Heteroaggregation in binary mixtures of oppositely charged colloidal particles

Heteroaggregation (or heterocoagulation) rate constants have been measured in mixtures of well-characterized colloidal particles of opposite charge with multiangle static and dynamic light scattering. This technique permits routine measurements of absolute heteroaggregation rate constants, also in the presence of homoaggregation. Particularly with multiangle dynamic light scattering, one is able to estimate absolute heteroaggregation rate constants accurately in the fast aggregation regime for the first time. Heteroaggregation rate constants have also been measured over a wide range of parameters, for example, ionic strength and different surface charge densities. Amidine latex particles, sulfate latex particles, and silica particles have been used for these experiments, and they were well characterized with respect to their charging and homoaggregation behavior. It was shown that heteroaggregation rate constants of oppositely charged particles increase slowly with decreasing ionic strength, and provided the surface charge is sufficiently large, the rate constant is largely independent of the surface charge. These trends can be well described with DLVO theory without adjustable parameters.     

Subwavelength confinement in an integrated metal slot waveguide on silicon

We demonstrate propagation losses of less than 0.8 dB/microm in a metal slot waveguide on silicon with a predicted confinement substantially below the optical wavelength (approximately 1.55 microm). We also show compact and efficient coupling of the high-confinement metal slot waveguide with a standard silicon dielectric waveguide with a coupling efficiency of approximately 2.5 dB per facet.     

Covalent and noncovalent interactions for [metal(dien)nucleobase](2+) complexes with L-tryptophan derivatives: formation of palladium-tryptophan species by nucleobase substitution under biologically relevant conditions

The interaction of the complexes [Pd(dien)(1-MeCyt)]2+ (2) and [Pd(dien)(9-EtGH)]2+ (3) with the amino acids L-tryptophan (Trp) and N-acetyltryptophan (N-AcTrp) was studied and compared with the previously studied platinum analogues [Pt(dien)(1-MeCyt)]2+ (4) and [Pt(dien)(9-EtGH)]2+ (5). Solid-state structures for 2 and 4 are reported. For the palladium complexes, the interaction is pH sensitive. Below pH 5, the noncovalent interaction with stacking between the aromatic amino acid residue and the metalated nucleobase was observed. Fluorescence quenching experiments indicated similar association constants for platinum and palladium derivatives 2-5. Unusual substitution of the model nucleobases 1-methylcytosine (1-MeCyt) and 9-ethylguanine (9-EtGH) by tryptophan was observed in the range of pH 5-11. The resulting species [Pd(dien)(Trp)]+ (6) and [Pd(dien)(N-AcTrp)]+ (7) were characterized using 1H NMR, 13C NMR, and ESI-MS spectroscopy with coordination indicated through the amino and deprotonated amido nitrogens, respectively. Complexes 6 and 7 were also obtained from a solution of [Pd(dien)Cl]+ (1) incubated with either Trp or N-AcTrp, respectively.     

Underivatized amylose and cellulose as new stationary phases for hydrophilic interaction chromatography

Two polysaccharide stationary phases have been newly suggested for application in hydrophilic interaction chromatography (HILIC). Both columns (amylose‐silica, 250 × 4.6 mm, 5 μm and cellulose‐silica, 250 × 4.6 mm, 5 μm) demonstrated a satisfactory retention of polar compounds. The influence of the mobile‐phase composition (acetonitrile content, pH, salt concentration) on the retention was in agreement with the HILIC concept. The phases showed a very similar behavior, typical efficiency of about 50 000 plates/m, cellulose retained test compounds somewhat more strongly. Under the experimental conditions, electrostatic (non‐HILIC‐type) interactions due to the dissociation of silanol groups on the silica surface did not influence the retention, noticeably. The applicability of polysaccharide stationary phases for the chromatography of polar compounds was proven by the separation of mixtures of sugars (fructose, glucose, saccharose, maltose, trehalose) or vitamins (nicotinamide, pyridoxine, riboflavin, thiamine, nicotinic acid, ascorbic acid).     

A photoemission study of the interaction of Ga with CeO2(1 1 1) thin films

The interaction of gallium with CeO₂(1 1 1) layers was studied using standard and resonant photoelectron spectroscopy, by means of both a laboratory X-ray source and tunable synchrotron light. Firstly a 1.5-nm thick CeO₂ film was grown on a Cu(1 1 1) substrate. Secondly Ga was deposited in six steps up to a thickness of 0.35 nm, at room temperature. The interaction of gallium with the oxide layer induced partial CeO₂ reduction, and gallium oxidation. The photoemission data suggest that a mixed Ga-Ce-O oxide was established similarly to the Sn-Ce-O case for Sn deposited on cerium oxide layers. As a consequence, gallium-induced weakening of Ce-O bonds provides a higher number of active sites on the surface that play a major role in its catalytic behaviour.     

Second-order optimality conditions for nondominated solutions of multiobjective programming with C 1,1 data

We examine new second-order necessary conditions and sufficient conditions which characterize nondominated solutions of a generalized constrained multiobjective programming problem. The vector-valued criterion function as well as constraint functions are supposed to be from the class C ^1,1. Second-order optimality conditions for local Pareto solutions are derived as a special case.     

Synthesis and characterization of micrometer‐sized particles of narrow size distribution with chloromethyl functionality on the basis of single‐step swelling of uniform polystyrene template microspheres

Polystyrene template microspheres of 1.4 ± 0.1 μm were prepared by dispersion polymerization of styrene in a mixture of ethanol and 2‐methoxy ethanol. These template particles were then swelled at room temperature in a single step with emulsion that was prepared in sodium dodecyl sulfate aqueous solution from a swelling solvent (dibutyl phthalate) containing the initiator (benzoyl peroxide) and monomer(s) (chlormethylstyrene, divinylbenzene, or ethylene dimethacrylate). Composite uniform particles composed of the template polystyrene and noncrosslinked or crosslinked polychloromethylstyrene were prepared by polymerizing the monomer(s) within the swelled particles at 73 °C. Crosslinked uniform polychloromethylstyrene particles of higher surface area were formed by dissolving the template polystyrene polymer of the composite particles. The influence of various reaction parameters, such as dibuthyl phthalate concentration, chloromethylstyrene concentration, crosslinker type and concentration, and so forth on the molecular weight, size, size distribution, shape, morphology, surface area, and decomposition temperature of the particles was investigated. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1342–1352, 2002     

Elimination versus ring opening: a convergent route to alkylidene-cyclobutanes

Functionalized alkylidene-cyclobutanes have been prepared from 2-fluoropyridinyl-6-oxy precursors derived from vinyl cyclobutanols by a radical addition-elimination process. A wide range of functional groups is tolerated, and the alkylidene-cyclobutanes can be further elaborated into cyclopentanones. The limitation of this approach resides in the competition with opening of the cyclobutane ring.