Properties of iodine complexes of monosubstituted polyacetylenes

Iodine complexes of six monosubstituted polyacetylenes with methyl, ethyl, propyl, pentyl, t-butyl, and phenyl substituents have been characterized by electronic spectroscopy. UV spectra allow the determination of the nature and the amount of active species, and photoelectronic spectra confirm the nature of these species. These measurements indicate the presence of iodine in the I and I₂ forms. The concentration of I is low (0.12–4.0 mol%), and it depends on the nature of the substitutent, but this amount does not decrease when the films are left under vacuum. On the other hand, the adsorption of ε high concentration of iodine is possible; this adsorption is governed by a diffusion mechanism and is reversible. Iodine doping leads to a cis-to-trans isomerization of the polymers, except for poly(3-3-dimethyl-1-butyne), which can be isomerized to the cis or to the trans form, depending on the solvent employed. Electrical properties of polymer I complexes are also reported. Conductivities of about 10^?4 Ω^?1 cm^?1 are obtained for all polymers in the presence of an excess of iodine.     

Simulations of NMR experiments employing static and/or radio-frequency field gradients: application to slice selection by the inhomogeneous radio-frequency field of a standard coil

A general computer program has been developed in order to simulate any nuclear magnetic resonance (NMR) experiment. It includes, in addition to the action of radio-frequency (rf) pulses and of gradients of both the static and the rf magnetic fields, the effects of inhomogeneity of the latter. It has been used here for devising a slice selection procedure on the basis of the inhomogeneity of the rf field delivered by a standard coil (e.g., a saddle-shaped coil). Two sequences have been investigated, a DANTE-like pulse train and a very simple one (named S²P for slice selection with 2π pulses), (2π - τ) _n , where 2π corresponds to the flip angle of the region to be selected, whereas τ has to be chosen according to the relaxation time values;n, the number of cycles, must be sufficiently large, its actual value being uncritical. Simulations show that performances (in terms of selectivity) of both sequences are comparable, while experimental verifications favor S²P for its robustness and for the absence of any signal loss.     

A versatile approach to affinitychromic polythiophenes

The preparation of both postfunctionalizable and chromic poly[3-(N-succinimido-p-phenylcarboxylate(tetraethoxy)oxy)-4-methylthiophene] is reported. The N-hydroxysuccinimide ester side group can easily react with different amine-bearing molecules in the solid state to yield a library of new polythiophene derivatives. The resulting polymers can be dissolved in various solvents, and interactions between the side chains (ligands) and different analytes (targets) can be detected from modifications of both the side-chain and the backbone conformations resulting in important color changes (i.e., affinitychromism). This colorimetric polymeric transducer could therefore lead to highly valuable, versatile, and inexpensive tools for highthroughput screening and drug discovery.     

Synthesis of a new series of purine derivatives and their anti‐cyclin‐dependent kinase activities

The synthesis of new purine derivatives designed to inhibit cell cycle regulating cyclin‐dependent kinases (CDKs), is reported. These compounds, related to olomoucine and roscovitine, are characterised by the presence of apyrrolidine methanol substituent at C‐2 and a variety of ortho, meta and/or para substituents on the C‐6 arylamino group.     

A New Poly(2,7‐Dibenzosilole) Derivative in Polymer Solar Cells

A new soluble conjugated copolymer based on 2,7‐dibenzosilole and 4,7‐dithien‐2‐yl‐2,1,3‐benzothiadiazole units has been synthesized (PBSDTBT). Bulk heterojunction solar cell devices are fabricated using this material as the donor and [6,6]‐phenyl‐C₆₁ butyric acid methyl ester (PCBM) as the acceptor. The power conversion efficiency is 1.6% under AM1.5 illumination. This material also shows a good V_OC (0.97 V). The results are quite promising considering the relatively large bandgap (1.9 eV) of this polymer.

     

Synthesis and evaluation of a broad range of new chiral phosphine–carbene ligands for asymmetric hydrogenation

A straightforward and gram scale synthesis (six-step synthesis from enantioenriched β-hydroxy esters) of new structurally simple phosphine-carbene ligands bearing a single stereogenic centre has been achieved. Enantioselectivities of up to 60-63% could be achieved in the hydrogenation of methylstilbene and dehydroaminoacids when the reactions were performed under 20-50 bar hydrogen pressure.     

Oxidation of small unsaturated methyl and ethyl esters

The ignition delay times were measured behind reflected shock waves for temperatures from 1280 to 1930 K, pressures from of 7–9.65 atm, fuel concentrations of 0.4, 0.5, and 1%, and equivalence ratios equal to 0.25, 1.0, and 2.0 in the cases of four unsaturated esters: methyl crotonate, methyl acrylate, ethyl crotonate, and ethyl acrylate. Ignition delay times were measured using chemiluminescence emission from OH at 306 nm and piezoelectric pressure measurements made at the shock tube sidewall. No important difference of reactivity was observed between methyl and ethyl unsaturated esters, methyl and ethyl crotonate having the same reactivity as methyl butanoate. The reactivity of acrylates is greater than that of crotonates especially at the lowest investigated temperatures. Detailed mechanisms for the combustion of the four studied unsaturated esters have been automatically generated using the version of EXGAS software recently improved to take into account this class of oxygenated reactants. These mechanisms have been validated through satisfactory comparison of simulated and experimental results. The main reaction pathways have been derived from flow rate and sensitivity analyses. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 204–218, 2011     

Thiadiazole fused indolo[2,3-a]carbazoles as new building blocks for optoelectronic applications

New indolo[2,3-a][1,2,5]thiadiazolo[3,4-c]carbazoles including functional groups (halide or hydroxyl groups) on the meta positions relative to the nitrogen atoms which are known to be the most conjugated, have been synthesized following two synthetic routes. The characterizations of their optical and electrochemical properties evidence their potential as new building blocks for optoelectronic materials.     

Impact of DNA Sequence and Oligonucleotide Length on a Polythiophene‐Based Fluorescent DNA Biosensor

DNA hybridization is a universal and specific mechanism for the recognition of biological targets. Some cationic polythiophene transducers sensitive to DNA structure have been previously utilized to detect such biomolecules. Further characterization of these systems indicates that both DNA sequence composition and length modulate the biosensor performance. It appears that different repeated sequence patterns cause different conformational changes of the polythiophene, from a more relaxed form to an extremely rigid one. A length difference between the DNA oligonucleotide probe and target has a detrimental effect on the fluorescent signal, but it can be attenuated by changing the sequence composition of the protruding target sequence. This demonstrates that the nature of DNA can be critical for hybridization‐based detection systems.

     

An Efficient Synthesis of Isofraxidin

An improved procedure for the preparation of isofraxidin 1 a well known natural coumarin, through transformation of syringaldehyde is reported. The cyclization of 7 to the coumarinic carboxylic acid 8 is readily performed by cold concentrated sulfuric acid. The overall yield to 1 by this convenient route is near 50%.