Photochimie d'hétérocycles azotés. IV. Transposition de type photo-fries des N-acétyl benzimidazolones

The photolysis of benzene or alcoholic solutions of N-acetyl-and N,N-diacetylbenzimidazolones gave mixtures of ortho- and para-rearrangements products accompanied to some extent with de-N-acylation. The different products have been identified by means of nmr, mass spectrometry and unambiguous synthesis.     

Screening mercury levels in fish with a selective fluorescent chemosensor

Societal concerns over toxic mercury accumulation in humans from fish and other dietary and environmental sources provide motivation to develop new tools and tactics for mercury detection in a wide range of laboratory and field settings. Here we report the synthesis, properties, and application of a selective and sensitive small-molecule chemosensor for fluorescence screening of mercury levels in fish. Mercuryfluor-1 (MF1) is a water-soluble, fluorescein-based reagent that features excellent selectivity for Hg2+ over competing analytes and the largest turn-on fluorescence response to date (>170-fold increase) for reporting this heavy metal ion in aqueous solution. Combining this chemoselective Hg2+ probe with a microwave digestion protocol provides a facile method for assaying mercury levels in fish samples with mercury concentrations spanning 0.1 to 8 ppm, a range well matched with the United States Environmental Protection Agency (U.S. EPA) standard for the maximum safe level of mercury in edible fish (0.55 ppm).     

O-Directed free-radical hydrostannations of propargyl ethers, acetals, and alcohols with Ph3SnH and Et3B

[reaction: see text] The O-directed hydrostannation of various propargyloxy substrates is reported with Ph(3)SnH/Et(3)B.     

Neutron reflection and small-angle neutron scattering studies of a fluorocarbon telomer surfactant

Dilute aqueous phase behavior of a novel tris(hydroxymethyl)acrylamidomethane (THAM)-derived telomer bearing a perfluorohexyl hydrophobic chain, F6THAM6, has been investigated. Fluorinated polyhydroxy surfactants of this kind find use in emerging biomedical applications. Neutron reflection (NR) and drop volume surface tension (DVT) methods have been used to determine the critical micelle concentration (cmc=4.7 x 10(-4) mol x dm(-3)) and surface adsorption parameters (at the cmc NR gives a molecular area a(cmc)=67.4 and 62 A(2) and surface excess gamma(cmc)=2.46 x 10(-6) mol x m(-2)). The aggregation structures were determined by small-angle neutron scattering (SANS), indicating globular (polydisperse spheres) micelles of radius approximately 30 A are present. These findings are compared with literature on surfactants with related structures, to identify how the unusual molecular structure of F6THAM6 affects surfactant properties.     

Constructions of covering triangulations with folds

Let G be a graph with a known triangular embedding in a surface S, and consider G_(m), the composition of G with an independant set of order m. The purpose of this paper is to construct a triangular embedding of G_(m) into a surface by using a covering triangulation with folds. We make the construction for three cases. One of them is used for proving that G_(m) can be triangularly embedded into a surface if G is an Eulerian graph which can be triangularly embedded into a surface S with the same orientability characteristic as .     

Classification of Phase Transitions and Ensemble Inequivalence, in Systems with Long Range Interactions

Systems with long range interactions in general are not additive, which can lead to an inequivalence of the microcanonical and canonical ensembles. The microcanonical ensemble may show richer behavior than the canonical one, including negative specific heats and other non-common behaviors. We propose a classification of microcanonical phase transitions, of their link to canonical ones, and of the possible situations of ensemble inequivalence. We discuss previously observed phase transitions and inequivalence in self-gravitating, two-dimensional fluid dynamics and non-neutral plasmas. We note a number of generic situations that have not yet been observed in such systems.     

Pebble game algorithms and sparse graphs

A multi-graph G on n vertices is (k,?)-sparse if every subset of n^′?n vertices spans at most kn^′-? edges. G is tight if, in addition, it has exactly kn-? edges. For integer values k and ?∈[0,2k), we characterize the (k,?)-sparse graphs via a family of simple, elegant and efficient algorithms called the (k,?)-pebble games.     

Synthesis of galactosides locked in a B boat conformation and functionalized at the anomeric position

A new methodology for the preparation of carbohydrates locked in a ^1,4B boat conformation is presented. The constrained molecules thus obtained are functionalized at the anomeric position by iodo-, fluoro-, hydroxyl- or/and phosphono-methylene moieties. A remarkable diastereoselective opening of these quaternary acetals was also observed under non-acidic conditions.