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1.
2.
Oxygen stable isotope ratios of tree-ring cellulose: the next phase of understanding 总被引:3,自引:0,他引:3
Leonel da Silveira Lobo O'Reilly Sternberg 《The New phytologist》2009,181(3):553-562
Analysis of the oxygen isotope ratio of tree-ring cellulose is a valuable tool that can be used as a paleoclimate proxy. Our ability to use this tool has gone through different phases. The first began in the 1970s with the demonstration of empirical relationships between the oxygen isotope ratio of tree-ring cellulose and climate. These empirical relationships, however, did not provide us with the confidence that they are robust through time, across taxa and across geographical locations. The second phase began with a rudimentary understanding of the physiological and biochemical mechanisms responsible for the oxygen isotope ratios of cellulose, which is necessary to increase the power of this tool. This phase culminated in a mechanistic tree-ring model integrating concepts of physiology and biochemistry in a whole-plant system. This model made several assumptions about leaf water isotopic enrichment and biochemistry which, in the nascent third phase, are now being challenged, with surprising results. These third-phase results suggest that, contrary to the model assumption, leaf temperature across a large latitudinal gradient is remarkably constant and does not follow ambient temperature. Recent findings also indicate that the biochemistry responsible for the incorporation of the cellulose oxygen isotopic signature is not as simple as has been assumed. Interestingly, the results of these challenges have strengthened the tree-ring model. There are several other assumptions that can be investigated which will improve the utility of the tree-ring model. 相似文献
3.
《Biocatalysis and Biotransformation》2013,31(2):260-271
AbstractThe impacts of two hybrid cloned commercial cellulases designed for detergency on cotton fibres were compared. HiCel45 has a family 45 catalytic domain and a fungal cellulose binding module (CBM) from the fungus Humicola insolens. BaCel5 has a family 5 catalytic domain and a fungal CBM from Bacillus spp. BaCel5 bound irreversibly to cellulose under the buffer conditions tested while HiCel45 was found to bind reversibly to cellulose because it showed low adsorption. BaCel5 seems to yield more activity towards cotton than HiCel45 under mild stirring conditions, but under strong mechanical agitation both enzymes produce similar amount of sugars. HiCel45 had a more progressive production of residual reducing ends on the fabric than BaCel5. These studies seem to indicate that HiCel45 is a more cooperative enzyme with detergent processes where high mechanical agitation is needed. 相似文献
4.
5.
Metabolites of corticosteroids that contain the 21-oic acid moiety are found in human urine. The acids from neutral steroids and urinary pigments have been separated by passing the mixture through a column of polyethyleneimine cellulose. The acids adhering to the column are quantitatively eluted with dilute formic acid. The purified preparation is suitable for derivatization and chromatographic analysis. 相似文献
6.
It was demonstrated experimentally that the vapors of a mesophase-generating solvent, i.e., a solvent forming a lyotropic liquid-crystalline phase with a polymer, changed the spatial structure and optical density of natural polysaccharides (cellulose acetates). In this process, the value of specific optical rotation of the polymer modified by the vapors varied in a wide range up to sign inversion. The action of vapors on the polymer follows a peculiar dose-effect pattern, with lower doses producing a stronger effect. Application of this approach to the study into specific structural characteristics of biopolymers, such as DNA, is proposed. 相似文献
7.
8.
The simultaneous action of shear deformation and high pressure (SDHP) creates changes in the structure of wood and its main
components (cellulose, hemicelluloses, lignin). The formation of water and alkali soluble polysaccharides under SDHP action,
proceeds in seconds in the solid state, without the use of any reagents and solvents. Therefore, SDHP seems to be a technologically
safe method and friendly to the environment. The amorphization of cellulose crystallites and depolymerization of cellulose
chains were observed under a wide range of pressures (1–6 GPa), both for cellulose samples and the cellulose part of wood.
Similar depolymerization occurs in the hemicellulose part of wood. The decomposition of polysaccharides under SDHP causes
the formation of the water soluble part, whose content increases with pressure and the applied shear deformation. A maximum
solubility of 40% and 55% was registered at 6 GPa following treatment of cellulose and birch wood samples. A higher output
in the case of wood can be explained by a specific role of lignin under SDHP, which acts as a ‘grinding stone’ during cellulose
and hemicelluloses destruction. As shown by high-performance size exclusion chromatography, the water soluble fraction obtained
from cellulose contained glucose (2.6%), cellobiose (9.6%), cellotriose (16.6%) and other higher water soluble oligomers (71%).
Almost complete dissolution (98%) of the treated cellulose sample can be achieved by extraction with 10% NaOH solution. The
SDHP treated birch wood was subjected to submerged fermentation (with Trichoderma viride), and a 13% output of proteins was
obtained. In this case, the water soluble part played the role of the so called ‘start sugars’. Abbreviations: ASF, alkali
soluble fraction; DP, degree of polymerization; EC, energy consumption; HP, high pressure; LMWS, low molecular weight sugars;
MC, moisture content; MCC, microcrystalline cellulose; SD, shear deformation, SDHP, shear deformation under high pressure;
SS, shear strength; WSF, water soluble fraction
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
9.
《Journal of molecular recognition : JMR》2017,30(9)
Materials with new and improved functionalities can be obtained by modifying cellulose with gold nanoparticles (AuNPs) via the in situ reduction of a gold precursor or the deposition or covalent immobilization of pre‐synthesized AuNPs. Here, we present an alternative biomolecular recognition approach to functionalize cellulose with biotin‐AuNPs that relies on a complex of 2 recognition elements: a ZZ‐CBM3 fusion that combines a carbohydrate‐binding module (CBM) with the ZZ fragment of the staphylococcal protein A and an anti‐biotin antibody. Paper and cellulose microparticles with AuNPs immobilized via the ZZ‐CBM3:anti‐biotin IgG supramolecular complex displayed an intense red color, whereas essentially no color was detected when AuNPs were deposited over the unmodified materials. Scanning electron microscopy analysis revealed a homogeneous distribution of AuNPs when immobilized via ZZ‐CBM3:anti‐biotin IgG complexes and aggregation of AuNPs when deposited over paper, suggesting that color differences are due to interparticle plasmon coupling effects. The approach could be used to functionalize paper substrates and cellulose nanocrystals with AuNPs. More important, however, is the fact that the occurrence of a biomolecular recognition event between the CBM‐immobilized antibody and its specific, AuNP‐conjugated antigen is signaled by red color. This opens up the way for the development of simple and straightforward paper/cellulose‐based tests where detection of a target analyte can be made by direct use of color signaling. 相似文献
10.
Harlan W. Stockman 《Soil & Sediment Contamination》1998,7(5):615-647
The solubility of plutonium was estimated for waste buried at the Greater Confinement Disposal site in Nevada. The EQ3/6 thermochemical database was modified to include recent data on Pu complex formation, and the solubilities of two critical phases (probertite (CaNaB5O9·5H2O), added as a backfill material; and Ca sac-charate) were determined by experiment. Reaction path runs were used to model effects of cellulose degradation, including complexation of actinides by organic acids and carbonate, decay of the complexing agents, and the buildup and diffusive loss of CO2 through the permeable alluvium. For most waste interaction scenarios, long-term (≈103 years) concentrations of Pu in pore waters are ≤10?7 molal and are dominated by carbonate complexes, although organic complexes could dominate in the first ≈103 years. In unusual circumstances, carbonation of buried lithium could produce very high Pu solubilities; however, even in such a system, a slight lowering of the effective redox potential dramatically lowers Pu solubility. A sensitivity analysis suggests that the “base case” calculations are conservative, tending to overestimate long-term solubility, with the system redox and the identity of the organic acids the major sources of uncertainty. 相似文献