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PubMed2001

Studies on adsorption characteristics and mechanism of adsorption of chlorhexidine mainly by carbon black.

The extent of adsorption of chlorhexidine to carbon black and sanitary cotton was determined by measuring the amounts of chlorhexidine adsorbed to carbon black or sanitary cotton from the chlorhexidine solution containing specific amount of carbon black or sanitary cotton. As another comparative antiseptic example of adsorption phenomena, adsorption of acrinol to sanitary cotton was also studied. The specific surface area of carbon black was measured by the BET method of adsorption isotherm. The pattern of adsorption of chlorhexidine to carbon black was temperature-dependent Langmuir isotherms, and the amounts adsorbed increased as the temperature was raised. Since chlorhexidine, whose pKa's are 2.2 and 10.3, is considered to exist in aqueous solution as the di-cation, an ion-ion interaction should be formed between protonated biguanide and anionic portions of carbon black or sanitary cotton. The chlorophenyl and hexane moieties interact with hydrophobic portions of carbon black or sanitary cotton. The perturbation experiment conducted on this interaction system showed that the nature of interaction was irreversible. The enthalpy change calculated from Langmuir constants was small, indicating the existence of ion-ion interaction. The entropy values, 27.4 to 28.2 e.u. obtained in this system, suggested that the hydration shells of the ions were rather tightly bound. The area occupied by a chlorhexidine molecule, 548 (A)(2), was twice greater than the projection area, 276 (A)(2), suggesting that chlorhexidine was adsorbed in such a way that each molecule is sufficiently well spaced.

Adsorption↗
PubMed1995

Adsorption of human salivary proteins to titanium powder. I. Adsorption of human salivary albumin.

Titanium (Ti) is among the most widely used implant materials in dentistry today. The success of Ti implants is associated with their interactions with the surrounding tissues and biological fluids. In the present study, the adsorption of salivary proteins to Ti and the effect of calcium (Ca) on this process were investigated. Untreated and Ca-treated Ti powders were suspended in human clarified whole saliva. After incubation, the supernatant fluid was collected for protein analysis. The powders were then washed and resuspended in EDTA to desorb proteins from Ti surfaces. Sodium dodecylsulphate polyacrylamide gel electrophoresis and Bradford protein assay were conducted to determine the concentration and type of proteins that adsorbed onto Ti surfaces. The presence of Ca ions enhanced the adsorption of salivary proteins to Ti. A 66 kDa protein, identified by immunoblotting as albumin, was found as the main adsorbed salivary protein. Adsorption of albumin to Ti pretreated with Ca was significantly greater than to native Ti. The Ca-dependent adsorption process was reversed by EDTA. The data suggest that salivary albumin is one of the main constituents of a salivary biofilm formed on Ti dental implants and its adsorption to Ti surfaces is Ca-dependent. The presence of albumin on Ti dental implants may affect plaque accumulation on the implants and the biocompatibility of Ti implants.

Adsorption↗
PubMed1988

Kinetics of adsorption of proteins at interfaces: role of protein conformation in diffusional adsorption.

To elucidate the role of protein conformation in the kinetics of adsorption at interfaces, seven structural intermediates of bovine serum albumin were prepared and their adsorption at the air/water interface was studied. Molecular area calculations indicated two distinct molecular processes, the first being the creation of an area, delta A1, for anchoring the molecule during the initial phase of adsorption and the second being the delta A2 cleared during subsequent reorientation and rearrangement of adsorbed molecules at the interface. The delta A1 values for all the albumin intermediates were the same, indicating that the initial work pi delta A1 needed to anchor the molecule at the interface was independent of solution conformation of the protein. Unlike delta A1, delta A2 exhibited a bell-shaped relationship with the extent of refolded state of the intermediates. Calculation of diffusion coefficients indicated that greater the unfolded state of the albumin intermediate, the greater was the diffusion coefficient. It is shown that the simple diffusion theory is inadequate to explain quantitatively the kinetics of protein adsorption. Specific, conformation-dependent, solute-solvent and solute-interface interactions also seem to influence the kinetics of adsorption of proteins.

Adsorption↗
PubMed2006

Volumetric interpretation of protein adsorption: mass and energy balance for albumin adsorption to particulate adsorbents with incrementally increasing hydrophilicity.

The solution-depletion method of measuring human serum albumin (HSA) adsorption to surface-modified glass-particle adsorbents with incrementally increasing hydrophilicity is implemented using SDS gel electrophoresis as a separation and quantification tool. It is shown that adsorbent capacity for albumin measured in interfacial-concentration units (mg/mL) decreases monotonically with increasing surface energy (water wettability) to detection limits near an adsorbent-particle water adhesion tension tau(0)=30 dyne/cm (nominal water contact angle theta=65( composite function)) and that albumin does not adsorb to (concentrate within the surface region of) more hydrophilic adsorbents. These adsorbed-mass measurements corroborate predictions based on interfacial energetics and are consistent with AFM measurement of protein-surface adhesion. Interpretive mass-balance equations are derived from a model premised on the idea that protein reversibly partitions from bulk solution into a three-dimensional (3D) interphase volume separating the physical adsorbent surface from bulk solution. Theory is shown to both anticipate and accommodate experimental results for all test adsorbents, suggesting that the underlying model is descriptive of the essential physical chemistry of albumin adsorption to surfaces spanning the full range of observable water wetting. In particular, application of theory to experimental data shows that the free-energy cost of dehydrating the surface region by protein displacement upon adsorption increases with increasing adsorbent hydrophilicity in a manner that controls ultimate capacity for protein. It is concluded that a simple, three-component free-energy rule adequately describes protein adsorption from aqueous solution, at least for materials bearing varying surface concentrations of anionic (not cationic) functional groups. IMPACT STATEMENT: This work yields detailed insights into the physical chemistry of protein adsorption by elucidating relationships among adsorbent surface energy, capacity to adsorb the protein human serum albumin, and the energy required to displace vicinal water from the interface.

Adsorption↗
PubMed2006

Adsorption of copper and zinc on Pseudomonas putida CZ1: particle concentration effect and adsorption reversibility.

The adsorption and desorption processes of Cu(II) and Zn(II) on the biomass of Pseudomonas putida CZ1 as a function of particle concentrations (C(p)) were studied. In a 0.01 M KNO3 solution, the Cu-biomass and Zn-biomass adsorption systems displayed a clear C(p) effect. The overall adsorption isotherms under three C(p) conditions could be described as a Freundlich-type C(p) effect isotherm equation: gamma = 2.553C(p)(-0.7106) C(eq)(0.8971) for Cu-biomass system, gamma = 2.412C(p)(-0.8305) C(eq)(0.6504) for Zn-biomass system. The results of experiments, designed to eliminate several typical sources of experimental artifact, agree with the prediction of the metastable-equilibrium adsorption theory. Results from laboratory equilibration studies also indicate that biomass-adsorbed Cu(II) or Zn(II) fractions may be comprised of both reversibly and strongly bound or resistant components. A computational method has been derived to allow prediction of the magnitude of the reversible and more strongly adsorbed Cu(II) or Zn(II) fractions from conventional isotherm data. This methodology provides an initial quantitative approximation of the strongly bound, resistant, biomass fractions while utilizing relatively simple experimental adsorption-desorption data.

Adsorption↗
PubMed2004

Adsorption of anionic dyes on chitosan beads. 1. The influence of the chemical structures of dyes and temperature on the adsorption kinetics.

In this work, chitosan beads were synthesized in acidic medium and cross-linked in 1% glutaraldehyde solution. The characterization of the materials using TG/DTG, XRD, and BET surface areas showed that the beads did not modify their characteristics after the cross-linking reaction. The cross-linked beads were utilized as adsorbents for the removal of the yellow-, blue-, and red-anionic reactive dyes from aqueous solutions at pH 2.0. Adsorption of the yellow-dye increased from 25 to 50 degrees C. However, adsorption of the blue-dye decreased from 25 to 50 degrees C. Interestingly, the adsorption of the red-dye decreased from 25 to 35 degrees C and increased from 45 to 50 degrees C. The kinetic data were evaluated using an Avrami kinetic model, where the parameter n was related to the determination of changes in the adsorption mechanisms. Adsorption data of the dyes in relation to the contact time, the chemical structures of the dyes, and temperature were presented and were discussed.

Adsorption↗
PubMed1996

Adsorption of globular proteins on locally planar surfaces: models for the effect of excluded surface area and aggregation of adsorbed protein on adsorption equilibria.

Equilibrium statistical-thermodynamic models are presented for the surface adsorption of proteins modeled as regular convex hard particles. The adsorbed phase is treated as a two-dimensional fluid, and the chemical potential of adsorbed protein is obtained from scaled particle theory. Adsorption isotherms are calculated for nonassociating and self-associating adsorbing proteins. Area exclusion broadens adsorption isotherms relative to the Langmuir isotherm (negative cooperativity), whereas self-association steepens them (positive cooperativity). The calculated isotherm for adsorption of hard spheres using scaled particle theory for hard discs agrees well with that calculated from the hard disc virial expansion. As the cross section of the adsorbing protein in the plane of the surface becomes less discoidal, the apparent negative cooperativity manifested in the isotherm becomes more pronounced. The model is extended to the case of simultaneous adsorption of a tracer protein at low saturation and a competitor protein with a different size and/or shape at arbitrary fractional saturation. Area exclusion by competitor for tracer (and vice versa) is shown to substantially enhance the displacement of tracer by competitor and to qualitatively invalidate the standard interpretation of ligand competition experiments, according to which the fractional displacement of tracer by competitor is equal to the fractional saturation by competitor.

Adsorption↗
PubMed2000

Protein adsorption on novel acrylamido-based polymeric ion-exchangers. I. Morphology and equilibrium adsorption.

The protein uptake equilibrium and particle morphology are determined for novel polymeric ion-exchange media based on acrylamido monomers with a high density of functional groups and a variety of morphological characteristics. The study considers two anion-exchangers and a cation-exchanger. Physical properties determined experimentally include particle density, ion-exchange capacity, particle size distribution, and equilibrium isotherms for model proteins. The pore structure was evaluated using size exclusion chromatography with neutral probe molecules and transmission electron microscopy. For the anion-exchangers, two types of structures were inferred. The first is comprised of particles that contain a low-density gel supported by denser polymer aggregates. This material had a very low size-exclusion limit for neutral probes, but exhibited an extremely high and reversible protein adsorption capacity (280-290 mg BSA/ml). The second structure is comprised of particles with large, open macropores. While the size-exclusion limit was very high, the protein adsorption capacity was low (60 mg BSA/ml). Moreover, the adsorption was nearly irreversible. The physical structure of the cation-exchanger appeared to be intermediate between those of the anion-exchangers, containing both large pores and smaller pores yielding an intermediate, but reversible, protein uptake capacity (120-130 mg alphaCHY/ml). The different behavior of these materials with regards to protein adsorption correlates well with their physical structure. For these ion-exchangers, high protein adsorption capacities are attained when a low-density polymer gel with a high concentration of functional groups is present.

Acrylamides↗
PubMed1987

Interaction of proteins with immobilized Cu2+. Quantitation of adsorption capacity, adsorption isotherms and equilibrium constants by frontal analysis.

The interaction of lysozyme, ovalbumin, bovine and pig serum albumins with Cu2+ immobilized on Chelating Sepharose Fast Flow or TSK gel chelate-5PW was studied by frontal analysis at various initial concentrations of these solutes. The chromatographic data so obtained served as a basis for evaluating some relevant affinity chromatography parameters by adapting previously reported equations to this system. The TSK-based adsorbent had lower adsorption capacity for all the model proteins compared to the agarose-based adsorbent, due primarily to its lower porosity which has a marked influence on the accessibility of the immobilized ligand to the proteins. On the other hand, the TSK-based adsorbent offers almost ideal conditions for studying adsorption equilibria under column chromatographic conditions. The adsorption capacity of these adsorbents for the model proteins ranges from about 0.6 to 7 mumol/ml, equivalent to 40-100 mg/ml, of adsorbent. The following equilibrium constants for the interaction of the proteins with immobilized Cu2+ were obtained: lysozyme, 1.8.10(4); ovalbumin, 1.5.0(5); BSA, 1.7.10(5); PSA, 3.7.10(5) and imidazole, 8.10(3) M-1. Despite the comparatively low affinity of imidazole for the adsorbent, it is an effective competing ligand, at comparatively high concentrations, for adsorbed proteins primarily because all adsorption sites are available to it. The results obtained suggest that about 1/3 to 1/2 of the potential adsorption sites on the model proteins are involved in forming coordination complexes with Cu2+ immobilized to covalently bound iminodiacetate groups on insoluble gel matrices.

Adsorption↗
PubMed2005

Adsorption of myoglobin to Cu(II)-IDA and Ni(II)-IDA functionalized langmuir monolayers: study of the protein layer structure during the adsorption process by neutron and X-ray reflectivity.

The structure and orientation of adsorbed myoglobin as directed by metal-histidine complexation at the liquid-film interface was studied as a function of time using neutron and X-ray reflectivity (NR and XR, respectively). In this system, adsorption is due to the interaction between iminodiacetate (IDA)-chelated divalent metal ions Ni(II) and Cu(II) and histidine moieties at the outer surface of the protein. Adsorption was examined under conditions of constant area per lipid molecule at an initial pressure of 40 mN/m. Adsorption occurred over a time period of about 15 h, allowing detailed characterization of the layer structure throughout the process. The layer thickness and the in-plane averaged segment volume fraction were obtained at roughly 40 min intervals by NR. The binding constant of histidine with Cu(II)-IDA is known to be about four times greater than that of histidine with Ni(II)-IDA. The difference in interaction energy led to significant differences in the structure of the adsorbed layer. For Cu(II)-IDA, the thickness of the adsorbed layer at low protein coverage was < or = 20 A and the thickness increased almost linearly with increasing coverage to 42 A. For Ni(II)-IDA, the thickness at low coverage was approximately 38 A and increased gradually with coverage to 47 A. The in-plane averaged segment volume fraction of the adsorbed layer independently confirmed a thinner layer at low coverage for Cu(II)-IDA. These structural differences at the early stages are discussed in terms of either different preferred orientations for isolated chains in the two cases or more extensive conformational changes upon adsorption in the case of Cu(II)-IDA. Subphase dilution experiments provided additional insight, indicating that the adsorbed layer was not in equilibrium with the bulk solution even at low coverages for both IDA-chelated metal ions. We conclude that the weight of the evidence favors the interpretation based on more extensive conformational changes upon adsorption to Cu(II)-IDA.

Adsorption↗
PubMed2004

Copper adsorption with Pb and Cd in sand-bentonite liners under various pHs. Part II. Effect on adsorption sites.

The project examined the effect of Pb and Cd on Cu adsorption using sand liners containing 0, 5, and 10% sodium bentonite and exposed to metal solutions at three pH levels (3.7, 5.5, and 7.5). Aliquots of 2 g of liner material were exposed in duplicate, for 14 days, to solutions containing Cu alone or Cu with either Pb or Cd. Selective sequential extraction (SSE) was used to quantity the Cu adsorbed by each liner particle adsorption site (exchangeable, carbonate and hydroxide, oxides and residual). The results indicated that two main factors affected liner material behavior in adsorbing Cu, besides Cd and Pb competition: pH either above or below 6.5; liner cation exchange capacity (CEC) greater or equal and greater than the solution cation equivalence. In general, the liner carbonate and hydroxide fractions precipitated the greatest amount of Cu, under all environmental conditions while the exchangeable, oxide and residual adsorbed more or less the same amount. Lead, and to a lesser extent Cd, significantly increase the mobility of Cu, by competing especially for the exchangeable sites. While Cd also competed against Cu for oxide adsorption, Pb competes for calcium and hydroxide precipitation. Lead, and to a lesser extent Cd, competed especially for the exchangeable site where the adsorption is more dynamic, and less for the more permanent adsorption sites, involving precipitation, and electrostatic bonding.

Adsorption↗
PubMed2001

Adsorption of acetanilide herbicides on soil and its components. II. Adsorption and catalytic hydrolysis of diethatyl-ethyl on saturated Na(+)-, K(+)-, Ca(2+)-, and Mg(2+)-montmorillonite.

Adsorption and catalytic hydrolysis of the herbicide diethatyl-ethyl [N-chloroacetyl-N-(2,6-diethylphenyl)glycine ethyl ester] on homoionic Na(+)-, K(+)-, Ca(2+)-, and Mg(2+)-montmorillonite clays were investigated in water solution. The Freundlich adsorption coefficient, Ki, got from isotherms on clay followed the order of Na+ approximately K+ > Mg2+ approximately Ca2+. Analysis of FT-IR spectra of diethatyl-ethyl adsorbed on clay suggests probable bonding at the carboxyl and amide carbonyl groups of the herbicide. The rate of herbicide hydrolysis in homoionic clay suspensions followed the same order as that for adsorption, indicating that adsorption may have preceded and thus caused hydrolysis. Preliminary product identification showed that hydrolysis occurred via nucleophilic substitution at the carboxyl carbon, causing the cleavage of the ester bond and formation of diethatyl and its dechlorinated derivative, and at the amide carbon, yielding an ethyl ester derivative and its acid. These pathways also suggest that hydrolysis of diethatyl-ethyl was catalyzed by adsorption on the clay surface.

Acetanilides↗
PubMed2004

[Adsorption of cation-nonionic mixed surfactants onto sediment and their effects on adsorption of nitrobenzene from water].

Adsorption behaviors of nitrobenzene, a nonionic surfactant (Triton X-100), a cation surfactant (CPC) and their mixture onto a sediment were investigated. The adsorption of Triton X-100 onto the sediment is enhanced with increasing of co-existed CPC at relatively low concentrations but decreased at relatively high concentrations. The adsorption of CPC onto the sediment decreased a little with increasing of co-existed Triton X-100. In natural waters, cation surfactants and nonionic surfactants will be largely adsorbed by soils or sediments. The adsorption of nitrobenzene onto sediment is linear and enhanced by the co-existed Triton X-100 or CPC, and will be significantly enhanced by the mixture of CPC-Triton X-100. Therefore, cation-nonionic mixed surfactants are potentially used to enhance adsorption of organic contaminants onto soils or sediments and to prepare organobentonite for improving their performance in wastewater treatment.

Adsorption↗
PubMed2004

Adsorption of zinc on manganite (gamma-MnOOH): particle concentration effect and adsorption reversibility.

The adsorption and desorption processes of Zn(II) on gamma-MnOOH as a function of particle concentrations (Cp) were studied. An obvious Cp effect was observed in this adsorption system. The degree of adsorption hysteresis increased greatly with the increasing of Cp, indicating that the extent of the real metastable-equilibrium states deviating from the ideal equilibrium state was enhanced with the increasing of Cp. The Cp-reversibility relationship confirmed the metastable-equilibrium adsorption (MEA) inequality (Pan, 1998a), which was the core formulation of the MEA theory. Because the MEA inequality was based on the basic hypothesis of MEA theory that adsorption density [see symbol in text] is not a state variable, the Cp-reversibility relationship gave indirect evidence to the basic hypothesis of MEA theory.

Adsorption↗
PubMed1980

Surface adsorption of factor XI. Association of adsorption sites with the heavy chain of activated factor XI.

These experiments study surface adsorption of native and activated factor XI using purified radiolabelled human factor XI and trypsin activated factor XI. Both forms of factor XI adsorb not only to glass but also to polypropylene, polyethylene and polystyrene. Albumin (10 mg/ml) markedly reduces adsorption to plastics but not to glass. Sodium dodecyl sulfate prevents adsorption to all surfaces tested. Reduction of 125I-activated factor XI in the presence of sodium dodecyl sulfate yields labelled chains of molecular weight of about 46,000 (heavy chain), 37,000 (light chain) and a further breakdown product of about 26,000. Reduction of activated factor XI in glass or plastic in the absence of sodium dodecyl sulfate yields only light chain and breakdown product in solution; heavy chain is removed by adsorption. Therefore, we conclude that the adsorption site (s) in trypsin activated factor XI and presumably also in native factor XI is (are) located in the heavy chain subunit of the molecule.

Adsorption↗
PubMed1999

Adsorption of Hydrophobically Modified Polyacrylic Acid on a Hydrophobic Surface: Hysteresis Caused by an Electrostatic Adsorption Barrier.

The adsorption of hydrophobically modified polyacrylic acid (HM-PAAc) has been compared to the adsorption of unmodified polymers by means of reflectometry. The polymers were adsorbed onto a noncharged hydrophobic polystyrene surface. The adsorption kinetics of both types of polymer is the same until a certain surface coverage. Then the unmodified sample shows a saturation while the hydrophobically modified polyacrylic acid continues to adsorb. The adsorption behavior of the polyelectrolyte can be controlled by the pH and the ionic strength of the solution. For ionic strengths of 0.001 M NaCl the hydrophobically modified polymer shows a larger adsorbed amount at pH 3 to 4 compared to the unmodified polymer. At pH higher than 4 the differences are less significant. At higher ionic strength the amount of adsorbed material increases for both polymers. While doing adsorption-desorption cycles a hysteresis-effect was detected. At the same pH the hydrophobically modified polymer sticks to the surface while the unmodified polymer is already desorbing completely. The hysteresis vanishes when the ionic strength of the solution is increased. Copyright 1999 Academic Press.

Journal Article↗
PubMed2003

Kinetics of adsorption of polyvinylamine on cellulose fibers. I. Adsorption from salt-free solutions.

Adsorption of fully hydrolyzed polyvinylamine on cellulose fibers in the short term was investigated by supplying the polymer to the fibers, first instantaneously by pouring the polymer solution into a jar containing the fiber dispersion (jar experiments) and second, at controlled rates (the reactor experiments). In the latter case, the rate of supply of polymer to the fiber dispersion confined in the reactor was monitored by setting the concentration of the solution being injected at a controlled rate. The concentration of the polymer solution exerts a paramount influence on the kinetics of adsorption and on the amount of polymer adsorbed at (or near) fiber surface saturation, while the rate of polymer supply only plays a minor role. The main observation is the emergence of two types of polymer layers corresponding to diffuse and dense layers. The former were characterized by adsorption layers of density smaller than 0.65 mg/g cellulose that are composed of adsorbed polymers having sustained extended flattening in the adsorbed state. The latter reach densities as high as 10 mg/g cellulose when the fiber surface is fully coated, thus indicating that reconformation is limited or even impeded at short terms. The threshold adsorption corresponds more or less to equilibrated layers, since the final coverage determined at adsorption equilibrium did not exceed 0.6 to 0.7 mg/g cellulose.

Journal Article↗
PubMed2004

Heats of adsorption of linear CO species adsorbed on the Au degrees and Ti+delta sites of a 1% Au/TiO2 catalyst using in situ FTIR spectroscopy under adsorption equilibrium.

The heats of adsorption of two linear CO species adsorbed on the Au degrees particles (denoted L(Au degrees)) and on the Ti(+delta) sites (denoted L(Ti+delta)) of a 1% Au/TiO(2) catalyst are determined as the function of their respective coverage by using the AEIR procedure (adsorption equilibrium infrared spectroscopy) previously developed. Mainly, the evolutions of the IR band area of each adsorbed species (2184 cm(-1) for L(Ti+delta) and at 2110 cm(-1) for L(Au degrees)) as a function of the adsorption temperature T(a), at a constant CO adsorption pressure P(CO), provide the evolutions of the coverages theta(LTi+delta) and theta(LAu degrees ) of each adsorbed CO species with T(a) in isobar conditions that give the individual heats of adsorption. It is shown that they linearly vary from 74 to 47 kJ/mol for L(Au degrees ) and from 50 to 40 kJ/mol for L(Ti+delta) at coverages 0 and 1, respectively. These values are consistent with literature data on model Au particles and TiO(2). In particular, it is shown that the mathematical formalism supporting the AEIR procedure can be applied to literature data on Au-containing solids (single crystals and model particles).

Journal Article↗