Heteroarylthiomethylsilanes. Synthesis and application to heteroarylthiomethylation of carbonyl compounds [1]

Heteroarylthiomethyltrimethylsilanes bearing a 2-pyridyl, 2-imidazolyl, 5-tetrazolyl, or 2-pyrimidinyl group, readily prepared by the reaction of heteroarylmercaptans with halomethyltrimethylsilane in the presence of a base, are synthetic equivalents of heteroarylthiomethyl anions, otherwise inaccessible, and are effective reagents for the introduction of a heteroarythiomethyl group at a carbonyl carbon atom in the presence of a catalytic amount of tetrabutylammonium fluoride.     

Simultaneous detection of ammonia and humidity using transmission surface plasmon resonance technique

Abstract

Gas sensing by using the transmission surface plasmon resonance (T-SPR) technique was demonstrated. Polyacrylic acid (PAA)/5-nm-thick gold/40-nm-thick silver/polycarbonate grating substrate structure (Sensor A) responded to ammonia; however, it exhibited a strong humidity dependence. Polyvinyl alcohol (PVA)/5-nm-thick gold/40-nm-thick silver/polycarbonate grating substrate structure (Sensor B) as the sensing material was also prepared and it mainly responded to humidity. The T-SPR properties of Sensors A and B were observed simultaneously by a stacking arrangement that enabled us to obtain the responses by using a single spectrophotometer. The ammonia concentration under various humidity conditions could be accurately obtained by simultaneous measurement of Sensors A and B.     

Poly(2,5-dimethoxyaniline) film coating for corrosion protection of iron

A poly(2,5-dimethoxyaniline) (PDMA) film was coated on the iron surface by the electropolymerization of 2,5-dimethoxyaniline in neutral buffer solution (pH?6.86). The PDMA film strongly adhered to the surface because of the polar methoxy groups of the PDMA molecules. The fact that no electrochemical response of the PDMA film-coated iron electrode to dissolved Fe²⁺ exhibited that the PDMA film was less permeable to dissolved species, acting as a diffusion barrier against agents causing corrosion such as H₂O and O₂. The PDMA film coating greatly lowered the anodic current peak ascribed to the anodic dissolution of iron and the corrosion current in strongly acidic medium, 0.5?M H₂SO₄ aqueous solution (1?M?????mol?dm^??) as well as neutral medium (pH?6.86). The high anti-corrosion ability was due to a hybrid effect of the PDMA film not only as the diffusion barrier, but also as an in situ oxidant in spite of the slight redox activity of PDMA. In addition, the PDMA film is much more durable and adhesive than polyaniline film against over-oxidation.     

Metal-to-Oxide Charge Transfer Observed by a Kelvin Probe Force Microscope

The charge transfer from a nanometer-sized transition metal particle to a catalyst support is thought to affect reactions over the metal surface. We propose the application of Kelvin probe force microscope, which is an extension of the atomic force microscope, to observe the charge transfer particle-by-particle. Our recent results on Na adatoms, Cl adatoms, Pt adatoms and particles, and Ni particles evaporated on TiO₂(110) are reviewed.     

Liquid crystal polymers 23. Steric and polar effects of large substituents in thermotropic aromatic polyesters with decamethylene spacers

A series of thermotropic aromatic polyesters based on a triad ester mesogenic unit containing an arylsulfonyl substituted hydroquinone group and a decamethylene spacer group was prepared. The large arylsulfonyl substituent was substituted in the para-position with either electron donating or accepting groups to study the effect of steric and polar interactions on the thermal transitions of these polymers and on the thermodynamic parameters of their isotropization transitions. All polymers formed nematic melts, and a regular decrease in T₁, ΔH₁ and ΔS₁ was observed with increasing molecular radius of the substituted hydroquinone group. However, a polarity or polarizability effect was superimposed on these relationships. Model compounds containing the same aromatic ester triad were prepared and their thermotropic properties were compared to those of the polymers. Essentially identical effects were observed for both.     

Topological charge quantization via path integration: An application of the Kustaanheimo-Stiefel transformation

Editorial note: The complete text of this paper, dedicated to Professor Asim O. Barut, will appear in the August 1993 issue ofFoundations of Physics.     

Variable-priority queue and doughnut routing

This paper proposes a new data structure called a variable-priority queue. The queue supports, in addition to the ordinary queue operations, an operation MIN to find an item of minimum key and three operations to change keys of items. Any sequence of these m operations can be processed in O(m) time. Furthermore, as its application, this paper presents two efficient algorithms for network problems. The first finds multicommodity flows in cycles in linear time. The second, using the first, finds edge-disjoint paths connecting terminal pairs in a doughnut-shaped grid. The grid is bounded by two nested rectangles, and terminals are specified on the two rectangular boundaries outside the four corners. If there are k terminal pairs and all the terminals are ordered in clockwise order around rectangles, then the algorithm decides in O(k) time whether there are edge-disjoint paths connecting terminals in the grid, and actually finds edge-disjoint paths in O(k log k) time.