Protein adsorption at solid-liquid interfaces: Part I--Affinities of proteins for alumina surface

Extent of adsorption (gamma pw) of bovine serum albumin, beta-lactoglobulin, gelatin and myosin at the alumina-water interface has been measured as function of protein concentration (Cp) at several temperatures, pH, and ionic strengths of the medium. gamma pw for proteins in most cases increases with increase of protein concentration but it attains maximum value gamma pw(m) when Cp is high. Values of maximum adsorption have been examined in terms of molecular orientation, molecular size and shape and unfolding of the packed proteins at the interface. In few cases, gamma pw increases with increase of Cp without reaching a real state of saturation as a result of aggregation of molecules or extensive unfolding of the protein at the interface. In the case of beta-lactoglobulin at pH 5.2 and ionic strength 0.05, gamma pw in high concentration region decreases to zero value when Cp increases. For myosin at 45 degrees C and pH 6.4, and also at 27 degrees and pH 7.8, the values of gamma pw are all negative and these negative values increase with increase of Cp. All these results have been explained in terms of significant competitions of water and protein for binding to the surface sites of the powdered alumina. Adsorption of myosin has also been found to be affected in the presence of NaCl, KCl, CaCl2, KI, Na2SO4, LiCl and urea. The relative affinities of the adsorption of various proteins for the surface of alumina at different physical conditions of the system have been compared in terms of maximum values of adsorption attained when gamma pw is varied with Cp. The affinities are shown to be compared more precisely in terms of the standard free energy decrease for the saturation of the surface by protein as a result of the change in its concentration from zero to unity in the mole fraction scale.     

Protein adsorption at solid-liquid interfaces: Part II--Adsorption from binary protein mixture

Extent of adsorption of proteins at alumina-water interface from solutions containing binary mixture of beta-lactoglobulin and bovine serum albumin (BSA), beta-lactoglobulin and gelatin, and gelatin and bovine serum albumin has been estimated as functions of protein concentrations at varying pH, ionic strength, temperature and weight fraction ratios of protein mixture. The extent of adsorption (gamma lacw) of lactoglobulin in the presence of BSA increases with increase of protein concentration (Clac) until it reaches a maximum but a fixed value gamma lacw(m). Extent of adsorption gamma serw also initially increases with increase of protein concentrations until it reaches maximum value gamma serw(m). Beyond these protein concentrations, adsorbed BSA is gradually desorbed due to the preferential adsorption of lactoglobulin from the protein mixture. In many systems, gamma serw at high protein concentrations even becomes negative due to the strong competition of BSA and water for binding to the surface sites in the presence of lactoglobulin. For lactoglobulin-gelatin mixtures, adsorption of both proteins is enhanced as protein concentration is increased until limiting values for adsorption are reached. Beyond the limiting value, lactoglobulin is further accumulated at the interface without limit when protein concentration is high. For gelatin-albumin mixtures, extent of gelatin adsorption increases with increase in the adsorption of BSA. The limit for saturation of adsorption for gelatin is not reached for many systems. At acid pH, adsorbed BSA appears to be desorbed from the surface in the presence of gelatin. From the results thus obtained the role of electrostatic and hydrophobic effects in controlling the adsorption process has been analysed.     

Effect of organic Cr(III) complexes on chromium speciation

Abstract

Chromium speciation in the presence of organic chromium(III) complexes was investigated using solid-phase extraction. The adsorptions of Cr(VI) and Cr(III) on alumina and pumice powder were studied. Maximum sorption of Cr(VI) was obtained by alumina (90.22%), while Cr(III) was highly adsorbed onto pumice powder (86.65%). This result shows that pumice may be a new and promising adsorbent for Cr(III). The experimental equilibrium data for Cr(VI) adsorption onto alumina and Cr(III) sorption onto pumice were analysed using Langmuir and Freundlich isotherms. The separation and adsorption of Cr(VI), Cr(III) and five organic chromium(III) complexes onto pumice and alumina at different pH values were evaluated. Ethylenediaminetetraacetate (EDTA), oxalate, citrate, glycine, alanine and 8-hydroxyqinoline were used as ligands. Sorption of alanine and ethylenediaminetetraacetate complexes was higher onto alumina than pumice at pH>3. The enhancement of adsorption of chromium(III) complexes onto pumice was achieved by surface modification of pumice using a surfactant, namely hexadecyltrimethylammoniumbromür (HDTMA). The presence of surfactant enhanced the adsorption of Cr(III) citrate, oxalate, glycine and 8-hydroxyquinoline complexes onto pumice. However, the adsorption of EDTA and alanine complexes decreased, with ratio of 13.40% and 4.00% respectively. Here we demonstrate that chromium speciation methods depending on adsorption onto various adsorbents including alumina may lead erroneous results. Analytical measurements were performed by flame AAS, data were obtained by standard addition method.     

Protein adsorption at solid-liquid interfaces: Part III--Adsorption from ternary protein mixture.

Simultaneous adsorption of bovine serum albumin (BSA), beta-lactoglobulin and gelatin from aqueous solutions of their ternary mixture to the alumina-water interface has been studied as a function of protein concentration at different values of pH, ionic strength, temperature and weight fraction ratios of proteins. At a fixed weight fraction of beta-lactoglobulin, preferential adsorption (gamma w(lac)) of this protein significantly depends on the amounts of BSA and gelatin present in the solution before adsorption. At higher ranges of protein concentrations, extent of adsorption (gamma w(ser)) of BSA decreases sharply with increase of gamma w(lac) until gamma w(ser) becomes significantly negative, thereby indicating that beta-lactoglobulin and water preferentially adsorbed at the interface are responsible for complete displacement of BSA from the surface. On the other hand, adsorption (gamma w(gel)) of gelatin under similar situation increases mutually with increase in the values of gamma w(lac) in many systems. In few systems, gamma w(gel) also decreases with increase of gamma w(lac) depending upon solution parameters. At pH 5.2, increase of ionic strength and temperature, respectively, increases the extent of adsorption of each protein in the mixture considerably. Extents of adsorption of all proteins are observed to increase when pH is changed from 5.2 to 6.4. The affinities of different proteins in the mixture are expressed in unified scales either in terms of maximum extents of total adsorption or in terms of standard free energies of adsorption of protein mixtures with respect to surface saturation.     

Novel thymine-functionalized polystyrenes for applications in biotechnology. 2. Adsorption of model proteins

This paper investigates the adsorption of bovine serum albumin (BSA) and bovine hemoglobin (BHb) model proteins onto novel thymine-functionalized polystyrene (PS-VBT) microspheres, in comparison with polystyrene (PS) microspheres. Maximum adsorption was obtained for both proteins near their corresponding isoelectric points (pI at pH = 4.7 for BSA and 7.1 for BHb). FTIR and adsorption isotherm analysis demonstrated that, although both proteins were physisorbed onto PS through nonspecific hydrophobic interactions, adsorption onto the functionalized copolymers occurred by both physisorption and chemisorption via hydrogen bonding. FTIR analysis also indicated conformational changes in the secondary structure of BSA and BHb adsorbed onto PS, whereas little or no conformation change was seen in the case of adsorption onto PS-VBT. Atomic force microscopy (AFM), consistent with the isotherm results, also demonstrated monolayer adsorption for both proteins. AFM images of BSA adsorbed onto copolymers with 20 mol % surface VBT loading showed exclusively end-on orientation. Adsorption onto copolymers with lower functionality showed mixed end-on and side-on orientation modes of BSA, and only the side-on orientation was observed on PS. The AFM results agreed well with theoretically calculated and experimentally obtained adsorption capacities. AFM together with calculated and observed adsorption capacity data for BHb indicated that this protein might be highly compressed on the copolymer surface. Adsorption from a binary mixture of BSA and BHb onto PS-VBT showed good separation at pH=7.0; approximately 90% of the adsorbed protein was BHb. The novel copolymers have potential applications in biotechnology.     

Chemisorption of proteins and their thiol derivatives onto gold surfaces: characterization based on electrochemical nonlinearity

This study was conducted to monitor the electrochemical responses of two proteins (bovine serum albumin (BSA) and gelatin) and their thiol derivatives adsorbed onto gold (Au) electrodes, which were analyzed by a "nonlinear" impedance method. A sinusoidal voltage is applied to a protein-containing aqueous solution and the waveform of the output current is analyzed by fast Fourier transformation (FFT). The intensities of the higher harmonics in the FFT varied with the species of protein and their thiol derivatives, and with time. From the higher harmonics, voltage-dependent capacitance and conductance were quantitatively evaluated to differentiate the state of adsorbed protein. Adsorption and desorption characteristics of BSA and its thiol derivative on the Au surface were continuously measured by a quartz crystal microbalance (QCM) in situ. The microscopic state of thiol-derivatized BSA adsorbed onto the Au surface was imaged by atomic force microscopy (AFM). In general, thiol-derivatized proteins were tightly adsorbed on the Au surface and showed no desorption. The present electrochemical measurements clearly differentiated adsorption characteristics of physically adsorbed (physisorbed) and chemically adsorbed (chemisorbed) proteins on Au surfaces.     

Structural features of a hyperthermostable endo-beta-1,3-glucanase in solution and adsorbed on "invisible" particles

Conformational characteristics and the adsorption behavior of endo-beta-1,3-glucanase from the hyperthermophilic microorganism Pyrococcus furiosus were studied by circular dichroism, steady-state and time-resolved fluorescence spectroscopy, and calorimetry in solution and in the adsorbed state. The adsorption isotherms were determined on two types of surfaces: hydrophobic Teflon and hydrophilic silica particles were specially designed so that they do not interact with light and therefore do not interfere with spectroscopic measurements. We present the most straightforward method to study structural features of adsorbed macromolecules in situ using common spectroscopic techniques. The enzyme was irreversibly adsorbed and immobilized in the adsorbed state even at high temperatures. Adsorption offered further stabilization to the heat-stable enzyme and in the case of adsorption on Teflon its denaturation temperature was measured at 133 degrees C, i.e., the highest experimentally determined for a protein. The maintenance of the active conformation and biological function particularly at high temperatures is important for applications in biocatalysis and biotechnology. With this study we also suggest that nature may employ adsorption as a complementary mode to maintain structural integrity of essential biomolecules at extreme conditions of temperature.     

Adsorption of histidine-containing dipeptides on copper(II) immobilized chelating resin from saline solution

Adsorption of histidine-containing dipeptides such as carnosine (Car) was investigated using copper(II) immobilized cation exchange resins. Adsorption of Car was enhanced using Cu(II) immobilized resins, on the basis of metal affinity interactions. In particular, iminodiacetic acid chelating resin with immobilized Cu(II) (Cu-IDA) can adsorb Car from saline water. Car was adsorbed on Cu-IDA even in the presence of 1000 mM of NaCl. Adsorption of various amino acids on Cu-IDA was compared under same conditions. Histidine and the histidine-containing dipeptides were selectively adsorbed on Cu-IDA over other amino acids, both in the absence and in the presence of NaCl. Therefore, immobilized metal affinity adsorption is an efficient method for recovering histidine-containing dipeptides from saline water.     

Adsorption-desorption of BSA to highly substituted dye-ligand adsorbent: quantitative study of the effect of ionic strength

Cibacron Blue 3GA was immobilized on Sepharose CL-6B to obtain a highly substituted dye-ligand adsorbent which dye concentration was 17.4?μmol dye per gram wet gel. This adsorbent had a highly binding capacity for bovine serum albumin (BSA). The effects of ionic strength on the adsorption and desorption of BSA to the adsorbent were studied. Adsorption isotherms were expressed by the Langmuir model. The quantitative relationships between the model parameters and the ionic strength were obtained. The desorptions were performed by adding salt to the BSA solutions in which adsorption equilibria had been reached. Adding salt to the solution resulted in the desorption of the bound protein. It was found that the isotherm obtained from the desorption experiments agreed well to the isotherm obtained from the adsorption experiments at the same ionic strength. The result demonstrated that the adsorption of BSA to the highly substituted adsorbent was reversible.     

The effect of the phase transition on the hydration and electrical conductivity of phospholipids.

Adsorption isotherms for various saturated phosphatidylcholines have been obtained. Lipids above and below their phase transition temperature differ only in the amount of water adsorbed and not in the nature of their adsorption isotherms. Cholesterol has an effect similar to that of increasing unsaturation in the hydrocarbon chains. Decreasing the length of the hydrocarbon chains for lipids below their phase transition temperature has no effect on the isotherms. If the chain length is short enough so that the lipids are above their transition temperature, however, a large increase in water adsorption occurs. All of the phospholipids exhibit a rapid increase of electrical conductivity for a few water molecules adsorbed per lipid molecule. All of the phospholipids show a saturation in conductivity at greater amounts of adsorbed water; the shape of the saturation region depends on whether the lipids are above or below their phase transition temperature. The activation energy for the electrical conductivity process depends on whether the hydrated lipids are in the "liquid-like" of the crystalline state, being lower for phospholipids in the liquid-like state. If the lipids are hydrated above their phase transition temperatures, their activation energies are lower than if they are hydrated below the transition temperature. Cholesterol lowers the activation energy. The phosphatidylcholines can be characterized by different activation energies, depending both upon their physical state and the presence of unsaturation in their hydrocarbon chains.     

Regulation of carboxylester lipase adsorption to surfaces. 1. Chemical specificity

The chemical specificity of the adsorption of porcine pancreatic carboxyl ester lipase to pure lipid surfaces was examined. Adsorption of native and catalytically inactivated enzyme was measured at the argon-buffer interface by using lipid films near the point of collapse. Protein adsorbed readily to films of triolein, 1,3-diolein, methyl oleate, oleonitrile, oleyl alcohol, and 13,16-docosadienoic acid. However, recovery of enzyme activity was variable. These differences and the changes in surface pressure accompanying adsorption indicated the occurrence of enzyme denaturation at the interface. Denaturation was controlled largely by surface free energy but showed some chemical specificity at high surface pressures. Adsorption of protein to the lipids was comparable when measured under either equilibrium or initial rate conditions. Together with surface pressure changes that accompany adsorption, the data indicate a relative lack of specificity for the enzyme-surface interaction. Adsorption to 13,16-docosadienoic acid and 1,3-diolein obeyed the Langmuir adsorption isotherm. Dissociation constants ranged from 10 to 50 nM, depending on enzyme form, ionic strength, and pH. With both lipids, a monolayer of enzyme was adsorbed at saturation. In contrast to these results, adsorption of enzyme activity and protein to films of 1-palmitoyl-2-oleoyl-phosphatidylcholine was less than or equal to 5% of that observed with the other lipids under all conditions. Comparison of rate constants for adsorption to 13,16-docosadienoic and 1,3-diolein as a function of subphase pH indicated a marked dependence on the ionization state of the fatty acid. Overall, the data suggest that the presence of zwitterionic and anionic lipids may regulate the interaction of the enzyme with substrate-containing surfaces in vivo.     

The influence of radioiodination on the adsorption of IgG and serum albumin to polystyrene

The adsorption of radioiodinated rabbit IgG and bovine serum albumin (BSA) to polystyrene tubes was investigated. Adsorption isotherms where the proportion of the protein bound was relatively constant over a range of intermediate protein concentrations, and where the proportion bound was protein dependent, were obtained. To investigate the effects of radioiodination, proteins labeled to give a wide range of substitution ratios (0.03 to 3.7 125I/protein molecule) were employed. While labeling did not appear to affect BSA adsorption, the kinetics of IgG binding were altered in a number of ways. The proportion bound in the concentration independent region was decreased even at substitution ratios less than or equal to 0.2. In addition, while all preparations of iodinated BSA, and IgG preparations with less than or equal to 1.6 125I/IgG, gave bimodal adsorption isotherms, with more heavily labeled IgG (greater than or equal to 2.5 125I/IgG) the apparent high affinity binding to the plastic surface was abolished. These results indicate that radioiodination substantially alters the kinetics of the binding of IgG to polystyrene. In addition, the results obtained are discussed with respect to previous relevant and often apparently contradictory findings.     

Adsorption of Bovine Serum Albumin from salt solution onto activated carbon

One of the wastewaters from tanning industry (soak liquor) contains 0.4 g/l of dissolved protein. During coagulation and flocculation 41 % of protein was removed. A suggestion has been made to remove the residual protein by adsorption technique. The optimum conditions for adsorption of Bovine Serum Albumin (BSA) on rice bran based activated carbon (RBAC) have been determined. Maximum adsorption of BSA took place at pH 7.O. Ionic strength was found to have influence on the adsorption behaviour. Adsorption capacity of BSA onto charcoal surface decreased with increase in temperature. Enthalpy of adsorption in all cases was found to be within –19 to –57 kJ/mole, indicating exothermic nature of the process. Applicability of adsorption technique to the removal of dissolved protein from soak water has been studied. The maximum removal of protein occurred at pH 7.0 and the ratio of protein removed to weight of adsorbent was 3.22×10^–3 g/g.     

Adsorptive characteristics of iron(III) onto hydrous manganese dioxide in model lake water under acidic conditions

The adsorption of iron(III) onto hydrous manganese dioxide was studied in the model water of Lake Tjeukemeer, The Netherlands, as a function of pH under the condition where no precipitation of iron(III) hydroxide occurs.Adsorption isotherms obtained in the pH range 3.5–5.0, fitted the Langmuir equation. Langmuir constants were strongly pH-dependent and increased with an increase in pH.Especially, the value for the conditional adsorption binding constant for iron(III), log B, was relatively high compared to that for copper in natural water. The extent of iron(III) adsorbed was more affected by the surface loading at lower pH. According to the Kurbatov plot, the average number of protons released to solution per mole of iron(III) adsorbed was estimated to be 2.2.     

Chemical camouflage of nanospheres with a poorly reactive surface: towards development of stealth and target-specific nanocarriers

A two-step approach is described to chemically camouflage the inert surface of model polystyrene nanospheres of 60 nm in diameter against recognition by the body's defenses. The first step was based on the strong protein adsorbing potency of polystyrene, and the second step utilized the chemical reactivity of the adsorbed proteins for conjugation with cyanuric chloride-activated methoxypoly(ethyleneglycol)5000, mPEG5000. Bovine serum albumin (BSA) and rat IgG were used as models of non-immune and immune proteins, respectively. The maximum adsorbance values for both proteins were near expectation for a close-packed monolayer. Adsorption isotherms studies and analysis of the hydrodynamic thickness of the adsorbed protein layer confirmed the close-packed side-on mode of adsorption for BSA and the end-on mode of adsorption for IgG, respectively. Nucleophiles on the adsorbed proteins were then reacted with cyanuric chloride activated mPEG5000. The average poly(ethyleneglycol) (PEG) content for a 60-nm nanospheres was found to be 13.7+/-0.4 micromol PEG/micromol BSA and 3.6+/-0.3 micromol PEG/micromol IgG. The interaction of both PEG-bearing nanospheres with the hydrophobic column material octyl-agarose indicated surface heterogeneity among the nanospheres. Only nanospheres with the most hydrophilic phenotype (approximately 70% of the total population) exhibited stealth properties after intravenous injection to rats. In contrast to the described approach, incubation of uncoated nanospheres with preformed BSA-mPEG5000 conjugates failed to produce long circulating entities. For design of splenotropic particles cyanuric chloride-activated mPEG5000 was conjugated to BSA-coated polystyrene beads of 225 nm in diameter. Despite their stealth property to hepatic Kupffer cell recognition, these nanospheres were cleared by the splenic red pulp macrophages.     

Lipid demixing and protein-protein interactions in the adsorption of charged proteins on mixed membranes

The adsorption free energy of charged proteins on mixed membranes, containing varying amounts of (oppositely) charged lipids, is calculated based on a mean-field free energy expression that accounts explicitly for the ability of the lipids to demix locally, and for lateral interactions between the adsorbed proteins. Minimization of this free energy functional yields the familiar nonlinear Poisson-Boltzmann equation and the boundary condition at the membrane surface that allows for lipid charge rearrangement. These two self-consistent equations are solved simultaneously. The proteins are modeled as uniformly charged spheres and the (bare) membrane as an ideal two-dimensional binary mixture of charged and neutral lipids. Substantial variations in the lipid charge density profiles are found when highly charged proteins adsorb on weakly charged membranes; the lipids, at a certain demixing entropy penalty, adjust their concentration in the vicinity of the adsorbed protein to achieve optimal charge matching. Lateral repulsive interactions between the adsorbed proteins affect the lipid modulation profile and, at high densities, result in substantial lowering of the binding energy. Adsorption isotherms demonstrating the importance of lipid mobility and protein-protein interactions are calculated using an adsorption equation with a coverage-dependent binding constant. Typically, at bulk-surface equilibrium (i.e., when the membrane surface is "saturated" by adsorbed proteins), the membrane charges are "overcompensated" by the protein charges, because only about half of the protein charges (those on the hemispheres facing the membrane) are involved in charge neutralization. Finally, it is argued that the formation of lipid-protein domains may be enhanced by electrostatic adsorption of proteins, but its origin (e.g., elastic deformations associated with lipid demixing) is not purely electrostatic.     

Adsorption of biopolymers at hydrophilic cellulose-water interface

The extent of adsorption (Gamma2(1)) of bovine serum albumin (BSA), beta-lactoglobulin, lysozyme, gelatin, and DNA from aqueous solution onto the hydrophilic surface of cellulose has been measured as function of biopolymer concentration at different temperatures, pHs, and ionic strengths, and in the presence of a high concentration of inorganic salts and denaturants. In all cases, the value of Gamma2(1) increases with the increase of biopolymer concentration (X2) in bulk and it attains a maximum value at a critical mole fraction concentration X2m. The value of Gamma2m depends upon the nature of protein, temperature, pH, and ionic strength, as well as the nature of neutral salts present in excess. Gamma2m for proteins at a fixed physicochemical condition stands in the following order: Gelatin>betalactoglobulin>lysozyme>BSA. The isotherms for adsorption of DNA nucleotides on cellulose surface at pH 4.0 have been compared at different temperatures and ionic strengths, and in the presence of high concentration of inorganic salts LiCl, NaCl, KCl, and Na2SO4. Values of Gamma2m for different systems have been evaluated and critically compared. At pH 6.0 and 8.0, Gamma2(1) values of DNA nucleotides on cellulose are all negative due to the excess positive hydration of cellulose. At pH 4.0, adsorption of nucleotides of acid, alkali, and heat-denatured DNA widely differ from each other and in the presence of excess concentration of urea becomes negative. The probable mechanisms of biopolymer-cellulose adsorption in terms of polymer hydration, steric interaction, London-van der Waals, hydrophobic, and other types of interactions have been discussed qualitatively. The standard free energy change for the adsorption of protein and DNA nucleotides on the cellulose surface at the state of adsorption saturation has been calculated in kJ per kg of cellulose using an integrated form of the Gibbs adsorption equation. The relation between DeltaG degrees and maximum affinities between biopolymers and the polysaccharide interface have been discussed for various systems.     

Changes in conformation and function of hemoglobin and myoglobin induced by adsorption to silica.

Adsorption of myoglobin (Mb) or hemoglobin (Hb) to silica (Cab-O-Sil) causes marked alterations in protein hydrogen exchange kinetics. The exchange is slower for cyanometMb and faster for both cyanometHb and oxyHb in adsorbed state than for the corresponding species in the free state. For Hb, adsorption increases oxygen affinity (P₅₀ = 12.9 mmHg vs. 16.7 for free) and decreases cooperativity (n = 2.05 vs. 2.87 for free). Myoglobin has the same oxygen affinity in both the free and adsorbed states.     

Adsorption of Agrobacterium tumefaciens to Susceptible Potato Tissues: a Physisorption Process

Adsorption of Agrobacterium tumefaciens cells to potato tuber disks reached equilibrium after coincubation for about 30 min. More than 10% of the number of bacteria bound at equilibrium were adsorbed within 30 s. Adsorption isotherms obtained at three temperatures showed that the heat of adsorption was nearly zero.     

Application of adsorption isotherms to chromium adsorption onZ.ramigera

Summary Adsorption isotherms for the adsorption of chromium onZoogloea ramigera are developed. The rates were affected by the pH and temperature of adsorption medium. The biomass ofZ. ramigera at pH 2.0 where the optimum pH for biosorption lies exhibited the highest chromium adsorptive uptake capacity. In general, higher adsorptive uptake was observed at 25°C than 35°C and 45°C.