Evaluation of the interaction of propranolol with 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) liposomes: the partitioning model

The sorption behavior of the amine containing beta-receptor blocking agent propranolol (Ppn) in 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) vesicles was investigated. Both protonated and unprotonated Ppn were measured in the continuous phase after removal of the vesicles containing sorbed Ppn by centrifugation. In contrast, by analyzing the surface charge density, deduced from electrophoretic mobility measurements, only the sorbed protonated Ppn was determined. A partitioning model was used to describe the sorption behavior. Sensitivity analysis revealed that sufficiently reliable and independent parameters were obtained. The partition coefficient of the unprotonated Ppn was about 22 times higher than that of the protonated analogue. Statistical analysis revealed a significant increase in the intrinsic partition coefficients of both Ppn analogues with an increase in the salt concentration.     

Dual Reactive Domain Model for Sorption of Aqueous Organics by Wood Fiber

An experimental study of 2,4,5-trichlorophenol (2,4,5-TCP) sorption to kraft papermaking fiber demonstrates that the dual reactive domain model (DRDM) effectively characterizes the process over a broad concentration region. Isotherm data were deconvoluted into linear partitioning and nonlinear adsorption contributions in accordance with the model demonstrating the importance of both mechanisms to the overall process. DRDM accurately fit concentration-dependent distribution coefficient, K(d)(C), data that could not be characterized with the Freundlich or Langmuir equations, and the model predicts the asymptotic movement toward a limiting K(d)(C) value at high solute or cosolute concentrations observed in experiments. Competitive effects were accounted for by modifying the adsorption portion of the model. With its limitations understood, the extended Langmuir equation was utilized and provided an effective fit of data. Langmuir fitting parameters for competitive data with five different n-alcohol homologs allowed estimates of free energy values per methylene linkage, which were in agreement with previously reported values. Also obtained from competitive data were relative sorption values for various benzene analogs, indicating that interactions in addition to those stemming from solute hydrophobicity often contribute in driving the overall sorption process. These results have implications for papermaking given the ubiquitous nature and importance of sorption in the process. Copyright 2001 Academic Press.     

Sorption of aluminate from alkaline solutions on D-403 anion exchanger

The sorption of aluminate from alkaline solutions on D-403 anion exchanger is studied. The sorption isotherm is described by the Langmuir and Freindlich classical equations and the Redlich-Peterson generalized equation. Thermodynamic parameters of sorption are determined using the Langmuir equation, modified to describe ion-exchange eqiulibria. A method for determining the type of the sorbed ion in the solid phases is proposed.     

Characteristics of phenol and chlorinated phenols sorption onto surfactant-modified bentonite

Surfactant-modified bentonite was synthesized by replacing adsorbed Na+ with long-chain alkyl quaternary ammonium cation, hexadecyltrimethylammonium bromide (HDTMAB). The sorption isotherms of phenol, p-chlorophenol, and 2,4-dichlorophenol were modeled according to the Langmuir and Freundlich equations. The Langmuir isotherm was found to describe the equilibrium adsorption data well. The mechanisms and characteristics of sorption of these ionizable organic contaminants onto surfactant-modified bentonite from water were investigated systematically and described quantitatively. The sorption properties are affected by the treatment conditions, such as amount of organobentonite, and the properties of organic compounds. Results indicated that adsorption of phenols from water was in proportion to their hydrophobicities, which increased with chlorine addition (phenol相似文献   

Sorption and diffusion of a tribasic acid dye in nylon 6 membrane in the presence of NaCl

Measurements of sorption and diffusion of a tribasic acid dye in nylon 6 membranes in the presence of NaCl are reported and critically analyzed by the dual-mode sorption and diffusion models consisting of either simple partition plus ion exchange, or simple partition plus “Langmuir” modes. It is shown that the former treatment, which is the physically more realistic one, also provides a generally better fit to the data.     

Analysis of hydrocarbon gas sorption and transport in ethyl cellulose using the dual sorption/partial immobilization models

Low pressure sorption and transport data reported by Barrer et al. [1] for various C₄ and C₅ hydrocarbons in ethyl cellulose are analyzed in terms of current models of sorption and transport in glassy polymers. The popular dual sorption model, which was first qualitatively justified by these investigators, is used to estimate the frozen free volume fraction in the polymer which can accommodate Langmuir sorption. New CO₂ sorption data in ethyl cellulose are also presented and shown to be consistent with the dual sorption model and the frozen free volume fraction estimated from the hydrocarbon sorption. p]Transport of the hydrocarbons in ethyl cellulose is adequately described in terms of the partial immobilization model which attributes mobilities to each of the two sorbed species. The ratio of the mobility of the Langmuir species to that of the Henry's law species was found to be considerably less than unity for all of the gases.     

Mechanism of sorption of phenols from aqueous solutions onto surfactant-modified montmorillonite

Equilibrium and kinetic studies on the sorption of phenol, m-nitrophenol (m-NP), and o-cresol from water onto montmorillonite modified with cetyltrimethylammounium bromide (CTAB) were conducted. Experiments were carried out as a function of solution pH, sorbate concentration, and temperature (25-55 degrees C). It was shown that the sorption capacity decreased in the order phenol>o-cresol>m-NP. The Langmuir, dual-mode sorption, and Redlich-Peterson models were tested to fit the sorption isotherms of single-solute systems, whereas the Langmuir competitive model was used to describe bisolute sorption equilibria. Thermodynamic parameters (DeltaH degrees and DeltaS degrees ) and the mean free energy (E) for the sorption of phenols were determined from the temperature dependence of the distribution constant and the Dubinin-Radushkevick equation, respectively. A simplified kinetic model was proposed to confirm the sorption mechanism.     

Sorption of selenite onto chlorite considering mineral dissolution

In this study we investigated the sorption of selenite (SeO₃ ^2?) onto chlorite as a function of Se(IV) concentration, pH, and ionic strength. The sorption isotherm of Se(IV) onto chlorite was successfully presented by both the Langmuir isotherm and Tempkin equation although the Langmuir isotherm is somewhat better than the Tempkin equation. The sorption of Se(IV) onto chlorite was maintained to be constant at an acidic pH region, while the sorption decreased with an increasing pH at neutral and alkaline pH regions. However, the Se(IV) sorption onto chlorite was independent of the ionic strength of NaClO₄ solution. The amount of Se(IV) sorbed onto chlorite was significantly low compared to those of iron oxides such as apatite, goethite, hematite, and magnetite because of the lower content of Fe. We also investigated the effect of Fe(II) ions dissolved from chlorite on the Se(IV) sorption as a function of contact time. The chemical oxidation states of selenium sorbed onto chlorite surface were identified using X-ray absorption near edge structure (XANES) at the Pohang synchrotron light source. The amount of Fe(II) dissolved was increased by the contact time of 28 days but decreased after 28–56 days although the amount of dissolved Fe(II) ions was significantly small. This decrease of the dissolved Fe(II) may be due to the formation of Fe-oxyhydroxides such as ferrihydrite. The results of XANES measurements also showed that the Se(IV) sorbed onto chlorite was not reduced into Se(0) or Se(-II) even in the presence of Fe(II) ions in the solution because of the low Fe content of the chlorite although the mechanism was not clearly understood.     

On pressure dependence of the parameters of the dual-mode sorption model

Sensitivity of the parameters of the dual-mode sorption (DMS) model on the pressure range, in which sorption of gases in polymers have been studied, was analyzed. Different “gas-polymer” systems were considered but the most detailed analysis was performed for sorption of argon and nitrogen in poly[5,5-difluoro-6,6-bis(trifluoromethyl)] norbornene and polysulfone. It was shown that the model parameters depend upon the range of gas pressure studied. Expanding of the pressure range (0-p_i) results in an increase in the Langmuir adsorption capacity C′_H and in reduction of Henry's law solubility coefficient k_D and Langmuir affinity parameter b. These behaviors does not depend on a choice of an experimental apparatus or software and procedure of nonlinear least squares treatment of the data. As statistical analysis indicated, a systematic error of the measurement cannot call forth the observed dependencies of the model parameters. Different physical reasons of these behaviors were considered, among them: the pressure dependence of the affinity parameter, and the dilation of a polymer. The results obtained showed that although the DMS model, as a rule, gives an excellent fit of the experimental curves, and, hence, can be used as a form of compact storage of information on gas sorption in polymers, one should be careful in using it outside the pressure range in which its parameters have been determined. © 1996 John Wiley & Sons, Inc.     

Evaluation of Dry Protonated Calcium Alginate Beads for Biosorption Applications and Studies of Lead Uptake

Alginate polysaccharide is a promising biosorbent for metal uptake. Dry protonated calcium alginate beads for biosorption applications were prepared, briefly characterized and tested for lead uptake. Several advantages of this biosorbent are reported and discussed in comparison with other alginate-based sorbents. The alginate beads contained 4.7 mmol/g of COOH groups, which suffered hydrolysis near pH 4. The Weber and Morris model, applied to kinetic results of lead uptake, showed that intraparticle diffusion was the rate-controlling step in lead sorption by dry alginate beads. Equilibrium experiments were performed and the data were fitted with different isotherm models. The Langmuir equation was the most adequate to model lead sorption. The maximum uptake capacity (q _max) was estimated as 339 mg/g and the Langmuir constant (b) as 0.84 l/mg. These values were compared with that of other sorbents found in the literature, indicating that dry protonated calcium alginate beads are among the best biosorbents for the treatment and recovery of heavy metals from aqueous streams.     

Equilibrium sorption of heavy metals and phosphate from single- and binary-sorbate solutions on goethite

The amounts of Cu(II), Zn(II), and phosphate sorbed from single- and binary-sorbate systems on goethite (alpha-FeOOH) were measured. Experiments were carried out as a function of equilibrium pH (2-7), sorbate concentration (0.21-1.57 mM), and temperature (15-35 degrees C). The aqueous phase contained 0.1 M NaNO3 to maintain ionic strength constant. A convenient method was used to obtain sorption isotherms of single Cu(II), Zn(II), and phosphate at a fixed equilibrium pH, which could be well described by the Langmuir equation. Thermodynamic parameters for the sorption of single Cu(II) and phosphate including the free energies, isosteric enthalpies, and entropies were determined. In contrast to the single-sorbate systems, the sorption of metals was inhibited in the binary Cu(II)-Zn(II) system, whereas the sorption of both sorbates was enhanced in the binary Cu(II)-phosphate system under the conditions studied. The validity of the Langmuir competitive model for the prediction of the sorption isotherms in a binary Cu(II)-Zn(II) system was also discussed.     

Sorption of nitroaromatic compounds to synthesized organoclays

This project quantifies the ability of seven engineered organoclays to sorb TNT and two of its reduction products: 2-amino-4,6-dinitrotoluene (2-A-4,6-DNT) and 4-amino-2,6-dinitrotoluene (4-A-2,6-DNT). The organoclays used in the TNT sorption studies were synthesized in the laboratory by combining bentonite with benzyltriethylammonium chloride (BTEA) at 50, 75, and 100% of the bentonite's cation exchange capacity and with hexadecyltrimethylammonium bromide (HDTMA) at 25, 50, 75, and 100% of the bentonite's cation exchange capacity. For sorption of 2-A-4,6-DNT and 4-A-2,6-DNT, two organoclays were tested: BTEA at 50% CEC and HDTMA at 75% CEC. Sorption data with HDTMA organoclay and TNT were fit to linear isotherms and demonstrated that the clay's sorptive capacity increased as the amount of total organic carbon exchanged onto the clay increased. Sorption data with BTEA organoclay and TNT were fit to Langmuir isotherms; however, the clay's sorptive capacity increased as the amount of total organic carbon sorbed to the clay's surface was decreased. Sorption behavior for TNT reduction products 2-A-4,6-DNT and 4-A-2,6-DNT to one HDTMA organoclay and one BTEA organoclay demonstrated that HDTMA organoclay at 10.3% total organic carbon was a more effective sorbent than BTEA organoclay at 5.2% total organic carbon.     

Carbon dioxide sorption and transport in polycarbonate

The solubility, permeability, and diffusion time lag for carbon dioxide in polycarbonate are reported at 35°C for pressures ranging from 1 atm to 23 atm. The solubility data are very well described by the dual sorption mechanism model, Henry's law plus Langmuir adsorption, proposed for glassy polymers. Both the permeability and time lag decrease with increased CO₂ pressure. These observations are not consistent with the proposal that CO₂ sorbed by the Langmuir contribution is totally immobilized; however, all of the results are entirely consistent with an extension of this proposal which considers partial immobilization. The data have been quantitatively analyzed in terms of this partial immobilization model, and the results suggest for polycarbonate at 35°C that the CC₂ sorbed by the Langmuir portion of the isotherm behaves as if it has only about 10% of the mobility of the gas sorbed by the Henry's law part of the isotherm. The results have also been interpreted in terms of a concentration-dependent diffusion coefficient which is shown to be mathematically equivalent to the partial immobilization model. The latter model was also formulated in thermodynamic terms, whereby fugacity was used rather than pressure, and diffusion coefficients were defined in terms of chemical potential gradients rather than concentration, but the consequences of these changes proved to be minor and no better. The significance of these observations and their interpretation is discussed.     

基于非线性拟合的污泥衍生吸附剂对铅子等温吸附特性研究

利用城市污水厂污泥制取污泥衍生吸附剂，对溶液中铅离子进行吸附实验，研究一定条件下的等温吸附特性。利用线性拟合和非线性拟合两种方法对等温吸附方程进行模拟，得到非线性拟合求得的模型参数比较可靠，同时得到Langmuir模型比Freundlich方程更适合于描述铅离子在污泥衍生吸附剂表面上的吸附行为。     

超积累植物李氏禾叶细胞干粉对Cr(VI)的吸附特性研究

借助拟合吸附动力学和等温热力学方程, 研究了湿生超积累植物李氏禾叶细胞干粉对Cr(VI)的吸附性能. 考察了pH值、吸附时间等多种因素对吸附性能的影响; 利用扫描电镜(SEM), X射线能谱(EDS)对李氏禾干粉表面形貌及元素分布进行了表征. 结果表明, 该吸附是单分子吸附的伪二级动力学过程, 吸附过程包含两个步骤: Cr(VI)离子通过静电作用富集在干粉材料表面, 随后干粉表面存在的功能配位官能团会与Cr(VI)发生化学作用. 结合红外光谱图发现对铬起吸附作用的主要是含O, N功能原子的配位官能团, 并且不同功能原子与Cr(VI)的作用方式不同.     

Comparison of Linear and Nonlinear Forms of Isotherm Models for Strontium Sorption on a Sodium Bentonite

Sorption on bentonite will play an important role in retarding the migration of radionuclides from a waste repository. Bentonite is characterized by low permeability, water swelling capability and excellent sorption potential for cationic radionuclides. To correctly assess the sorption potential of radionuclides on bentonite is essential for the development of predictive migration models. The sorption isotherm model is usually used to describe the sorption behavior and assess the sorption potential of radionuclides on bentonite. However, there are few studies to investigate the feasibility of isotherm models for the sorption of radionuclides on bentonite. Thus, in this study, we compared the goodness-of-fit of linear and nonlinear forms of two common isotherm models, Langmuir and Freundlich equations. The experimental sorption isotherms of strontium (Sr) on Wyoming bentonite, MX-80, were used for illustration. The results showed that the nonlinear forms of Langmuir and Freundlich isotherm models are more suitable for fitting the experimental sorption isotherms of Sr on MX-80 than are the linear forms. Thus, the nonlinear forms of isotherm models should be primarily adopted to fit experimental isotherms. On the other hand, we also found that the goodness-of-fit of Langmuir model is better than that of Freundlich model. Moreover, based on the theoretical assumptions of Langmuir isotherm model, the parameters M and K _L represent the sorption capacity and affinity, respectively. One can use the values of M and K _L , obtained from fitting the experimental isotherms, to assess the sorption potential of radionuclides in bentonite. Thus, we suggested that the Langmuir isotherm model is more useful for investigating the sorption behavior of radionuclides on bentonite.     

自然水体中3种固相物质吸附有机氯农药的动力学特征

研究了自然水体中生物膜、 悬浮颗粒物和表层沉积物3种典型固相物质对有机氯农药的吸附动力学特征. 研究结果表明, 有机氯农药在3种固相物质上的吸附动力学过程可分为快吸附阶段和慢吸附阶段. 准二级动力学模型较好地描述了三者对有机氯农药的吸附动力学过程. 吸附平衡时, 3种固相物质对有机氯农药吸附量的大小与它们的有机质含量顺序一致, 即, 生物膜>悬浮颗粒物>表层沉积物; 而在吸附初期阶段, 有机质含量最低的表层沉积物对有机氯农药的吸附速率最快, 吸附量的波动变化幅度最大, 其次为悬浮颗粒物和生物膜.     

Absorption studies of neutral retinal Schiff base chromophores

The neutral retinal Schiff base is connected to opsin in UV sensing pigments and in the blue-shifted meta-II signaling state of the rhodopsin photocycle. We have designed and synthesized two model systems for this neutral chromophore and have measured their gas-phase absorption spectra in the electrostatic storage ring ELISA with a photofragmentation technique. By comparison to the absorption spectrum of the protonated retinal Schiff base in vacuo, we found that the blue shift caused by deprotonation of the Schiff base is more than 200 nm. The absorption properties of the UV absorbing proteins are thus largely determined by the intrinsic properties of the chromophore. The effect of approaching a positive charge to the Schiff base was also studied, as well as the susceptibility of the protonated and unprotonated chromophores to experience spectral shifts in different solvents.