Synthesis of three‐arm star block copolymers

We describe the synthesis and characterization of three‐arm star block copolymers based on polystyrene, poly(ethylene oxide), poly(ϵ‐caprolactone), poly(methyl methacrylate), poly(tert‐butyl methacrylate) and poly(L‐lactide) blocks. The copolymers were obtained by a route consisting of two successive initiation steps on functional macroinitiator. Some results on micellization and crystallization are given. They indicate an increase in the miscibility of different incompatible blocks.     

Coordination compounds from the planar tridentate Schiff-base ligand 2-methoxy-6-((quinolin-8-ylimino)methyl)phenol (mqmpH) with several transition metal ions: Use of [Fe(mqmp)(CH3OH)Cl2] in the catalytic oxidation of alkanes and alkenes

Four coordination compounds were synthesized in high yields from different transition metal ions (Fe^III, Co^II, and Cu^II) and an in situ generated Schiff-base ligand, i.e. 2-methoxy-6-((quinolin-8-ylimino)methyl)phenol (mqmpH). The compounds were characterized by single-crystal X-ray diffraction, ESI-MS, IR spectroscopy, and ligand-field spectroscopy. The iron(III) complex is an efficient catalyst for the oxidation of alkanes and alkenes, under relatively mild conditions and with dihydrogen peroxide as terminal oxidant.     

Novel acyclic nitroxides for nitroxide‐mediated polymerization: Kinetic,electron paramagnetic resonance spectroscopic,X‐ray diffraction,and molecular modeling investigations

This work describes the synthesis of new hydrophobic acyclic nitroxides [derived from 2,2,5‐trimethyl‐4‐phenyl‐3‐azahexane‐3‐nitroxide (TIPNO)] designed to be employed in radical miniemulsion polymerization. We present the synthetic strategies employed to obtain these different nitroxides and the determination of certain important parameters, such as the dissociation rate constant, the combination rate constant, and the decomposition rate constant, of the corresponding alkoxyamines. All these new nitroxides give good control of the bulk radical polymerization of styrene in comparison with the parent TIPNO. The molecular structure of some nitroxides presented herein has been elucidated by single‐crystal X‐ray diffraction, and their structural determination helps us to understand better the influence of the nitroxide structure on the activation energy. A molecular modeling study has also been conducted on these new nitroxides, and a good linear correlation between the activation energy and the CNC bond angle for a series of nitroxides with the same type of leaving radical has been found. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1926–1940, 2006     

First synthesis of (±)-harzianopyridone by metalation of polysubstituted O-pyridylcarbamates

The first synthesis of (±)-harzianopyridone, an antifungal metabolite of Trichoderma harzianum, has been achieved by metalation of 6-substituted-2,3-dimethoxy-4-pyridyl-N,N-diisopropylcarbamates. Moreover, the chosen strategy allowed the preparation of harzianopyridone analogs, by varying the groups at C-4, C-5 and C-6 on the pyridine ring.     

Evaluation of end-capped tubes for transverse heated graphite atomizer electrothermal atomic absorption spectrometry

Transverse heated graphite tubes with (EC-THGA) and without (THGA) ends caps have been tested with respect to characteristic mass, detection limits and reproducibilities at two levels of concentration for four different types of analytes. Compared for Cd, Pb and Cr with a standard THGA tube, the EC-THGA tube exhibits a gain of sensitivity by a factor of about 1.4 in terms of characteristic masses. Also detection limits are significantly improved for the end-capped tube design tested. The presence of end caps increases the mass of the tube and decreases consequently the heating rate achieved. As shown on the molybdenum example, the atomization efficiency of refractory metals is not so good as with standard THGA tubes. Interference effects studied on the Cd, Pb and Cr determinations in environmental samples (sediments, plants and animal tissues) are similarly negligible for the two tubes tested.     

Boophiline,an antimicrobial sterol amide from the cattle tick boophilus microplus

Boophiline ( 1 ), a new sterol amide was isolated from the cattle tick Boophilus microplus (Ixodidae). The structure was assigned as N-[3-(sulfooxy)-25ξcholest-5-en-26-oyl]-L-isoleucine by detailed 2D NMR investigations in conjunction with FAB mass spectrometry and acidic hydrolyses. Complete assignment of the diastereotopic methylene protons of the ring system could be deduced from the NMR data. In agar dilution assays, 1 exhibited antifungal properties against Cladosporium cucumerinum and antibacterial activity against Bacillus subtilis and Escherichia coli.     

Characterization by ultra-micro indentation of an oxidized epoxy polymer: Correlation with the predictions of a kinetic model of oxidation

This study aims to understand better the influence of thermo-oxidation on the degradation of an epoxy resin used as the matrix of aeronautical composite laminates. Neat epoxy resin plates have been aged at 150 °C, under vacuum and ambient air. Using an instrumented ultra-micro indentation device, modifications of mechanical properties due to oxidation at elevated temperature are characterized through the measurements of elastic indentation modulus, Vickers hardness and indentation creep. By using a kinetic model of oxidation developed specifically for this epoxy resin, the local values of oxidation product concentration are calculated and correlated to experimental indentation measurements.     

Activation of 1-halonaphthalenes by electrogenerated [Co-salen]

We report in this paper an electroanalytical study of the reaction of 1-halonaphthalenes with electrogenerated [Co^I-salen]. With 1-iodonaphthalene, the reaction observed is a substitution, with a release of the iodide ion. Conversely, the reaction is much slower with 1-bromonaphthalene, and the intermediate adduct is observed at the time scale of cyclic voltammetry. The corresponding rate constants have been determined.