NaCl介质中盐浓度、pH对α－Al~2O~3表面相互作用力的影响

利用原子显微镜研究NaCl介质浓度及体pH值对氧化铝表面作用力的影响规律。发现较低的盐浓度下,相互作用表示为长程排斥力,双电层厚度的实际值与理论值较好地吻合,随NaCl介质浓度的提高,双电层压缩长程斥力减弱,测定了pHMH4.0变化到9.67的作用力曲线,发现当pH等于7/90时,两表面的相互作用表现为吸引力,通过恒电荷、恒电位拟合,发现氧化铝的等电点在pH8.2处,与Zeta电位的测定结果相一致。     

Microcalorimetric studies of interactions between proteins and hydrophobic ligands in hydrophobic interaction chromatography: effects of ligand chain length, density and the amount of bound protein

Using isothermal titration calorimetry (ITC), this investigation directly measured the adsorption enthalpies of proteins on various hydrophobic adsorbents. Various amounts of butyl and octyl groups were attached onto CM-Sepharose to form C4 and C8, two types of hydrophobic adsorbents. The adsorption enthalpies of both trypsinogen and alpha-chymotrypsinogen A were measured at 4.0 M NaCl and pH 10.0, in which most ionic interaction was suppressed. The adsorption isotherms of both proteins on various adsorbents were also measured, thus allowing us to calculate the Gibbs free energy and entropy of adsorption. Experimental results indicated that the adsorption of both proteins on butyl-containing adsorbents was exothermic, while their adsorption on octyl ones was endothermic. In addition, binding of both proteins with the butyl ligand is basically an adsorption process, while binding with the octyl ligand is adsorption and partition processes. Moreover, on both butyl or octyl, the adsorption enthalpy became increasingly positive as the ligand density increased, while the adsorption entropy became more positive as the alkyl chain length or density of the adsorbent increased. In addition, ITC was used to measure protein-protein interaction. The adsorption enthalpy of both proteins increased as the amount of bound protein increased, and the enthalpy increase of trypsinogen appeared to be higher than that of alpha-chymotrypsinogen A. This observation implies that protein-protein repulsion was stronger among trypsinogen molecules in the experiments.     

Microcalorimetric studies of the mechanism of interaction between designed peptides and hydrophobic adsorbents

To understand the mechanism of interaction between peptides and peptides with hydrophobic ligands, the oligomers (GWG, GWWG, GWWWG) were designed and synthesized to study adsorption behavior with octyl sepharose and CM-octyl sepharose. By batch equilibrium binding analysis and dilution heat of peptide solution measurement, the binding isotherm and adsorption enthalpy were obtained and the binding thermodynamics parameters were calculated and analyzed. In the isotherm analysis, we reveled that the affinity of GWG for both adsorbents is stronger than that of GWWG and GWWWG. The results demonstrate that the cation-pi interaction between the peptides and the buffer molecules is significant for solutions of peptides with tryptophan residues, and the solvation is competitive with the hydrophobic interaction between the peptides and the hydrophobic ligands. From the dilution heat measurements, we observed an endothermic dilution heat for GWG and exothermic for GWWG and GWWWG. All these results indicate that the increased tryptophan chain length can promote the solvation behavior of the peptides by the peptide-buffer interaction in this buffer system. Comparing the types of ligands reveals that the binding affinities of each peptide for the two adsorbents are similar. However, the mechanism of adsorption for peptides with hydrophobic ligands might be quite different with respect to the binding enthalpy between peptides and adsorbents. The adsorption of the peptides on octyl sepharose is an entropy-driven process for all the peptides. In contrast, the adsorption of CM-octyl sepharose with GWG and GWWG is an enthalpy-driven process, whereas that with GWWWG is entropy-driven. These findings indicate that the amount of tryptophan controls the characteristics of the peptides and the interaction mechanism in the binding procedure. This study of the adsorption mechanism of the designed peptide could provide fundamental information for peptide purification and amino acid residue behavior in peptide drug design.     

Surface interaction forces mediated by poly(N-isopropylacrylamide) (PNIPAM) polymers: effects of concentration and temperature

Total internal reflection microscopy was used to directly measure the interaction potentials between a micron-sized silica sphere and a flat silica surface in the presence of a linear poly(N-isopropylacrylamide) (PNIPAM) aqueous solution. When the PNIPAM concentration was low, no discernible forces were detected. A further increase in PNIPAM concentration resulted in a long-range attraction which was likely due to a combined of the reduced electrostatic interaction between the silica particle and the flat surface after the polymer adsorption and polymer bridges formation. On the other hand, for a fixed PNIPAM concentration, the interaction potential profiles between the particle and flat surface were once again characterized by attraction as temperature was increased. This attractive force can be explained in terms of the conformational changes of PNIPAM chains at the surfaces, which subsequently affected the polymer adsorption and enhanced the segment–segment interaction among the adsorbed polymer chains.     

The effects of NaCl concentration and pH on the stability of hyperthermophilic protein Ssh10b

Background  

Hyperthermophiles constitute a group of microorganisms with an optimum growth temperature of between 80°C and 100°C. Although the molecular underpinnings of protein thermostabilization have been the focus of many theoretical and experimental efforts, the properties leading to the higher denaturation temperature of hyperthermophilic proteins are still controversial. Among the large number of factors identified as responsible for the thermostability of hyperthermophilic proteins, the electrostatic interactions are thought to be a universally important factor.     

Theoretical studies on the interaction mechanisms between tetrachloro-p-benzoquinone and hydrogen peroxide

A detailed knowledge of the initial complexes is crucial for the better understanding of the reaction mechanisms between tetrachloro-p-benzoquinone (TCBQ) and hydrogen peroxide (H₂O₂). In the present study, the interaction modes and interaction mechanisms between TCBQ and H₂O₂ in the absence and presence of one, two, and three water molecules have been systematically investigated employing the B3LYP/6-311++G** level of theory in combination with the atoms in molecules theory and natural bond orbital (NBO) method. It was found that the introduction of water molecules can influence the original interaction modes between TCBQ and H₂O₂ through the formation of the intermolecular H-bonds. The interaction energies between TCBQ and H₂O₂ range from ?0.37 to ?2.75 kcal/mol for four stable complexes, which are smaller than that of the interaction between H₂O₂ and water molecule. Further energy decomposition analyses suggest that the coupling interactions between TCBQ and H₂O₂ are predominated by the electrostatic interactions regardless of the presence or absence of water molecules. In addition, the significant heat released from the interaction process in the presence of water molecules is expected to be favorable for the following reactions involving the production of the hydroxyl radical.     

U(VI) sorption on kaolinite: effects of pH,U(VI) concentration and oxyanions

U(VI) sorption on kaolinite was studied as functions of contact time, pH, U(VI) concentration, solid-to-liquid ratio (m/V) by using a batch experimental method. The effects of sulfate and phosphate on U(VI) sorption were also investigated. It was found that the sorption kinetics of U(VI) can be described by a pseudo-second-order model. Potentiometric titrations at variable ionic strengths indicated that the titration curves of kaolinite were not sensitive to ionic strength, and that the pH of the zero net proton charge (pH_PZNPC) was at 6.9. The sorption of U(VI) on kaolinite increased with pH up to 6.5 and reached a plateau at pH >6.5. The presence of phosphate strongly increased U(VI) sorption especially at pH <5.5, which may be due to formation of ternary surface complexes involving phosphate. In contrast, the presence of sulfate did not cause any apparent effect on U(VI) sorption. A double layer model was used to interpret both results of potentiometric titrations and U(VI) sorption on kaolinite.     

Experimental evidence of the reversibility of the first stage of protein adsorption at a hydrophobic quartz surface near the isoelectric point

The reversibility of the first stage of adsorption of zwitterionic cytochrome c on a hydrophobic quartz surface was investigated using time‐resolved slab optical waveguide (SOWG) absorption spectroscopy. Using a novel prism‐free broadband coupling approach, absorbance data were collected successfully at a 50 ms time interval during the first few seconds after solution–surface contact. Near the isoelectric point where the cytochrome c molecules possess a net charge of zero and hence cannot be influenced by an electric field, the speed at which adsorption proceeded was found to be dependent on cytochrome c concentration as well as on surface hydrophobicity. It was also observed that the degree of protein adsorption increased as the surface hydrophobicity was increased. Within 6 s the adsorption process appeared to be reversible, as revealed by extremely low chi‐squared values when the absorbance data were fitted into the reversible Langmuir‐type kinetic model. The standard Gibbs free energy of adsorption was also calculated from the absorbance data. Copyright © 2003 John Wiley & Sons, Ltd.     

菲咯啉铜切割DNA反应的微量热法研究

利用流动式和间歇式微量热法研究了菲咯啉铜(Ⅱ)-巯基乙醇-O~2体系切割小牛胸腺双链DNA(dsDNA)反应的热力学,确定该DNA断链的总反应为较快的放热反应和焓驱动的反应,但该反应的前期为快速吸热过程,310.15K和pH=7.0时该反应的总摩尔反应焓(Δ~rH~m~,~3)和前期摩尔反应焓(Δ~rH~m~,~1)分别为-35.1和7.29kJ·mol^-^1。同时采用琼脂糖凝胶电泳法观察到了菲咯啉铜(Ⅱ)-巯基乙醇-O~2体系对DNA链的断裂现象。     

Orientation dependence of the isoelectric point of TiO2 (rutile) surfaces

The electroosmotic behavior of the rutile polymorph of titanium dioxide was explored as a function of the crystallographic orientation. Atomic force microscopy (AFM) was employed to make high-resolution force spectroscopy measurements between a silica sphere attached to a traditional, contact-mode AFM cantilever and TiO2(110), TiO2(100), and TiO2(001) surfaces in aqueous solutions. Measurements were taken in multiple solution conditions across a broad range of pH values, and the resultant force-distance curves were used to deduce relative behaviors of each orientation of rutile, with particular interest in changes of the isoelectric point (iep). Differences in the iep as a function of orientation are explained in terms of differences in both the coordination number and density of acidic and basic sites on the surface. The results were supported by angle-resolved X-ray photoelectron spectroscopy (XPS) measurements of a nominal monolayer of palladium metal deposited on each of the three orientations studied. The palladium monolayer served as a means of probing the relative electron affinities of the three surfaces studied, which were exhibited in shifts of the palladium XPS peak that corresponded to differences in the binding energy as a function of the substrate orientation. The correlation between the rutile orientation and the shift in the palladium binding energy corresponded directly to the relationship between the isoelectric point and the orientation, with the surface of lowest isoelectric point exhibiting the highest Pd binding energy.     

Adsorption of UO2 2+ on poly(N,N-diethylacrylamide-co-acrylic acid): effects of pH, ionic strength, initial uranyl concentration, and temperature

We prepared poly(N,N-diethylacrylamide-co-acrylic acid) (P(DEA-co-AA)) microgels which could efficiently remove UO₂ ²⁺ from aqueous solutions. In this study, the effect of adsorption parameters such as pH value, adsorbent dose, shaking time, and temperature has investigated. It is found that the pseudo-second-order model is more suitable for our experiment. The adsorption kinetic data indicated that the chemical adsorption was the swiftness processes, the adsorption equilibrium could be achieved within 30 min. And there are very good correlation coefficients of linearized equations for Langmuir isotherm model, which indicated that the sorption isotherm of the hydrogel for UO₂ ²⁺ can be fitted to the Langmuir isotherm model. The adsorption process was spontaneous (?G ⁰ < 0) and exothermic (?H ⁰ < 0). The adsorbed UO₂ ²⁺ can be desorbed effectively by 0.1 M HNO₃ and the adsorption capacity is not significantly reduced after five cycles. Present study suggests that this P(DEA-co-AA) can be used as a potential adsorbent for sorption UO₂ ²⁺ and also provide a simple, fast separation method for removal of UO₂ ²⁺ ions from aqueous solution.     

Description of the turbidity measurements near the phase transition temperature of poly(N-isopropyl acrylamide) copolymers: the effect of pH, concentration, hydrophilic and hydrophobic content on the turbidity

Absorbance values between 300 and 800 nm of aqueous solutions of poly(N-isopropyl acrylamide-co-itaconic acid-9.80), poly(N-isopropyl acrylamide-co-itaconic acid-52.05) and poly(N-isopropyl acrylamide)s containing Tegomer H-Si 2111 end groups and/or blocks were measured using a Shimadzu 160-A UV-visible spectrometer. Turbidities obtained from these absorbance values were used to interpret the macromolecular phase transition from a hydrophilic to a hydrophobic structure of the polymers. The effects of comonomer type and content, concentration of the solutions, pH and temperature on the coil-globule transition were discussed in terms of turbidity form factor, β related to size and shapes of particles and calculated by using the simplified form of Debye equation.The results presented in this work show that the presence of Tegomer H-Si 2111 (Si containing end groups and/or blocks) or high amount of itaconic acid (IA) in the chains prevent a collapse transition from hydrated extended coils to hydrophobic globules, which aggregate and form a separate phase (β<2). Furthermore, it was observed that in the case of concentrated solutions intermolecular hydrophobic interactions between isopropyl groups overcame the repulsive forces resulting from the ionized carboxylic acid groups of IA or surface active nature of Si containing hydrophobic groups (β>2). This stage of the transition corresponds to macroscopic phase separation after an intramolecular process.     

pH dependence of the interaction between rhodamine B and the water-soluble poly(sodium 4-styrenesulfonate)

The binding of rhodamine B (RB) to the polyanion containing aromatic groups poly(sodium 4-styrenesulfonate) (PSS) is studied by separation and spectroscopic techniques at pH between 2 and 7. Significant binding is found at pH below 5, together with a red-shift of the RB maximum of absorbance to 564 nm, and RB fluorescence quenching. The dependence of the pH is related with protonation of RB molecules. Fluorescence quenching is a consequence of a more hydrophobic environment and may occur on territorially or site-specifically bound molecules, and/or on self-aggregated molecules in a hydrophobic polymer domain. Remarkably, the basicity of RB is increased by the influence of the polymer.     

Rheological characteristics of municipal thickened excess activated sludge (TEAS): impacts of pH,temperature, solid concentration and polymer dose

Rheological characterization of sludge is known to be an essential tool to optimize flow, mixing and other process parameters in wastewater treatment plants. This study deals with the characterization of thickened excess activated sludge in comparison to raw primary sludge and excess activated sludge. The effects of key parameters (total solid concentration, temperature, and pH) on the rheology and flow behavior of thickened excess activated sludge were studied. The rheological investigations were carried out for total solid concentration range of 0.9–3.7 %w/w, temperature range of 23–55 °C, and pH range of 3.6–10.0. Different rheological model equations were fitted to the experimental data. The model equations with better fitting were used to calculate the yield stress, apparent, zero-rate, infinite-rate viscosities, flow consistency index, and flow index. The decrease in concentration from 3.7 to 3.1 %w/w resulted in a drastic reduction of yield stress from 27.6 to 11.0 Pa, while a further reduction of yield stress to 1.3 Pa was observed as solid concentration was reduced to 1.3 %w/w. The viscosity at higher shear rate (>600 s^?1) decreased from 0.05 Pa·s down to 0.008 Pa·s when the total solid concentration was reduced from 3.7 to 0.9 %. Yield stress decreased from 20.1 Pa down to 8.3 Pa for the Bingham plastic model when the temperature was raised from 25 to 55 °C. Activation energy and viscosity also showed decreasing trends with increasing temperature. Yield stress of thickened excess activated sludge increased from a value of 6.0 Pa to 8.3 Pa when the pH was increased from 3.6 to 10.0. The effect of polymer dose on the rheological behavior of the thickening of excess activated sludge was also investigated, and the optimum polymer dosage for enhanced thickener performance was determined to be 1.3 kg/ton DS.     

分子光谱法研究铝酞菁与牛血红蛋白的相互作用

利用紫外可见吸收光谱和荧光光谱研究了在生理pH条件下铝酞菁与牛血红蛋白(BHb)的相互作用.实验结果表明:铝酞菁分子与BHb发生反应生成基态复合物,导致BHb内源荧光的猝灭,该猝灭属于静态猝灭.测定了不同温度下该反应的表观结合常数、结合位点数及结合热力学参数,热力学参数的变化表明铝酞菁与BHb之间以静电和疏水作用力为主;根据Frster能量转移理论,测得供体与受体间结合距离r和能量转移效率E;并用同步荧光光谱法探讨了铝酞菁对BHb构象的影响.     

Small angle neutron scattering (SANS) studies of diffusion in bulk polystyrene near the glass transition temperature (Tg)

Ultraslow diffusion in bulk polymers has been measured by SANS. The experiment begins by measuring scattering from heterogeneous specimens containing domains of protonated-and deuterated-polymers at temperatures far below T_g. The samples are subsequently held [annealed] above T_g for a known time-interval, then cooled below T_g where SANS is measured again. Scattering changes, from before to after annealing, are analysed to obtain diffusion coefficients. The recent Summerfield - Ullman procedure is used to deconvolute portions of the scattering curve that decrease and increase with annealing time. Because of SANS sensitivity to small distances, the method yields D ≈ 10⁻¹⁸ to 10⁻¹⁵ cm²/s after annealing times of 1–24 h. Data analysis is complicated by “smearing effects” which produce apparent Q-dependent diffusion coefficients. Representative experimental results on polystyrene at 108°–130°C are discussed.     

M?ssbauer spectroscopic studies of the interaction between iron(III) and molybdenum(VI) oxides

At 400°C an appreciable interaction between the title oxides is observed, resulting in iron molybdate formation

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400°C .