Study of blends of HDPE and different grades of CaCO3. Part I. Factorial experimental design

Calcium carbonate (CaCO₃)/high density polyethylene (HDPE) composites were prepared in a HAAKE twin screw extruder. The influence of the CaCO₃ particle size and content and the processing conditions were investigated by using a factorial experimental design. The dependent variables studied were tensile properties, such as Young's modulus, stress at break and toughness, and the rheological property, zero-shear viscosity, η₀. Preliminary results have shown that the most significant processing variables were content and mineral filler type. Mathematical modeling has given us a more efficient evaluation of the results obtained and has become an important tool in the development of this work.     

Microwave-assisted solvent-free synthesis of a quinoline-3,4-dicarboximide library on inorganic solid supports

Inorganic solid supports are useful media for the rapid and efficient synthesis of a library of quinoline-3,4-dicarboximides. In particular, wet clay K10 was shown to be the best medium for the condensation reaction between 2-methylquinoline-3,4-dicarboxylic anhydride and several primary amines. Microwave irradiation is essential for a rapid and complete conversion.     

SmI(2)-promoted oxidation of aldehydes in the presence of electron-rich heteroatoms

[reaction: see text] The Evans-Tishchenko reaction provides an efficient and practical solution for the oxidation of aldehydes possessing sensitive electron-rich heteroatoms to the corresponding esters. Careful selection of the sacrificial beta-hydroxy ketone provides considerable subsequent flexibility to access the desired carboxylic acid.     

Energy transfer between singlet (1Delta(g)) and triplet (3Sigma(g)-) molecular oxygen in aqueous solution

We clearly demonstrate the occurrence of energy transfer between 18O2 (1Deltag) and 16O2 in the ground state (3Sigmag-) with subsequent conversion of the latter species into its singlet excited state (1Deltag) in aqueous solution. This was inferred from the results of incubation experiments involving DHPN18O2 as a chemical generator of 18O2 (1Deltag) and the water-soluble disodium salt of anthracene (EAS) used as a chemical trap of singlet oxygen. The products of the reaction were accurately analyzed by HPLC-ESI-MS.     

Photodynamic studies and photoinactivation of Escherichia coli using meso-substituted cationic porphyrin derivatives with asymmetric charge distribution

The photodynamic activities of novel asymmetrically meso-substituted cationic porphyrins, 5,10-di(4-methylphenyl)-15,20-di(4-trimethylammoniumphenyl)porphyrin iodide 1 and 5-(4-trifluorophenyl)-10,15,20-tris(4-trimethylammoniumphenyl)porphyrin iodide 2 and its metal complex with Pd(II) 3, have been investigated in both homogeneous medium bearing photooxidizable substrates and in vitro on a typical gram-negative bacterium Escherichia coli. The amphiphilic character of porphyrin 2 was increased by the presence of a high-lipophilic trifluoromethyl group and its photophysical properties changed by forming a complex with Pd(II). Absorption and fluorescence spectroscopic studies were compared in different media. Fluorescence quantum yields (phi(F)) of 0.16 for 1 in tetrahydrofuran and 0.08 for 2 in N, N-dimethylformamide (DMF) were calculated, whereas no significant emission was detected for Pd(II) porphyrin 3. The singlet molecular oxygen, O(2)((1)Delta(g)), production was evaluated using 9,10-dimethylanthracene in DMF yielding relative values of 1, 0.55 and 0.47 for porphyrins 3, 2 and 1, respectively. A faster decomposition of l-tryptophan was obtained using Pd(II) porphyrin 3 as sensitizer with respect to the free-base porphyrins 1 and 2. In biological medium, the behavior of cationic porphyrins 1-3 were compared with that of 5-(4-carboxyphenyl)-10,15,20-tris(4-methylphenyl)porphyrin 4, which was used as a noncationic sensitizer. These porphyrins are rapidly bound to E. coli cells in 5 min and the amount of cell-bound sensitizer is not appreciably changed incubating the cultures for longer times. The recovered porphyrin 2 after one washing step reaches a value of approximately 2.9 nmol/10(6) cells and this amount remains high even after three washes, indicating that this sensitizer is tightly bound to cells. Photosensitized inactivation of E. coli was analyzed using cells without and with one washing step. In both cases, a higher photoinactivation of cells was found for tricationic porphyrin 2 and 3, causing a approximately 5.5 log (99.999%) decrease of cell survival, when treated with 10 microM of sensitizer. Under these conditions, a lower effect was found for porphyrin 1 (approximately 4 log) whereas sensitizer 4 did not produce appreciable photodamage. The results were also confirmed by growth delay experiments. These studies show that the amphiphilic tricationic porphyrin 2 and 3 bearing a trifluoromethyl group can be a promising model for phototherapeutic agents with potential applications in inactivation of bacteria by photodynamic therapy.     

Synthesis and X-ray structures of dinitrato-bis[2-(2′-thienyl)-1-(2′-thienylmethyl)benzimidazole]copper(II) and dichloro-bis-[2-(2′-thienyl)-benzimidazole]copper(II)-ethanol

Summary The reactions of Cu(NO₃)₂ · 3 H₂O with 2- (2-thienyl)-1-(2-thienylmethyl)benzimidazole (L) and of CuCl₂ · 2H₂O with 2-(2-thienyl)benzimidazole (L) have been carried out. The crystal structure of two isolated complexes,(1) and(2), have been determined by single-crystal x-ray diffraction methods. Crystals of(1) are monoclinic, space groupP2₁ /c, witha=9.884(4),b=9.892(4),c=18.732(8) Å, =114.89(2)°,Z=2;R=0.068 for 1909 observed reflections. Crystals of (2) are orthorhombic, space groupPbcn, witha=14.835(1),b=8.193(1),c=20.493(1) Å,Z=4;R=0.086 for 415 observed reflections. In the complex (1) the copper co-ordination is tetragonal (compressed octahedral) and involves a nitrogen atom of the organic ligand [Cu-N 1.970(6) Å] and two oxygen atoms of the nitrate group [Cu-O 2.318(7) and 2.246(9) Å] which appears to coordinate nearly symmetrically to the metal; however it has unusually large thermal motion which suggests a fluxional behaviour. In the complex (2) the co-ordination is square planar and involves an imidazole nitrogen [Cu-N 1.95(3) Å] and a chlorine atom [Cu-Cl 2.27(1) Å]. A long interaction Cu-S=3.37(2) Å completes the co-ordination polyhedron to a very elongated distorted tetragonal bipyramid. In both compounds a thiophene ring is disordered.     

Ab initio molecular electrostatic potentials

The ab initio isopotential map of guanine is given and compared to that of adenine. It shows that in contrast to the situation in adenine, the most basic site of guanine is N₇ with a secondary potential minimum at O₆. These results as well as those concerning the secondary out-of-plane attractive regions over the NH₂ group and C₈ H bonds of the two molecules are discussed in connection with the available experimental knowledge concerning the bonding of alkylating carcinogens and mutagens.     

Dolbeault Cohomology for G2-Manifolds

Cocalibrated G₂-manifolds are seven-dimensional Riemannian manifolds with a distinguished 3-form which is coclosed. For such a manifold M, S. Salamon in Riemannian Geometry and Holonomy Groups (Longman, 1989) defined a differential complex related with the G₂-structure of M.In this paper we study the cohomology of this complex;it is treated as an analogue of a Dolbeault cohomologyof complex manifolds. For compact G₂-manifoldswhose holonomy group is a subgroup of G₂ special propertiesare proved. The cohomology of any cocalibrated G₂-nilmanifold \K is also studied.