Adsorption of anionic and cationic dyes by activated carbons, PVA hydrogels, and PVA/AC composite

The textural and adsorption characteristics of a series of activated carbons (ACs), porous poly(vinyl alcohol) (PVA) gels, and PVA/AC composites were studied using scanning electron microscopy, mercury porosimetry, adsorption of nitrogen (at 77.4 K), cationic methylene blue (MB), anionic methyl orange (MO), and Congo red (CR) from the aqueous solutions. Dye-PVA-AC-water interactions were modeled using the semiempirical quantum chemical method PM6. The percentage of dye removed (C(rem)) by the ACs was close to 100% at an equilibrium concentration (C(eq)) of less than 0.1 mM but decreased with increasing dye concentration. This decrease was stronger at C(eq) of less than 1 mM, and C(rem) was less than 50% at a C(eq) of 10-20 mM. For PVA and the PVA/AC composite containing C-7, the C(rem) values were minimal (<75%). The free energy distribution functions (f(ΔG)) for dye adsorption include one to three peaks in the -ΔG range of 1-60 kJ/mol, depending on the dye concentration range used and the spatial, charge symmetry of the hydrated dye ions and the structural characteristics of the adsorbents. The f(ΔG) shape is most complex for MO with the most asymmetrical geometry and charge distribution and adsorbed at concentrations over a large C(eq) range. For symmetrical CR ions, adsorbed over a narrow C(eq) range, the f(ΔG) plot includes mainly one narrow peak. MB has a minimal molecular size at a planar geometry (especially important for effective adsorption in slit-shaped pores) which explains its greater adsorptive capacity over that of MO or CR. Dye adsorption was greatest for ACs with the largest surface area but as molecular size increases adsorption depends to a greater extent on the pore size distribution in addition to total and nanopore surface areas and pore volume.     

Transient resonance Raman and density functional theory investigation of the chlorine atom/carbon disulfide molecular complex involved in selective alkane photochlorination reactions

The structure and bonding of the chlorine atom/carbon disulfide (CS(2)/Cl) complex involved in selective photochlorination reactions with alkanes was directly probed using transient resonance Raman spectroscopy. The experimental Raman vibrational frequencies were compared to those computed from density functional theory calculations for probable structures of the CS(2)/Cl complex. Our results indicate that the S [double bond] C [double bond] S...Cl complex species is responsible for the approximately 370 nm transient absorption band observed after ultraviolet photolysis of CCl(4) in the presence of CS(2). We discuss the structure and properties of the S [double bond] C [double bond] S...Cl complex and compare them with those for the related benzene/Cl and pyridine/Cl complexes.     

Total synthesis of dysiherbaine

A convergent total synthesis of the marine natural product dysiherbaine was accomplished. The key steps of the synthesis are an alkylation at the gamma-carbon of a protected glutamate with a highly substituted pyran derived from mannose, which was followed by a ring-contraction cascade reaction, which simultaneously gave the tetrasubstituted carbon and the hexahydrofuro[3,2-b]pyran ring system of the natural product.     

Syntheses of 3-Chloro-7-[(Chlorocarbonyl)Methoxy]-4-Methylcoumarin

Two efficient syntheses of 3-chloro-7-[(chlorocarbonyl)methoxy]-4-methylcoumarin are described, one utilizing traditional chemistry starting from 3-chloro-7-hydroxy-4-methylcoumarin, while the other uses a novel reagent, sulfuryl chloride/thionyl chloride, in a one-pot reaction starting from 7-(carboxymethoxy)-4-methylcoumarin.     

Effect of Showerhead Configuration on Coherent Raman Spectroscopically Monitored Pulsed Radio Frequency Plasma Enhanced Chemical Vapor Deposited Silicon Nitride Thin Films

The effect of showerhead design, number of holes and geometry, in a parallel plate reactor was studied by measuring the concentration of silane reactant by coherent anti-Stokes Raman scattering (CARS) spectroscopy as a function of radio frequency (rf) pulse width and peak power during pulsed power plasma enhanced chemical vapor deposition (PECVD) of silicon nitride thin films. Film deposition rate, stress, SiH/NH ratio, and thickness and index of refraction homogeneity were correlated with the change in silane concentration for each of the three head geometries: radial, square, and asymmetrical. The asymmetrical head caused plasma quality problems which affected the films' qualities. The square pattern showed good mixing qualities, but produced a film with high compressive stress. The radial head provided the most homogenous film, with respect to index of refraction and film thickness. With a 10 ms pulse width, however, the radial head plasma acted as a continuous plasma for depletion and stress data. The showerhead geometry affects plasma qualities, like stability and intensity, and reactant gas velocities, which in turn affect the nitride film thickness, nitride composition, and stress.     

Studies on monobactams II. Synthesis and β-lactamase inhibitory activity of 4α-methyl-3-[(thien-2-yl)-methylene]-2-azetidinone-1-sulfonate

Two monobactam derivatives, potassium 4-methyl-(3E)-[(thien-2-yl)methylene]-2-azetidinone-1-sulfonate and its (3Z)-isomer, were prepared and evaluated for their -lactamase inhibitory activities. These compounds were devoid of -lactamase inhibitory activity.SynPhar Laboratories Inc., #2, 4290-91A Street, Edmonton, Alberta T6E 5V2, Canada. Tokushima Research Institute, Taiho Pharmaceutical Co., Ltd., 224-2 Ebisuno Hiraishi, Kawauchi-cho, Tokushima 771-01, Japan. Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1548–1552, November, 1998.     

Synthesis of azepino[3,4b]indoles via the Plancher rearrangement

The reaction of benzyl 3-formylpiperidine-1-carboxylate and aryl hydrazines under standard Fisher Indole conditions followed by reductive work-up affords azepino[3,4b]indoles in moderate to good yields. The products are proposed to be derived via a Plancher rearrangement [(a) Plancher, G. Gazz. Chim. Ital. 1898, 28, II, 374; (b) Plancher, G. Atti. Accad.Lincei1900, 9, 5, 115; (c) Boyd-Barrett, H. S. J. Chem. Soc.1932, 321].     

Shape changes induced by N-terminal platination of ubiquitin by cisplatin

The three-dimensional conformation of a protein is an important property and plays a key role in its biological activity. We show here that ion mobility-mass spectrometry (IM-MS) can be used to detect conformational changes in the protein ubiquitin in the gas phase induced by reaction with the anticancer drug cisplatin. The primary adduct was ubiquitin-{Pt(NH₃)₂} under denaturing conditions. Up to three different conformations appear to be generated upon platination depending on the charge state. The collision cross-sections (Ω) for each conformation indicate that the conformations of the platinated protein are contracted in size compared with unmodified ubiquitin with generally smaller Ω values. Ion mobility-tandem MS allowed determination of the platinum binding site without a requirement for prior Chromatographic separation. A rapid 30-min digestion of cisplatin-modified ubiquitin with trypsin allowed the platination site to be identified as the N-terminal methionine following low-energy collision-induced dissociation (CID) studies of the modified peptide. The data were generated using a Traveling-Wave based ion mobility-MS approach. Such cisplatin-induced shape changes may have a significant effect on its function in vivo. This work highlights the usefulness of the ion-mobility mass spectrometry technique for shedding new light on such protein interactions.     

Molecular associations in acacia gums

The tendency of polysaccharides to associate in aqueous solution has long been recognised. Molecular associations can profoundly affect their performance in a given application due to its influence on the molecular weight, shape and size. This will ultimately determine how the molecules will interact with each other, with other molecules and with water. There are several factors, such as hydrogen bonding, hydrophobic association, ion mediated association, electrostatic interaction, concentration dependence and the presence of proteinaceous components, which affect this behaviour. Our objective is to highlight the role of the proteinaceous component, present in acacia gum, to promote associations when the gum is subjected to various processing treatments such as maturation, spray drying and irradiation. The results demonstrate the ability of the proteinaceous component to promote hydrophobic associations which influence the size and proportion of the arabinogalactan high molecular weight component (AGP). Heat treatment in solid state (maturation) increases the hydrophobic character of the gum and hence its emulsification performance. Spray drying also involves aggregation through hydrophobic association but changes the surface properties of peptide moieties to become more hydrophilic compared to the association promoted by the maturation treatment in the solid state. Irradiation induced cross-linking, in the presence of unsaturated gas, was used to introduce C–C bonds into the carbohydrate moiety and thus confirms the hydrophobic association prompted by the heat used in the maturation and spray drying. This association can be reversed by treatments, such as filtration or high pressure homogenisation. The results reported here reconcile the contradiction about structure of gum arabic proposed by the wattle-blossom and twisted hairy rope models and shows that the AGP fraction is basically an aggregated fraction made up of AG units stabilized by low molecular weight highly proteinaceous components.

An economic and environmental comparison of a biochemical and a thermochemical lignocellulosic ethanol conversion processes

With the world’s focus on rapidly deploying second generation biofuels technologies, there exists today a good deal of interest in how yields, economics, and environmental impacts of the various conversion processes of lignocellulosic biomass to transportation fuels compare. Although there is a good deal of information regarding these conversion processes, this information is typically very difficult to use on a comparison basis because different underlying assumptions, such as feedstock costs, plant size, co-product credits or assumed state of technology, have been utilized. In this study, a rigorous comparison of different biomass to transportation fuels conversion processes was performed with standard underlying economic and environmental assumptions so that exact comparisons can be made. This study looked at promising second-generation conversion processes utilizing biochemical and thermochemical gasification technologies on both a current and an achievable state of technology in 2012. The fundamental finding of this study is that although the biochemical and thermochemical processes to ethanol analyzed have their individual strengths and weaknesses, the two processes have very comparable yields, economics, and environmental impacts. Hence, this study concludes that based on this analysis there is not a distinct economic or environmental impact difference between biochemical and thermochemical gasification processes for second generation ethanol production.