Synthesis and reactivity of (C6F5)3B-N-heterocycle complexes. 1. Generation of highly acidic sp3 carbons in pyrroles and indoles

The reaction of pyrroles and indoles with B(C(6)F(5))(3) and BCl(3) produces 1:1 B-N complexes containing highly acidic sp(3) carbons, for example, N-[tris(pentafluorophenyl)borane]-5H-pyrrole (1) and N-[tris(pentafluorophenyl)borane]-3H-indole (2), that are formed by a new formal N-to-C hydrogen shift, the mechanism of which is discussed. With some derivatives, restricted rotation around the B-N bond and/or the B-C bonds was observed by NMR techniques, and some rotational barriers were calculated from experimental data. The acidity of the sp(3) carbons in these complexes is shown by their ability to protonate NEt(3), with formation of pyrrolyl- and indolyl-borate ammonium salts. The driving force for this reaction is given by the restoration of the aromaticity of the heterocycle.     

Synthesis and characterization of high-molecular-weight syndiotactic amorphous polypropylene

Heterocycle-fused titanium indenyl silylamido dimethyl complexes produce very high molecular weight polypropylene having a prevailingly syndiotactic microstructure with syndiotactic pentad contents rrrr up to 40-55% (sam-PP). The samples are basically amorphous and may slowly develop a low level of crystallinity (16-20%) at room temperature. A structural characterization has shown that sam-PP samples crystallize in disordered modifications of the helical form I of syndiotactic polypropylene (s-PP). The stretching of compression-molded films of sam-PP samples produce oriented crystalline fibers in the trans-planar mesomorphic form of s-PP. The low stereoregularity prevents the formation of the ordered trans-planar form III of s-PP, which instead is obtained in stretched fibers of the highly stereoregular and crystalline s-PP. The trans-planar mesomorphic form, obtained in stretched fibers, in turn transforms into the helical form I upon releasing the tension. The analysis of the mechanical properties has shown that sam-PP samples show good elastic behavior in a large range of deformation with remarkable strength, due to the presence of crystallinity. A comparison with the mechanical properties of less syndiotactic and fully amorphous samples is reported. These fully amorphous samples present lower strength and experience rapid viscous flow of the chains at high deformations and/or by application of stresses for long times. The higher strength in the semicrystalline sam-PP samples makes these materials interesting thermoplastic elastomers showing high toughness and ductility.     

Characterization of nutraceuticals and functional foods by innovative HPLC methods

In recent years there is a growing interest in food and food ingredient which may provide health benefits. Food as well as food ingredients containing health-preserving components, are not considered conventional food, but can be defined as functional food. To characterise such foods, as well as nutraceuticals specific, high sensitive and reproducible analytical methodologies are needed. In light of this importance we set out to develop innovative HPLC methods employing reversed phase narrow bore column and high-performance anion-exchange chromatographic methods coupled with pulsed amperometric detection (HPAEC-PAD), which are specific for carbohydrate analysis. The developed methods were applied for the separation and quantification of citrus flavonoids and to characterize fructooligosaccharide (FOS) and fructans added to functional foods and nutraceuticals.     

Ethanol production in immobilized-cell bioreactors from mixed sugar syrups and enzymatic hydrolysates of steam-exploded biomass

We investigated ethanol production from mixed sugar syrups. Hydrolysates were prepared from enzymatic saccharification of steam-pretreated aspen chips. Syrups containing 45 g/L of glucose and 12 g/L of xylose were detoxified through two ion-exchange resins and then fermented with Pichia stipitis and Saccharomyces cerevisiae immobilized in Ca-alginate gel beads. Combinations of different gel fractions in the fermentation volume, amount of yeast cells, and ratios of P. stipitis vs S. cerevisiae within each bead were compared. In the best conditions, by using a total beads volume corresponding to 25% of the working volume, we obtained a yield of 0.39 g_ethanol/g_{initial sugars}. This amount of gel entrapped an initial cell concentration of 6×10¹²cells/L with ratio of S. cerevisiae/P. stipitis of 0.25 g/g. Modified stirredtank reactors were obtained either by adding marbles or by inserting a perforated metal cylinder, which reduced considerably the rupture of beads while visibly improving oxygenation of the medium.     

Animal glues in mixtures of natural binding media used in artistic and historic objects: identification by capillary zone electrophoresis

Animal glues were often used in historic and artistic objects, e.g. as paint ground, as binders for pigments, or as adhesives. The sources were egg, casein, or different collagens. For restoration and conservation purposes it is important to know which kind of animal glue a museum object contains. Capillary electrophoresis can deliver such information, because it enables differentiation among the three proteinaceous glue classes according to their different amino acid patterns after hydrolysis. This work deals with the most relevant problem in practice, whether this identification is obstructed by the presence of other binders, with which they are mixed in many real samples; in particular, interference from plant gums and drying oils was investigated. Capillary electrophoresis of the hydrolysates (after reaction with 6 mol L^–1 HCl) was performed with an acidic background electrolyte consisting of chloroacetic acid (51.9 mmol L^–1) adjusted with LiOH to pH 2.26. The underivatised analytes were detected with a contactless conductivity detector. It was found that the constituents of the plant gums (monosaccharides) or drying oils (long-chain fatty acids and short-chain dicarboxylic acids) never interfered with identification of the animal glues, as shown for artificial mixtures of the different binders even at tenfold excess over the animal glue, and for egg tempera samples. The method was used to identify the filling material from a statue from the eighteenth century.     

Polycondensed nitrogen heterocycles. X. 5,6,7,8-Tetrahydropyrrolo[1,2-e][1,5]benzodiazocin-7-ones. A new ring system

The synthesis of a new heterocyclic ring system is described. Condensation of 1,4-diketones 1a,b with β-alanine gave the substituted propionic acids 2a,b which upon reduction with palladium on charcoal afforded compounds 3a,b . Title compounds 4a,b were obtained by refluxing 3a,b in toluene with p-toluenesulphonic acid as catalyst.     

Random ethene/propene copolymerization from a catalyst system based on a “constrained geometry” half‐sandwich complex

Ethene/propene copolymerizations were performed in solution with a single centre catalyst system composed of a “constrained geometry” half‐sandwich organometallic complex {η¹: η⁵‐[(tert‐butylamido)dimethylsilyl](2,3,4,5‐tetramethyl‐1‐cyclopentadienyl)}titanium dichloride, and methylaluminoxane. The statistical treatment of polymerization data allowed to determine the reactivity ratios for ethene and propene: r_E = 1.35 ± 0.09, r_P = 0.82 ± 0.05, r_Er_P = 1.10 ± 0.14. This catalyst system promotes an almost random distribution of ethene and propene and gives rise to values of r_P and r_E very similar to each other.     

Algorithms for central-median paths with bounded length on trees

The location of path-shaped facilities on trees has been receiving a growing attention in the specialized literature in the recent years. Examples of such facilities include railroad lines, highways and public transit lines. Most of the papers deal with the problem of locating a path on a tree by minimizing either the maximum distance from the vertices of the tree to the facility or of minimizing the sum of the distances from all the vertices of the tree to the path. However, neither of the two above criteria alone capture all essential elements of a location problem. The sum of the distances criterion alone may result in solutions which are unacceptable from the point of view of the service level for the clients who are located far away from the facilities. On the other hand, the criterion of the minimization of the maximum distance, if used alone, may lead to very costly service systems. In the literature, there is just one paper that considers the problem of finding an optimal location of a path on a tree using combinations of the two above criteria, and efficient algorithms are provided. In particular, the cases where one criterion is optimized subject to a restriction on the value of the other are considered and linear time algorithms are presented. However, these problems do not consider any bound on the length or cost of the facility. In this paper we consider the two following problems: find a path which minimizes the sum of the distances such that the maximum distance from the vertices of the tree to the path is bounded by a fixed constant and such that the length of the path is not greater than a fixed value; find a path which minimizes the maximum distance with the sum of the distances being not greater than a fixed value and with bounded length. From an application point of view the constraint on the length of the path may refer to a budget constraint for establishing the facility. The restriction on the length of the path complicates the two problems but for both of them we give O(n log² n) divide-and-conquer algorithms.     

Arithmetic of algebraic curves from diophantus to Poincaré

This article contains an analysis of the methods for solving diophantine equations of second and third degrees in two unknowns, from the most ancient times to Poincaré. Special attention is paid to the works of Fermat, Euler, and Jacobi.     

τ→μγ and μ→eγ as probes of neutrino mass models

We discuss the possibility of discriminating between different supersymmetric see-saw models by improving the experimental sensitivity to charged lepton flavour violating processes. Assuming a hierarchical neutrino mass spectrum, we classify see-saw models according to how the hierarchy Δm²Δm²_atm is generated, and study the predictions of each class for the branching ratios of τ→μγ and μ→eγ. The process τ→μγ is found to be a particularly promising tool to probe the fundamental see-saw parameters, and especially to identify the origin of the large atmospheric mixing angle. Predictions for μ→eγ are more model-dependent. We point out that, even with an improvement of the experimental sensitivities by three orders of magnitude, both τ→μγ and μ→eγ could escape detection in models where Δm²_atm is determined by one of the lightest right-handed neutrinos.