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51.
Recovering hydrolysis enzymes and/or alternative enzyme addition strategies are two potential mechanisms for reducing the cost during the biochemical conversion of lignocellulosic materials into renewable biofuels and biochemicals. Here, we show that enzymatic hydrolysis of acid-pretreated pine wood with continuous and/or fed-batch enzyme addition improved sugar conversion efficiencies by over sixfold. In addition, specific activity of the hydrolysis enzymes (cellulases, hemicellulases, etc.) increased as a result of continuously washing the residual solids with removal of glucose (avoiding the end product inhibition) and other enzymatic inhibitory compounds (e.g., furfural, hydroxymethyl furfural, organic acids, and phenolics). As part of the continuous hydrolysis, anion exchange resin was tested for its dual application of simultaneous enzyme recovery and removal of potential enzymatic and fermentation inhibitors. Amberlite IRA-96 showed favorable adsorption profiles of inhibitors, especially furfural, hydroxymethyl furfural, and acetic acid with low affinity toward sugars. Affinity of hydrolysis enzymes to adsorb onto the resin allowed for up to 92 % of the enzymatic activity to be recovered using a relatively low-molar NaCl wash solution. Integration of an ion exchange column with enzyme recovery into the proposed fed-batch hydrolysis process can improve the overall biorefinery efficiency and can greatly reduce the production costs of lignocellulosic biorenewable products. Figure
A semicontinuous process for the biochemical production of renewable products using detoxification and fed-batch enzyme addition/recycle can increase enzymatic hydrolysis and fermentation efficiencies. Hydrolysis enzymes, inhibitors, sugars, and water can be separated and utilized as high-value steams within the process 相似文献
52.
Prenyl esters were selectively and efficiently cleaved under slightly acidic reaction conditions using silica-supported sodium hydrogen sulfate as a heterogenous catalyst at room temperature to regenerate the parent carboxylic acids in very high yields. 相似文献
53.
54.
Dawn S Dewal MB Sobransingh D Paderes MC Wibowo AC Smith MD Krause JA Pellechia PJ Shimizu LS 《Journal of the American Chemical Society》2011,133(18):7025-7032
There is much interest in designing molecular sized containers that influence and facilitate chemical reactions within their nanocavities. On top of the advantages of improved yield and selectivity, the studies of reactions in confinement also give important clues that extend our basic understanding of chemical processes. We report here, the synthesis and self-assembly of an expanded bis-urea macrocycle to give crystals with columnar channels. Constructed from two C-shaped phenylethynylene units and two urea groups, the macrocycle affords a large pore with a diameter of ~9 ?. Despite its increased size, the macrocycles assemble into columns with high fidelity to afford porous crystals. The porosity and accessibility of these channels have been demonstrated by gas adsorption studies and by the uptake of coumarin to afford solid inclusion complexes. Upon UV-irradiation, these inclusion complexes facilitate the conversion of coumarin to its anti-head-to-head (HH) photodimer with high selectivity. This is contrary to what is observed upon the solid-state irradiation of coumarin, which affords photodimers with low selectivity and conversion. 相似文献
55.
Sanjiv Arora Mahesh Kumar Mahender Kumar 《Journal of Thermal Analysis and Calorimetry》2012,107(3):1277-1286
Wood, one of the flammable material, was treated with aqueous solution of guanidine nitrate (GUN) and also with small amount
of bases like N,N-dimethylformamide, 4-dimethylaminopyridine, pyridine, and triethylamine in the treating solution. These bases catalyze the
impregnation of GUN as indicated by increase in mass gain percentage, elemental analysis, and scanning electron microscopy.
To study their thermal behavior, dynamic thermogravimetry (TG) and derivative thermogravimetry (DTG) analysis under nitrogen
atmosphere have been applied from ambient temperature to 973 K on all samples, at multiple linear heating rates 2.5, 5, 10,
and 20 K min−1. Non-isothermal, “model free” iso-conversional multiple heating rate methods, Ozawa–Flynn–Wall (O–F–W) and modified Coats–Redfern
are used to calculate activation energy of samples. The activation energy of samples is found in the range 109–208 kJ mol−1. Thermal parameters like overall pyrolysis duration, maximum mass loss rate, corresponding to DTG peak maximum and percentage
char yield calculated at 873 K from TG curves are used to appraise the flammability of samples. Also, flammability of samples
is determined by reliable methods namely limiting oxygen index and underwriters laboratories 94 (UL 94) test. The aforesaid
study indicates that base catalyzed impregnated samples are less flammable than those impregnated with only GUN and untreated
ones. 相似文献
56.
Mahender Singh 《Results in Mathematics》2010,57(1-2):53-67
Let X be a finitistic space having the mod 2 cohomology algebra of the product of two projective spaces. We study free involutions on X and determine the possible mod 2 cohomology algebra of orbit space of any free involution, using the Leray spectral sequence associated to the Borel fibration ${X \hookrightarrow X_{\mathbb{Z}_2} \longrightarrow B_{\mathbb{Z}_2}}$ . We also give an application of our result to show that if X has the mod 2 cohomology algebra of the product of two real projective spaces (respectively, complex projective spaces), then there does not exist any ${\mathbb{Z}_2}$ -equivariant map from ${\mathbb{S}^k \to X}$ for k ≥ 2 (respectively, k ≥ 3), where ${\mathbb{S}^k}$ is equipped with the antipodal involution. 相似文献
57.
A. Mahender Reddy M. S. B. Nayar G. Sudhakar Reddy K. G. Das 《Journal of mass spectrometry : JMS》1982,17(1):42-44
Stereochemical effects were observed in the electron ionization, methane, isobutane and ammonia positive ion chemical ionization and hydroxy negative ion chemical ionization behaviour of some isomeric triaryl nitrocyclohexenes. cis-Eliminations leading to loss of HNO2, H2NO2 and arene were found to be stereochemically preferred in gaseous ions. 相似文献
58.
We report a highly selective 2 + 2 cycloaddition of 2-cyclohexenone in the presence of self-assembled bisurea macrocycles that yields the head-to-tail photodimer. The reaction proceeds with high conversion and with decreased incidence of secondary photorearrangement. Furthermore, the product can be extracted from the assembly, and the solid assembly is readily recovered and reused, much like a zeolite. 相似文献
59.
A. Mahender Reddy Mark L. J. Reimer Karl H. Schram Mario Grifantini Gloria Cristalli 《Journal of heterocyclic chemistry》1990,27(5):1297-1305
The low and high resolution electron ionization mass spectra of 1-deazaadenosine, 3-deazaadenosine and 7-deazaadenosine are reported. Fragmentation pathways and ion structures are proposed with the aid of linked-scan, daughter-ion spectra. Results indicate that the N-3 position of the purine ring serves as an important acceptor site in fragmentation processes involving hydrogen transfer from the sugar to the base. A mixture analysis of the trimethylsilyl derivatives of adenosine, 1-, 3- and 7-deazaadenosine by combined gas chromatography/mass spectrometry is also described. 相似文献
60.
Mahender Reddy MarriArun Kumar Macharla Swamy PerakaNarender Nama 《Tetrahedron letters》2011,52(49):6554-6559
A simple, efficient, mild, and regioselective method for oxyiodination of carbonyl compounds has been reported by using NH4I as the source of iodine and Oxone® as an oxidant. Various carbonyl compounds such as aralkyl ketones, aliphatic ketones (acyclic and cyclic), and β-keto esters proceeded to the respective α-monoiodinated products in moderate to excellent yields. Unsymmetrical aliphatic ketones reacted smoothly yielding a mixture of 1-iodo and 3-iodo ketones with the predominant formation of 1-iodoproduct. 相似文献