Semi‐Covalent Surface Molecular Imprinting of Polymers by One‐Stage Mini‐emulsion Polymerization: Glucopyranoside as a Model Analyte

This paper describes a new type of surface imprinting technique that combines the advantages of both the semi‐covalent approach and one‐stage miniemulsion polymerization. This process has been successfully applied for the preparation of glucose surface‐imprinted nanoparticles. The selective artificial receptors for glucopyranoside were fully characterized by IR, TEM and BET analyses, and their molecular recognition abilities by binding experiments carried out in batch processes. The molecular affinity and selectivity of the glucose molecularly imprinted polymers were accurately quantified. These characteristics are essential for verification of the efficiency of the developed surface imprinting process. The imprinting effect was clearly demonstrated using the batch rebinding method. We have found that the glucose imprinted polymers produced using the optimized one‐stage mini‐emulsion exhibited quite fast kinetics of binding and equilibration with glucopyranoside templates, compared to polymers prepared by bulk polymerization technique, as well as extremely low levels of unspecific bindings. We also demonstrated that glucose molecular imprinted polymer (MIP) exhibited very good selectivity for its original template compared to other glycopyranoside derivatives, such as galactose. Finally, the extraction of the binding properties from isotherms of binding by fitting to the bi‐Langmuir and Freundlich models allowed the determination of the affinity constant distribution of the binding sites. This imprinting protocol allowed the determination of an affinity constant (K_D), involving exclusively H‐bonding interactions, for the glucose MIP ( P2C ) with the best template 1 , in CH₃CN as the solvent system.

     

Molecular and biochemical studies of chondramide formation-highly cytotoxic natural products from Chondromyces crocatus Cm c5

The jaspamide/chondramide family of depsipeptides are mixed PKS/NRPS natural products isolated from marine sponges and a terrestrial myxobacterium that potently affect the function of the actin cytoskeleton. As a first step to improve production in heterologous host cells and permit genetic approaches to novel analogs, we have cloned and characterized the chondramide biosynthetic genes from the myxobacterium Chondromyces crocatus Cm c5. In addition to the expected PKS and NRPS genes, the cluster encodes a rare tyrosine aminomutase for beta-tyrosine formation and a previously unknown tryptophan-2-halogenase. Conditions for gene transfer into C. crocatus Cm c5 were developed, and inactivation of several genes corroborated their proposed function and served to define the boundaries of the cluster. Biochemical characterization of the final NRPS adenylation domain confirmed the direct activation of beta-tyrosine, and fluorinated chondramides were produced through precursor-directed biosynthesis.     

Enantioselective total synthesis of cytotoxic taiwaniaquinones A and F

The first synthesis of cytotoxic (-)-taiwaniaquinone A and (-)-taiwaniaquinone F has been achieved through the intramolecular aldol condensation of a ketoaldehyde and the oxidative cleavage of an isopropylidene ketal.     

Synthesis of mono-, di-, and trinitro tricarboxymethyl calix[6]arenes for the complexation of uranium(VI)

Mono-, di-, and trinitro tricarboxymethyl calix[6]arenes 3(a-c) have been synthesised and their acid-base behaviour determined by potentiometric investigations. It was shown that the nitro groups do not play a major role on the acid-base properties. Preliminary complexation of uranyl is presented.     

Room-temperature ionic liquids as new solvents for organic electrosynthesis. The first examples of direct or nickel-catalysed electroreductive coupling involving organic halides

Direct or Ni-catalysed electroreductive homocouplings of organic halides and couplings of organic halides with activated olefins are efficiently conducted by constant current electrolyses in an undivided cell in room-temperature ionic liquids as the solvent-electrolyte media.     

Photosensitive polymers with cinnamate units in the side position of chains: Synthesis, monomer reactivity ratios and photoreactivity

Ethyl α-cyano-4-(methacryloxy)cinnamate was synthesized to prepare new photosensitive polymers. Homopolymerization and copolymerizations were carried out in solution in chloroform at 65 °C using AIBN as an initiator. Methyl methacrylate was chosen as comonomer for the studies of copolymerzation. The structures formed were characterized by IR and ¹H NMR spectroscopies. The values of reactivity ratios of the comonomers calculated according to the Finneman-Ross method indicated that the reactivity of the synthesized photosensitive monomer is lower than that of MMA. Thin films of the obtained polymers were prepared to study their ability to crosslink under UV irradiation. The photodimerization of the cinnamate moieties was characterized.     

Transport of kaolinite colloids through quartz sand: influence of humic acid, Ca(2+), and trace metals

To evaluate the risk of contaminant transport by mobile colloids, it seems essential to understand how colloids and associated pollutants behave during their migration through uncontaminated soil or groundwater. In this study, we investigated at pH 4 the influence of flow velocity, humic acid, solution Ca(2+) concentrations, and trace metals (Pb(2+), Cu(2+)) on the transport and deposition of kaolinite particles through a pure crystalline quartz sand as porous medium. A short-pulse chromatographic technique was used to measure colloid deposition. Adsorption of humic acid to the kaolinite increase its negative surface charge and then decrease colloid deposition. Experiments with different flow rates showed that humic-coated kaolinite colloid deposition followed a first-order kinetic rate law. The deposition rate coefficients of humic-coated kaolinite colloids increase with increasing Ca(2+) concentration in the suspension. The effect of trace metals on the mobility is studied by injecting two suspensions with different concentrations of Pb(2+) and Cu(2+). At very low cation concentration, the fraction of colloids retained is low and roughly independent of the nature of divalent cations. At high concentration, the deposition is higher and depends on the affinity of divalent cations toward humic-coated kaolinite colloids.     

Expedient total syntheses of rhein and diacerhein via Fries rearrangement

Short and practical total syntheses of rhein (1) and diacerhein (2) have been achieved via a Fries rearrangement and bis-carbonylation strategy followed by cyclization in molten salt, starting from dibromoester 7.     

Global optimization of Hölder functions

We propose a branch-and-bound framework for the global optimization of unconstrained Hölder functions. The general framework is used to derive two algorithms. The first one is a generalization of Piyavskii's algorithm for univariate Lipschitz functions. The second algorithm, using a piecewise constant upper-bounding function, is designed for multivariate Hölder functions. A proof of convergence is provided for both algorithms. Computational experience is reported on several test functions from the literature.