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61.
Sorption of Cu(II) and Cd(II) by extracellular polymeric substances (EPS) from Aspergillus fumigatus
Yurong Yin Yongyou Hu Fen Xiong 《International biodeterioration & biodegradation》2011,65(7):1012-1018
Sorption of Cu(II) and Cd(II) onto the extracellular polymeric substances (EPS) produced by Aspergillus fumigatus was investigated for the initial pH of the solution, EPS concentrations, contact time, NaCl concentration, initial metal ion concentration and the presence of other ions in the solution. The results showed that the adsorption of metal ions was significantly affected by pH, EPS concentrations, initial metal concentration, NaCl concentration and co-ions. The sorption of Cu(II) and Cd(II) increased with increasing pH and initial metal ion concentration but decreased with an increase in the NaCl concentration. The maximum sorption capacities of A. fumigatus EPS calculated from the Langmuir model were 40 mg g−1 EPS and 85.5 mg g−1 EPS for Cu(II) and Cd(II), respectively. The binary metal sorption experiments showed a selective metal binding affinity in the order of Cu(II) > Pb(II) > Cd(II). Both the Freundlich and Langmuir adsorption models described the sorption of Cu(II) and Cd(II) by the EPS of A. fumigatus adequately. Fourier transform infrared spectroscopy (FTIR) analysis revealed that carboxyl, amide and hydroxyl functional groups were mainly correlated with the sorption of Cu(II) and Cd(II). Energy dispersive X-ray (EDX) system analysis revealed that the ion-exchange was an important mechanism involved in the Cu(II) and Cd(II) sorption process taking place on EPS. 相似文献
62.
The toxic effects of lead(II) have been studied in Escherichia coli cells. Using microcalorimetric analysis, it was shown that E. coli growth was inhibited in the presence of Pb2+ resulting from damage to the cell membrane and that Pb2+ takes part in the metabolism of cells. Treatment with lysozyme confirms damage to the cell’s outer membrane. Similarities
between the ionic radii and charge/radius ratio cause Pb(II) to replace Ca(II) at the binding sites of lipopolysacharides,
leading to rupture of protecting areas on the cell’s surface. Consequently, the protection and functionality of outer membrane
is lost, thus becoming the basis for the biological effect of Pb2+ on E. coli. 相似文献
63.
Scanning microcalorimetry has been used to study the high pressure effect on the main transition from the ripple gel P′β phase to the liquid crystal (Lα) phase in DPPC (dipalmitoylphosphatidylcholine). It has been demonstrated that an increase of the pressure by 200 MPa shifts the transition to higher temperatures by 36.4 degrees. The pressure increase does not affect the cooperativity of transition but reduces noticeably its enthalpy. The changes of the molar partial volume, isothermal compressibility as well as volume thermal expansibility during transition in DPPC suspension have been estimated. It has been shown that monovalent ions (Na+, Cl−) in solution slightly affect the main thermodynamic parameters of the transition. Calcium ions significantly decrease distinction in compressibility and thermal expansibility between liquid-crystal and ripple gel phases of lipid suspension, which in its turn reflects less difference in their volume fluctuations. 相似文献
64.
The green alga Chlorella vulgaris has the ability to bind high amounts of uranium(VI) in the pH range from 3 to 6. At pH 3 up to 40% of the uranium are bound
by the algal cells. The uranium removal is almost complete at pH 5 and 6 under the given experimental conditions. Scanning
electron microscopy and laser-induced fluorescence spectroscopy were used to characterize uranyl species formed in the selected
pH range. The micrographs show a regular distribution of U(VI) on the cell surface. Fluorescence spectroscopic investigations
of formed algal uranyl complexes indicate that the binding of U(VI) to carboxyl groups plays a dominating role at pH 3, whereas
a minor impact of organic phosphate compounds on the U(VI) sorption cannot be excluded. In contrast, at pH 5 and 6 the phosphate
groups are mainly responsible for the removal and binding of U(VI) by formation of organic and/or inorganic uranyl phosphates. 相似文献
65.
Král V Mader P Collard R Fábry M Horejsí M Rezácová P Kozísek M Závada J Sedlácek J Rulísek L Brynda J 《Proteins》2008,71(3):1275-1287
Specific antibodies interfere with the function of human tumor-associated carbonic anhydrase IX (CA IX), and show potential as tools for anticancer interventions. In this work, a correlation between structural elements and thermodynamic parameters of the association of antibody fragment Fab M75 to a peptide corresponding to its epitope in the proteoglycan-like domain of CA IX, is presented. Comparisons of the crystal structures of free Fab M75 and its complex with the epitope peptide reveal major readjustments of CDR-H1 and CDR-H3. In contrast, the overall conformations and positions of CDR-H2 and CDR-L2 remain unaltered, and their positively charged residues may thus present a fixed frame for epitope recognition. Adoption of the altered CDR-H3 conformation in the structure of the complex is accompanied by an apparent local stabilization. Analysis of domain mobility with translation-libration-screw (TLS) method shows that librations of the entire heavy chain variable domain (V(H)) decrease and reorient in the complex, which correlates well with participation of the heavy chain in ligand binding. Isothermal titration microcalorimetry (ITC) experiments revealed a highly unfavorable entropy term, which can be attributed mainly to the decrease in the degrees of freedom of the system, the loss of conformational freedom of peptide and partially to a local stabilization of CDR-H3. Moreover, it was observed that one proton is transferred from the environment to the protein-ligand complex upon binding. Molecular dynamics simulations followed by molecular mechanics/generalized Born surface area (MM-GBSA) calculations of the ligand (epitope peptide) binding energy yielded energy values that were in agreement with the ITC measurements and indicated that the charged residues play crucial role in the epitope binding. Theoretical arguments presented in this work indicate that two adjacent arginine residues (ArgH50 and ArgH52) are responsible for the observed proton transfer. 相似文献
66.
Fluorescence and circular dichroism stopped-flow have been widely used to determine the kinetics of protein folding including folding rates and possible folding pathways. Yet, these measurements are not able to provide spatial information of protein folding/unfolding. Especially, conformations of denatured states cannot be elaborated in detail. In this study, we apply the method of fluorescence energy transfer with a stopped-flow technique to study global structural changes of the staphylococcal nuclease (SNase) mutant K45C, where lysine 45 is replaced by cysteine, during folding and unfolding. By labeling the thiol group of cysteine with TNB (5,5'-dithiobis-2-nitrobenzoic acid) as an energy acceptor and the tryptophan at position 140 as a donor, distance changes between the acceptor and the donor during folding and unfolding are measured from the efficiency of energy transfer. Results indicate that the denatured states of SNase are highly compact regardless of how the denatured states (pH-induced or GdmCl-induced) are induced. The range of distance changes between two probes is between 25.6 and 25.4 A while it is 20.4 A for the native state. Furthermore, the folding process consists of three kinetic phases while the unfolding process is a single phase. These observations agree with our previous sequential model: N(0) left arrow over right arrow D(1) left arrow over right arrow D(2) left arrow over right arrow D(3) (Chen et al., J Mol Biol 1991;220:771-778). The efficiency of protein folding may be attributed to initiating the folding process from these compact denatured structures. 相似文献
67.
How are pharmaceutical and personal care products (PPCPs) removed from urban wastewaters? 总被引:5,自引:0,他引:5
Sonia Suárez Marta Carballa Francisco Omil Juan M. Lema 《Reviews in Environmental Science and Biotechnology》2008,7(2):125-138
The presence of bioactive trace pollutants such as pharmaceuticals and ingredients of personal care products (PPCPs) in different
environmental compartments (rivers, lakes, groundwaters, sediments, etc.) is an emerging issue due to the lack of existing
information about the potential impact associated with their occurrence, fate and ecotoxicological effects. Due to the low
PPCP concentrations reported in wastewaters (ppb or ppt) and their complex chemical structure, common technologies used in
sewage and drinking water treatment plants may not be efficient enough to accomplish their complete removal. Information about
physico-chemical characteristics such as acidity, lipophilicity, volatility and sorption potential is a useful tool to understand
the different removal patterns observed. In order to perform an accurate overall mass balance along the different units of
sewage treatment plants, it is necessary to gather information not only about the presence of micropollutants in the aqueous
phase, but also on the fraction sorbed onto solids. Since only some PPCPs are very well eliminated by conventional sewage
treatment configurations, new strategies such as modification of operating conditions (e.g. solids retention time), implementation
of new technologies (e.g. biomembrane reactors) or additional advanced post-treatment steps (e.g. oxidation, adsorption, membranes)
have been suggested for an increased efficiency. 相似文献
68.
69.
限制性条件下药物对细菌抑制作用微量量热法研究 总被引:9,自引:0,他引:9
用微量量热计测定了福氏志贺氏菌(Shipella flexneri)中7株菌(6、2b、3b、sb、la、x、y)在合成药物抑制作用下生长的热谱图,按限制性条件下微生物生长的模型进行了数学处理,得出了比生长速率(μ),由此确定了各细菌比生长速率(μ)与药物浓度?之间的定量关系,求出了比生长速率(μ)为零时的用药浓度,并对该合成药对各细菌的抑菌效果进行了分析. 相似文献
70.
Removal of perfluorooctane sulfonate from aqueous solution by crosslinked chitosan beads: sorption kinetics and uptake mechanism 总被引:3,自引:0,他引:3
The crosslinked chitosan beads were used as an efficient biosorbent to remove perfluorooctane sulfonate (PFOS) from aqueous solution. The chitosan biosorbent had a sorption capacity up to 5.5 mmol/g for PFOS at the equilibrium concentration of 0.33 mmol/L, much higher than some conventional adsorbents. The sorption kinetics indicated that the sorption equilibrium was reached quickly at high pH and low PFOS concentrations, and the adsorbent size also affected the sorption rate to some extent. The double-exponential model described the kinetic data well, and the sorption of PFOS on the chitosan beads was a diffusion-controlled process. Based on the sorption kinetics and adsorbent characterization, the uptake mechanisms including electrostatic and hydrophobic interactions were identified to be responsible for PFOS sorption, and the hemi-micelles and micelles may form in the porous structure due to high PFOS concentrations within the adsorbent, which had the main contribution to the high sorption capacity. 相似文献