Chromism of soluble polythienylenes

Thermochromism and solvatochromism of solutions of poly(3-alkylthienylenes) are reported. The experimental results indicate the presence of two coexisting phases: polymer in solution and polymer in microcrystalline aggregates. From the concentration independence of the thermochromism, it is concluded that the transition is fundamentally driven by a single chain mechanism, and that the aggregation (microcrystallization) of the poly(3-alkylthienylene) macromolecules can occur only after the single chain conformational change has occurred.     

Spectroscopic studies of polydiacetylene solutions and glasses

Absorption, fluorescence excitation and emission spectra of a soluble polydiacetylene, obtained by the solid-state polymerization of the bis-(phenyl acetate) ester of 10,12-docosadiyne-1. 22-diol, have been recorded at room and liquid-nitrogen temperatures for different solvents. Spectral shifts, similar to those reported for other soluble polydiacetylenes, are observed on addition of a non-solvent or on cooling the solutions. The fluorescence quantum yield was measured from 2-methyl tetrahydrofuran solution at room temperature. The yield, was roughly one hundred times larger for this system at 77 K and well-structured fluorescence spectra were observed for this low-temperature glass.     

A weight-function approach for determining watershed initial conditions for combustion waves

In many generic combustion models, one finds that a combustionwave will develop with a specific wave speed. However, thereare possible initial temperature profiles which do not evolveinto such waves, but rather die out to the ambient temperature.There can exist, in some models, a clear distinction betweenthose initial conditions that do evolve into combustion wavesand those that do not; this is sometimes referred to as thewatershed initial condition. When fuel consumption is consideredto be negligible, analytical methods can be used to obtain theexact watershed. In this paper, we consider the problem of determiningpseudo-watersheds and ascertaining the relationship betweenthese pseudo-watersheds and the exact watersheds. In the processa novel weight-function approach for infinite spatial domainsis developed.     

Synthesis of cytotoxic cyanobactin,Wewakazole B

We report herein the synthesis of cytotoxic cyanobactin, Wewakazole B through an efficient solution-phase approach. The key steps of the synthesis are the macrocyclic lactamization of linear dodecapeptide and construction of two hexapeptides with three different substituted oxazole rings.     

Soluble conducting polymers: The poly(3–alkylthienylene)s

The conjugated poly(3-alkylthienylene)s, P3ATs, can be processed from solution and subsequently used as semiconducting and metallic polymers. Both as-synthesized and solution-cast films can be readily doped with resulting electrical conductivities which are quite high, σ-30–100 S/cm.     

Neural network based chemical structure indexing.

Searches on chemical databases are presently dominated by the text-based content of a paper which can be indexed into a keyword searchable form. Such traditional searches can prove to be very time-consuming and discouraging to the less frequent scientist. We report a simple chemical indexing based on the molecular structure alone. The method used is based on a one-to-one correspondence between the chemical structure presented as an image to a neural network and the corresponding binary output. The method is direct and less cumbersome (compared with traditional methods) and proves to be robust, elegant, and very versatile.