13C NMR spectra of cassane diterpenoids. The stereochemistry of the caesalpins

Assignments of the ¹³C NMR resonances for some cassane diterpenoids have been made. The data have proved to be a useful tool for the stereochemical examination of the caesalpins.     

The give-up problem for blocked regional lists with multi-winners

The current electoral law for the Italian Parliament prescribes blocked, linearly ordered lists of candidates for each party within each constituency. The peculiarity of the Italian electoral system is that a party can present the same candidate in different constituencies. There are several seats at stake in each constituency; these seats are allocated to the parties proportionally to the total number of votes they get. If the blocked list mechanism-which assigns the seats obtained by a party in a constituency to the first candidates of the corresponding ordered list-causes some candidates to win in more than one constituency, they may retain only one of the seats, giving up all the remaining ones. Thus, the problem arises for a party to find a suitable “schedule of give-ups” that produces the final set of winners for that party. In order to do this, we assume that such decision is centralized and based on some models of global (inter-regional) preferences over the set of candidates. In this paper, we introduce two classes of models to formulate the “give-up problem”, i.e., utility and ordinal models, and we show that for both of them some natural formulations of the problem can be efficiently solved by network flows techniques.     

Formation of complex organics from acetylene catalyzed by ionized benzene

We present direct evidence for low temperature associative charge transfer (ACT) reactions of acetylene onto the benzene cation that catalyze the conversion of acetylene molecules into polymerized cations and for high temperature addition/elimination reactions that lead to the generation of naphthalene-type ions. At low temperatures acetylene molecules bind noncovalently to the benzene cation, where partial charge transfer from the ion activates an acetylene molecule for addition polymerization with other associated acetylene molecules, thus amounting to catalytic cyclization/polymerization of the acetylene molecules. At high temperatures the barrier of the covalent addition of acetylene to the benzene cation to form a styrene-type ion is measured as 3.5 kcal/mol. The second acetylene addition followed by H elimination to form a naphthalene-type ion is calculated to be highly exothermic and without a barrier. These reactions can explain the formation of complex organics by gas phase ion-molecule reactions under a wide range of temperatures and pressures in astrochemical environments.     

New additives in glass reinforced polyolefins

Poly(butyl acrylate)-g-poly(4-vinylpyridine) graft copolymer and polypropylene modified with maleic anhydride or poly(maleic anhydride) have been prepared and characterised. These products have been tested as coupling agents in glass reinforced polyolefins. The adhesion of glass fiber or glass filler to polyolefin has been evaluated by “Single fiber composite” method or studying the volume variation under tensile strength. The results indicate that all the prepared additives improve the adhesion between olefin matrix and glass filler or fiber.     

Flame surface modification of polyethylene sheets

High density polyethylene sheets 2 mm thick were flame treated to modify the surface properties. Sheets treated using a flame with air to gas (methane) ratio ∼ 10:1 at different distances between the inner cone tip of the flame and the polymer surface were investigated. Grafting of selected monomers as maleic anhydride, acrylamide and glycidyl methacrylate was attempted by flame treatment of sheets covered with a monomer layer. Good grafting results were obtained with acrylamide and maleic anhydride. The surface temperature-time dependence during the flame treatment was measured with a high resolution thermocouple. Scanning Electron Microscopy (SEM) allowed evidencing a modified thickness of about 120 μ. The chemical surface modification was studied by X ray Photoelectron Spectroscopy (XPS) and Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFT). The hydroxyl, carbonyl and carboxyl content was measured after derivatization with reagents containing an elemental tag to facilitate XPS analysis of surface functional groups. In comparison to the untreated polyethylene, wetting tension and contact angle of the flamed materials showed a strong variation. This variation was almost independent of the distance between the flame and the polymer surface. Adhesion between treated polyethylene and a polyurethane adhesive was determined using T-peel test measurements. High adhesion levels were found with flame treated polyethylene at 5 mm distance. XPS results indicate that when adhesion is high, the hydroxyl is in excess compared to the other measured functions, i.e. carbonyl and carboxyl species.