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151.
It is commonly observed that the rate of enzymatic hydrolysis of solid cellulose substrates declines markedly with time. In
this work the mechanism behind the rate reduction was investigated using two dominant cellulases of Trichoderma reesei: exoglucanase Cel7A (formerly known as CBHI) and endoglucanase Cel7B (formerly EGI). Hydrolysis of steam-pretreated spruce
(SPS) was performed with Cel7A and Cel7B alone, and in reconstituted mixtures. Throughout the 48-h hydrolysis, soluble products,
hydrolysis rates, and enzyme adsorption to the substrate were measured. The hydrolysis rate for both enzymes decreases rapidly
with hydrolysis time. Both enzymes adsorbed rapidly to the substrate during hydrolysis. Cel7A and Cel7B cooperate synergistically,
and synergism was approximately constant during the SPS hydrolysis. Thermal instability of the enzymes and product inhibition
was not the main cause of reduced hydrolysis rates. Adding fresh substrate to substrate previously hydrolyzed for 24 h with
Cel7A slightly increased the hydrolysis of SPS; however, the rate increased even more by adding fresh Cel7A. This suggests
that enzymes become inactivated while adsorbed to the substrate and that unproductive binding is the main cause of hydrolysis
rate reduction. The strongest increase in hydrolysis rate was achieved by adding Cel7B. An improved model is proposed that
extends the standard endo-exo synergy model and explains the rapid decrease in hydrolysis rate. It appears that the processive
action of Cel7A becomes hindered by obstacles in the lignocellulose substrate. Obstacles created by disordered cellulose chains
can be removed by the endo activity of Cel7B, which explains some of the observed synergism between Cel7A and Cel7B. The improved
model is supported by adsorption studies during hydrolysis. 相似文献
152.
M. S. Shvartsberg I. D. Ivanchikova S. F. Vasilevsky 《Russian Chemical Bulletin》1998,47(10):1971-1974
I-Acetylenyl-9,10-anthraquinones react with an excess of NH2NH2 at 80–115°C to give a mixture of substituted 7H-dibenzo[de,h]quinolin-7-ones and anthra[9,1-cd]-1,2-diazepin-8-ones. The latter compounds undergo reductive contraction of the sevenmembered ring to give the corresponding
7H-dibenzo[de,h]quinolin-7-ones. Bulky substituents in position 2 of the initial acetylenylanthraquinones prevent the formation of the sevenmembered
heterocycle. A scheme of the cyclocondensation was proposed.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2027–2030, October, 1998. 相似文献
153.
Focant JF Reiner EJ Macpherson K Kolic T Sjödin A Patterson DG Reese SL Dorman FL Cochran J 《Talanta》2004,63(5):1231-1240
Comprehensive two-dimensional gas chromatography with isotope-dilution time-of-flight mass spectrometry (GC × GC-IDTOFMS) was used to measure polychlorinated dibenzo-p-dioxin (PCDD), polychlorinated dibenzofuran (PCDF), and coplanar polychlorinated biphenyl (cPCB) concentrations in ash, sediment, vegetation, and fish samples. The GC × GC capability was achieved by using a quad jet, dual stage, thermal modulator. Zone compression of the GC peaks from modulation resulted in a significant increase of the signal intensity over classical GC-IDTOFMS. The GC × GC column set used an Rtx-Dioxin 2 phase as the first dimension (1D) and an Rtx-500 as the second dimension (2D). The chromatographic separation of the 17 PCDD/Fs and the 4 cPCBs was attained in 1D except for 2,3,7,8-TCDD and CB126 for which deconvoluted ion currents (DIC) were required to be reported separately. The Rtx-500 phase separated the bulk matrix interfering compounds from the target analytes in 2D. The instrumental limit of detection (iLODs) was 0.5 pg for 2,3,7,8-TCDD. The calibration curves showed good correlation coefficients for all the compounds investigated in the concentration range of 0.5–200 pg. GC × GC-IDTOFMS results compared favorably to those from conventional isotope-dilution one-dimensional gas chromatography-high resolution mass spectrometry (GC-IDHRMS). The comprehensive mass analysis of the TOFMS further permitted the identification of other contaminants of concern in the samples. 相似文献
154.
甲醇氨化反应中交联皂石的催化行为 总被引:1,自引:1,他引:1
层柱材料是具有规则孔结构且其表面酸性及孔结构可调变的固体酸催化剂.本文合成了皂石,并用十三聚铝羟基络离子(Al_(13))与其交联,在醇氨化反应中研究了此层柱材料孔结构及表面酸性与催化性能间的关系. 相似文献
155.
The mercury perrhenates with the empirical formulas HgReO4 and Hg2ReO5 were prepared by annealing powdered mixtures of mercury(II)oxide and mercury(II)metaperrhenate Hg(ReO4)2 in sealed silica tubes. Their crystal structures were determined from single-crystal X-ray data. HgReO4 crystallizes dimeric with nearly linear O3Re? O? Hg? Hg? O? ReO3 molecular units and Hg2ReO5 has a solid state structure, where Hg(I) and Hg(II) together with oxygen atoms form 14-membered rings, which are condensed to two-dimensionally infinite polycationic nets of composition (Hg22+ · 2 HgO)n. These nets are separated from each other by tetrahedral ReO4? anions. 相似文献
156.
Virginia Lea Miller Wei-li Lee Nai-Phuan Ong 《Journal of solid state chemistry》2005,178(5):1508-1512
We report the synthesis and elementary properties of the Co7Se8−xSx (x=0-8) and Ni7Se8−xSx (x=0-7) solid solutions. Both systems form a NiAs-type structure with metal vacancies. In general, the lattice parameters decrease with increasing x, but in the Ni7Se8−xSx system c increases on going from x=5 to 7. Magnetic susceptibility measurements show that all samples exhibit temperature-independent paramagnetism from 25-250 K. Samples within the Co7Se8−xSx system, as well as Ni7Se8 and Ni7SeS7, were found to be poor metals with resistivities of ∼0.20 and ∼0.06 mΩ cm at 300 K, respectively. The Sommerfeld constant (γ) was determined from specific heat measurements to be ∼13 mJ/molCoK2 and ∼7 mJ/molNiK2 for Co7Se8−xSx and Ni7Se8−xSx, respectively. 相似文献
157.
Synthesis of 12-deoxyroyleanone, cryptoquinone, 11,14-dihydroxy-8,11,13-abietatrien-7-one, and related derivatives from dehydroabietic acid 总被引:1,自引:0,他引:1
Yoh-ichi Matsushita Yoshihisa Iwakiri Satoru Yoshida Kazuhiro Sugamoto Takanao Matsui 《Tetrahedron letters》2005,46(21):3629-3632
Naturally occurring abietane quinones and hydroquinone, namely, 12-deoxyroyleanone (1a), cryptoquinone (4a), and 11,14-dihydroxyabieta-8,11,13-trien-7-one (5a), together with the epimers of tryptoquinones D (2) and F (3), were first synthesized from dehydroabietic acid (6). 相似文献
158.
Nickel acetate promoted reaction of diethyl acetone-1,3-dicarboxylate with N-cyanobenzamidine led to ethyl 4-amino-6-ethoxycarbonylmethyl-2-phenylpyrimidine-5-carboxylate, upon treatment of which with
RNH2, the corresponding 6-(carbamoylmethyl)pyrimidines were obtained. Cyclization of the latter upon treatment with MeONa afforded
6-R-4-amino-7-hydroxy-2-phenylpyrido[4,3-d]pyrimidin-5(6H)-ones.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2212–2214, November, 2007. 相似文献
159.
Stereochemistry of 7-aryl-1,7,8,8a-tetrahydro-3(2H)-indolizinones was studied by1H and13C NMR. Complete assignment of1H NMR signals and analysis of1H-1H coupling constants were performed using the iterative PANIC program. Values of3
J
6,7,3
J
7,8endo, and4
J
5,7 allow one to unambiguously identify the correspondingexo- andendo-stereoisomers. For stereoisomers with exo-orientation of H(7), complete assignment of13C NMR signals was performed on the basis of analysis of the13C-1H coupling constants using two dimensional heteronuclear shift-correlating spectroscopy.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 591–593, March, 1996. 相似文献
160.
V. V. Bakharev A. A. Ghidaspov D. B. Krivolapov E. V. Mironova I. A. Litvinov 《Chemistry of Heterocyclic Compounds》2006,42(8):1051-1058
2-Amino-4-azido-1,3,5-triazin-6(1H)-ones were synthesized by successive substitution of the trinitromethyl groups in 2-amino-4,6-bis(trinitromethyl)-1,3,5-triazines
under the influence of azide and nitrite ions. Interaction of 2-amino-4-azido-1,3,5-triazin-6(1H)-ones with bases led to the
azido-tetrazole tautomeric conversion give salts of 5-aminotetrazolo[1,5-a]-1,3,5-triazin-7-one.
__________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1211–1219, August, 2006. 相似文献