Studies on polymers and composites from lignin and fiber derived from sugar cane

Sugarcane fiber (i.e. bagasse) lignin has a larger fraction of aromatics unsubstitution in the ortho position than hardwood or softwood lignin and hence has the greater ability to be derivatized. Furthermore, organosolv lignin has a higher purity than sulfonated and kraft lignins. This work examines the purification of organosolv lignin derived from bagasse and the physico‐chemical properties of the lignin and lignin‐phenol formaldehyde (PF) resin coatings, and composites. The wetability tests have shown that lignin and lignin‐PF resin films are effective water barrier coatings, though the contact angles of lignin‐PF resin films were considerably less than the wax films. The overall mechanical properties (i.e. peak stress, peak strain and modulus) of the bagasse fiber composites were lower than the values obtained with the composites without the inclusion of bagasse fiber. Copyright © 2007 John Wiley & Sons, Ltd.     

Studies on the inactivation of bovine liver enoyl-CoA hydratase by (methylenecyclopropyl)formyl-CoA: elucidation of the inactivation mechanism and identification of cysteine-114 as the entrapped nucleophile

The inhibitory properties of (methylenecyclopropyl)formyl-CoA (MCPF-CoA), a metabolite derived from a natural amino acid, (methylenecyclopropyl)glycine, against bovine liver enoyl-CoA hydratase (ECH) were characterized. We have previously demonstrated that MCPF-CoA specifically targets ECHs, which catalyze the reversible hydration of alpha,beta-unsaturated enoyl-CoA substrates to the corresponding beta-hydroxyacyl-CoA products. Here, we synthesized (R)- and (S)-diastereomers of MCPF-CoA to examine the stereoselectivity of this inactivation. Both compounds were shown to be competent inhibitors for bovine liver ECH with nearly identical second-order inactivation rate constants (k(inact)/K(I)) and partition ratios (k(cat)/k(inact)), indicating that the inactivation is nonstereospecific with respect to ring cleavage. The inhibitor, upon incubation with bovine liver ECH, labels a tryptic peptide, ALGGGXEL, near the active site of the protein, where X is the amino acid that is covalently modified. Cloning and sequence analysis of bovine liver ECH gene revealed the identity of the amino acid residue entrapped by MCPF-CoA as Cys-114 (mature sequence numbering). On the basis of gHMQC (gradient heteronuclear multiple quantum coherence) analysis with [3-(13)C]-labeled MCPF-CoA, the ring cleavage is most likely induced by the nucleophilic attack at the terminal carbon of the exomethylene group (C(2)'). We propose a plausible inactivation mechanism that involves relief of ring strain and is consistent with examples found in the literature. In addition, these studies provide important clues for future design of more efficient and selective inhibitors to control and/or regulate fatty acid metabolism.     

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.     

Effect of electric field on liquid chromatographic separation of peptide digests. Combining capillary separation techniques

A system is described which allows operation of a range of capillary based liquid phase separations including capillary electrophoresis, isocratic and gradient capillary electrochromatography, isocratic and gradient capillary liquid chromatography and electrically assisted gradient capillary liquid chromatography. The system was coupled to electrospray ionization mass spectrometry in the electrically assisted capillary liquid chromatography mode to investigate the effect of applied voltage on the selectivity in peptide mapping separations. Analyses were performed on tryptic digests of recombinant human growth hormone and tissue plasminogen activator. The results show a small but useful effect on selectivity that can be used to fine tune specific separations.     

Synthesis and Characterization of the Isocyanide Ligated Centered Zirconium Halide Cluster [(Zr6Be)Cl12(CNXyl)6]

The first isocyanide ligated hexanuclear zirconium halide cluster is reported. The unoxidized [(Zr₆Be)Cl₁₂(CNXyl)₆] (CNXyl = 2,6-dimethylphenyl isocyanide) was obtained from the solid state precursor K₃Zr₆Cl₁₅Be by dissolution in CH₃CN in the presence of CNXyl. The CNXyl ligands occupy all the axial positions on the cluster. The compound was recrystallized from CH₂Cl₂ and Et₂O. [(Zr₆Be)Cl₁₂(CNXyl)₆].2CH₂Cl₂ crystallizes in the space group (#2) with a = 12.092(5) Å, b=12.728(5) Å, c = 14.102(8) Å, = 104.98(4)°, =107.11°, = 100.94°, V = 1919(2) ų, Z = l, R = 11.3% and R _W = 27.0%. For the bound isocyanide ligands, v _CN increases to 2140 cm^–1.     

In-situ HEED structure analysis of AlNx films grown by the simultaneous use of a radical beam source and ICB technique

A reactive ionized cluster beam technique (RICB) which was composed of a conventional ICB source and a radical beam source has been used to deposit stable and metastable polycrystalline AlN_x (0≤x≤1) films. Using in-situ high energy electron diffraction (HEED) at grazing incidence geometry, crystallographic properties such as structure, preferred orientation and interplanar dspacing values were determined and the relation to deposition parameters investigated. It could be shown that the simultaneous use of the ICB technique and a radical beam source to separately control the kinetic energy of the Al ions and the dissociation rate of molecular nitrogen, allows AlN films to be deposited with variable composition and crystal structures. In-situ HEED used in the transmission mode is an effective tool to investigate the crystallography of growing compound films such as AlN_x.     

THE RELATIONSHIP OF ACCESSORY PIGMENTS TO CHLOROPHYLL a CONTENT IN CHLOROPHYLL-DEFICIENT PEANUT AND SOYBEAN VARIETIES

Abstract— A relationship between Chl a and each of its accessory pigments, neoxanthin, violaxanthin, lutein, Chl b and carotene, is demonstrated in soybean and peanut genotypes. These genotypes include normal and Chl-deficient types. Plots of Chl a content against accessory pigment content generate straight-line relationships that are extrapolated to intersect the Chl a axis. The points of intersection correctly predict the order of origin of certain accessory pigments (lutein, carotene and Chl b ), but incorrectly predict that neoxanthin and violaxanthin arise after the introduction of Chl a .     

Planar defects in β-alumina

Sodium β-alumina crystals were elaborated by melting of a mixture of Na₂CO₃ and Al₂O₃ or by PbO flux evaporation and were studied by transmission electron microscopy. They exhibit regular planar defects lying in the {11.0} prismatic planes. These defects are described as antiphase boundaries for the cationic sublattice with fault vectors $\text{1}\text{2}\text{〈10.0〉}$ (such faults do not affect the anionic sublattice). As a consequence it would be interesting to study precisely the structure of the sodium β cationic lattice in the vicinity of the melting point.     

Untersuchungen zur sprungartigen Bruchausbreitung in Polymethylmethacrylat

Zusammenfassung In PMMA ist der Übergang von der langsamen, unterkritischen Bruchausbreitung zur schnellen, überkritischen Bruchausbreitung mit einer Änderung in der Bruchflächenstruktur und einem Geschwindigkeitssprung verbunden. Die Bruchgeschwindigkeiten wurden mit zwei verschiedenen Methoden gemessen; die registrierten Endgeschwindigkeiten des langsamen Bruchausbreitungsbereiches liegen zwischen 6 und 21 cm/s, der Geschwindigkeitssprung beträgt etwa 3 Zehnerpotenzen. Dieses Bruchverhalten wird nachWilliams auf einen isotherm/adiabatischen Effekt zurückgeführt. Mit Hilfe einer vonWeichert,Schönert angegebenen Berechnung des Isothermenfeldes einer bewegten Wärmequelle kann dieser Effekt konkreter gefaßt und die Endgeschwindigkeit im langsamen Bruchausbreitungsbereich eingegrenzt werden.

---

Summary In PMMA there is a transition from slow subcritical to fast critical crack growth accompanied by a change in the fracture surface and a sharp increase in the crack velocity. The crack velocities were measured by two different methods; the limiting velocities in the slow crack propagation region were in the range 6–21 cm/s; at the transition the velocity increases by about three orders of magnitude. Such crack propagation behaviour has been attributed byWilliams to an isothermal/adiabatic transition. With the help of recent calculations byWeichert andSchönert of the isothermal field around a moving heat source, it is shown that these limiting velocities of slow crack propagation can be estimated.