts per million (ppm)-levels of H2O (10-300 ppm) in an organic solvent with robust, osmium chromophore-based monolayers is demonstrated. The H2O-induced reduction of the covalently bound osmium(III) complex is fully reversible and can be readily monitored by UV/vis absorption spectroscopy. The thermally robust sensor can be reactivated chemically within 3 min.     

Coulomb attraction during the carpet growth mode of NaCl

The submonolayer growth of NaCl bilayer high-rectangular shaped islands on Ag(111) is investigated at around room temperature by using low temperature scanning tunneling microscopy. The growth at the step edges is preferred. Two kinds of islands are observed. They either grow with their non-polar edge at the step edge of Ag(111) or the islands overgrow in a carpet-like mode with the polar direction parallel to the edge. In the latter case, the Ag step is rearranged and considerable, while the NaCl layer is bent. This study clarifies the nature of the interaction of an alkali halide nanostructure with a metal step edge.