Hydrogen Isotope Exchange Catalyzed by Ru Nanocatalysts: Labelling of Complex Molecules Containing N-Heterocycles and Reaction Mechanism Insights

Ruthenium nanocatalysis can provide effective deuteration and tritiation of oxazole, imidazole, triazole and carbazole substructures in complex molecules using D₂ or T₂ gas as isotopic sources. Depending on the substructure considered, this approach does not only represent a significant step forward in practice, with notably higher isotope uptakes, a broader substrate scope and a higher solvent applicability compared to existing procedures, but also the unique way to label important heterocycles using hydrogen isotope exchange. In terms of applications, the high incorporation of deuterium atoms, allows the synthesis of internal standards for LC-MS quantification. Moreover, the efficacy of the catalyst permits, even under subatmospheric pressure of T₂ gas, the preparation of complex radiolabeled drugs owning high molar activities. From a fundamental point of view, a detailed DFT-based mechanistic study identifying undisclosed key intermediates, allowed a deeper understanding of C−H (and N−H) activation processes occurring at the surface of metallic nanoclusters.     

Gelatin‐Alginate Gels and Their Enzymatic Modifications: Controlling the Delivery of Small Molecules

The release of molecules entrapped within biogels is dictated by diffusion laws. Innovative biogel architectures are conceived and tested to control small molecule delivery from gelatin gels. The ionic interactions modulate the release of small molecules. Alginate is then added to gelatin gels and further hydrolyzed; the influence of viscosity is discussed. Next, various mixed gels are compared, such as a gelatin‐alginate IPN and the original architecture of an alginate gel entrapped in a gelatin gel with or without a polysaccharidase. The relative influence of ionic interactions and diffusional constraints on the delivery of small charged molecules is explored, and a solution for controlling diffusion is proposed for any situation.

     

Ethene adsorption, dehydrogenation and reaction with Pd(110): Pd as a carbon 'sponge'

The interaction of ethene with the Pd(110) surface has been investigated, mainly with a view to understanding the dehydrogenation reactions of the molecule and mainly using a molecular beam reactor. Ethene adsorbs with a high probability over the temperature range 130 to 800 K with the low-coverage sticking probability dropping from 0.8 at 130 K to 0.35 at 800 K. The adsorption is of the precursor type, with a weakly held form of ethene being the intermediate between the gas phase and strong chemisorption. Dehydrogenation begins at approximately 300 K and is fast above 350 K. If adsorption is carried out at temperatures up to approximately 380 K, adsorption saturates after about 0.25 monolayer have adsorbed, but above approximately 450 K, adsorption continues at a high rate with continuous hydrogen evolution and C deposition onto the surface. It appears that, in the intermediate temperature range, the carbonaceous species formed is located in the top layer and thus interferes with adsorption, whereas the C goes subsurface above 450 K, the adsorption is almost unaffected, and the C signal is significantly attenuated in XPS. However, the deposited carbon can easily be removed again by reaction with oxygen, thus implying that the carbon remains in the selvedge, that is, in the immediate subsurface region probably consisting of a few atomic layers. No well-ordered structures are identified in either LEED or STM, though some evidence of a c(2 x 2) structure can be seen. The Pd surface, at least above 450 K, appears to act as a "sponge" for carbon atoms, and this effect is also seen for the adsorption of other hydrocarbons such as acetaldehyde and acetic acid.     

Computational and experimental study of the cluster size distribution in MAPLE

A combined experimental and computational study is performed to investigate the origin and characteristics of the surface features observed in SEM images of thin polymer films deposited in matrix-assisted pulsed laser evaporation (MAPLE). Analysis of high-resolution SEM images of surface morphologies of the films deposited at different fluences reveals that the mass distributions of the surface features can be well described by a power-law, Y(N) ∝ N^−t, with exponent −t ≈ −1.6. Molecular dynamic simulations of the MAPLE process predict a similar size distribution for large clusters observed in the ablation plume. A weak dependence of the cluster size distributions on fluence and target composition suggests that the power-law cluster size distribution may be a general characteristic of the ablation plume generated as a result of an explosive decomposition of a target region overheated above the limit of its thermodynamic stability. Based on the simulation results, we suggest that the ejection of large matrix-polymer clusters, followed by evaporation of the volatile matrix, is responsible for the formation of the surface features observed in the polymer films deposited in MAPLE experiments.     

The synthesis and self‐assembly of ABA amphiphilic block copolymers containing styrene and oligo(ethylene glycol) methyl ether methacrylate in dilute aqueous solutions: Elevated cloud point temperatures for thermoresponsive micelles

A series of ABA amphiphilic triblock copolymers possessing polystyrene (PS) central hydrophobic blocks, one group with “short” PS blocks (DP = 54–86) and one with “long” PS blocks (DP = 183–204) were synthesized by atom transfer radical polymerization. The outer hydrophilic blocks were various lengths of poly(oligoethylene glycol methyl ether) methacrylate, a comb‐like polymer. The critical aggregation concentrations were recorded for certain block copolymer samples and were found to be in the range circa 10⁻⁹ mol L⁻¹ for short PS blocks and circa 10⁻¹² mol L⁻¹ for long PS blocks. Dilute aqueous solutions were analyzed by transmission electron microscopy (TEM) and demonstrated that the short PS block copolymers formed spherical micelles and the long PS block copolymers formed predominantly spherical micelles with smaller proportions of cylindrical and Y‐branched cylindrical micelles. Dynamic light scattering analysis results agreed with the TEM observations demonstrating variations in micelle size with PS and POEGMA chain length: the hydrodynamic diameters (D_H) of the shorter PS block copolymer micelles increased with increasing POEGMA block lengths while maintaining similar PS micellar core diameters (D_C); in contrast the values of D_H and D_C for the longer PS block copolymer micelles decreased. Surface‐pressure isotherms were recorded for two of the samples and these indicated close packing of a short PS block copolymer at the air–water interface. The aggregate solutions were demonstrated to be stable over a 38‐day period with no change in aggregate size or noticeable precipitation. The cloud point temperatures of certain block copolymer aggregate solutions were measured and found to be in the range 76–93 °C; significantly these were ∼11 °C higher in temperature than those of POEGMA homopolymer samples with similar chain lengths. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7739–7756, 2008     

The effect of supplier capacity on the supply chain profit

In this paper, we study the role of capacity on the efficiency of a two-tier supply chain with two suppliers (leaders, first tier) and one retailer (follower, second tier). The suppliers compete via pricing (Bertrand competition) and, as one would expect in practice, are faced with production capacity. We consider a model with differentiated substitutable products where the suppliers are symmetric differing only by their production capacity. We characterize the prices, production amounts and profits in three cases: (1) the suppliers compete in a decentralized Nash equilibrium game, (2) the suppliers “cooperate” to optimize the total suppliers’ profit, and (3) the two tiers of the supply chain are centrally coordinated. We show that in a decentralized setting, the supplier with a lower capacity may benefit from restricting her capacity even when additional capacity is available at no cost. We also show that the loss of total profit due to decentralization cannot exceed 25 % of the centralized chain profits. Nevertheless, the loss of total profit is not a monotonic function of the “degree of asymmetry” of the suppliers’ capacities. Furthermore, we provide an upper bound on the supplier profit loss at equilibrium (compared with the cooperation setting) that depends on the “market power” of the suppliers as well as their market size. We show that there is less supplier profit loss as the asymmetry (in terms of their capacities) increases between the two suppliers. The worst case arises when the two suppliers are completely symmetric.     

Micellar behavior of well‐defined polystyrene‐based block copolymers with triethoxysilyl reactive groups and their hydrolysis–condensation

Block copolymers of acryloxy propyl triethoxysilane and styrene were prepared through nitroxide‐mediated polymerization using alkoxyamine initiators based on N‐tert‐butyl‐1‐diethylphosphono‐2,2‐dimethylpropyl nitroxide. The copolymers were characterized by ¹H NMR, size exclusion chromatography and differential scanning calorimetry. Their micellar behavior in dioxane/methanol solutions was examined through static light scattering and transmission electron microscopy (TEM). TEM indicated the successful formation of spherical micelles which were subsequently frozen by the sol–gel process. Hydrolysis–condensation of the reactive ethoxysilyl side groups was followed by FTIR, ¹H NMR, and ²⁹Si NMR. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 784–793, 2010     

Making molecular balloons in laser-induced explosive boiling of polymer solutions

The effect of the dynamic molecular rearrangements leading to compositional segregation is revealed in coarse-grained molecular dynamics simulations of short pulse laser interaction with a polymer solution in a volatile matrix. An internal release of matrix vapor at the onset of the explosive boiling of the overheated liquid is capable of pushing polymer molecules to the outskirts of a transient bubble, forming a polymer-rich surface layer enclosing the volatile matrix material. The results explain unexpected "deflated balloon" structures observed in films deposited by the matrix-assisted pulsed laser evaporation technique.     

A kinetic investigation of surfactant‐free emulsion polymerization of styrene using laponite clay platelets as stabilizers

We report the kinetics and mechanism of soap‐free emulsion polymerization of styrene using laponite platelets as stabilizers. The polymerization was initiated by potassium persulfate and the latex particles were stabilized by laponite platelets dispersed in water. Laponite adsorption on the polymer particles was enhanced by the addition of poly(ethylene glycol) monomethylether methacrylate (PEGMA). Particle nucleation can be described using the classical homogeneous nucleation mechanism followed by coagulation of unstable precursors. Oligomeric radicals formed in the water phase become insoluble and precipitate on the laponite surface leading to primary precursor particles composed of a few polymer chains and one or several clay platelets. Mature latex particles are then generated by coagulation and growth of the previously formed precursor particles. Both the nucleation and initial aggregation rates increased in the presence of PEGMA. Calorimetric monitoring of the polymerization allowed estimating the heat produced by the reaction and the monomer conversion. Hence, using the monomer material balance, the number of radicals in the polymer particles could be estimated precisely. The average number of radicals per particle, $ \bar n $ , was found to be high in the range 3–6. This result was attributed to strong attractive interactions between the growing radicals and the clay surface. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

New ammonium surfactant-stabilized rhodium(0) colloidal suspensions: influence of novel counter-anions on physico-chemical and catalytic properties

Novel anionic species, such as hydrogen carbonate (HCO(3)(?)), fluoride (F(?)), triflate (CF(3)SO(3)(?)), tetrafluoroborate (BF(4)(?)) and chloride (Cl(?)) were investigated as new partners of water soluble N,N-dimethyl-N-cetyl-N-(2-hydroxyethyl) ammonium salts, used as a protective agent of rhodium colloids. The effect of the surfactant polar head on the micellar behavior, size and morphology of the nanospecies was studied by adapted physico-chemical experiments (surface tension measurements, dynamic light scattering, thermogravimetric and TEM analyses) and discussed in terms of strong or weak stabilization of the growing nanoparticles surface. Finally, the influence of the nanoenvironment generated by the surfactant with various counter-anions was evaluated via the hydrogenation of aromatics.