Optical Sensing by Silica/Titania Thin Films Doped with Oxacarbocyanine Dye

Photocurrent responses of sol-gel films of silica/titania doped with oxacarbocyanine dye were investigated with a sandwich-type photocell constructed with polymer electrolyte membrane and indium-tin-oxide glass electrodes. At an equilibrium and positive bias voltages, a typical photocell exhibited negative and positive current peaks when the visible light illumination was on and off, respectively. The wavelength dependence of the photocurrent responses well matched to the absorption band of the doped dye. This differential photocurrent response was attributed to trapping of carriers photoexcited in the dye molecules at the defect states in the matrix film. At negative bias voltages, on the other hand, the cell exhibited constant, negative photoelectrochemical currents under illumination. These differential and linear photocurrent responses were affected by the SiO₂/TiO₂ matrix structures depending on the Si : Ti ratio.     

How to Cut Pseudoparabolas into Segments

Let Γ be a collection of unbounded x -monotone Jordan arcs intersecting at most twice each other, which we call pseudoparabolas, since two axis parallel parabolas intersect at most twice. We investigate how to cut pseudoparabolas into the minimum number of curve segments so that each pair of segments intersect at most once. We give an Ω( n ^4/3 ) lower bound and O(n ^5/3 ) upper bound on the number of cuts. We give the same bounds for an arrangement of circles. Applying the upper bound, we give an O(n ^23/12 ) bound on the complexity of a level in an arrangement of pseudoparabolas, and an O(n ^11/6 ) bound on the complexity of a combinatorially concave chain of pseudoparabolas. We also give some upper bounds on the number of transitions of the minimum weight matroid base when the weight of each element changes as a quadratic function of a single parameter. Received January 17, 1996, and in revised form November 7, 1996.     

Cp*RuCl-catalyzed [2 + 2 + 2] cycloadditions of alpha,omega-diynes with electron-deficient carbon-heteroatom multiple bonds leading to heterocycles

In the presence of a catalytic amount of Cp*RuCl(cod), 1,6-diynes were allowed to react chemo- and regioselectively with electron-deficient nitriles and heterocumulenes at 60-90 degrees C to afford heterocyclic compounds. The mechanism of the ruthenium-catalyzed regioselective formations of bicyclic pyridines and pyridones were analyzed on the basis of density functional calculations. Cyclocotrimerizations of ethyl propiolate with ethyl cyanoformate or propyl isocyanate gave rise to two of the four possible pyridine or pyridone regioisomers.     

Domino coupling relay approach to polycyclic pyrrole-2-carboxylates

CuBr2-catalyzed three-component coupling of N-benzylallylamine, ethyl glyoxalate, and terminal alkynes afforded glycine-tethered 1,6-enynes, which were further transformed into polycyclic pyrrole-2-carboxylates via novel cycloisomerization/Diels-Alder cycloaddition/dehydrogenation sequence under iridium-catalyzed conditions.     

On Burgess's theorem and related problems

Let be a graph. We determine all graphs which are -like. We also prove that if are graphs, then in order that each -like continuum be -indecomposable for some it is necessary and sufficient that if is a graph, then is not -like for some integer with . This generalizes a well known theorem of Burgess.

     

Reductive dehalogenation of α-halogenated carbonyl and cyano compounds with the hexamethyldisilane/tetrakis(triphenylphosphine)palladium system

Treatment of α-halogenated carbonyl or cyano compounds with hexamethyldisilane in the presence of catalytic amounts of tetrakis(triphenylphosphine)-palladium gives the corresponding parent carbonyl or cyano compounds in excellent yields via oxy-π-allyl(trimethylsilyl)palladium intermediates.     

Preparation and synthetic application of 3-bromoallyltrimethylsilane as hydroxypropenyl synthons

3-Trimethylsilylpropen-1-yl group, as hydroxypropenyl synthons, was easily introduced to several epoxides with the corresponding Grignard reagent derived from 3-bromoallyltrimethylsilane. The introduced skeleton of allyltrimethylsilane was regiospecifically converted to 3-hydroxy-propen-3-yl or 3-hydroxypropen-1-yl group.     

Preparation and synthetic application of 2-bromoallyltrimethylsilane as a 1-hydroxymethylvinyl anion equivalent

The 1-trimethylsilylmethylvinyl group, as a 1-hydroxymethylvinyl equivalent, was readily introduced to epoxides with the corresponding Grignard reagent derived from 2-bromoallyltrimethylsilane. Obtained 2-(2-hydroxy-ethyl)-allylsilanes were converted to α-methylene-γ-lactones via diols.