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Gabriele E. Schaumann 《植物养料与土壤学杂志》2006,169(2):145-156
This contribution reviews and discusses structural aspects of soil organic matter (SOM) and humic substances (HS) with special respect to the macromolecular and the supramolecular view. It can be concluded that (1) dissolved humic acids behave as supramolecular associations of relatively small molecules with an enormous flexibility of reaction of environmental conditions, (2) multivalent cations may increase the apparent molecular weight by the formation of coordinative crosslinks in dissolved and undissolved natural organic matter (NOM), (3) sorption nonlinearity in solid humic acids and SOM may be due to polymer properties of NOM, (4) sorbates affect sorbent characteristics of SOM, and (5) hysteresis and conditioning effects in SOM can up to now best be explained with the polymer analogy. A distinct polydispersivity of SOM over a wide range of molecular masses is to be assumed. The supramolecular and the macromolecular models were derived from humic acids with different composition and on the basis of different sample states. Although the supramolecular model has not explicitely been shown for unfractionated DOM, the combination of all discussed studies suggests supramolecular as well as macromolecular characteristics of NOM. Neither macromolecules nor small molecules can be fully excluded in solid and dissolved SOM. Microregions with different properties provide different types of sorption sites. SOM is suggested to be regarded as amorphous material. This point of view is not restricted to high molecular masses and may supplement our understanding of SOM by the model of physical aging. 相似文献
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阿片系统是调节机体生理活动的系统之一。根据近几十年进行的调查,阿片被认为在控制家畜和其他种类动物生长中起着重要作用。然而有关阿片对家畜组织重量及组织DNA、RNA和蛋白质影响的研究甚少。阐述了阿片对豚鼠、负鼠以及真螈组织大分子成分的影响。虽然阿片是否影响组织功能尚不清楚,但是阿片可以抑制小白鼠和人类的免疫功能。 相似文献
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采用溶剂提取法从香菇中提取香菇多糖,通过酶解法和Seveg法除去多糖中的蛋白质,得到香菇精多糖。通过超滤分离手段将香菇多糖按照分子量的大小分成4个组分,LE1、LE2、LE3和LE4。将4种香菇多糖以不同重量比添加到烟丝中,分别测量其在30%和80%湿度下的平衡含水率,表征其物理保润性能。结果表明,添加香菇多糖能明显提升烟丝在干燥环境下的平衡含水率,并降低潮湿环境下的平衡含水率。随着香菇多糖分子量的增加,其在潮湿环境下的防潮性能不断提升,而干燥环境下的保湿性能先增加后降低。 相似文献
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两亲性大分子季铵盐对水稻纹枯病菌抑菌活性表征方法研究 总被引:1,自引:0,他引:1
【目的】为两亲性大分子季铵盐对植物病原真菌的抑菌活性表征方法的选择提供参考。【方法】
分别采用生长速率法和菌丝称重法表征一类新型两亲性大分子季铵盐〔聚二甲基硅氧烷 -b- 聚丙烯酸酯季铵盐
嵌段共聚物,PDMS-b-(PDMAEMA-BC),简称 Six-Q5〕、亲水性大分子季铵盐(PQD-BC)和小分子季铵盐(BC)
对水稻纹枯病菌(Rhizoctonia solani)的抑菌活性。【结果】生长速率法可用于 PQD-BC 和 BC 的抑菌活性表征,
但不适合 Six-Q5 的抑菌活性表征;菌丝称重法可用于 3 类季铵盐抑菌活性的表征。PDMS 嵌段长度适中的 Si5-Q5 对 R. solani 的 IC50 与 IC90 分别为 12、59 μg/mL,其抑菌活性与小分子季铵盐相当。【结论】对于两亲性大分子
季铵盐,菌丝称重法较生长速率法更适合其抑菌活性的表征。 相似文献
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Xu Longjun Xian Xuefu Zhang Daijun 《保鲜与加工》1997,(2):69-73
In the light of ultimate analysis data and density of specific gravity liquid, we put forward a formula to calculate the real density of vitrinite, and get a relatively exact computational formula of condensation ring index. The molar fraction of carbon atom ( x C ) could be used to describe the metamorphic degree of coal. Relationship between the macromolecular structure and the probability of coal outburst has been discussed. 相似文献
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Starches from various botanical sources, having different amylose–amylopectin levels, were treated with 95% (v/v) dimethylsulphoxide and then dissolved by microwave heating in a high pressure vessel (MWHPV). This procedure led to an almost complete dissolution of the starch sample when it was subsequently taken up in water. Various treatment times were tested, and optimal conditions corresponded to 35 s heating time in MWHPV (maximum temperature 143 °C). Under these conditions, degradation of the polymers was not noticeable and the degree of solubilisation of starch in the samples was in the range 87 to 100%. High-performance size exclusion chromatography (HPSEC) in tandem with multi-angle laser light scattering and refractive index detection was used to investigate apparent weight-average molar mass (
w) and z-average gyration radius (
G) of the starch components. Apparent
wand
Gvalues for samples with different amylose contents (between ≈0 and 65·8%) were between 2·2±0·2×108and 2·4±0·2×107g/mol and between 250±10 and 163±5 nm, respectively. These values were higher than those reported previously1,2probably due to our more complete but less severe solubilisation procedure. When the heating time was increased from 35 to 90 s (maximum temperature 211°C), the
wand
Gdecreased, demonstrating possible polymer degradation due to temperature. Partial precipitation of high amylose samples after 24 h storage was detected by modifications in chromatograms, compared with freshly prepared samples. 相似文献
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Gabriele E. Schaumann 《植物养料与土壤学杂志》2006,169(2):157-167
Glassy, rubbery, and crystalline phases are representatives of supramolecular structures which strongly differ in order, density, and other characteristics. In this contribution, the amorphous nature of soil organic matter (SOM) is reviewed with respect to the glassy/rubbery model, glass transition mechanisms, interactions of SOM with water, and physical aging. Glass‐transition behavior and physical aging are inherent properties of amorphous solids, and numerous spectroscopic investigations give insights into different domain mobilities of humic substances (HS). The correlation between sorption nonlinearity and glassiness of polymers and HS supports a relation between sorption and amorphicity in Aldrich humic acid. Further evidence is still required for the transfer to soil HS and SOM. Sorption and differential scanning calorimetry (DSC) data suggest a correlation between aromaticity and glassiness in HS, and the available data do currently not allow to decide unambiguously between specific sorption and hole filling as explanation. This needs to be verified in future research. Although parts of the investigations have up to now only been conducted with humic substances, the collectivity of available data give strong support for the glassy/rubbery conception of SOM. They clearly indicate that amorphous characteristics cannot be excluded in SOM. This is further supported by the observation of different types of glass‐transition behavior in samples of whole humous soil. In addition to classical glass transitions in water‐free soil samples, water surprisingly acts in an antagonistic way as short‐term plasticizer and long‐term antiplasticizer in a second, nonclassical transition type. Latter is closely connected with physico‐chemical interactions with water and suggests water bridges between structural elements of SOM (HBCL‐model). The gradual increase of Tg* in SOM indicates physico‐chemical aging processes, which are not restricted to polymers. They may be responsible for contaminant aging, changes in surface properties and increased soil compaction in agricultural soils. 相似文献
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盐渍土壤通常因盐分含量大、pH偏高、结构差、水盐运动强烈等原因,植物难以生长。本研究选择聚丙烯酰胺(Polyacrylamide,PAM)、壳聚糖(Chitosan,CTS)、羟乙基纤维素(Hydroxyethyl Cellulo,HEC)等3种高分子化合物,以土壤表面喷洒高分子化合物溶液成膜的方式,研究了高分子化合物膜对盐渍土壤基本物理性质与水分蒸发的影响,结果表明:本研究选择的3种高分子化合物能够不同程度的降低土壤水分蒸发、提高土壤保水性能和显著抑制土壤盐分的表聚,利用主成分分析进行对比发现:PAM 20 kg/hm2、CTS 80 kg/hm2、HEC 80 kg/hm2的用量下的土壤抑蒸控盐效果最佳,盐渍土表喷洒高分子化合物溶液成膜对盐渍土壤改良利用具有确切的正效应。 相似文献
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