Cellulose-polyamide 66 blends. Part II: Mechanical behavior

Blends of the natural polymer cellulose with a synthetic polymer, polyamide 66, are studied in order to determine if the expected strong interaction between them, due to hydrogen bonds, could improve their mechanical properties such as strength and elongation at break. In a previous work {Part I, J. Polym. Sci. Polym. Phys., 32 , 1437 (1994)}, the preparation technique and the characterization of cellulose-polyamide 66 (PA66) blends were described in detail. Several samples in the composition range between 0 to 70 wt % of PA66 were carefully dried and examined using dynamic mechanical and tensile tests. Based on previous work a new percolation model has been developed. It takes both linear and nonlinear mechanical behaviors into account and allows for the effect of adhesion between material domains. From comparison between experimental and predicted data, it is concluded that a partial miscibility between the amorphous phases of cellulose and PA66 exists and is responsible for a strong adhesion at their interface. Solid-state ¹³C nuclear magnetic resonance has also been used to study these samples and supports the existence of strong interactions between both homopolymers. © 1995 John Wiley & Sons, Inc.     

Tungsten(VI)-gluconic acid complexes: Polarimetric and13C-N.m.r. Studies in an excess of tungsten(VI)

Summary A polarimetric study of the tungsten (VI)-gluconic acid system in an excess of metal reveals the formation of four stable complexes: two monomers with 1 : 2 and 2: 1 stoichiometries and two dimers of 2:2 composition. The pH ranges of these species, the amount of acid equivalents their formation requires, and their conditional stability constants have also been calculated.The probable coordination of the organic ligand to the metallic centre in solutions containing different metal : ligand ratios has been investigated by¹³C-n.m.r. spectroscopy. The results confirm the formation of different complexes depending on the reagent which is in excess. The behaviour of the system when the metal is in excess is related to that of other polyhydroxylic ligands such as mannitol and sorbitol.     

Reaction of monocyclic ferrocenyl-4,5-dihydropyrazoles with β-dicarbonyl compounds

Monocyclic 3- and 5-ferrocenyl-4,5-dihydropyrazoles with a free NH group in the molecule react with acetylacetone to form the corresponding enaminocarbonyl compounds. The latter were isolated as a single isomer, presumably E. 3-Ferrocenyldihydropyrazoles and 5-ferrocenyl-3-(p-methoxyphenyl)-4,5-dihydropyrazole analogously react with acetoacetic ester. 5-Ferrocenyl-3-phenyl-, 3-(p-bromophenyl)-5-ferrocenyl, and 3,5-diferrocenyl-4,5-dihydropyrazoles react with acetoacetic ester to form acetoacetylpyrazolides.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 12, 2004, pp. 1942–1947.Original Russian Text Copyright © 2004 by E. Klimova, Vazquez Lopez, T. Klimova, Martinez Garcia, Meleshonkova, Ruiz Ramirez.This revised version was published online in April 2005 with a corrected cover date.     

Multinuclear NMR studies and ab initio structure calculations of hindered phencyclone diels‐alder adducts from symmetrical cyclic dienophiles: Cyclohexene,vinylene carbonate,vinylene trithiocarbonate and two N‐aryl maleimides

A series of hindered Diels‐Alder adducts have been prepared from phencyclone, 1 , with various unusual symmetrical cyclic dienophiles, including cyclohexene, 2a ; vinylene carbonate, 2b ; vinylene trithiocarbonate, 2c ; and the N‐aryl maleimides: N‐(4‐dimethylamino‐3,5‐dinitrophenyl)maleimide (“Tuppy's maleimide”), 2d ; and N‐[3,5‐bis(trifluoromethyl)phenyl]maleimide, 2e . The highly hindered adducts, 3a‐e , respectively, were extensively characterized by one‐ and two‐dimensional NMR methods, observing proton, carbon‐13 and fluorine‐19. High resolution COSY45 spectra permitted rigorous proton NMR assignments. The 2D heteronuclear C‐H chemical shift correlation spectra (HETCOR, XHCORR) were obtained for adducts 3a‐d , allowing specific assignments for protonated carbons. Corrections to earlier proton NMR assignments for the vinylene carbonate adduct are given; results of the gated decoupling ¹³C NMR experiment for this adduct supported endo adduct stereochemistry. Relative proton chemical shifts for bridgehead phenyls of adduct 3c appeared anomalous relative to other adducts, suggesting possible special anisotropic interactions (with endocyclic sulfur or other anisotropic groups in the product) due to the unusual calculated orientation of the phenyls. The unsubstituted bridgehead phenyls in all adducts were shown to exhibit slow exchange limit (SEL) ¹H and ¹³C spectra on the NMR timescales at ambient temperatures (7 tesla) showing slow rotations about the C(sp³)‐C(aryl sp²) bonds. The rapid rotation of the N‐aryl rings of the maleimide adducts was indicated by fast exchange limit spectra, suggesting that ortho substitution of the N‐aryl ring may be necessary to slow this rotation to the SEL regime. Ab initio geometry optimizations at the Hartree‐Fock level were carried out for each adduct, with the 6‐31G* basis sets. Appreciable geometry differences were seen in calculated structures, and significant NMR chemical shift differences were experimentally observed, depending on the nature of the groups attached to the (Z)‐HC=CH moiety of the dienophiles.     

Compounds with the YbFe2O4Structure Type: Frustrated Magnetism and Spin-Glass Behavior

The YbFe₂O₄structure type consists of triangular layers of lanthanide oxygen octahedra stacked with triangular double layers of transition metal oxygen triangular bipyramids. The crystallographic structures determined by neutron diffraction powder profile analysis at 300 and 11 K for new members of this structural family are reported. The compounds are found to be magnetically frustrated, by both lattice geometry and disorder. The magnetic properties of YbCuGaO₄, LuCuGaO₄, LuZnFeO₄, LuCoGaO₄, and LuCuFeO₄reveal the effects of total spin, spin mixing, and interaction between spins on different sublattices on the magnetic frustration. The magnetism is increasingly frustrated as the spin on the magnetic ions is decreased.     

Phototoxic effects of Hypericum extract in cultures of human keratinocytes compared with those of psoralen

Extracts of Hypericum perforatum (St. John's wort) are used in the treatment of depression. They contain the plant pigment hypericin and hypericin derivates. These compounds have light-dependent activities. In order to estimate the potential risk of phototoxic skin damage during antidepressive therapy, we investigated the phototoxic activity of hypericin extract using cultures of human keratinocytes and compared it with the effect of the well-known phototoxic agent psoralen. The absorbance spectrum of our Hypericum extract revealed maxima in the whole UV range and in parts of the visible range. We cultivated human keratinocytes in the presence of different Hypericum concentrations and irradiated the cells with 150 mJ/cm2 UVB, 1 J/cm2 UVA or 3 h with a white light of photon flux density 2.6 mumol m-2 s-1. The determination of the bromodeoxyuridine incorporation rate showed a concentration- and light-dependent decrease in DNA synthesis with high hypericin concentrations (> or = 50 micrograms/mL) combined with UVA or visible light radiation. In the case of UVB irradiation a clear phototoxic cell reaction was not detected. We found phototoxic effects even with 10 ng/mL psoralen using UVA with the same study design as in the case of the Hypericum extract. These results confirm the phototoxic activity of Hypericum extract on human keratinocytes. However, the blood levels that are to be expected during antidepressive therapy are presumably too low to induce phototoxic skin reactions.     

Single‐electron‐transfer/degenerative‐chain‐transfer mediated living radical polymerization of vinyl chloride catalyzed by thiourea dioxide/octyl viologen in water/tetrahydrofuran at 25 °C

The single‐electron‐transfer/degenerative‐chain‐transfer mediated living radical polymerization (SET–DTLRP) of vinyl chloride (VC) in H₂O/tetrahydrofuran at 25 °C catalyzed by thiourea dioxide [(NH₂)₂C?SO₂] is reported. This polymerization occurs only in the presence of a basic sodium bicarbonate (NaHCO₃) buffer and the electron‐transfer cocatalyst octyl viologen. The resulting poly(vinyl chloride) (PVC) has a number‐average molecular weight of 1500–7000 and a weight‐average molecular weight/number‐average molecular weight ratio of 1.5. This PVC does not contain detectable amounts of structural defects and has both active chloroiodomethyl and inactive chloromethyl chain ends. Because of possible side reactions caused by the primary sulfoxylate anion (SO), the catalytic activity of (NH₂)₂C?SO₂ in the SET–DTLRP of VC is lower than that of the single‐electron‐transfer agent sodium dithionite. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 287–295, 2005