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31.
芳香族化合物是一类具有苯环结构的有机物,它们结构稳定,不易分解,并可通过食物链进行生物富集和生物放大,对生态环境及人类健康造成极大危害。细菌具有超强的分解代谢能力,能降解多环芳烃(polycyclic aromatic hydrocarbons, PAHs)等多种难降解芳香族污染物。吸附和转运是细菌进行芳香族化合物细胞内代谢的前提。虽然芳香族化合物的细菌降解已取得较为显著的研究进展,但吸附和转运机理仍不甚清楚。本文讨论了细菌对芳香族化合物的吸附有积极作用的细胞表面疏水性、生物被膜形成和细菌趋化性等影响因素,总结了FadL家族、TonB依赖性受体蛋白、OmpW家族等外膜转运系统和主要协同转运蛋白超家族(major facilitator superfamily, MFS)转运体、ATP结合盒(ATP-binding cassette, ABC)转运蛋白等内膜转运系统对该类化合物跨膜运输作用,并对跨膜转运机制进行了讨论和阐述,旨在为芳香族污染物的防控和治理提供一定理论参考。 相似文献
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The pollution of heavy metals in soil to the environment is becoming more and more serious, resulting in the reduction of crop production and the occurrence of medical accidents. In order to remove heavy metal ions from soil and reduce the harm of heavy metals to the environment, modified peanut shell was used to adsorb Cr3+ in this article. The effects of different adsorption conditions on the adsorption rate and adsorption capacity of Cr3+ on ZnCl2 modified peanut shell were studied, the best adsorption conditions were explored, and the relationship of kinetics, thermodynamics and adsorption isotherm properties of adsorption process were explored. The results showed that the optimum adsorption pH value, dosage, initial concentration, adsorption temperature and contact time of ZnCl2 modified peanut shell were 2.5, 2.5 g/L, 75 μg/mL, 25 °C and 40 min, respectively. The prepared materials were characterized and analyzed by scanning electron microscope (SEM) and X-ray diffraction (XRD) analyzer. It was concluded that the modified peanut shell had a good adsorption capacity to Cr3+. The kinetic study showed that the adsorption process of Cr3+ on peanut shell modified by zinc chloride was in accordance with the quasi-second-order kinetic model. The adsorption process belonged to exothermic reaction and belonged to spontaneous reaction process. In summary, it is proved that zinc chloride modified peanut shell can efficiently adsorb Cr3+, which can be used for the treatment of heavy metal wastes in industry, which is beneficial to environmental protection and avoid heavy metal pollution. 相似文献
34.
基于渗透理论、马尔柯夫过程理论,采用中性模型方法,建立了3个不同的城郊景观动态模型,模型中分别介入不同自然因子和决策因子.利用模型对研究区景观进行了动态变化模拟.对模拟结果进行了评价,评价方法与指标包括:1)多分辨率拟合分析;2)最近邻概率;3)斑块大小和数目.结果发现,综合介入决策因素和自然因子的模型具有最好的效果. 相似文献
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Equilibria for the adsorption of antibiotics onto neutral polymeric sorbents: Experimental and modeling studies 总被引:1,自引:0,他引:1
The objective of this work was to study the equilibria for adsorption of three antibiotics (penicillin V, tetracycline, and cephalosporin C) from water onto commercially available neutral polymeric sorbents. The pH was observed to be an important factor in adsorption as our results suggest that the neutral forms of penicillin V and cephalosporin C are preferentially adsorbed onto the neutral sorbents. Also, sorbent surface chemistry was observed to be important for adsorption, as the antibiotics adsorbed more favorably (both in terms of affinities and enthalpies) onto the aromatic sorbent as compared to the aliphatic ester sorbent. In addition to these thermodynamic measurements, molecular modeling studies and Monte Carlo simulations suggest that adsorption onto aromatic sorbents may involve specific interactions between the planar regions of the antibiotic molecules and the phenyl rings of the aromatic sorbent. The interaction energies predicted from Monte Carlo simulations were observed to provide qualitative agreement with experimentally determined adsorption affinities. (c) 1995 John Wiley & Sons, Inc. 相似文献
37.
Purification of monoclonal antibodies from whole hybridoma fermentation broth by fluidized bed adsorption 总被引:6,自引:0,他引:6
To achive the coarse purification of a monoclonal antibody from whole hybridoma fermentation broth a fluidized bed cation exchange process was used. The procedure consisted of application of the crude sample and washing of the bed in a fluidized mode and elution in a fixed bed mode. A completely clarified eluate was obtained with purification factors between 4 and 8 and a concentration of the desired product (monoclonal antibody) by a factor of more than 3 was achived. Thus, a combination of the three early steps of the downstream process clarification, concentration and coarse purification was possible. Two different materials were tested: a commercially available agarose-based matrix (Stream-line-SP), and a self-derivatized material based on controlled-pore glass (Bioran). Initial experiments were performed to describe the fluidization of the glass material. Comparison with the agarose material showed several differences, the agarose matrix allowing liquid flow closer to plug flow than the glass material. Increased backmixing in the liquid phase was detected when fluidizing the glass adsorbent compared with the agarose-based matrix. Despite this fact, comparison of the two materials with respect to antibody binding and elution demonstrated a similar performance. (c) 1995 John Wiley & Sons, Inc. 相似文献
38.
Sulfur cycling in forests 总被引:6,自引:5,他引:1
D. W. Johnson 《Biogeochemistry》1984,1(1):29-43
Sulfur is essential for the production of certain amino acids in plants. As amino acid sulfur is the major form of sulfur in trees, there is a strong relationship between organic S and organic N in tree tissue. Sulfur deficiencies occur in parts of southeastern Australia and northwestern North America, remote from pollutant inputs. Since bilogical S requirements of forests are modest (< 5 kg · ha–1 yr–1 for net vegetative increment), however, atmospheric S inputs in polluted regions (10–80 kg · ha–1 yr–1 ) often exceed not only the forest ecosystem S requirement but also its ability to biologically accumulate S. There is some increase in the SO2–
4–S content of forest vegetation in response to elevated atmospheric S inputs, but this capacity is apparently easily saturated. Soil SO2–2
4adsorption is often the dominant feature of S cycling in polluted ecosystems and often accounts for net ecosytem S accumulations.Contribution from a symposium on the role of sulfur in ecosystem processes held August 10, 1983, at the annual meeting of the A.I.B.S., Grand Forks, ND; Myron Mitchell, convenor. 相似文献
39.
Summary Elevating the pH of two extremely acid tropical soils from an initial pH of 4 to 5 with Ca(OH)2 and NaOH solutions resulted in a sharp decrease in urea adsorption. Further increases in pH to 9 caused only slight further decrease in urea adsorption. Ca treatment resulted in slightly higher adsorption than Na treatment over the full range of pH values studied for a clay soil with high smectite content, and for a loam with kaolinite mineralogy below pH 7. Above pH 7 a kaolinitic loamy soil gave slightly higher adsorption with Na treatment than with Ca. 相似文献
40.
Dynamic light scattering has been used to study the temperature dependence of Ca2+-induced fusion of phosphatidylserine vesicles and mixed vesicles containing phosphatidylserine and different phosphatidylcholines. The final vesicle size after Ca2+ and EDTA incubation serves as a measure of the extent of fusion. With phosphatidylserine vesicles, the extent of fusion shows a sharp maximum at an incubation temperature which depends on the Ca2+ concentration between 0.8 and 2 mM. The shift in the fusion peak temperature with Ca2+ concentration is similar to the typical shift in the phase transition temperature with divalent cation concentration in acidic phospholipids. The results suggest a direct correlation between the fusion peak temperature and the phase transition temperature in the presence of Ca2+ prior to fusion. With mixed vesicles containing up to 33% of a phosphatidylcholine in at least 2 mM Ca2+, the extent of fusion as a function of incubation temperature also shows a maximum. The fusion peak temperature is essentially independent of the quantity and type of phosphatidylcholine and the Ca2+ concentration, and identical to that with pure phosphatidylserine in excess Ca2+. The results imply that Ca2+-induced molecular segregation occurs first, and fusion subsequently takes place between pure phosphatidylserine domains. 相似文献