The reactions of carbohydrates with anthraquinones in alkaline pulping processes are reviewed. AQ reacts mainly with the short-lived intermediates that are formed in the degradation reactions of wood polysaccharides. Oxidation of the reducing end groups of polysaccharides to stable aldonic acid end groups is marginal and corresponds to less than 1 % of all reactions of AQ. The stabilization of the polysaccharides may be enhanced by the use of salts of alkaline earth metals which increase the relative oxidation rate of sugar enediols and promote the hydride shift reaction of the intermediate aldos-2-ulose end groups to stable hexonic acid end groups. Analysis of the monomeric carbohydrate-derived oxidation products indicates that hardwood lignin probably contains more structures that react with anthrahydroquinone than does softwood lignin. This difference may partly explain the more facile delignification of hardwoods. 相似文献
Summary The increased carbohydrate yield after NaOH cooking of wood resulting from NO2/O2 pretreatment is related to the oxidation of reducing sugar end groups to aldonic acid groups during both the pretreatment and the subsequent alkali cook. This leads to a suppressed end-wise degradation during the alkali cook, reflected in a lowered formation of 3-deoxyaldonic and 2-C-methylglyceric acid end groups in competing reactions. 相似文献
A Pinus radiata refiner mechanical pulp (RMP) sample and a range of lignin model compounds were treated with a solution of 25% w/w acetyl bromide (AcBr) in acetic acid to assess the reactions which take place during the dissolution of wood with the AcBr solution. The lignin model reactions were also carried out in solutions to which 4% w/w perchloric acid was added. The RMP sample gave a product which contained 9.2% bromine, and was severely degraded to low molecular weight products, the polysaccharides more so than the lignin fraction. The reactions of the lignin model compounds with AcBr included O-acetylation of phenolic and aliphatic hydroxyl groups, cleavage of β-ether bonds, C-acetylation of aromatic rings, particularly in positions para to methoxyl groups, demethylation of aromatic methoxyl groups and probable replacement of benzyl alcohol groups by bromine functions. The reactions were accelerated by perchloric acid, and the rates appeared to decrease in the order O-acetylation π bromine substitution >> β-ether cleavage π C-acetylation > demethylation. It is concluded that dissolution of wood in the AcBr solution is a consequence of depolymerisation of the polysaccharides and lignin, and acetylation to give products which would be soluble in the reaction medium. 相似文献
Gum polysaccharides are one of the most abundant bio‐based polymers. They are generally derived from plants as exudates or from microorganisms and have diverse applications in many industries, especially in the food industries where they are used as emulsifiers and thickeners. In their natural form, gum polysaccharides have poor mechanical and physical properties; therefore, they are frequently modified with various synthetic monomers such as acrylamide and acrylic acid using graft copolymerization. Graft copolymerization is one of the most trusted and widely used synthetic methods for the modification of gum polysaccharides. Gum polysaccharides modified in this way have improved mechanical and physicochemical properties. Furthermore, gum polysaccharides contain a variety of functional groups, for example, carboxylic acid and hydroxyl groups; therefore, they have been used extensively as adsorbents for the removal of different impurities from wastewater such as toxic heavy metal cations and synthetic dyes. Here, the chemical and physical properties of gum polysaccharides, different methods of graft copolymerization, and the use of graft copolymer gum‐polysaccharide‐based hydrogels are reviewed in detail for the removal of toxic heavy metal cations and synthetic dyes from aqueous solutions.
The isolation and purification of polysaccharides extracted from the cones, bark, and needles of Pinus koraiensis (Korean pine) were studied. The amounts of polysaccharides were 42.7%, 53.4%, and 48.4% for cones, bark, and needles, respectively. All these samples contained uronic acid. The total protein and polyphenols were <4.5% for all three samples. With acid hydrolysis, seven polysaccharides were found in different molar ratios in each sample: D-ribose, L-rhamnose, L-arabinose, D-xylose, D-mannose, D-glucose, and D-galactose. The relationships between in vitro antioxidant properties (AOP) of polysaccharides extracted from different parts of the P. koraiensis tree are correlated with physicochemical properties (the amount of neutral sugars, uronic acid, and proteins). Moreover, the pinecone polysaccharides (PKCP) confirmed previously observed beneficial antioxidant capacity with an EC50 of OH radical, ABTS radical scavenging, and reducing power of 6.54, 5.06, and 9.15 mg/mL, respectively. PKCP had the best antioxidant activity among the three samples. 相似文献
Summary Chitosan and four cross-linked amino-starches (CAS) were employed to remove the acid dye acid black 1 (C. I. 20470) from aqueous
solution. The optimum initial pH value is 3.0 and the adsorptions reach equilibrium after 3h. To describe the interactions
of acid black 1 with different amino-polysaccharides, the linearized Langmuir and Freundlich isotherms were tested to fit
the experimental data. The results indicate that the best-fit model is Langmuir isotherm and the mechanism is based on electrostatic
attraction. The adsorption capacity of chitosan is highest amongst the amino-polysaccharides examined. The FT-IR spectra suggest
that the amino groups of polysaccharides are protonated and the acid black 1 molecules were effectively adsorbed. 相似文献
Photosynthetic organisms such as diatoms microalgae provide innovative routes to eco-friendly technologies for environmental pollution bioremediation. Living diatoms are capable to incorporate in vivo a wide variety of chemical species dispersed in seawater, thus being promising candidates for eco-friendly removal of toxic contaminants. However, their exploitation requires immobilization methods that allow to confine microalgae during water treatment. Here we demonstrate that a biofilm of Phaeodactylum tricornutum diatom cells grown on the surface of a glassy substrate bearing boronic acid protruding moieties is stably anchored to the substrate resisting mechanical stress and it is suitable for removal of up to 80 % metal ions (As, Cr, Cu, Zn, Sn, Pb, Sb) in a model polluted water sample. Control experiments also suggest that stabilization of the biofilm adhesion occurs by interaction of boronic acid surface groups of the substrate with the hydroxyl groups of diatoms extracellular polysaccharides. 相似文献
A laboratory trial and a six-year field experiment were carried out to evaluate the changes in the composition of humic substances in a soil amended for six years with urban waste compost (UWC), and to compare the results obtained by FT-IR spectroscopy with empirical humification parameters. The fulvic acid FT-IR spectra showed that amended soils contain a higher concentration of carboxylic and aliphatic groups compared to unamended soil (UNAS). The six-year amended soil (SYAS) also showed a higher content of polysaccharides on FT-IR spectra of both humic and fulvic acids. The polysaccharide increase in the six-year amended soil is attributable to the humification process since polysaccharides were not present in a high quantity in the UWC or laboratory amended soil (LAAS). The humification index and the degree of humification values indicate that the urban waste compost and soils studied can be classified in decreasing order of humification as follows: UNAS > SYAS > LAAS > UWC. This behaviour is the consequence of an increasing presence of the non humified fraction in NaOH extracted organic matter. The carboxylic and aliphatic groups content from FT-IR spectra confirmed this behaviour, thus indicating the validity of the humification parameters used to evaluate the status of the organic matter from refuse and soil. 相似文献
Anthraquinone-1-acetic acid is a less effective delignification catalyst than anthraquinone but it gives an enhanced carbohydrate stabilization by converting reducing sugar end groups more effectively to aldonic acid end groups. This reaction produces the hydroquinone form of the additive which is then easily oxidized by oxygen at 80°C. Oxygen treatment favors the end group stabilization. Depolymerization of the cellulose is suppressed by the presence of magnesium hydroxide but cannot be avoided completely. 相似文献
Water sorbence by saponified polyacrylonitrile-grafted polysaccharides was studied in relation to practical end uses. Graft copolymers prepared from wheat flour, corn flour, cotton wool, and rayon fibers swelled to a gel, exhibiting a 10- to 20-fold increase in sorbency over the starting materials. A further enhanced water capacity was obtained when homopolymer was not removed. Soaking the wheat flour copolymer in salts or dilute mineral acid nullified the enhanced water sorbence, which could be reversible restored by neutralization of acrylic acid functions with alkali. Swelling the copolymer in aqueous D-glucose did not impair its water capacity. The mechanism of swelling to a gel appears to involve electrolyte osmotic pressure generated by a Donnan equilibrium. Grafting starch elevated its heat of water vaporization above that of pure water, and increased its capacity to absorb water from ethanol-water vapor at 40° above that of native starch. At higher temperatures, however, the dehydrating capacity decreased to that of native flour. 相似文献
Determinations of reducing and carboxylic acid end groups in hydrocellulose treated with hot alkali showed that the end-wise degradation proceeded to such an extent that some of the molecules were brought completely into solution. The major carboxylic acid end groups formed in reactions competing with the end-wise degradation were 3-deoxyhexonic and 2-C-methylglyceric acids; but 2-deoxypentonic, 2-C-methylpentonic, and minor amounts of aldonic acids were also formed. The formation of these stable end groups explains the observed increase in number average degree of polymerization during the treatment. The ratio between the number of lost glucose moieties and the number of carboxylic acid groups formed in the solid phase was about 170 and was only slightly affected by the duration of the hot alkali treatment. 相似文献
Four kinds of well defined poly(N-methacryloyl-L-amino acid)s were prepared via reversible addition fragmentation chain transfer polymerization. The effects of molecular structure, molecular weight, and end-group on their responsive properties in water were investigated. We found that the monomer structure is critical for the polymer to exhibit stimuli-responsive properties in water; only polymers derived from aspartic acid showed defined dual thermo- and pH-responsive properties. To study the effects of molecular weight and end group on the lower critical solution temperature behavior of poly(N-methacryloyl-L-β-isopropyl aspartic acid) (PMAIPAC), a series of PMAIPAC homopolymers with controlled molecular weights and narrow polydispersities were prepared and treated with excess radical initiators to give defined end groups. The cloud point of PMAIPAC was found to increase with the increase of solution pH, due to the ionization of carboxylic acid groups, and decrease with the increase of molecular weight. The structure of end groups also affects the cloud point of PMAIPAC particularly for low molecular weight samples at low pH. 相似文献
Changes in the chemical structure of poly(tetrafluoroethylene) (PTFE) induced by electron beam irradiation at room temperature in air have been studied by 19F solid-state NMR and IR spectroscopy. Chain scission associated with the formation of trifluoromethyl (-CF3), carboxylic acid fluoride (-COF) and carboxylic acid (-COOH) end groups was confirmed to be the predominant process under these conditions. The number-average molecular weight of radiation-degraded PTFE as a function of irradiation dose was calculated based on quantitative end group analysis. It strongly decreases with increasing dose to approximately 4000 g/mol at a irradiation dose of 4 MGy. The molar ratio of CF3 end groups to oxygen-containing (-COF, -COOH) end groups was found to depend on the irradiation dose and the irradiation conditions. For low dose level, the molar ratio determined experimentally coincides well with the mechanism proposed for radiation-induced degradation of PTFE. 相似文献