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PubMed2005

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.

Adsorption↗
PubMed2004

Adsorption of fluorescein by protein crystals.

Adsorption characteristics of native and cross-linked lysozyme crystals were examined using fluorescein as model adsorbate. The adsorption isotherms exhibited Langmuir or linear behavior. The affinity constant (b1) and the adsorption capacity (Qsat) for fluorescein were found to depend on the type and concentration of co-solute present in the solution. The dynamics of adsorption isotherm transition from Langmuir to linear showed that affinity of lysozyme for solutes increases in the order 2-(cyclohexylamino)ethanesulphonic acid (CHES), 4-morpholinepropanesulphonic acid (MOPS), acetate, fluorescein. Furthermore, the crystal morphology, the degree of cross-linking of the crystals, and, in particular, solution pH were identified as factors determining fluorescein adsorption by the lysozyme crystals. These factors seem to affect crystal capacity for the solute more than affinity for the solute. Adsorption of fluorescein by cross-linked tetragonal lysozyme crystals was exponentially dependent on the lysozyme net charge calculated from the final solution pH. The 3-5-fold increase in the fluorescein adsorption as a result of cross-linking is presumably due to the increasing hydrophobicity of the lysozyme crystal.

Adsorption↗
PubMed1994

Inhibition of adsorption of human T-cell-leukemia virus type 1 by a plant lectin, wheat-germ agglutinin.

Thirty-six lectins that recognize various sugar chains were examined for inhibitory activities against infection with human T-cell leukemia virus type I (HTLV-I). Wheat-germ agglutinin (WGA) was the most inhibitory among them: plating of the pseudotype of vesicular-stomatitis virus (VSV) bearing envelope antigens of HTLV-I was markedly inhibited by treatment of indicator cells with WGA just before adsorption, but not by treatment after virus adsorption. Treatment with WGA before adsorption, however, could not inhibit the plating of VSV, VSV pseudotypes of bovine leukemia virus, Moloney murine leukemia virus and human immunodeficiency virus type I. Syncytium formation induced by HTLV-I was also inhibited by WGA upon co-cultivation of U-251 MG human glioma cells or MOLT-4 human T-cells with HTLV-I-producing C91/PL cells. Formation of proviral DNA detected one day after infection was also inhibited when indicator cells had been treated with WGA before adsorption of HTLV-I, but not after its adsorption. These findings indicated that WGA specifically inhibits plating of HTLV-I when added to culture just before adsorption and suggested that a substance(s) containing sugar chains recognized by WGA might be involved in an adsorption step of HTLV-I.

Adsorption↗
PubMed1988

Correlations between mouse 3T3 cell spreading and serum fibronectin adsorption on glass and hydroxyethylmethacrylate-ethylmethacrylate copolymers.

The interaction of cells with solid surfaces is important in many settings, including the response of tissue to implanted materials. Protein adsorption to the surface plays a critical role in controlling cell interactions with surfaces. However, few comprehensive studies of both cell behavior and protein adsorption in complex protein mixtures (e.g., serum) have been done so the connection between these events is not well understood. In particular, methods to systematically perturb both protein adsorption and cell behavior in order to understand their relationship have been lacking. To induce changes in cell and protein behavior, the effects of serum dilution and substrate surface chemistry were studied. Surface chemistry was varied by using a series of polymers and copolymers of hydroxyethyl methacrylate (HEMA) and ethylmethacrylate (EMA) varying in their hydrophobic/hydrophilic balance. Large changes in cell spreading and fibronectin adsorption were observed when either serum concentration or polymer type was varied. The spreading of 3T3 cells in serum was found to be well correlated with the amount of fibronectin adsorption to the substrates. Attachment was not correlated with fibronectin adsorption, especially on glass preadsorbed with diluted serum. For 3T3 cells and perhaps other cells that have a receptor for a protein which is present in the medium, the amount of adsorption of this protein to the substrate appears to be a critical factor controlling cell interactions with the substrate.

Adsorption↗
PubMed1989

Transient adsorption of fibrinogen on foreign surfaces: similar behavior in plasma and whole blood.

The adsorption of fibrinogen from both human whole blood and plasma to a number of "foreign" surfaces is reported. Adsorption was measured as a function of plasma or blood dilution using radioiodine labeling. We showed previously that adsorption of fibrinogen from plasma exhibits a maximum at a plasma dilution of about 100:1, and have attributed this behavior to competition from other plasma proteins. (The same phenomenon is manifest as a time transient in fibrinogen adsorption.) In the present work we show that exactly the same trends are observed in whole blood. For each of the four surfaces, glass, siliconized glass, collagen-coated glass and polyethylene, the adsorption of fibrinogen as a function of dilution is the same in whole blood as in plasma. Each of these surfaces shows a unique dependence of fibrinogen adsorption on plasma or blood dilution. On cuprophane and a hydrophilic polyether urethane there is essentially no adsorption of fibrinogen from blood or plasma. For the hydrophilic polyurethane this result may be artifactual, but the absence of fibrinogen binding to cuprophane in blood or plasma is real since fibrinogen is found to be adsorbed in monolayer amounts from buffer.

Adsorption↗
PubMed1992

Kinetics supramolecular structure and equilibrium properties of fibrinogen adsorption at liquid-solid interfaces.

Adsorption of fibrinogen onto hydrophobic and hydrophilic quartz surfaces was studied by ellipsometry and transmission electron microscopy (TEM) of negatively stained proteins. The initial adsorption at the hydrophobic surface, measured by ellipsometry, can be described by an apparent forward rate constant k1 of 2 x 10(4) M-1 s-1. This constant was time-dependent and is therefore considered as a rate coefficient. The apparent forward rate coefficient of adsorption to a hydrophilic surface was both time-dependent and concentration-dependent, indicating a history-dependent process of adsorption. Plateau levels of adsorption were concentration-dependent and lower at the hydrophilic quartz surface (1.2 pmol/cm2) than at the hydrophobic surface (1.8 pmol/cm2). These surface concentrations correspond to rather tight-packed monolayers of molecules adsorbed end-on. The initial desorption can be described by a first order rate constant (k-1 approximately 10(-4) s-1), down to 80-90% of the initial surface concentration. The dissociation rate then decreased (k-1 approximately 10(-6) s-1) resulting in an apparently stable level of adsorbed protein. Slow changes of the binding strength of adsorbed proteins was seen during 24-72 h adsorption time. Deviations from an ideal equilibrium isotherm were seen both in the time dependence and as concavities in a Scatchard plot, suggesting intermolecular cooperativity. At low bulk concentrations a heterogeneous distribution of fibrinogen molecules was found at the surface below monolayer coverage. The supramolecular structure was characterized by the formation of end-to-end dimers and trimers laying down at the surface. At higher surface concentration adsorbed molecules showed polycrystalline structure with repeated nearest neighbor distances at 16 nm. The distribution of adsorbed fibrinogen molecules indicates that surface-adsorbed fibrinogen may form a two-phase system, containing significant amounts of water. The atypical kinetics and concentration dependence of fibrinogen adsorption may thus be due to properties of a two-dimensional phase separation from a three-dimensional liquid bulk.

Adsorption↗
PubMed2003

Protein adsorption on mixtures of hydroxyl- and methyl-terminated alkanethiols self-assembled monolayers.

The effect of surface composition and wettability on the adsorption of human serum albumin (HSA) was studied. Self-assembled monolayers (SAMs) containing mixtures of longer chain methyl- and shorter chain hydroxyl-terminated alkanethiols on gold were used to produce a range of surfaces with different wettabilities and exposed functional groups. Different SAMs were characterized by X-ray photoelectron spectroscopy, water contact angles, and Fourier transform infrared reflection absorption spectroscopy (IRAS). HSA adsorption onto the different SAMs was evaluated by contact angle measurements (wetting tension determinations), radiolabeling of proteins, and IRAS. Concerning HSA adsorption, all the techniques demonstrated higher HSA adsorption on more hydrophobic surfaces. The wetting tension measurements and IRAS suggested a gradual decrease of the HSA adsorption with increases of surface hydrophilicity. Radiolabeled albumin measurements also demonstrated a significant decrease of HSA adsorption on the pure hydroxyl-terminated SAMs. However, no significant differences were detected between mixed and pure methyl-terminated SAMs. Studies of HSA exchangeability with human fibrinogen have suggested that an ideal percentage of hydroxyl groups on the surface may increase albumin affinity without fibrinogen adsorption.

Adsorption↗
PubMed2004

Small changes in the polymer structure influence the adsorption behavior of fibrinogen on polymer surfaces: validation of a new rapid screening technique.

Numerous studies conclude that the selective adsorption of plasma proteins on materials contacting blood or tissue affects all subsequent interactions related to the biocompatibility of artificial surfaces. However, there are only a few studies available, which clearly demonstrate that there is a correlation between surface chemistry and selective protein adsorption. Detailed knowledge of such correlations would facilitate the design of biocompatible materials. In this study, a rapid, fluorescence-based, screening technique using a 384-well format for polymer-protein interactions was developed. The screening assay was used to measure the adsorption of human fibrinogen on 46 test polymers (44 polyarylates selected from a combinatorial library of tyrosine-derived polyarylates, and two lactide-based polymers). In this library of polyarylates, structural changes are generated by variations in either the polymer backbone or the polymer pendent chain. Although no overall trend between polymer hydrophobicity and fibrinogen adsorption could be identified using the entire set of test polymers (R(2) = 0.43), fibrinogen adsorption was clearly correlated with variations in the pendent chain structure. Thus, when the test polymers were grouped by backbone composition, increased hydrophobicity of the pendent chain was significantly correlated with reduced fibrinogen adsorption. The following R(2) coefficients within the polymer backbone groups were determined: 0.87 (diglycolates); 0.98 (glutarates); 0.73 (adipates); 0.87 (suberates); 0.67 (3-methyl-adipates). Our results demonstrate that it is possible to screen for protein-material interactions in a cost-effective fashion using a miniaturized immunofluorescence technique. Further, we demonstrate that small changes in chemical composition can significantly influence the adsorption of human fibrinogen on polymer surfaces. The lactide-based polymers were among those polymers exhibiting the highest tendency to adsorb fibrinogen. This information may be useful when polymers have to be selected for specific biomaterial applications.

Adsorption↗
PubMed2004

Pesticide adsorption in the vadose zone: a case study on Eocene and Quaternary materials in Northern France.

We present a set of adsorption coefficients measured on various Eocene and Quaternary materials sampled from the vadose zone of a catchment in Northern France for three herbicides, atrazine, isoproturon and metamitron. Some vadose zone materials were found to have higher adsorption coefficients than the topsoil. The adsorption coefficients were strongly dependent on the clay content of the material. From 83% to 97% of the variability in the adsorption coefficients could be explained by a linear relationship to the clay content. Adsorption coefficients normalized for clay content, Kclay, ranged between 1.6 and 17.6 litre kg(-1) for atrazine. Neglecting the adsorption properties of the vadose zone and relying exclusively on Koc values to predict mobility may bias regional or local risk assessment of groundwater contamination by pesticides. More information on the adsorption properties of geological materials should be collected to improve our ability to predict pesticide concentrations in groundwaters.

Adsorption↗
PubMed1998

An electrochemical enzyme immunoassay for chicken luteinizing hormone: extension of the detection limit by adequate control of the nonspecific adsorption.

A noncompetitive heterogeneous enzyme immunoassay for the determination of chicken luteinizing hormone (LH) was equipped with an electrochemical endpoint in order to further enhance its sensitivity. The immunological principle of the original ELISA remained essentially unchanged, except for the fact that the peroxidase label was replaced by alkaline phosphatase, since in the upgraded version of the assay, p-aminophenyl phosphate was to be used as the substrate of alkaline phosphatase. Enzyme-generated p-aminophenol was injected into a flow-injection system and detected amperometrically in a thin-layer flow cell with a glassy carbon electrode at 0.325 V vs Ag/AgCl. A classical problem associated with this type of solid-phase immunoassay is the adsorption of proteins other than the capture antibody to the solid phase. The detection sensitivity is therefore often limited by a large background signal observed in the absence of antigen. In the present study, an experiment was designed to examine in each step of the assay the contribution of each of the potential sources of background current. It was shown that the major contribution to the background current was caused by the nonspecific adsorption of biotinylated secondary antibody. Adsorption of the secondary antibody (biotinylated goat anti-rabbit IgG) to the capture antibody (mouse anti-chicken LHbeta) was clearly a case of specific aspecificity, whereas adsorption to the solid phase itself had to be treated as a nonspecific aspecificity. Addition of 0.25% mouse serum to the secondary antibody as a source of mouse immunoglobulin could overcome the cross-reaction and markedly reduced adsorption to capture antibody. The second part of nonspecific adsorption was eliminated by using combinations of Tween 20 and bovine serum albumin as blocking agents. Controlling the adsorption of the biotinylated secondary antibody in this way decreased the detection limit from 39 pg/ml in the original assay to 2.5 pg/ml in the electrochemical version. This way, the plasma volume of samples containing on the order of 1 ng/ml LH was reduced to less than 10 microl. The linear range was 2.5-625 pg/ml. The method allowed us to measure LH in buffer and in adult and juvenile chicken plasma.

Adsorption↗
PubMed2002

The interplay of diffusional and electrophoretic transport mechanisms of charged solutes in the liquid film surrounding charged nonporous adsorbent particles employed in finite bath adsorption systems.

A model that describes the diffusive and electrophoretic mass transport of the cation and anion species of a buffer electrolyte and of a charged adsorbate in the liquid film surrounding nonporous adsorbent particles in a finite bath adsorption system, in which adsorption of the charged adsorbate onto the charged surface of the nonporous particles occurs, is constructed and solved. The dynamic behavior of the mechanisms of this model explicitly demonstrates (a) the interplay between the diffusive and electrophoretic molar fluxes of the charged adsorbate and of the species of the buffer electrolyte in the liquid film surrounding the nonporous adsorbent particles, (b) the significant effect that the functioning of the electrical double layer has on the transport of the charged species and on the adsorption of the charged adsorbate, and (c) the substantial effect that the dynamic behavior of the surface charge density has on the functioning of the electrical double layer. It is found that at equilibrium, the value of the concentration of the charged adsorbate in the fluid layer adjacent to the surface of the adsorbent particles is significantly greater than the value of the concentration of the adsorbate in the finite bath, while, of course, the net molar flux of the charged adsorbate in the liquid film is equal to zero at equilibrium. This result is very different than that obtained from the conventional model that is currently used to describe the transport of a charged adsorbate in the liquid film for systems involving the adsorption of a charged adsorbate onto the charged surface of nonporous adsorbent particles; the conventional model (i) does not consider the existence of an electrical double layer, (ii) assumes that the transport of the charged adsorbate occurs only by diffusion in the liquid film, and (iii) causes at equilibrium the value of the charged adsorbate in the liquid layer adjacent to the surface of the particles to become equal to the value of the concentration of the charged adsorbate in the liquid of the finite bath. Furthermore, it was found that a maximum can occur in the dynamic behavior of the concentration of the adsorbate in the adsorbed phase when the value of the free molecular diffusion coefficient of the adsorbate is relatively large, because the increased magnitude of the synergistic interplay between the diffusive and electrophoretic molar fluxes of the adsorbate in the liquid film allows the adsorbate to accumulate (to be entrapped) in the liquid layer adjacent to the surface of the adsorbent particles faster than the concentrations of the electrolyte species, whose net molar fluxes are significantly hindered due to their opposing diffusive and electrophoretic molar fluxes, can adjust to account for the change in the surface charge density of the particles that arises from the adsorption of the charged adsorbate. The results presented in this work also have significant implications in finite bath adsorption systems involving the adsorption of a charged adsorbate onto the surface of the pores of charged porous adsorbent particles, because the diffusion and the electrophoretic migration of the charged solutes (cations, anions, and charged adsorbate) in the pores of the adsorbent particles will depend on the dynamic concentration profiles of the charged solutes in the liquid film surrounding the charged porous adsorbent particles. The results of the present work are also used to illustrate how the functioning of the electrical double layer could contribute to the development of inner radial humps (concentration rings) in the concentration of the adsorbate in the adsorbed phase of charged porous adsorbent particles.

Adsorption↗
PubMed2006

Adsorption of ionisable pesticides in soils.

Understanding the fate of a pesticide in soil is fundamental to the accurate assessment of its environmental behaviour and vital in ensuring the safe use of new and existing products. Ionisable pesticides comprise a significant proportion of both existing and new active substances registered for use in agriculture worldwide. This group of pesticides includes chemicals that are frequently found in groundwater and surface waters in many different countries. Despite this, approaches to predict the influence of soil properties on the behaviour of ionisable pesticides in soils are poorly developed. Current regulatory assessments frequently default to methods developed for nonionic chemicals, although it is evident that ionisable compounds do not often react like neutral molecules. This review presents the state of knowledge on the adsorption of ionisable pesticides in soils. It first introduces the issues concerning adsorption and the characteristics of this particular kind of chemical. The mechanisms postulated for the adsorption of ionisable pesticides are then described: these are hydrophobic partitioning, ionic exchange, charge transfer, ligand exchange, cation or water bridging, and the formation of bound residues. Relatively little experimental evidence is available, and we are still unable to determine the quantitative contribution of each process in a particular situation. Knowledge is still lacking concerning phenomena occurring at the surfaces of soil particles. Measurements do not allow determination of the operative pH at the surface of soil particles or in microenvironments, and the influence of ionic strength or competition effects is difficult to assess. Subsequently, the review focuses on the influence of soil properties on adsorption and on potential to predict the behaviour of ionisable pesticides in soils. Unlike hydrophobic compounds, adsorption of ionisable pesticides is highly sensitive to variation in pH. This relationship mainly derives from the different proportion of ionic and neutral forms of the pesticide present at each pH level but also from the presence of surfaces with pH-dependent charges in soils. Soil organic matter generally promotes adsorption, although a negative influence has sometimes been reported. Clay and oxides can also play a significant role in some cases. So far, no modelling approach has been applied successfully to a range of ionisable pesticides to predict their adsorption in soils. The standardization of experimental settings and the application of approaches specific to a particular class of pesticide or different type of soil might be necessary to describe the complexity of interactions among ionisable molecules. Degradation of ionisable pesticides is influenced by soil pH in a particular way that relates to changes in sorption, changes in composition and activity of the microbial community, and to shifts in the balance between different degradative mechanisms.

Adsorption↗
PubMed1980

Adsorption of protein and non-protein amino acids on a clay mineral: a possible role of selection in chemical evolution.

The adsorption of protein and non-protein amino acids by Na-montmorillonite was studied at pH 3, 7, and 10, in order to determine whether clays could have played a part in selection of protein over non-protein amino acids in prebiotic times. Five pairs of amino acids, containing two to six carbons, were used at a concentration equal to 100% cation exchange capacity of the clay in adsorption experiments. The following pairs of protein and non-protein amino acids were used: glycine and sarcosine, alpha-alanine and beta-alanine, alpha-aminobutyric acid and gamma-aminobutyric acid, valine and norvaline, L-isoleucine and D-alloisoleucine. No selective adsorption of protein amino acids occurred at varying hydrogen ion concentrations. The one difference observed in the adsorption of amino acids in the mixtures was a three- and four-fold greater adsorption of beta- and gamma-amino acids, respectively, than their alpha-amino acid counterparts under acidic and neutral conditions. Strong and weak adsorption of amino acids on the clay were correlated with mechanisms such as cation exchange and hydrogen bonding. The results of this research are significant to understanding the role of clay in chemical evolution because they do not support the role of preferential adsorption of protein over non-protein amino acids by clays.

Adsorption↗
PubMed1987

Selective adsorption of porcine-amelogenins onto hydroxyapatite and their inhibitory activity on hydroxyapatite growth in supersaturated solutions.

The selective adsorption of amelogenins onto synthetic hydroxyapatite (HA) and their inhibitory activity on the seeded HA crystal growth were investigated using enamel proteins obtained from the outer layer of immature porcine-enamel (soft, cheeselike in consistency) of developing permanent incisors. Special interests were paid to the effect of a postsecretory degradation of the original amelogenin(s) on their adsorption and inhibitory activity. In the adsorption studies, it was apparent that the originally secreted amelogenin (25 K), proline, and histidine-rich protein (2a), as well as the higher molecular weight components (60-90 K), showed a strong adsorption affinity onto the HA. This adsorption of protein 2a was related to its inhibition of the crystal growth of seeded HA in a dilute supersaturated solution. On the other hand, the partially degraded product (20 K) of amelogenins, protein 2b, lost the high adsorption affinity onto the HA, and consequently showed no significant inhibitory activity. The observed selective adsorption of protein 2a onto HA was apparent at pH 6.0 and pH 7.4 even in the presence of dissociative solvents, such as 3 M urea or 2 and 4 M guanidine-HCl; however, this selective behavior was sensitive to changes in pH, and was not displayed at pH values of 7.8 or 10.8. The results suggest that the originally secreted amelogenin 2a may play an active role in amelogenesis, and that enamel mineralization could be regulated by the secretion of amelogenins and their inactivation through partial enzymic degradation, prior to their complete removal.

Adsorption↗
PubMed2003

Analysis of hydroxyapatite surface coverage by amelogenin nanospheres following the Langmuir model for protein adsorption.

The assembly of amelogenin protein into nanospheres is postulated to be a key factor in the stability of enamel extracellular matrix framework, which provides the scaffolding for the initial enamel apatite crystals to nucleate and grow. Adsorption isotherms were evaluated in order to investigate the nature of interactions of amelogenin nanospheres with hydroxyapaite crystals in solution, where their assembly status and particle size distribution are defined. We report that the adsorption isotherm of a recombinant mouse amelogenin (rM179) on synthetic hydroxyapatite crystals can be described using a Langmuir model indicating that amelogenin nanospheres adsorb onto the surface of apatite crystals as binding units with defined adsorption sites. The adsorption affinity and the maximum adsorption sites were 19.7 x 10(5) L/mol and 6.09 x 10(-7) mol/m2, respectively, with an r2 value of 0.99. Knowing the composition and particle size distribution of amelogenin nanospheres under the condition of adsorption experiments, we have calculated the number of nanospheres and the crystal surface area covered by each population of nanospheres at their maximum adsorption. It was found that total maximum binding covers 64% of the area unit. This observation supports the speculation that amelogenin binding onto apatite surface is selective and occurs only at certain sites.

Adsorption↗
PubMedDate not supplied

Phenanthrene adsorption by soils treated with humic substances under different pH and temperature conditions.

The mobility of phenanthrene (PHE) in soils depends on its sorption and is influenced by either the existing soil humus or exogenous humic substances. Exogenous humic acids (HAs) were added to soil to enhance the amount of soil organic carbon (SOC) by 2.5, 5.0, and 10.0 g kg(-1). PHE desorption of the treated soils was determined at two pH levels (3.0 and 6.0) and temperatures (15 and 25 degrees C). Soil PHE adsorption was related to pH and the type and quantity of added HAs. Humic acid (HA) and fulvic acid (FA) derived from peat had different effects on adsorption of PHE. Adsorption increased at first and then decreased with increasing quantity of exogenous FA. When the soil solution pH (in 0.005 M CaCl(2)) was 4.5 or 3.0, the turning points were 2.5 g FA kg(-1) at pH 3.0 and 5 g FA kg(-1) at pH 4.5. When soil solution pH was 6, the amount of adsorbed PHE was enhanced with increasing exogenous HAs (HA or FA) and amount of adsorption by soil treated with FA was higher than with HA. Adsorption of PHE in the FA treatment at 10.0 g kg(-1) was lower than the controls (untreated soil or treatment with HAs at 0 g kg(-1)) when the soil solution pH was 3.0. This suggests that FA adsorbed by soil was desorbed at low pH and would then increase PHE solubility, and PHE then combined with FA. PHE adsorption was usually higher under lower pH and/or lower temperature conditions. PHE sorption fitted the Freundlich isotherm, indicating that exogenous humic substances influenced adsorption of phenanthrene, which in turn was affected by environmental conditions such as pH and temperature. Thus, exogenous humic substances can be used to control the mobility of soil PAHs under appropriate conditions to decrease PAH contamination.

Adsorption↗
PubMed1985

Atypical Langmuir adsorption of inhalation anesthetics on phospholipid monolayer at various compressional states: difference between alkane-type and ether-type anesthetics.

Adsorption of chloroform, halothane, enflurane and diethyl ether on the air/water interface was compared with adsorption on the dipalmitoylphosphatidylcholine monolayer, spread on the air/water interface, at four compressional states; 88.5, 77.0, 66.5 and 50.5 A2 surface area per phosphatidylcholine molecule. Anesthetics were administered from the gas phase. The affinities of these agents to the phosphatidylcholine monolayer varied according to the state of the monolayer. Chloroform and halothane showed a stronger affinity to the highly compressed phosphatidylcholine monolayer (50.5 A2) than to the expanded monolayer (88.5 A2) or to the air/water interface without the monolayer. Diethyl ether behaved in reverse; a stronger affinity to the expanded monolayer was exhibited than to the compressed monolayer. Enflurane showed the highest affinity to the intermediately compressed monolayer (77.0 A2). The adsorption isotherm of anesthetics to the monolayer was characterized by atypical Langmuir-type, in which available number of binding sites changed when anesthetics were adsorbed. The mode of adsorption onto the monolayer was dissimilar to adsorption onto air/water interface, where adsorption followed the Gibbs surface excess. A theory is presented to explain the above differences. The adsorbed anesthetic molecules do not stick to phosphatidylcholine molecules but penetrate into the monolayer lattice and occupy the phosphatidylcholine sites at the interface. Quantitative agreement between the theory and the experimental data was excellent. For the monolayer at 50.5 A2 compression, the changes in the transfer free energy accompanying the anesthetic adsorption from the gas phase to the monolayer were in the order of chloroform greater than halothane greater than enflurane greater than diethyl ether, in agreement with the clinical potencies.

Adsorption↗
PubMed1987

Adsorption of ionized and neutral pentachlorophenol to phosphatidylcholine membranes.

We have studied adsorption of pentachlorophenol (PCP) to phosphatidylcholine (PC) membranes by measuring the electrophoretic mobility of multilayered lipid vesicles in PCP solutions. PC vesicles become negatively charged due to the adsorption of ionized PCP, and we have found that their zeta potential depends upon the ionic strength and pH of the aqueous suspension. We have shown that the experimental results can be adequately accounted for in terms of a two-component Langmuir-Stern-Grahame adsorption model assuming that the 'PCP adsorption sites' are occupied either by the neutral (HA) or the ionized (A-) species. The characteristics of adsorption isotherms of the PCP - PC membrane are as follows: the association constants are KA = 55,000 dm3/mol, KHA = 279,000 dm3/mol; 4.3 PC molecules make up each PCP adsorption site at saturation; the linear partition coefficients are beta HA = (15.5 +/- 0.7) x 10(-5) m and beta A = (3.0 +/- 0.3) x 10(-5) m. The properties of PCP adsorption isotherms for PC membranes predict an increased pKa value of membrane-bound PCP, which has been observed in related studies.

Adsorption↗