Conducting polyfurans by electropolymerization of oligofurans

Polyfurans have never been established as useful conjugated polymers, as previously they were considered to be inherently unstable and poorly conductive. Here, we show the preparation of stable and conducting polyfuran films by electropolymerization of a series of oligofurans of different chain lengths substituted with alkyl groups. The polyfuran films show good conductivity in the order of 1 S cm^–1, good environmental and electrochemical stabilities, very smooth morphologies (roughness 1–5 nm), long effective conjugation lengths, well-defined spectroelectrochemistry and electro-optical switching (in the Vis-NIR region), and have optical band-gaps in the range of 2.2–2.3 eV. A low oxidation potential needed for polymerization of oligofurans (compared to furan) is a key factor in achievement of improved properties of polyfurans reported in this work. DFT calculations and experiments show that polyfurans are much more rigid than polythiophenes, and alkyl substitution does not disturb backbone planarity and conjugation. The obtained properties of polyfuran films are similar or superior to the properties of electrochemically prepared poly(oligothiophene)s under similar conditions.     

The steady‐state probabilities for regenerative semi‐Markov processes with application to prevention and screening

There is a growing interest in planning and implementing broad‐scale clinical trials with a focus on prevention and screening. Often, the data‐generating mechanism for such experiments can be viewed as a semi‐Markov process. In this communication, we develop general expressions for the steady‐state probabilities for regenerative semi‐Markov processes. Hence, the probability of being in a certain state at the time of recruitment to a clinical trial can be calculated. An application to breast cancer prevention is demonstrated. Copyright © 1999 John Wiley & Sons, Ltd.     

Thionation of ω‐Acylamino Ketones with Lawesson's Reagent: Convenient Synthesis of 1,3‐Thiazoles and 4H‐1,3‐Thiazines

The reaction of ω‐acylamino ketones with Lawesson's reagent (=2,4‐bis(4‐methoxyphenyl)‐1,3,2,4‐dithiadiphosphetane 2,4‐disulfide; LR ) is described. Treatment of 2‐acylamino ketones 1 (n=0) with LR gave 1,3‐thiazole derivatives 3 in good yields (Scheme 1 and Table 1). The 4H‐1,3‐thiazines 4 were obtained as main products by treatment of 3‐acylamino ketones 2 (n=1) with an equimolar amount of LR , while mainly the corresponding 3‐(thioacyl)amino ketones 5 were isolated when 0.5 equiv. of LR was used. The 3‐acylamino esters 7 also reacted with LR to give the corresponding 3‐(thioacyl)amino esters 8 (Scheme 3 and Table 2).     

Chiroptical Properties of Twisted Acenes: Experimental and Computational Study

Acenes that are twisted out of planarity are expected to display chiroptical properties. However, the effect of twisting on the chiroptical properties of acenes has not been investigated computationally or experimentally. Herein, we present a computational investigation of the chiroptical properties of anthracenes to pentacenes, combined with an experimental study using a series of helically locked acenes, twisted to different torsional angles in their enantiopure form. The lowest energy transition, which is relatively weak in acenes, becomes dominant in their circular dichroism spectra upon twisting. We find that the rotational strength of acenes consistently increases with increasing twist. The experimental data obtained from enantiopure tethered twistacenes show the same trend as the calculated result, with a strong Cotton effect and anisotropy factor, rendering twisted acenes as excellent chiroptical materials.     

Small molecule correctors of F508del-CFTR discovered by structure-based virtual screening

Folding correctors of F508del-CFTR were discovered by in silico structure-based screening utilizing homology models of CFTR. The intracellular segment of CFTR was modeled and three cavities were identified at inter-domain interfaces: (1) Interface between the two Nucleotide Binding Domains (NBDs); (2) Interface between NBD1 and Intracellular Loop (ICL) 4, in the region of the F508 deletion; (3) multi-domain interface between NBD1:2:ICL1:2:4. We hypothesized that compounds binding at these interfaces may improve the stability of the protein, potentially affecting the folding yield or surface stability. In silico structure-based screening was performed at the putative binding-sites and a total of 496 candidate compounds from all three sites were tested in functional assays. A total of 15 compounds, representing diverse chemotypes, were identified as F508del folding correctors. This corresponds to a 3% hit rate, ~tenfold higher than hit rates obtained in corresponding high-throughput screening campaigns. The same binding sites also yielded potentiators and, most notably, compounds with a dual corrector-potentiator activity (dual-acting). Compounds harboring both activity types may prove to be better leads for the development of CF therapeutics than either pure correctors or pure potentiators. To the best of our knowledge this is the first report of structure-based discovery of CFTR modulators.     

Surface treatment of LiFePO4 cathode material with PPy/PEG conductive layer

In this work, we studied LiFePO₄ particles coated with thin films of highly conductive polypyrrole (PPy) and their electrochemical performance in cathode layers of lithium cells. Carbon-free LiFePO₄ particles were synthesized by a solvothermal method. Besides this, a part of the experiments were carried out on commercial carbon-coated LiFePO₄ for comparison. Polypyrrole coated LiFePO₄ particles (PPy-LiFePO₄) were obtained by a straightforward oxidative polymerization of dissolved pyrrole on LiFePO₄ particles dispersed in water. The use of polyethylene glycol (PEG) as an additive during the polymerization was decisive to achieve high electronic conductivities in the final cathode layers. The carbon-free and carbon-coated LiFePO₄ particles were prepared with PPy and with PPy/PEG coating. The obtained PPy-LiFePO₄ and PPy/PEG-LiFePO₄ powders were characterized by SEM, EIS, cyclic voltammetry, and galvanostatic charge/discharge measurements in lithium-ion cells with lithium metal as counter and reference electrode. Carbon-free LiFePO₄ coated with PPy/PEG hybrid films exhibited very good electrode kinetics and a stable discharge capacity of 156 mAh/g at a rate of C/10. Impedance measurements showed that the PPy/PEG coating decreases the charge-transfer resistance of the corresponding LiFePO₄ cathode material very effectively, which was attributed to a favorable mixed ionic and electronic conductivity of the PPy/PEG coatings.     

Surface modification of FePO4 particles with conductive layer of polypyrrole

Polypyrrole–FePO₄ powder was synthesized by an oxidative polymerization of pyrrole monomer on the surface of FePO₄ powder. The polymerization reaction was initiated using hydrogen peroxide in an acidified solution and catalysed with Fe³⁺. The samples were investigated by light microscopy (LM), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). These methods confirmed the presence of polypyrrole on FePO₄ particles and its homogeneous distribution in the composite material. To determine the PPy content in the PPy–FePO₄ composites a thermogravimetric analysis was used. Cyclic voltammetry curves (CV) were measured and compared in a non-aqueous lithium salt solution for electrodes consisting of pellets made from pure FePO4 and FePO₄/PPy. Electrochemical impedance spectroscopy (EIS) showed that coating of PPy significantly decreases the charge transfer resistance of PPy–FePO₄ electrodes.     

Frequency dynamics of semiconductor lasers with atomic absorbers: theory and experiments

In this paper we discuss the spectral behavior of monomode semiconductor laser systems whose output amplitude is constant, but whose frequency may be bistable, multistable, locked or present instabilities. The explored configurations are: (i) a laser diode (Fabry-Pérot) under orthogonal filtered optical feedback; and (ii) an extended-cavity diode laser with an intracavity strongly-saturated resonant vapor. Starting from rate equations for the carrier density and for the radiation field oscillating in the cavity of these systems we describe spectral features which are in very good quantitative agreement with experimental observations.     

α-Oligofurans show a sizeable extent of π-conjugation as probed by Raman spectroscopy

A Raman spectroscopic analysis revealed that π-conjugation does not reach saturation at least up to the octamer in long α-oligofurans and spreads over 14-15 furan units in the polyfuran. Comparing DFT calculations with experimental results suggests that a considerable amount of HF exchange is required to reproduce computationally the observed conjugation.