Amphiphilic Polyoxometalates for the Controlled Synthesis of Hybrid Polystyrene Particles with Surface Reactivity

Amphiphilic organo‐polyoxometalates (POMs) used in the radical emulsion polymerization of styrene allowed the preparation in aqueous medium of stable 50–100 nm polystyrene–POM composite latexes. Thanks to the presence of a trithiocarbonate group in the POM amphiphile, POMs could be covalently linked to the polymer particle surface. The chemical and catalytic integrity of the POMs was confirmed, and the POM‐mediated surface photoactivity of the latexes was demonstrated by the spatially controlled nucleation of silver nanoparticles at the periphery of the composites.     

Asymmetric Ion‐Pairing Catalysis

Charged intermediates and reagents are ubiquitous in organic transformations. The interaction of these ionic species with chiral neutral, anionic, or cationic small molecules has emerged as a powerful strategy for catalytic, enantioselective synthesis. This review describes developments in the burgeoning field of asymmetric ion‐pairing catalysis with an emphasis on the insights that have been gleaned into the structural and mechanistic features that contribute to high asymmetric induction.     

A threatened beluga (Delphinapterus leucas) population in the traffic lane: vessel-generated noise characteristics of the Saguenay-St. Lawrence Marine Park, Canada

The threatened resident beluga population of the St. Lawrence Estuary shares the Saguenay-St. Lawrence Marine Park with significant anthropogenic noise sources, including marine commercial traffic and a well-established, vessel-based whale-watching industry. Frequency-dependent (FD) weighting was used to approximate beluga hearing sensitivity to determine how noise exposure varied in time and space at six sites of high beluga summer residency. The relative contribution of each source to acoustic habitat degradation was estimated by measuring noise levels throughout the summer and noise signatures of typical vessel classes with respect to traffic volume and sound propagation characteristics. Rigid-hulled inflatable boats were the dominant noise source with respect to estimated beluga hearing sensitivity in the studied habitats due to their high occurrence and proximity, high correlation with site-specific FD-weighted sound levels, and the dominance of mid-frequencies (0.3-23 kHz) in their noise signatures. Median C-weighted sound pressure level (SPL(RMS)) had a range of 19 dB re 1 μPa between the noisiest and quietest sites. Broadband SPL(RMS) exceeded 120 dB re 1 μPa 8-32% of the time depending on the site. Impacts of these noise levels on St. Lawrence beluga will depend on exposure recurrence and individual responsiveness.     

The Pauson–Khand Mechanism Revisited: Origin of CO in the Final Product

The mechanism of the Pauson–Khand reaction has been studied by mass spectrometry and it has been found, through ion‐molecule reaction with ¹³CO, that the carbon monoxide incorporated into the product cyclopentenone is one that has been retained within the complex. Theoretical and kinetic calculations support this finding, which provides a complementary explanation for the effect of Pauson–Khand promoters.     

NMR Signatures of the Active Sites in Sn‐β Zeolite

Dynamic nuclear polarization surface enhanced NMR (DNP‐SENS), Mössbauer spectroscopy, and computational chemistry were combined to obtain structural information on the active‐site speciation in Sn‐β zeolite. This approach unambiguously shows the presence of framework Sn^IV‐active sites in an octahedral environment, which probably correspond to so‐called open and closed sites, respectively (namely, tin bound to three or four siloxy groups of the zeolite framework).     

Boundary conditions changing operators in non-conformal theories

Boundary conditions changing operators have played an important role in conformal field theory. Here, we study their equivalent in the case where a mass scale is introduced, in an integrable way, either in the bulk or at the boundary. More precisely, we propose an axiomatic approach to determine the general scalar products _bθ₁, … ,θ_mθ₁′, … ,θ_n′_a, between asymptotic states in the Hilbert spaces with a and b boundary conditions respectively, and compute these scalar products explicitly in the case of the Ising and sinh-Gordon models with a mass and a boundary interaction. These quantities can be used to study statistical systems with inhomogeneous boundary conditions, and, more interestingly maybe, dynamical problems in quantum impurity problems. As an example, we obtain a series of new exact results for the transition probability in the double-well problem of dissipative quantum mechanics.     

Characterization of groundwater contaminants using dynamic thermal stripping and adsorption/thermal desorption-GC-MS

Summary Alternate methods to the time consuming solvent extraction technique used in the characterization of groundwater contaminants were sought to reduce the analysis time and allow for automation. By adsorbing (ADS) groundwater samples on a quartz tube filled with graphitized charcoal (Carbotrap, Carbotrap C) and thermally desorbing it in a Envirochem Unacon 810 unit directly interfaced with a GC-MSD, it was possible to detect the major groundwater contaminants originating from several types of industrial landfills. Compounds such as aniline, dioxane, and phenols were measured simultaneously with minimal sample preparation. The results were compared to those obtained by dynamic thermal stripping (DTS) followed by GC-MS. These methods are much more cost effective than solvent extraction since they require only a few minutes of the analyst's time for the introduction of the sample. ADS was superior to DTS and solvent extraction for the analysis of water soluble compounds which are poorly extracted into solvents. DTS provided cleaner chromatograms and allowed for lower detection limit than ADS. The two techniques are therefore complementary.     

Synthesis of poly(tetrahydrofuran)‐b‐polystyrene block copolymers from dual initiators for cationic ring‐opening polymerization and atom transfer radical polymerization

A dual initiator (4‐hydroxy‐butyl‐2‐bromoisobutyrate), that is, a molecule containing two functional groups capable of initiating two polymerizations occurring by different mechanisms, has been prepared. It has been used for the sequential two‐step synthesis of well‐defined block copolymers of polystyrene (PS) and poly(tetrahydrofuran) (PTHF) by atom transfer radical polymerization (ATRP) and cationic ring‐opening polymerization (CROP). This dual initiator contains a bromoisobutyrate group, which is an efficient initiator for the ATRP of styrene in combination with the Cu(0)/Cu(II)/N,N,N′,N″,N″‐pentamethyldiethylenetriamine catalyst system. In this way, PS with hydroxyl groups (PS‐OH) is formed. The in situ reaction of the hydroxyl groups originating from the dual initiator with trifluoromethane sulfonic anhydride gives a triflate ester initiating group for the CROP of tetrahydrofuran (THF), leading to PTHF with a tertiary bromide end group (PTHF‐Br). PS‐OH and PTHF‐Br homopolymers have been applied as macroinitiators for the CROP of THF and the ATRP of styrene, respectively. PS‐OH, used as a macroinitiator, results in a mixture of the block copolymer and remaining macroinitiator. With PTHF‐Br as a macroinitiator for the ATRP of styrene, well‐defined PTHF‐b‐PS block copolymers can be prepared. The efficiency of PS‐OH or PTHF‐Br as a macroinitiator has been investigated with matrix‐assisted laser desorption/ionization time‐of‐flight spectroscopy, gel permeation chromatography, and NMR. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3206–3217, 2003