The simultaneous saccharification and fermentation of pretreated woody crops to ethanol

Four promising woody crops (Populusmaximowiczii x nigra (NE388), P.trichocarpa x deltoides (Nll), P.tremuloides, and SweetgumLiquidambar styraciflua) were pretreated by dilute sulfuric acid and evaluated in the simultaneous saccharification and fermentation (SSF) process for ethanol production. The yeastSaccharomyces cerevisiae was used in the fermentations alone, and in mixed cultures with β -glucosidase producingBrettanomyces dausenii. Commercial Genencor 150L cellulase enyme was either employed alone or supplemented with β- glucosidase. All SSFs were run at 37 …C for 8 d and compared to saccharifications at 45…C under the same enzyme loadings.S. cerevisiae alone achieved the highest ethanol yields and rates of hydrolysis at the higher enzyme loadings, whereas the mixed culture performed better at the lower enzyme loadings without β -glucosidase supplementation. The best overall rates of fermentation (3 d) and final theoretical ethanol yields (86–90%) were achieved with P.maximowiczii x nigra (NE388) and SweetgumLiquidambar styraciflua, followed by P.tremuloides and P.trichocarpa xdeltoides (N1l) with slightly slower rates and lower yields. Although there were some differences in SSF performance, all these pretreated woody crops show promise as substrates for ethanol production.     

Coulometric redox titrations of some biologically active thiols with iodine in methanol and bromine in acetic acid

The possibility of coulometric titrations of cysteine, 2-thio-uracil, 6-mercaptopurine, and 6-thioguanine with iodine and bromine in methanol and with bromine in acetic acid has been investigated. Conditions have been found for the direct titration of the test substances with iodine in methanol based on their 1-electron oxidation to the corresponding disulphides and for their direct and indirect determination with bromine in acetic acid based on their 6-electron oxidation to the corresponding sulphonic acids.On leave from Department of Analytical Chemistry, Charles University, Prague, Czechoslovakia     

Topographical properties of polymer films deposited in capillaries for electrophoretic separations of large organic molecules

Topography and thickness of hydrophilic polymer coatings of fused-silica capillaries for capillary electrophoresis (CE) were investigated using atomic force microscopy (AFM), scanning electron microscopy (SEM), and profilometry. Three hydrogels, poly(2-hydroxyethyl methacrylate) [poly(HEMA)], poly(diethylene glycol monomethacrylate) [poly(DEGMA)], and poly(triethylene glycol monomethacrylate) [poly(TEGMA)], were deposited using two procedures, either by simple physical sorption of the polymers, or by derivatization of the capillary wall surface with glycidyl methacrylate (EPMA) followed by polymerization of the appropriate monomers. The performance of the modified capillaries was tested under CE conditions (decrease in the electroosmotic flow, EOF dependence on pH, separation of milk and standard proteins). It has been found that the most important property of the polymer coating is its thickness, whereas its topography and the degree of its hydrophobicity are less significant. Film deposition by physical adsorption is preferable to polymerization on the derivatized surface.     

Sterically Congested Phosphite Ligands: Synthesis,crystallographic characterization,and observation of unprecedented eight-Bond 31P,31P coupling in the 31P-NMR spectra

The synthesis and characterization of 2-{1-{3,5-bis(1,1-dimethylethyl)-2-{[2,4,8,10-tetrakis(1,1-dimethylethyl)dibenzo[d,f][1,3,2]dioxaphosphepin-6-yl]oxy}phenyl}ethyl}-4,6-bis(1,1-dimethylethyl)phenyl diphenyl phosphite ( 6 ) is described. In the ³¹P-NMR spectrum (¹H-decoupled) of 6 , an unprecedented eight-bond P,P coupling of J = 72.8 Hz is observed. In the X-ray crystal structure of 6 , an intramolecular P–P distance of 3.67 Å is found, which is within the sum of the van-der-Waals radii of the P-atoms. The observed intramolecular P–P distance suggests that a through-space coupling mechanism is operative. The solid-state conformation of 6 is compared to the conformation obtained by semi-empirical MO geometry optimizations (PM3 method). The calculated geometry suggests that the solid-state structure is near a true energy minimum, but that crystal-packing forces decrease the intramolecular P–P distance in the solid state. In the absence of crystal-packing forces, however, the collisional and vibrational energy available in solution may lead to the population of states with a shortened intramolecular P–P distance in 6 . The proximity of the P-atoms in 6 is due to restricted conformational freedom resulting from steric congestion within the molecule. The free energy of activation (ΔG* = 10.2 and 10.8 kcal/mol for unequal populations of exchanging conformers) for ring inversion of the dibenzo[d,f][1,3,2]dioxaphosphepin ring in 6 is determined by variable-temperature ³¹P-NMR spectroscopy. Semi-empirical MO calculation on model compounds suggest that the structure of the transition state for ring inversion has the two aryl rings and O-atoms in a common plane, with the P-atom lying above this plane.     

Amperometric determination of hydrogen peroxide with a manganese dioxide film-modified screen printed carbon electrode

A carbon thick film electrode modified with an MnO₂-film is investigated as an amperometric detector for hydrogen peroxide in flow-injection analysis (FIA). At an operating potential of +0.48 V vs. Ag/AgCl catalytic oxidation of the analyte is exploited for amperometric monitoring. Experimental parameters, such as pH of the carrier, working potential, flow rate and injection volume, are optimized. The amperometric signals are linearly proportional to the concentration of H₂O₂ in the range from 0.005 to 10 mg/L, showing a detection limit (3σ) of 2.3 μg/L. The method is applied to the determination of H₂O₂ in rain water and to a simple assay to quantify glucose in human plasma.     

Discriminating the helical forms of peptides by NMR and molecular dynamics simulation

The HNCO NMR pulse sequence was applied to three selectively labeled (15)N and (13)C isotopic homologues of the peptide Ac-WAAAH(AAARA)(3)A-NH(2) to probe directly for hydrogen bonds between residues 8 and 11 (characteristic of a 3(10)-helix), 8 and 12 (alpha-helix), and 8 and 13 (pi-helix). The experiments demonstrate conclusively, and in agreement with circular dichroism studies, that the center of the peptide is alpha-helical; there is no discernible 3(10)- or pi-helix at these specific positions. Molecular dynamics simulations of the preceding peptide and Ac-(AAAAK)(3)A-NH(2) in water using the potential energy parameter set CHARMM22/CMAP correctly yield an alpha-helix, in contrast to simulations with the set CHARMM22, which result in a pi-helix.     

Calculation of the electronic properties of neutral and ionized divalent-metal clusters

The electronic properties of neutral and ionized divalent-metal clusters have been studied using a microscopic theory, which takes into account the interplay between van der Waals (vdW) and covalent bonding in the neutral clusters, and the competition between hole delocalization and polarization energy in the ionized clusters. By calculating the ground-state energies of neutral and ionized Hg _n clusters, we determine the size dependence of the bond character and the ionization potentialI _p (n). For neutral Hg _n clusters we obtain a transition from van der Waals to covalent behaviour at the critical sizen _c ～10–20 atoms. Results forI _p (Hg _n ) withn≤20 are in good agreement with experiments, and suggest that small Hg _n ⁺ clusters can be viewed as consisting of a positive trimer core Hg ₃ ⁺ surrounded byn?3 polarized neutral atoms.