Optimizing Dilute-Acid Pretreatment of Rapeseed Straw for Extraction of Hemicellulose

Biological conversion of biomass into fuels and chemicals requires hydrolysis of the polysaccharide fraction into monomeric sugars prior to fermentation. Hydrolysis can be performed enzymatically or with mineral acids. In this study, dilute sulfuric acid was used as a catalyst for the pretreatment of rapeseed straw. The purpose of this study is to optimize the pretreatment process in a 15-mL bomb tube reactor and investigate the effects of the acid concentration, temperature, and reaction time. These parameters influence hemicellulose removal and production of sugars (xylose, glucose, and arabinose) in the hydrolyzate as well as the formation of by-products (furfural, 5-hydroxymethylfurfural, and acetic acid). Statistical analysis was based on a model composition corresponding to a 3³ orthogonal factorial design and employed the response surface methodology to optimize the pretreatment conditions, aiming to attain maximum xylan, mannan, and galactan (XMG) extraction from hemicellulose of rapeseed straw. The obtained optimum conditions were: H₂SO₄ concentration of 1.76% and temperature of 152.6 °C with a reaction time of 21 min. Under these optimal conditions, 85.5% of the total sugar was recovered after acid hydrolysis (78.9% XMG and 6.6% glucan). The hydrolyzate contained 1.60 g/L glucose, 0.61 g/L arabinose, 10.49 g/L xylose, mannose, and galactose, 0.39 g/L cellobiose, 0.94 g/L fructose, 0.02 g/L 1,6-anhydro-glucose, 1.17 g/L formic acid, 2.94 g/L acetic acid, 0.04 g/L levulinic acid, 0.04 g/L 5-hydroxymethylfurfural, and 0.98 g/L furfural.     

Pre-averaged kernel estimators for the drift function of a diffusion process in the presence of microstructure noise

We consider estimation of the drift function of a stationary diffusion process when we observe high-frequency data with microstructure noise over a long time interval. We propose to estimate the drift function at a point by a Nadaraya–Watson estimator that uses observations that have been pre-averaged to reduce the noise. We give conditions under which our estimator is consistent and asympotically normal. Its rate and asymptotic bias and variance are the same as those without microstructure noise. To use our method in data analysis, we propose a data-based cross-validation method to determine the bandwidth in the Nadaraya–Watson estimator. Via simulation, we study several methods of bandwidth choices, and compare our estimator to several existing estimators. In terms of mean squared error, our new estimator outperforms existing estimators.     

Fucoidans from Brown Seaweeds <Emphasis Type="Italic">Sargassum hornery</Emphasis>, <Emphasis Type="Italic">Eclonia cava</Emphasis>, <Emphasis Type="Italic">Costaria costata</Emphasis>: Structural Characteristics and Anticancer Activity

Fucoidans were isolated by water extraction and ion-exchange chromatography from brown algae Eclonia cava, Sargassum hornery, and Costaria costata collected near of Korean coasts. The structures of fucoidans were investigated. Fucoidan from E. cava was mixture of sulfated rhamnogalactofucan and galactofucan. Fucoidan from C. costata was a sulfated galactofucan. Fucoidan isolated from S. hornery was separated into three fractions: a homofucan sulfate, a homofucan but without sulfate groups, and a sulfated rhamnofucan. The results clearly showed that fucoidans play an inhibitory role in colony formation in human melanoma and colon cancer cells and may be effective antitumor agents.     

Structure-reactivity correlations in nucleophilic substitution reactions of Y-substituted phenyl X-substituted benzoates with anionic and neutral nucleophiles

A kinetic study is reported for the reactions of 4-nitrophenyl X-substituted benzoates (1a-1) and Y-substituted phenyl benzoates (2a-1) with two anionic nucleophiles (OH(-) and CN(-)) and three amines (piperidine, hydrazine, and glycylglycine) in 80 mol% H(2)O-20 mol% dimethyl sulfoxide (DMSO) at 25.0 +/- 0.1 degrees C. Each Hammett plot exhibits two intersecting straight lines for the reactions of 1a-1 with the anionic nucleophiles and piperidine, while the Yukawa-Tsuno plots for the same reactions are linear. The Hammett plots for the reactions of 2a-1 with hydrazine and glycylglycine demonstrate much better linear correlations with sigma(-) constants than with sigma degrees or sigma constants, indicating that the leaving group departure occurs at the rate determining step (RDS). On the contrary, sigma(-) constants result in poorer Hammett correlation than sigma degrees constants for the corresponding reactions with OH(-) and CN(-), indicating that the leaving group departure occurs after the RDS for the reactions with the anionic nucleophiles. The large rho(X) value (1.7 +/- 0.1) obtained for the reactions of 1a-1 with the anionic nucleophiles supports the proposal that the reactions proceed through an addition intermediate with its formation being the RDS.     

Synthesis of Spirocyclic Ethers by Enantioselective Copper‐Catalyzed Carboetherification of Alkenols

Spirocyclic ethers can be found in bioactive compounds. This copper‐catalyzed enantioselective alkene carboetherification provides 5,5‐, 5,6‐ and 6,6‐spirocyclic products containing fully substituted chiral carbon centers with up to 99 % enantiomeric excess. This reaction features the formation of two rings from acyclic substrates, 1,1‐disubstituted alkenols functionalized with either arenes, alkenes, or alkynes, and clearly constitutes a powerful way to synthesize chiral spirocyclic ethers.     

Analysis of linear free-energy relationships combined with activation parameters assigns a concerted mechanism to alkaline hydrolysis of x-substituted phenyl diphenylphosphinates

A kinetic study is reported for alkaline hydrolysis of X‐substituted phenyl diphenylphosphinates ( 1 a – i ). The Brønsted‐type plot for the reactions of 1 a – i is linear over 4.5 pK_a units with β_lg=?0.49, a typical β_lg value for reactions which proceed through a concerted mechanism. The Hammett plots correlated with σ^o and σ^? constants are linear but exhibit many scattered points, while the corresponding Yukawa–Tsuno plot results in excellent linear correlation with ρ=1.42 and r=0.35. The r value of 0.35 implies that leaving‐group departure is partially advanced at the rate‐determining step (RDS). A stepwise mechanism, in which departure of the leaving group from an addition intermediate occurs in the RDS, is excluded since the incoming HO^? ion is much more basic and a poorer nucleofuge than the leaving aryloxide. A dissociative (D_N + A_N) mechanism is also ruled out on the basis of the small β_lg value. As the substituent X in the leaving group changes from H to 4‐NO₂ and 3,4‐(NO₂)₂, ΔH ^≠ decreases from 11.3 kcal mol^?1 to 9.7 and 8.7 kcal mol^?1, respectively, while ΔS ^≠ varies from ?22.6 cal mol^?1 K^?1 to ?21.4 and ?20.2 cal mol^?1 K^?1, respectively. Analysis of LFERs combined with the activation parameters assigns a concerted mechanism to the current alkaline hydrolysis of 1 a – i .     

Aminolysis of Y-substituted phenyl X-substituted cinnamates and benzoates: effect of modification of the nonleaving group from benzoyl to cinnamoyl

A kinetic study is reported for reactions of Y-substituted phenyl X-substituted cinnamates (1a-e and 3a-g) and benzoates (2a-e and 4a-g) with a series of alicyclic secondary amines in 80 mol % H2O/20 mol % DMSO at 25.0 +/- 0.1 degrees C. Reactions of 2,4-dinitrophenyl X-substituted cinnamates (1a-e) and benzoates (2a-e) with amines result in linear Yukawa-Tsuno plots. The rho(X) values are much smaller for the reactions of 1a-e than for those of 2a-e. A distance effect and the nature of the reaction mechanism (i.e., a concerted mechanism for 1a-e) have been suggested to be responsible for the small rho(X) values. The Br?nsted-type plots for the reactions of 2,4-dinitrophenyl X-substituted cinnamates (1a, 1c, and 1e) with amines are curved with a decreasing betanuc value from 0.65 to 0.3-0.4. The reactions of Y-substituted phenyl cinnamates (3a-g) with morpholine also result in a curved Br?nsted plot, while the corresponding reactions of Y-substituted phenyl benzoates (4a-e) exhibit a linear Br?nsted plot. It has been concluded that the curved Br?nsted plots found for the reactions of the cinnamates (1a, 1c, 1e, and 3a-g) are not due to a change in the rate-determining step (RDS) but due to a normal Hammond effect for a concerted mechanism, that is, an earlier transition state (TS) for a more reactive amine or substrate.     

Synthesis and catalytic performance on methanol conversion of NiAPSO-34 crystals (I): effect of preparation factors on the gel formation

In order to synthesize the NiAPSO-34 crystal with a pure CHA structure having a uniform size and stable catalytic activity, factors having influence on the crystallization at gel preparation were investigated. The results showed that the mixing order of starting materials influences on the crystallization rate. The concentration of the template was related to the morphology of crystals and the crystallinity, while the particle size obtained was controlled by the silica source and the amount of nickel. Moreover, it was elucidated that the mixing orders of starting materials influences on the crystal growth rate. Seed crystal addition (SAPO-34; 0.8 μm) and ultrasonic-wave treatment after the gel formation were effective in decreasing smaller particle size and in narrowing the size distribution.     

Synthesis of a Photoaffinity‐Labeled (11Z)‐Retinal: Identification of Retinal/Rhodopsin Cross‐Linked Sites along the Visual‐Transduction Path

The retinal chromophore (11Z)‐3‐diazo‐4‐oxoretinal ( 1 ) with two photo‐labile moieties has been synthesized by semi‐hydrogenation of an 11‐yne precursor with activated Zn in aqueous media. Incorporation of 1 into opsin yielded diazoketo rhodopsin (DK‐Rh), which, upon bleaching, gave rise to intermediates batho‐Rh, lumi‐Rh, meta‐Rh, and meta‐II‐Rh corresponding to those of native Rh but at lower temperatures. Photoaffinity labeling of DK‐Rh and these bleaching intermediates showed that the ionone ring cross‐linked to Trp265 of helix F in DK‐Rh and batho intermediate, and to Ala169 of helix D in lumi, meta‐I, and meta‐II intermediates. These results demonstrate the occurrence of large conformational changes along the visual transduction path, which, in turn, is responsible for activation of the G‐protein.