Use of Difunctional Compounds During Rapid Steam Hydrolysis (Rash) Pretreatment

Mixed hardwood chips were treated with difunctional compounds as catalysts to study the reaction of wood with steam. The Rapid Steam Hydrolysis (RASH) pretreatment process was used for steam treatment. The difunctional compounds studied were maleic anhydride, phthalic anhydride, isophthalic acid, and terephthalic acid at 1.5% concentration based on dry wood weight. RASH pretreatment was performed for one minute at 180°C, 200°, 220°C, 230°C, 240°C, and 260°C. These compounds strongly modified the RASH pretreated material, especially the physical structure. Overall recovery of the pretreated catalyzed and uncatalyzed solids decreased with an increase in RASH temperatures. Catalyst addition did not make a difference on the recovery of pretreated solids. Cellulose degradation increased with temperature for catalyzed systems. Hemicellulose solubilization and degradation were extremely sensitive to the type of catalyst and RASH temperatures. Almost all of the hemicellulose was lost at higher temperatures. Lignin losses did not appear to be affected by the addition of catalyst except at 260°C. Enzymatic rates were improved by addition of the catalysts, especially at the lower temperatures. The maleic anhydride gave the highest enzymatic rates at all temperatures, and phthalic anhydride gave the second highest. The water solubles generally followed the same trends as the enzymatic hydrolysis rates and increased with the addition of catalysts, especially maleic anhydride.     

When NHC Ligands Make a Difference in Gold Catalysis

Thanks to their unique electronic and steric properties, carbene ligands offer highly valuable features for catalysis, including homogenous gold catalysis. The use of carbene-gold complexes has improved existing reactions, either by modifying reactivity modes or by leading to highly asymmetric processes. These topics will be discussed on the basis of selected examples.     

Optimization of an herbicide release from ethylcellulose microspheres

Summary The herbicide 2,4-D was microencapsulated using ethyl cellulose to develop controlled release formulations that protect it from photodegradation and evaporation and to reduce the environment pollution. Ethyl cellulose microspheres loaded with 2,4-D were prepared by the emulsion solvent-evaporation technique. We have obtained the desired microspheres with higher drug entrapment and encapsulation yield by varying certain conditions as stirring speed, polymer-solvent ratio, drug-polymer ratio, pH of continuous phase and organic phase solvent. The shape and size of microspheres were analysed by scanning electron microscopy. The herbicide release was studied at 25 °C and the release data were analysed according to Fick’s Law. The results demonstrate that we can control the release rate by modifying the process parameters.     

Extrusion of Nanocellulose‐Reinforced Nanocomposites Using the Dispersed Nano‐Objects Protective Encapsulation (DOPE) Process

Cross‐linked alginate capsules a few millimeters in diameter have been formed by immersion in a CaCl₂ solution. When adding cellulose whiskers or microfibrillated cellulose to the aqueous alginate solution, nanocomposite capsules containing 40 wt.% cellulosic nanoparticles were obtained. The morphology and compression strength of these capsules were investigated by microscopic observations and crushing tests, respectively. The capsules were extruded with a thermoplastic polymer. Visual inspection of the ensuing films shows a nonhomogeneous dispersion of the capsules that kept their integrity after extrusion. It results in preliminary disappointing mechanical properties of the composite films. However, further investigation is in progress to optimize this simple and ecofriendly process.

     

Short poly(phenylene vinylene) chains grafted poly(organophosphazene)

Brominated poly(bis(4-methylphenoxyphosphazene) was allowed to react with 1,4-bischloromethylbenzene or 1,4-bischloromethyl-2,5-dimethoxybenzene in solution using phase transfer catalyst or potassium t-butoxide. Poly(p-phenylene vinylene) or poly(2,5-methoxy-1,4-phenylene vinylene) grafted organophosphazene copolymers were obtained. The UV-Vis absorption, photoluminescent, and thermal properties of the copolymers were measured. The copolymers are complete soluble in common organic solvents and fluoresce in the blue color range. The copolymers were used to build a series of organic light emitting diode (OLED). Only weak to nominated intensities with emission color from blue to red were obtained. The photoluminescent and electroluminescent (EL) spectra indicated there is a distribution in the PPV conjugated length. The compositions of the copolymers before and after the graft reaction were analyzed using NMR.     

Diffusion in porous silicon: effects on the reactivity of alkenes and electrochemistry of alkylated porous silicon

Alkenes are known to react with hydrogen-terminated silicon surfaces to produce robust organic monolayers that are attached to the surface via covalent SiC bonds. In this report we investigate the dependence of the rate of alkylation of porous silicon samples on the reaction time using photochemical initiation. The kinetics of the photochemical alkylation of hydrogen-terminated porous silicon by undec-1-ene in toluene were observed to be pseudo first order, however the apparent rate constant decreased as the concentration of undec-1-ene increased. This behaviour is opposite to what would be expected if the rate-limiting process was an elementary chemical reaction step involving the alkene. Instead, it suggests that transport of the alkene to reactive sites and in the correct orientation is the rate-limiting step. Comparison of the rates of alkylation of porous silicon by undec-1-ene and dimethoxytrityl (DMT)-undecenol is consistent with such an interpretation as the bulky DMT headgroup gives a lower rate of alkylation. The diffusion of some simple redox-active probe molecules in porous silicon was investigated using a scanning electrochemical microscope (SECM). The probe molecules are converted at diffusion-controlled rate at an inlaid disk ultramicroelectrode (UME) consisting of the cross-section of a microwire sealed in glass. If the microelectrode is placed a short distance above the porous silicon, the microelectrode current depends on kinetics of the electrochemical reactions at the porous silicon and the mass transport properties within the open thin layer cell formed by the microelectrode and the alkylated porous silicon. In order to differentiate the effects of finite heterogeneous kinetics at silicon from diffusion limitations, current-distance curves were fitted over a wide range of applied potentials (on the Si) and it was observed that the diffusion coefficient in the porous layer was strongly anisotropic. The measured diffusion rates are comparable to those in bulk water along the pores, but with negligible diffusion between pores. This indicates that few pore-pore interconnections exist in the porous silicon.     

Silphinene Sesquiterpenes as Model Insect Antifeedants

Silphinene sesquiterpenes are established chrysomelid antifeedants. In this work, nine silphinene analogs, 11-acetoxy-5-angeloyloxysilphinen-3-one (1), 11-acetoxy-5-tigloyloxysilphinen-3-one (2), 11-acetoxy-5-iso- butyryloxysilphinen-3-one (3), 11-hydroxy-5-angeloyloxysilphinen-3-one (4), 11,5-dihydroxysilphinen-3-one (5), 11,5-diacetoxysilphinen-3-one (6), 5,11-diisobutyryloxysilphinen-3-one (7), silphinen-3,5,11-trione (8), and O-methyl-5-epicantabrenolic acid methyl ester (10), and a presilphiperfolane sesquiterpene (9) were tested against several divergent insect species, including the lepidopteran Spodoptera littoralis, the chrysomelid Leptinotarsa decemlineata, and five aphid species, and their antifeedant effects were compared with those of picrotoxinin, a GABA-antagonist, and thymol, an allosteric modulator for insect GABA receptors. All insects tested responded to at least one silphinene analog and/or GABA antagonist. Compound 3 and thymol were effective antifeedants against all species tested except S. littoralis, with varying potencies according to their feeding ecologies. The toxicity of these compounds was species-dependent and did not correlate with their antifeedant effect.