Cation exchangers for selective sorption of large proteins

The sorption of bovine serum albumin, cytochrom c and fibrinogen on the series of carboxylic cation-exchangers with various concentrations of ionogenic groups has been investigated. The dependence of sorption selectivity on protein size and on concentration of ionogenic groups was demonstrated.     

Water sorption isotherms and enthalpies of water sorption by lysozyme using the quartz crystal microbalance/heat conduction calorimeter

The water sorption isotherm and the water vapor activity dependence of the enthalpy of water sorption Delta(sorp)Hdegrees of lysozyme have been measured at 25 degrees C. A thin film of lysozyme of mass 250 microg was exposed to H2O/N2 mixtures in a quartz crystal microbalance/heat conduction calorimeter (QCM/HCC). The QCM/HCC is a new gravimetric/calorimetric method that measures simultaneously and with high precision the mass change and the corresponding heat flow in a thin film exposed to a gas. Delta(sorp)Hdegrees for lysozyme agrees with previous determinations, although hysteresis effects are evident in the data. No van't Hoff analysis is necessary because sorption enthalpies are measured calorimetrically. The water vapor activity dependence of Delta(sorp)Hdegrees agrees with that measured previously by Bone. As the water content of the lysozyme film drops below 10 mass%, Delta(sorp)Hdegrees becomes more exothermic, indicating that water is being bound to the charged or highly polar groups of the solvent-accessible surface of lysozyme. The dynamics of water uptake and release from lysozyme thin films are much slower than in polymer films of comparable thickness. Because the QCM/HCC operates with sub-milligram samples, any protein is now amenable to study by this technique.     

Fate and Transport of Naproxen in a Sandy Aquifer Material: Saturated Column Studies and Model Evaluation

Naproxen-C₁₄H₁₄O₃ is a nonsteroidal anti-inflammatory drug which has been found at detectable concentrations in wastewater, surface water, and groundwater. Naproxen is relatively hydrophilic and is in anionic form at pH between 6 and 8. In this study, column experiments were performed using an unconsolidated aquifer material from an area near Barcelona (Spain) to assess transport and reaction mechanisms of Naproxen in the aquifer matrix under different pore water fluxes. Results were evaluated using HYDRUS-1D, which was used to estimate transport parameters. Batch sorption isotherms for Naproxen conformed with the linear model with a sorption coefficient of 0.42 (cm³ g^?1), suggesting a low sorption affinity. Naproxen breakthrough curves (BTCs) measured in soil columns under steady-state, saturated water flow conditions displayed similar behavior, with no apparent hysteresis in sorption or dependence of retardation (R, 3.85-4.24) on pore water velocities. Soil sorption did not show any significant decrease for increasing flow rates, as observed from Naproxen recovery in the effluent. Sorption parameters estimated by the model suggest that Naproxen has a low sorption affinity to aquifer matrix. Most sorption of Naproxen occurred on the instantaneous sorption sites, with the kinetic sorption sites representing only about 10 to 40% of total sorption.     

Acetate kinase chromatography on agarose derivatives]

Acetate kinase from E. coli K-12 was studied chromatographically on omega-aminoalkyl polysacharide sorbents. The dependence of the protein sorption-desorption on ionic strength and the effect of pH on the acetate kinase sorption were studied. The increase in the ionic strength caused a decrease in the amount of protein sorbed on the hexamethylenediamine- and chlorotriasinehexamethylenediamine sepharoses. On hexamethylenediamine-, octamethylenediamine- and dimethylhexamethylenediamine agaroses acetate kinase was adsorbed within the pH range of 6.5-9.0, whereas on the chlorotriasinehexamethylenediamine sepharose--at pH 6.5-8.0. The active protein was eluted at ionic strength of 0.14-0.17 M. Acetate kinase was not adsorbed on the carboxypropyonylaminohexyl sepharose within the pH range studied, i.e. 5.0-9.0 and was not adsorbed on hexamethylenediamine agarose at pH 4.0 and on chlorotriasinehexamethylenediamine sepharose--at pH 9.0. The mechanism of the enzyme-adsorbent interaction is discussed.     

Removal of cadmium and mercury ions from aqueous solution by sorption on treated Pinus pinaster bark: kinetics and isotherms

Formaldehyde pretreated Pinus pinaster bark was used to sorb Cd2+ and Hg2+ from aqueous solutions. The sorption kinetics showed hyperbolic dependence of the proportion of cation adsorbed on time, and the sorption isotherms were satisfactorily fitted by Freundlich equations, with k and n values showing Hg2+ to be more efficiently sorbed than Cd2+. Except for low cation concentrations, for which sorption was practically total at all initial pH > or = 6, sorption increased in this range, in keeping with a mechanism based on ion exchange with the hydroxyl protons of ring B of the procyanidin units of the tannins in the bark.     

Zinc consumption from the nutrient medium of Trichosporon capitatum and Aspergillus niger]

The sorption capacity of the cultures Trichosporon capitatum and Aspergillus niger towards zinc dissolved in the culture liquid was studied by radio active labelling. The curves of sorption kinetics and the so-called sorption quasi-isotherms showing the dependence of zinc sorption by the microbial biomass upon zinc concentration in the liquid medium were derived. For the Aspergillus niger culture at zinc concentrations of 0.5 to 52 mug/ml the sorption quasi-isotherm was linear. The zinc extraction by microorganisms was related not only to the physico-chemical sorption but also to the zinc accumulation in the cell biopolymers. The paper presents calculations of the microbiological purification of sewage waters from zinc by means of the Aspergillus niger culture.     

Study of water and oil diffusion in rape seeds with sorption-desorption and NMR techniques.

The sorption and desorption of water in rape seeds was measured. From the sorption isotherm it follows that for water content greater than about 6% the water molecules tend to form clusters. The mutual diffusion coefficient of water into and out of the seeds was determined from the time dependence of sorption and desorption. There is a pronounced hysteresis in the sorption-desorption process, desorption proceeds faster than sorption. The self-diffusion of water (at maximum humidity of the seeds) and oil within the seeds was investigated by the pulsed field gradient NMR. The measurement of oil self-diffusion shows restricted diffusion of the oil within droplets and allows the determination of the droplet radii and their distribution width.     

Mechanisms of human plasma protein adsorption on the surface of perfluorocarbon emulsion stabilized with proxanol 268

It has been shown that sorption of most proteins with the molecular weight lower than 200 kDa from human blood plasma on the surface of perfluorocarbon emulsion stabilized with proxanol 268 is mainly based on hydrophobic interaction, whereas sorption of immunoglobulin G is mainly the result of electrostatic interaction. The removal of lipidic components from plasma leads to an increase in the total amount of adsorbed proteins by 35%. Particularly, when lipidic components are removed, sorption of apolipoprotein AI and fibrinogen is considerably bettered as well as sorption of other proteins with the molecular weight of about 50 and 60 kDa occurs. It has been set that apolipoprotein AI in the adsorbed condition loses its capability of tryptophan fluorescence, which might be probably determined by the quenching influence of the perfluorocarbon core of nanoparticle. We think that the findings obtained also indicate considerable conformational rearrangements of this protein during adsorption. It was shown that the fluorescence of proteins with sorption on nanoparticles in emulsion based on the hydrophobic interaction is completely or partially quenched.     

Wechselwirkungen zwischen Mikroorganismen und Metallionen

Microorganisms are able to interact with metal ions in aqueous solutions and to accumulate considerable amounts of them. The mechanism of the accumulation depends on the physiological state of the cells. In the case of resting cells the binding reaction takes place on the surface of the cell wall as a sorption process. The kinetic of the sorption processes in dependence of the physiological state of the cells, the concentration of Hg²⁺ and Cd²⁺-ions on the solution and the pH and temperature has been investigated. Beyond that possibilities for the desorption of the metals from the biomass have been tested.     

Sorption of zinc and lead on coir

Pilot tests have shown that coir (fibres from Coco nucifera) is suitable as a metal ion sorbent. Batch sorption experiments were carried out with Zn and Pb to quantify the sorption kinetics, the pH dependence of the sorption, sorption isotherms at pH 3.0 and pH 5.6, and desorption. Unground and unmodified coir was used and the metal concentrations ranged between 0 and 0.015 mM (1000 microg/l) for Zn and 0 and 9.7 x 10(-4) M (200 microg/l) for Pb. The pH maximum was 4.5 (91%) for Zn and 2.5 (97%) for Pb. Pb had a higher sorption affinity than Zn, and the affinity was higher at pH 5.6 than at pH 3.0. The isotherms could be represented by the Freundlich, but not by the Langmuir models in the concentration range tested. Desorption experiments demonstrated that less than 1% and 13% of the sorbed Pb and Zn, respectively, could be desorbed at pH 5.6 during 2h.     

Mechanisms of human plasma proteins adsorption on the surface of perfluorocarbon emulsion stabilized with proxanol 268

It has been shown that sorption of most proteins with the molecular weight lower than 200 kDa from human blood plasma on the surface of perfluorocarbon emulsion, stabilized with proxanol 268, is mainly based on hydrophobic interaction, whereas sorption of immunoglobulin G is mainly the result of electrostatic interaction. The removal of lipidic components from plasma leads to the increase of a total amount of adsorbed proteins by 35%. Particularly, when lipidic components are removed, sorption of apolipoprotein AI and immunoglobulin G is considerably bettered as well as sorption of other proteins with the molecular weight of about 50 and 60 kDa occurs. It has been out that apolipoprotein AI in the adsorbed condition loses its capability of tryptophan fluorescence, which might be probably determined by the quenching influence of the perfluorocarbon core of nanoparticle. We think that the findings obtained also indicates considerable conformational rearrangements of this protein during adsorption. It was shown, that the fluorescence of proteins with sorption on nanoparticles in emulsion based on the hydrophobic interaction, is completely or partially quenched.     

The hydration of proteins in nearly anhydrous organic solvent suspensions

Water sorption isotherms at 27°C have been measured for lysozyme and chymotrypsin in suspensions of toluene, di(n-butyl) ether, n-propanol, and a solution of 1M n-propanol in benzene. Sorption isotherms for the different suspensions are compared by converting solvent water content to the thermodynamic activity of water in each solvent. The sorption behavior is also compared to that for the two proteins hydrated from the vapor phase. At low water activities, all sorption isotherms are similar when compared on the basis of water activity. However, at higher activities, water sorption by the proteins in the organic suspensions is suppressed relative to the sorption of water vapor. The greatest suppression is observed for n -propanol, which suggests that the suppression may be due to a competition for water-binding sites on the protein by the organic solvent. Sorption isotherms at low water activities have also been predicted using a thermodynamic model in which it is assumed that water binds selectively to the ionizable residues on the surface of the protein. A comparison of predicted and measured sorption isotherms shows that the model can provide reasonable estimates of water sorption in nonpolar or moderately polar organic solvent suspensions at low levels of hydration. © 1993 John Wiley & Sons, Inc.     

Studies on Uranium Removal by the Extracellular Polysaccharide of a Pseudomonas aeruginosa Strain

Extracellular polysaccharide (EPS) produced by a Pseudomonas aeruginosa strain BU2 was characterized for its ability to remove uranium from aqueous solution. The EPS was acidic in nature and found as a potent biosorbent for uranium (U), showing pH dependence and fast saturating metal sorption, being maximum (985 mg U g^{? 1} EPS) at pH 5.0. The polymer showed enhanced uranium sorption capacity and affinity with increasing solution pH, suggesting a preferential sorption of monovalent uranyl hydroxide ions over the nonhydroxylated divalent species. Pseudo-first-order and pseudo-second-order kinetic models were applied to the experimental data, assuming that the external mass transfer limitations in the system can be neglected and biosorption is sorption controlled. Equilibrium metal binding showing conformity to the Freundlich model suggested a multilayer sorption involving specific binding sites with affinity distribution. The presence of two types of metal binding sites corresponding to strong and weak binding affinity was interpreted from the Scatchard model equation. Uranium sorption by EPS was unaffected or only slightly affected in the presence of several interfering cations and anions, except iron and thorium. Fourier transform infrared (FTIR) spectroscopy ascertained the strong binding of uranium with the carboxylic groups of uronic acids of bacterial EPS at pH 5.0, whereas at lower pH, amino and hydroxyl groups played a major role in metal binding.     

Sorptive removal of Methylene blue from aqueous solution using palm kernel fibre: Effect of fibre dose

The use of palm kernel fibre, a readily available agricultural waste product for the sorption of Methylene blue from aqueous solution and the possible mechanism of sorption has been investigated at various fibre doses. The extent of dye removal and the rate of sorption were analyzed using two kinetic rate models (pseudo-first and pseudo-second-order kinetic models) and two diffusion models (intraparticle and external mass transfer models).

Analysis of the kinetic data at different sorbent dose revealed that the pseudo-first order kinetics fitted to the kinetic data only in the first 5 min of sorption and then deviated from the experimental data. The pseudo-second-order kinetic model was found to better fit the experimental data with high correlation coefficients at the various fibre dose used. The dye sorption was confirmed to follow the pseudo-second-order model by investigating the relationship between the amount of dye sorbed and the change in hydrogen ion concentration of the dye solution and also the dependence of dye uptake with solution temperature. It was found that the change in hydrogen ion concentration and increase in sorption temperature were directly related to the amount of dye sorbed, and activation energy was calculated to be −39.57 kJ/mol, indicating that the dye uptake is chemisorption, involving valence forces through sharing or exchange of electrons between sorbent and sorbate as covalent forces.

The intraparticle diffusion plots showed three sections indicating that intraparticle diffusion is not solely rate controlling. The intraparticle diffusion and mass transfer rate constants where observed to be well correlated with sorbent dose in the first 5 min of sorption, indicating sorption process is complex. It was found that at low sorbent dose the mass transfer is the main rate controlling parameter. However at high sorbent dose, intraparticle diffusion becomes rate controlling.     

Kinetics of water exchange between a mite,Laelaps echidnina,and the surrounding air

The temporal dependence of water exchange between an arthropod and its surroundings fits a mathematical model based on diffusion theory. The model requires that the mass change rate of L. echidnina results from a zeroorder component consisting primarily of water sorption and a first-order component made up largely of water loss. Tentatively, transpiration of water is associated with primarily the tracheal system, and sorption of water primarily with other surfaces. Placing mites in a CO₂ atmosphere greatly increased their water loss, but had little effect on sorption of water. The effect of increase in temperature on the sorption rate ($\text{m}\text{?}{}_{\mathrm{s}}$) and transpiration rate constant (k_T) was to increase them. The influence of the activity of the water in the vapour phase in the ambient air (a_v) was primarily on sorption.     

Lysozyme film hydration events: an ir and gravimetric study.

By a combined gravimetric and ir technique, spectra of protein films are recorded during sorption isotherms at constant water content h (mg D₂O/mg dry protein) in the range 0 les; h ? 0.35 at 27 and 38°C. Computer-aided differential analysis shows the effect of progressive hydration on some significant sites of the protein such as the ionizable acidic side chains and the backbone amide carbonyls, as well as the spectrum of the adsorbed water itself. In order to derive thermodynamic properties of these sites, the measured sorption isotherm is decomposed in terms of a model which postulates the existence of two classes of primary sorption sites only, and these two contributions are independently checked by the ir data. The free energy of binding of the strong and weak binding sites is found to be 2.0 ± 0.2 and 0.40 ± 0.1 kcal/mol, respectively. A water-induced transition region is clearly detected in all the observed properties at 0.06 < h < 0.10 at 38°C and is shown to be due to changes involving both the structure of the absorbed water and the coverage of the absorption sites. A detailed picture of the hydration events is offered, and the relevance of these findings to protein dynamics is discussed.     

Hydration force parameters of phosphatidylcholine lipid bilayers as determined from 2H-NMR studies of deuterated water.

The continuous decrease of the quadrupolar splitting of deuterated water interacting with phosphocholine lipid bilayers with growing water concentration is analyzed as a function of the water activity. From the apparent linear dependence on water activity a measure for hydration forces is obtained. The forces calculated are in the range of published data using sorption isotherms and osmotic stress technique in combination with SAXS. A simple interaction potential which includes orientational order of water adsorbed on surfaces gives a physical base for these findings. Therefore, deuterium NMR may become a powerful tool for hydration force analysis complementing well-known methods.     

Impact of Cell Wall Structure on the Behavior of Bacterial Cells as Sorbents of Cadmium and Lead

Batch metal sorption studies were conducted to compare the behavior of Gram-positive Bacillus subtilis and Gram-negative Escherichia coli as sorbents of Cd 2+ and Pb 2+ . A pH range from 3.0 to 6.5 was investigated at total metal concentrations of 1 2 10 -4.0 and 3.2 2 10 -5 M. Concentration apparent equilibrium sorption constants (K s n M ) and sorption capacity (S max n ) values were determined for the bacteria by fitting experimental data to one- ( n = 1) and two-site ( n = 2) Langmuir sorption isotherms. The sorption data for each of the bacteria were described well by a one-site model (r 2 > 0.9), Cd 2+ exhibited somewhat lower sorption affinities (log K s M =- 1.5 for B. subtilis , and -0.7 for E. coli ) than Pb 2+ (log K s M =-0.6 for B. subtilis and -0.8 for E. coli ). Corresponding S max values for Cd 2+ and Pb 2+ on B. subtilis were 0.36 mmole/g and 0.27 mmole/g, respectively. For E. coli Cd 2+ and Pb 2+ S max values were lower at 0.10 mmole/g and 0.21 mmole/g. A two-site sorption model yielded an improved fit for only the E. coli data with several orders of magnitude difference evident between high (Cd 2+ log K s1 M = 0.9; Pb 2+ log K s1 M = 1.5) and low (Cd 2+ log K s2 M =- 1.1; Pb 2+ log K s2 M = -1.6) affinity sorption sites. In addition, allowing for the presence of low affinity sorption (i.e., S max2 ) sites further increased the total E. coli metal sorption capacity closer to that of B. subtilis . As expected, the sorption of Cd 2+ and Pb 2+ by the bacteria exhibited a strong dependence on pH with sorption edges in the range of pH 4.2 to 5.6. The results of this study show that, despite differences in cell wall structure and composition, B. subtilis and E. coli exhibit remarkably similar sorption behavior toward Cd 2+ and Pb 2+ , respectively. These similarities can be attributed to the specific chemical reactivity of acidic functional groups (e.g., carboxyl, phosphoryl) that occur in the cell walls of both bacteria.     

In vitro conversion of mammalian prion protein into amyloid fibrils displays unusual features

The "protein only" hypothesis of prion propagation postulates that the abnormal isoform of the prion protein, PrP(Sc), acts as a causative and transmissible agent of prion disease. In attempt to reconstitute prion infectivity in vitro, we previously developed a cell-free conversion protocol for generating amyloid fibrils from a recombinant prion protein encompassing residues 89-231 (rPrP 89-230) [Baskakov et al. (2002) J. Biol. Chem. 277, 21140]. When inoculated into transgenic mice, these amyloid fibrils induced prion disease, which can be efficiently transmitted to both wild-type and transgenic mice [Legname et al. (2004) Science 305, 673]. Here we show that the polymerization of rPrPs into the fibrils displays a number of distinctive kinetic features that are not typical for polymerization by other amyloidogenic polypeptides. Specifically, the lag phase of polymerization showed only modest dependence on protein concentration, and the conversion reaction displayed a dramatic volume-dependent threshold effect. To explain these unique kinetic features, we proposed that the conversion reaction is regulated by the dynamics between the rates of multiplication and deactivation of self-propagating fibrillar isoforms. Our further studies demonstrated that surface-dependent sorption of fibrillar isoforms is responsible for their deactivation in vitro, while fibril fragmentation seems to account for the multiplication of the active centers of polymerization. Our findings support the hypothesis that development of prion disease is controlled by a fine dynamic balance between self-propagation and clearance/deactivation of PrP(Sc).     

Protein sorption with mineral colloids]

A study was made of the effect on sorption of the molecular weight of model proteins (ribonuclease with a molecular weight of 12 10(3), trypsin with a molecular weight of 24-10(3), bovine albumin with a molecular weight of 64-10(3) and gamma-globulin with a molecular weight of 160-10(3)) and dispersity of suspensions of aluminium hydroxide, aluminum phosphate and calcium phosphate used as biopreparation sorbents. The expediency of using phosphate and calcium phosphate used as biopreparation sorbents. The expediency of using for effective sorption of a definite area of sorption surface necessary and adequate for the distribution of protein macromolecules with the best degree of conformational liberty was revealed.