摘要:

Cα-Oxidation (benzyl alcohol oxidation) is a prominent reaction in the degradation of lignin by white-rot fungi. This study showed that such oxidation markedly retards metabolism of a nonphenolic β-O-4 model compound, 1-(3-methoxy-4-ethoxyphenyl)-2-(o-methoxyphenoxy)propane-1,3-diol, by cultures ofPhanerochaete chrysosporiumBurds. Surprisingly, however, selective chemical Cα-oxidation of spruce ligninsenhancedtheir depolymerization by the cultures. Thus the decrease in intrinsic degradability of substructures is more than compensated by another effect of Cα-oxidation in lignin. One possibility is that the oxidation increases the accessibility of the lignin to enzymes by decreasing its steric complexity. This study also revealed that the β-O-4 model, like lignin in wood, is degraded in part via Cα-oxidation byP.chrysosporium. Reduction of the α-carbonyl groups thus formed does not occur. Addition of L-glutamate to ligninolytic cultures completely suppresses their competence to degrade the model compound, as it does their ability to oxidize lignin to CO2. This result strengthens past evidence indicating that substructure models are metabolized by the same enzyme system as lignin.

ISSN:0277-3813    

DOI:10.1080/02773818408081148

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Extensive loss of anthraquinone (AQ) or the active catalyst anthrahydroquinone (AHQ) from the AQ –- AHQ catalytic cycle has been explained in part by side reactions leading to the reaction product anthrone (anthracen-9-one), followed by subsequent formation of adducts with lignin quinone methides. Degradation of an adduct between anthrone and the quinone methide of guaiacylglycerol-β-guaiacyl ether, under soda pulping conditions, resulted in a complex mixture of products. The mixture included 3-guaiacylbenzanthrone, bianthronyl, bianthrone, guaiacol, AQ,trans-coniferyl alcohol,trans-coniferylaldehyde,cis- andtrans-1-(3-methoxy-4-hydroxyphenyl)-2-(2-methoxyphenoxy)ethene, vanillin, and 2-methoxy-4-vinylphenol. C-13 NMR studies of lignins isolated from soda/AQ spent liquors indicated the presence of residual anthrone adducts and a significant content of chemically attached AQ.

ISSN:0277-3813    

DOI:10.1080/02773818408081149

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The chlorine contents in different morphological regions of chlorinated spruce kraft pulp fibers were determined by the TEM-EDXA technique. Observations were made before and after extraction with aqueous NaOH. The highest chlorine content was found in a spot in the cell comer primary wall. In the primary wall between the cell comers the chlorine content was lower than that at the cell comer but higher than that in the secondary wall. After the extraction stage, there was a low and approximately equal concentration of chlorine in all the morphological regions studied.

ISSN:0277-3813    

DOI:10.1080/02773818408081150

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Spent liquor fractions from soda and soda/anthraquinone cooks of loblolly pine wood meal were examined by C-13 NMR spectroscopy. The material which precipitated from the liquors at pH 7 as well as that remaining in solution were acetylated and fractionated on a styrene-divinylbenzene gel column. This technique was an attempt to simplify spectral interpretation and to elucidate the distribution of anthracenyl structures within the spent liquor components. The NMR spectra of fractions of the precipitated material revealed that anthracenyl structures chemically bound to lignin increased with decreasing molecular weight (MW), whereas, polysaccharide content decreased markedly with decreasing MW. The NMR spectra of the soluble material had no anthracenyl peaks, but did contain a significant peak at 105 ppm. This is in the same location as a predominant peak observed in C-13 NMR spectra of hardwood lignins, and which has been assigned to C2 and C6 of syringyl structures. However, in the present study the 105 ppm peak has been tentatively assigned to a carbohydrate carbon since it is prominent only in carbohydrate-rich fractions. Also, its aliphatic nature was confirmed by double resonance NMR experiments.

ISSN:0277-3813    

DOI:10.1080/02773818408081151

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The hemicellulose content (solubility in 18% NaOH) of a delignified mechanical aspen pulp was lowered from 23.4% to 18.2% by one-hour hydrolysis with xylanase isolated from the fungusSchizophpllum communeby fractional precipitation. After 24 h hydrolysis, the hemicellulose content was reduced further to 12.9%. The predominant hydrolysis products, xylose and xylobiose, confirmed the specificity of hydrolysis. A crude mixture of cellulolytic and hemicellulolytic enzymes from the same microorganism gave glucose as the major hydrolysis product, and a pulp with higher relative hemicellulose content. Xylan-specific hydrolysis of a low-yield sulfite pulp gave only a small decrease in pentosan content.

ISSN:0277-3813    

DOI:10.1080/02773818408081152

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Hemicellulose molecules available for fiber-fiber bonding should also be among those most readily extracted by alkali. With this premise in mind the extraction rates of hemicellulose from chemical pulps were examined and interpreted as being dependent on hemicellulose distribution. Measurements of the rates of extraction of glucuronoxylan and glucomannan from primarily southern pine oxygen pulps showed that the bulk of hemicellulose was not immediately available to extraction. After a few seconds of initial rapid extraction by 6% NaOH, removal rates quickly decreased but extraction continued indefinitely. Adsorbed hemicellulose by comparison was initially more rapidly extracted. About half of the hemicellulose most rapidly extracted from high-yield oxygen pulps was associated with lumens and large pores. The remaining half (perhaps 5% of the xylan and 2–3% of the glucomannan) was estimated to be the maximum amount potentially, but not necessarily, available for fiber-fiber bonding.

ISSN:0277-3813    

DOI:10.1080/02773818408081153

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

When peracetylated wood, prepared in an acetic anhydride-pyridine medium, was saponified and recrystallized, almost no conversion of cellulose I to cellulose II took place. Neither was conversion detected, when thirteen species of wood, differing in density from 0.17 to 0.71, as well as in lignin content from 18.1 to 38.8 %, were treated with 17.5 % aqueous NaOH, followed by recrystallization. The corresponding treatments for cellulose triacetate or cellulose resulted in complete conversion to cellulose II. Partial delignification of wood preceding the alkali-induced mercerization was found to cause partial lattice conversion to cellulose II, and the ratio of lattice conversion (L.C.R.) increased with the degree of delignification. The L.C.R. value reaches slightly more than 50 %, when one third of the lignin is removed, and the removal of about two third of the lignin from wood results in an almost complete conversion. The effect of lignin removal on lattice conversion was similar among the wood species, irrespective of their density and lignin content, Introduction of acyl groups larger than caproyl into wood, followed by saponification and mercerization resulted in a high conversion of cellulose in wood from cellulose I to cellulose II.

ISSN:0277-3813    

DOI:10.1080/02773818408081154

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

This is a scanned image of the original Editorial Board page(s) for this issue.

ISSN:0277-3813    

DOI:10.1080/02773818408081147

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor