De-aggregation of a polyfluorene derivative in clay nanocomposites: A photophysical study

The de-aggregation of a very luminescent polyfluorene derivative poly(9,9-di-hexylfluorenediyl divinylene-alt-1,4-phenylenevinylene), which has a high tendency to π-stacking aggregation was achieved through the interaction of the polymer with clay in clay/polymer nanocomposites. The mixing of diluted toluene polymer solutions with kaolinite was enough to promote the de-aggregation, even without the indication of polymer intercalation, indicating that the polymer de-aggregation was obtained due to its interactions with clay platelet surfaces. The photoluminescence observed for the dispersed polymer on clays showed an increase in intensity and a blue-shift of the photoluminescence, when compared with pure pristine material in thin film form. The results presented bring the possibility to produce more efficient polymer based devices and to carry single molecule studies using nanocomposite film formation.     

Efficient synthesis of α-(fluoro/chloro/methoxy)disulfonylmethane derivatives as tunable substituted methyl synthons via a new C-S bond forming strategy

A new synthetic protocol for the preparation of α-fluoro(disulfonyl)methane and its chloro as well as methoxy analogues has been developed. Due to the synthetic utility of α-fluoro(bisphenylsulfonyl)methane (FBSM) as a versatile synthon in the preparation of various useful fluoromethylated organic molecules, search for an easy and economic for its preparation route has been essential. The C-S bond forming strategy is utilized in this new synthetic approach, which can be applied to a variety of substrates with high efficiency and selectivity.     

Lysozyme Adsorption onto Different Supports: A Comparative Study

The interaction between proteins and solid surfaces has been investigated. The aim of this work is to compare three different materials (hydroxyapatite, polystyrene with core-shell structure (PE-CS) and a functionalized styrene divinylbenzene copolymer) to be used as adsorbents for lysozyme, known as a “hard” protein. Tests were performed according to an experimental design in order to compare the effects of pH, lysozyme and phosphate buffer concentration onto the adsorbed amount of protein. A 2³ factorial design and a cross design, which was performed in triplicate, were used to distinguish the most important variables and to infer about the interaction between them. Hydroxyapatite showed the best performance—higher adsorbed amount of lysozyme and smaller dispersion (72.2 ± 0.9 mg/g). However, PE-CS can be regarded as a promising support as high amounts of lysozyme are adsorbed onto this material with relatively small dispersion.     

Sorbitol and gluconic acid production using permeabilized Zymomonas mobilis cells confined by hollow-fiber membranes

Immobilization of Zymomonas mobilis by different methods was investigated. Experiments were performed order to choose the most appropriate support for the immobilization of the cells. The most advantageous option was to use permeabilized cells in the bore of microporous hollow fibers. Whereas the reaction rate was about 33 g of gluconate/ (g of protein·h) using hollow fibers, which is comparable to that observed by using free cells, the calcium alginate immobilized cells presented a reaction rate of 4 g of gluconate/ (g of protein·h). These results can be explained by the mass transfer resistance effect, which, indeed, was much lower in the case of hollow-fiber membranes than in the alginate gel beads. A loss of enzymatic activity during the reaction was observed in all experiments, which was attributed to the lactone produced as an intermediate of the reaction.     

Stereocontrolled assembly of tetrasubstituted tetrahydrofurans: a concise synthesis of virgatusin

The condensation of substituted allylsiloxanes with aldehydes leads to the highly stereoselective construction of 2,3,4,5-tetrasubstituted tetrahydrofurans. With electron-rich aryl and alpha,beta-unsaturated aldehydes as substrates, the stereochemical outcome at C5 can be dictated by appropriate choice of Lewis acid. The reaction has been applied to a concise (nine step) synthesis of (+)-virgatusin (ent-1). [reaction: see text]     

Measurement of glycogen synthase activity in crude extracts by CE

Glycogen synthase catalyzes the incorporation of UDP-glucose into glycogen. The activity of the enzyme is usually measured either by a spectrophotometric method or by a radioassay. The first one is not suitable because of the difficulties regarding the use of coupled enzymes in crude extracts, while the second is a time-consuming method involving glycogen isolation and manipulation of radioactivity. We have used a CZE technique as a novel approach to measure glycogen synthase activity. The separations were performed at 22 kV (36 microA) in uncoated capillaries (53 cmx50 microm). Sample injection time was 30 s and nucleotides were monitored at 254 nm. Best resolution was achieved in 20 mM tetraborate buffer, pH 9.2. Curves of absorbance as a function of UDP and UDP-glucose concentration were linear. Enzyme activity in oocyte extracts was linear with respect to time (up to15 min) and enzyme concentration. The K(m app.) for UDP-glucose was 0.87 mM, a value identical to the one reported using the radioassay. CZE enables easy quantitation of compounds, high sensitivity, and automation of the process. Small sample sizes are required, interferences by auxiliary enzymes and manipulation of radioactivity are avoided, and analysis time is significantly diminished.     

Intermediate motions as studied by solid-state separated local field NMR experiments

In this report, the application of a class of separated local field NMR experiments named dipolar chemical shift correlation (DIPSHIFT) for probing motions in the intermediate regime is discussed. Simple analytical procedures based on the Anderson-Weiss (AW) approximation are presented. In order to establish limits of validity of the AW based formulas, a comparison with spin dynamics simulations based on the solution of the stochastic Liouville-von-Neumann equation is presented. It is shown that at short evolution times (less than 30% of the rotor period), the AW based formulas are suitable for fitting the DIPSHIFT curves and extracting kinetic parameters even in the case of jumplike motions. However, full spin dynamics simulations provide a more reliable treatment and extend the frequency range of the molecular motions accessible by DIPSHIFT experiments. As an experimental test, molecular jumps of imidazol methyl sulfonate and trimethylsulfoxonium iodide, as well as the side-chain motions in the photoluminescent polymer poly[2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene], were characterized. Possible extensions are also discussed.