Gas barrier and adhesion of interpenetrating polymer networks based on poly(diurethane bismethacrylate) and different epoxy-amine networks

Interpenetrating polymer networks (IPNs) composed of poly(methacrylate) and epoxy-amine networks made in situ between two oriented polypropylene sheets were examined in terms of their oxygen barrier and adhesion to the substrate properties. A particular attention was devoted to a system presenting an obvious phase separation. Kinetics of network formation and phase behavior were investigated by infrared and UV-visible spectroscopy, respectively. Since the poly(methacrylate) network could be instantaneously generated by photoirradiation, IPNs differing in network sequence formation were prepared. The influence of the moment at which irradiation was induced, on gas barrier properties of different films was examined. It was shown that similar oxygen transmission rates are obtained whatever the moment of irradiation.     

Kinetics and mechanisms of homogeneous catalytic reactions. Part 3. Regioselective,catalysed [RuH(CO)(NCMe)2(PPh3)2]BF4 reduction of quinoline

Summary A kinetic study of the regioselective homogeneous hydrogenation of quinoline (Q) to 1,2,3,4-tetrahydroquinoline (THQ) was carried out using the cationic complex [RuH(CO)(NCMe)₂(PPh₃)₂]BF₄ (1) as the precatalyst. The experimentally determined rate law wasr = {k ₂ K ₁/(1+K ₁[H₂])}[Ru₀][H₂]², which becomesr = {k ₂ K ₁[Ru₀]–[H₂]² at low hydrogen concentrations (k ₂ K ₁ = 28.5M ^–2 s^–1 at 398 K). The corresponding activation parameters were found to be H = 42 + 6 kJ mol^–1, S = – 115 ± 2JK^–1mol^–1 and G = 92 ± 8 kJ mol^–1. Complex(1) was found to react with Q in CHCl₃ under reflux to yield [RuH(CO)(NCMe)(N-Q)(PPh₃)₂]BF₄ (2) which was also isolated from the hydrogenation runs. These experimental findings, together with the results ofab initio self-consistent-field molecular orbital calculations on the free organic molecules involved, are consistent with a mechanism involving a rapid and reversible partial hydrogenation of(2) to yield the corresponding dihydroquinoline (DHQ) species [RuH(CO)(NCMe)(DHQ)(PPh₃)₂]BF₄ (4), followed by a rate-determining second hydrogenation of DHQ to yield [RuH(CO)(NCMe)(THQ)(PPh₃)₂]BF₄ (3).     

Electropolymerization of <Emphasis Type="Italic">trans</Emphasis>-[RuCl<Subscript>2</Subscript>(vpy)<Subscript>4</Subscript>] complex—EQCM and Raman studies

The electropolymerization of trans-[RuCl₂(vpy)₄] (vpy=4-vinylpyridine) on Au or Pt electrodes was studied by cyclic voltammetry, electrochemical quartz crystal microbalance (EQCM) technique, and Raman spectroscopy. Cyclic voltammetry of the monomer at a microelectrode shows the typical Ru(III/II) and Ru(IV/III) waves, together with the vinyl reduction waves at −1.5 and −2.45 V and adsorption wave at −0.8 V. Electrodeposition on EQCM technique performed under potential cycling between −0.9 and −2.0 V revealed that the polymerization proceeded well in advance of the vinyl reduction waves. At potentials more positive than −0.9 V, soluble oligomers were deposited irreversibly on the electrode during the oxidative sweep. The film also showed reversible mass changes due to the oxidation and accompanying ingress of charge-balancing anions and solvent into the film. In contrast, potentiostatic growth of the polymer at −1.6 V was slower because the oligomeric material was lost completely from the electrode. Unreacted vinyl groups were detected by in situ Raman spectroscopy for films grown at −0.7, −0.9, and −1.6 V but were absent when the polymerization was carried out at −2.9 V vs Ag/Ag⁺.     

Complexes of Al(III) with 3'4'-dihydroxy-flavone: characterization, theoretical and spectroscopic study

Complex formation between aluminium chloride and 3'4'-dihydroxyflavone (3'4'diOHF) in methanol has been studied by UV-visible and Raman spectroscopies combined with quantum chemical calculations. Job's method of continuous variation and the molar ratio method were applied to ascertain the stoichiometry composition of the chelate in pure methanol. A 1:1 complex was indicated by both the methods. Geometry optimizations of free and complexed molecules by AMI and DFT methods show that structural modifications of the ligand, induced by complexation, are minor, and are localized on the chelating site. The good agreement between experimental and theoretical electronic spectra of both 3'4'diOHF and complex confirm the structural models. The great similarities between Raman spectra of the free and complexed form constitute an another proof of the absence of pronounced electronic and geometric changes, and notably demonstrate that the quinoidal form induced by the deprotonation of the two hydroxyl groups does not participate in the 3'4'diOHF complex structure. Whereas no complexation occurs in acidic medium, complexes of high stoichiometry are formed in alkaline medium. (Al(3'4'diOHF)2)- and (Al(3'4'diOHF)3)3- species are observed in methanol in the presence of sodium acetate or sodium methanoate.     

Superparamagnetic poly(methyl methacrylate) nanoparticles surface modified with folic acid presenting cell uptake mediated by endocytosis

The encapsulation of superparamagnetic nanoparticles (MNPs) in polymeric nanoparticles (NPs) with modified surfaces can improve targeted delivery and induce cell death by hyperthermia. The goals of this study were to synthesize and characterize surface modified superparamagnetic poly(methyl methacrylate) with folic acid (FA) prepared by miniemulsion polymerization (MNPsPMMA-FA) and to evaluate their in vitro cytotoxicity and cellular uptake in non-tumor cells, murine fibroblast (L929) cells and tumor cells that overexpressed folate receptor (FR) β, and chronic myeloid leukemia cells in blast crisis (K562). Lastly, hemolysis assays were performed on human red blood cells. MNPsPMMA-FA presented an average mean diameter of 135 nm and a saturation magnetization (Ms) value of 37 emu/g of iron oxide, as well as superparamagnetic behavior. The MNPsPMMA-FA did not present cytotoxicity in L929 and K562 cells. Cellular uptake assays showed a higher uptake of MNPsPMMA-FA than MNPsPMMA in K562 cells when incubated at 37 °C. On the other hand, MNPsPMMA-FA showed a low uptake when endocytosis mechanisms were blocked at low temperature (4 °C), suggesting that the MNPsPMMA-FA uptake was mediated by endocytosis. High concentrations of MNPsPMMA-FA showed hemocompatibility when incubated for 24 h in human red blood cells. Therefore, our results suggest that these carrier systems can be an excellent alternative in targeted drug delivery via FR.     

Highly Strained Heterocycles Constructed from Boron–Boron Multiple Bonds and Heavy Chalcogens

The reactions of a diborene with elemental selenium or tellurium are shown to afford a diboraselenirane or diboratellurirane, respectively. These reactions are reminiscent of the sequestration of subvalent oxygen and nitrogen in the formation of oxiranes and aziridines; however, such reactivity is not known between alkenes and the heavy chalcogens. Although carbon is too electronegative to affect the reduction of elements with lower relative electronegativity, the highly reducing nature of the B?B double bond enables reactions with Se⁰ and Te⁰. The capacity of multiple bonds between boron atoms to donate electron density is highlighted in reactions where diborynes behave as nucleophiles, attacking one of the two Te atoms of diaryltellurides, forming salts consisting of diboratellurenium cations and aryltelluride anions.     

Total Synthesis of Salviachinensine A Using a Matteson Homologation Approach

Salviachinensine A, a natural product obtained from the Chinese medicinal plant Salvia chinensis, was synthesized for the first time by employing Donald Matteson's boronic ester homologation. The use of (R,R)-dicyclohexylethane-1,2-diol (DICHED) enabled the generation of the required stereogenic centers in a highly stereoselective fashion. Salviachinensine A was formed in a one-pot protecting group cleavage/lactonization/ intramolecular Friedel–Crafts alkylation, followed by Lewis acid-catalysed cleavage of the acetal protecting groups.     

Crystallization kinetics of polymer brushes with poly(ethylene oxide) side chains

Isothermal crystallization rates of semicrystalline poly(methoxypoly(ethylene glycol) methacrylate) brushes on gold‐coated substrates were measured by polarized optical microscopy. Growth rates for crystal radii, which were essentially constant for each film, initially increased with film thickness and then leveled off for film thicknesses >300 nm. Avrami–Evans theory suggests that the spherulites exhibit one‐dimensional growth with heterogeneous nucleation. Compared with physisorbed analogs, polymer brushes crystallized slower due to the restriction of chain mobility. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1955–1959, 2010