Influence of polymer structure on adsorption behavior at solid–liquid interface by Monte Carlo simulation

Monte Carlo simulations for the adsorption of polymers including random copolymer, homopolymer, diblock copolymer and two kinds of triblock copolymers, respectively, in nonselective solvent at solid–liquid interface have been performed on a simple lattice model. The effect of polymer structure on adsorption properties was examined. In simulations, all polymeric molecules are modeled as self-avoiding linear chains composed of two segments A and B while A is attractive to the surface and B is non-attractive. It was found that for all polymers, the size distribution of various configurations is determined by the linked sequence of segments and the interaction energy between segment and surface. The results of simulation show that the adsorbed amount always increases with increasing bulk concentration but the adsorption layer thickness is mostly dependent on the adsorption energy at a fixed fraction of segments A. On the other hand, diblock copolymer has always the highest surface coverage and adsorbed amount, while random copolymers and homopolymers give generally the smallest surface coverage and adsorbed amount. It is shown that the sequence of polymer chains, i.e. molecular structure, is the most important factor in affecting adsorption properties at the same composition and interaction between segment and surface. The results also show that the adsorption behavior of random copolymers is remarkably different from that of block copolymers, but acting like homopolymer.     

The production and application of a regenerable filter system for adsorption of some atmospheric contaminants

In this work, a new filter, used to prevent atmospherical pollution, has been developed. Spherical amorphous shaped silicates (such as KC-Siliperl AF 125 and Aluminium silicate 596 FA) were coated with different materials which were prepared from the hydrolysis-condensation products of organically modified silanes and metal alkoxides. The adsorption capacities of such silicates for different solvents; ethylacetate, toluene, n-hexane and cyclohexanone were investigated. It was found that KC-Siliperl AF 125 coated with IMEO (a commercial silane) adsorbed all the solvents better than Aluminium silicate 596 FA, and ethylacetate was adsorbed more than the other solvents.     

Action of Plant Growth Regulators. IV. Adsorption of Unsubstituted and 2,6-Dichloro-aromatic Acids to Oat Monolayers

The adsorption of chloro-aromatic acids to monomolecular layers of oat squashes is reported in earlier papers but it was not possible by the technique used, to measure unambiguously the adsorption of unsubstituted and 2,6-dichloro-aromatic acids. This has now been achieved by a modification of the earlier method and involves assessments of competitive adsorption between the unknown acid and a standard acid, using measurements of surface potential.

Benzoic and phenoxyacetic acids were not adsorbed but phenylacetic acid was weakly adsorbed. The second ring in naphthalene and naphthoxyacetic acids greatly increased adsorption. Substitution of the 2 and 6 positions in the phenyl and phenoxyacetic acids resulted in low adsorption but 2,6-disubstituted phenoxybutyric and benzoic acids were more highly adsorbed.

The adsorption values from earlier work are combined and discussed in relation to the growth-regulating activity of the acids. It is conciuded that there is no direct relation embracing all acids between adsorption and activity, notable exceptions being those substituted by chlorine in the 3-position of the aromatic ring. However, for a number of acids it is suggested that activity is limited not only by their ability to interact at enzyme sites but also by the amount of acid immobilised by adsorption when moving to these sites. It is also concluded that the hydrophilic/lipophilic balance of a growth regulator sometimes used as a guide to its activity, is an unreliable indication of interfacial behaviour.

     

Comparative adsorption of human enteroviruses, simian rotavirus, and selected bacteriophages to soils.

Virus adsorption to soils is considered to be the most important factor in removing viruses after land treatment of wastewater. Most of the studies on virus adsorption to soils have utilized poliovirus as the model system. In the present study, comparative adsorption of a number of different types and strains of human enteroviruses and bacteriophages to nine different soil types was studied. Under the experimental conditions of this study, greater than 90% of all viruses adsorbed to a sandy loam soil except echovirus types 1, 12, and 29 and a simian rotavirus (SA-11), which adsorbed to a considerably lower degree. A great deal of variability was observed between adsorption of different strains of echovirus type 1, indicating that viral adsorption to soils is highly strain dependent. Of the five phages studied, f2 and phi X174 adsorbed the least. In addition to being dependent on type and strain of virus, adsorption was found to be influenced also by type of soil. Thus, soils having a saturated pH of less than 5 were generally good adsorbers. From these results, it appears that no one enterovirus or coliphage can be used as the sole model for determining the adsorptive behavior of viruses to soils and that no single soil can be used as the model for determining viral adsorptive capacity of all soil types.     

Comparative adsorption of human enteroviruses, simian rotavirus, and selected bacteriophages to soils.

Virus adsorption to soils is considered to be the most important factor in removing viruses after land treatment of wastewater. Most of the studies on virus adsorption to soils have utilized poliovirus as the model system. In the present study, comparative adsorption of a number of different types and strains of human enteroviruses and bacteriophages to nine different soil types was studied. Under the experimental conditions of this study, greater than 90% of all viruses adsorbed to a sandy loam soil except echovirus types 1, 12, and 29 and a simian rotavirus (SA-11), which adsorbed to a considerably lower degree. A great deal of variability was observed between adsorption of different strains of echovirus type 1, indicating that viral adsorption to soils is highly strain dependent. Of the five phages studied, f2 and phi X174 adsorbed the least. In addition to being dependent on type and strain of virus, adsorption was found to be influenced also by type of soil. Thus, soils having a saturated pH of less than 5 were generally good adsorbers. From these results, it appears that no one enterovirus or coliphage can be used as the sole model for determining the adsorptive behavior of viruses to soils and that no single soil can be used as the model for determining viral adsorptive capacity of all soil types.     

The “specific” binding of insulin to polyethene and other materials

It is known that insulin is adsorbed onto glass but it has been assumed that it is not adsorbed onto plastic. We find that tritium-labelled insulin is adsorbed onto all materials tried. The adsorption is reduced in the presence of other proteins and can be prevented altogether by coating the vessels with cetyl alcohol.     

Polyelectrolyte-mediated adsorption of amelogenin monomers and nanospheres forming mono- or multilayers

We have applied optical waveguide lightmode spectroscopy combined with streaming potential measurements and Fourier-transformed infrared spectroscopy to investigate adsorption of amelogenin nanospheres onto polyelectrolytes. The long-term objective was to better understand the chemical nature of these assemblies and to gain further insight into the molecular mechanisms involved during self-assembly. It was found that monolayers of monomers and negatively charged nanospheres of a recombinant amelogenin (rM179) irreversibly adsorbed onto a positively charged polyelectrolyte multilayer films. On the basis of measurements performed at different temperatures, it was demonstrated that intermolecular interactions for the formation of nanospheres were not affected by their adsorption onto polyelectrolytes. Consecutive adsorption of nanospheres resulting in the formation of multilayer structures was possible by using cationic poly(l-lysine) as mediators. N-Acetyl-d-glucosamine (GlcNac) did not disturb the nanosphere-assembled protein's structure, and it only affected the adsorption of monomeric amelogenin. Infrared spectroscopy of adsorbed amelogenin revealed conformational differences between the monomeric and assembled forms of rM179. While there was a considerable amount of alpha-helices in the monomers, beta-turn and beta-sheet structures dominated the assembled proteins. Our work constitutes the first report on a structurally controlled in vitro buildup of an rM179 nanosphere monolayer-based matrix. Our data support the notion that amelogenin self-assembly is mostly driven by hydrophobic interactions and that amelogenin/PEM interactions are dominated by electrostatic forces. We suggest that similar forces can govern amelogenin interactions with non-amelogenins or the mineral phase during enamel biomineralization.     

On the Adsorption of Human Acidic Proline-rich Proteins (PRP-1 and PRP-3) and Statherin at Solid/liquid Interfaces

The objective of the present study was to investigate the adsorption of PRP-1, PRP-3 and statherin to solid surfaces in terms of dependence on concentration, the presence of electrolyte and surface wettability. Time resolved in situ ellipsometry was used to determine the adsorbed amounts and adsorption rates of pure PRP-1, PRP-3 and statherin onto pure (hydrophilic) and methylated (hydrophobized) silica surfaces. The initial film build-up was fast and plateaus were reached within 10 min at all concentrations for both types of surfaces and all proteins. The observed adsorption and calculated diffusion rates of PRP-1, PRP-3 and statherin, respectively, indicated that the initial adsorption was mass transport controlled at low concentrations. At hydrophobic surfaces, isotherm shapes and adsorbed amounts were similar for PRP-1 and PRP-3, while statherin adsorbed to a higher extent. At hydrophilic surfaces only PRP-1 adsorbed substantially, while for PRP-3 and statherin adsorbed amounts were low. The presence of Ca 2+ ions in the phosphate buffer solution increased the adsorption of statherin and PRP-3 on hydrophobic surfaces, while PRP-1 was unaffected. On hydrophilic surfaces, all three proteins adsorbed in higher amounts in NaCl, compared to CaCl 2 at similar ionic strength. It is concluded that acidic PRPs (PRP-1 and PRP-3) and statherin readily form films on a variety of materials and solution conditions, showing that their functions may be fulfilled under a wide range of conditions.     

Direct observation of intraparticle equilibration and the rate-limiting step in adsorption of proteins in chromatographic adsorbents with confocal laser scanning microscopy

The adsorption of different proteins in a single biospecific and hydrophobic adsorbent particle for preparative protein chromatography has been observed directly by confocal laser scanning microscopy as a function of time at a constant bulk concentration c(b). The bulk concentration was in the non-linear part of the adsorption isotherm. At all times the concentration of free protein at the particle surface was almost equal to the bulk content indicating that external mass transfer resistance is not rate limiting for the adsorption under these conditions. Inside the particles a distinct maximum in adsorbed and free protein concentration that moved inside to a distance of approximately 0.2 R (R particle radius) from the particle surface, was observed. This is due to a decreasing solid-phase density and adsorptive capacity in the particle between 0.8 R and R indicating that the fraction of macropores (or void space) is larger in the outer than in the inner part of the adsorbent particles. By increasing the bulk concentration by a factor of 10 the equilibration time was reduced by about the same magnitude. This is in agreement with the concentration dependence of the effective pore diffusion coefficient D(p,eff)=D(p)/[epsilon(p)[1+nK/(K +c)(2)]] derived from the mass conservation relations describing the adsorption process. The time dependence protein adsorption up to approximately 90% of the equilibration value q* could be described by a bilinear free driving force model. The rapid equilibration in the outer part of the particle with a half-life time of approximately 100 s in the studied systems accounted for 0.3-0.4 q*. The slower equilibration with a up to ten times longer half-life time, was the adsorption in the inner part of the particle that outside 0.5 R accounts for 0.5-0.6 q*. These data were compared with literature data for batch adsorption of proteins in biospecific, hydrophobic and ion-exchange adsorbents. They could also be described by a bilinear free driving force model, with about the same quantitative results as obtained for similar conditions in the single particle experiments. The static adsorption parameters, maximum binding site concentration n, and dissociation constant for the protein binding to a binding site K, were determined from Scatchard plots. For the same protein-adsorbent system the plots changed from linear to non-linear with increasing n. This change occurred when the average distance between adjacent binding sites become of the same order of magnitude as the size of the binding site or adsorbed protein. This causes a shielding of free binding sites increasing with n and the concentration of adsorbed protein, yielding a concentration dependence in K. These results show that for a high throughput and rapid adsorption in preparative chromatography, the adsorption step should be carried out in the non-linear part of the adsorption isotherm with concentrations up to c(b) where q*/c(b)>/=10 to obtain high protein recoveries. To avoid tailing due to the flow of adsorbed proteins in the inner part of the particles further into the particles at the start of the desorption, and to speed up desorption rates, protein adsorption in the particle within 0.5 R from the particle center should be avoided. This requires the further development of suitable pellicular particles for preparative protein chromatography that meet this requirement.     

The Interactions Between Monovalent Cations and Calcium During Their Adsorption on Isolated Cell Walls and Absorption by Intact Barley Roots

The adsorption of sodium, potassium, rubidium and calcium ionsat different concentrations was measured on cell walls frombarley roots (Hordeum vulgare L. cv. Union), prepared by detergenttreatment. It was found that sodium and calcium interacted verystrongly during their simultaneous adsorption, whereas potassiumdid not interfere with calcium. This has led us to concludethat calcium and sodium are adsorbed on identical sites in thecell wall, whereas potassium is adsorbed at another site. Rubidiumseems to be less specific for both sites and interferes onlymoderately with calcium. The adsorption on cell walls of thesecations was compared with their adsorption on intact roots at2 °C, where beside the cell wall, sites may be availableat the outer surface of the membrane, and further measurementswere made of absorption at 25 °C. The fact that sodium interactswith calcium and potassium alters the ratio of K to Na in thecell wall compared to their concentrations in the medium. Thepreferential shift towards potassium when calcium is presentcould be very important for the rates of initial uptake in lowsalt barley roots, since the membrane is in contact with a differentproportion of K to Na in the cell wall from the one suppliedin the medium. Hordeum vulgare L., barley, absorption of cations, adsorption, calcium, sodium, potassium rubidium     

In situ structure and activity studies of an enzyme adsorbed on spectroscopically undetectable particles

The structural characteristics and the activity of a hyperthermophilic endoglucanase were investigated upon adsorption. Silica (hydrophilic) and Teflon (hydrophobic) surfaces were selected for the study. The materials were specially designed so that the interaction of the particles with light was negligible, and the enzyme conformation in the adsorbed state was monitored in situ. The adsorption isotherms were determined, and the adsorbed endoglucanase was studied using a number of spectroscopic techniques, enzymatic activity tests, and dynamic light scattering. Experiments were performed at pH values below, at, and above the isoelectric point of the enzyme. It was shown that the enzyme adsorbed on the hydrophobic surface of Teflon with higher affinity as compared to the hydrophilic silica nanoparticles. In all cases, adsorption was followed by (slight) changes in the secondary structure resulting in decreased beta-structural content. The changes were more profound upon adsorption on Teflon. The adsorbed enzyme remained active in the adsorbed state in spite of the structural changes induced when interacting with the surfaces.     

界面上配基种类对BSA吸附行为的影响

利用双偏振极化干涉测量仪(DPI)研究了界面上配基种类对BSA吸附行为的影响。采用3-氨基丙基三乙氧基硅烷(APTES)、3-(甲氨基)丙基三甲氧基硅烷(MAPTMS)和N,N-二乙基-3-氨基丙基三甲氧基硅烷(DAPTMS)对DPI芯片进行了修饰,利用X射线光电子能谱比较了芯片上不同配基的密度,采用原子力显微镜(AFM)和DPI对界面上BSA吸附行为进行了研究。结果表明APTES修饰界面上BSA呈饼状,高配基密度易导致BSA多位点吸附。相同偶联密度条件下BSA在DAPTMS修饰芯片的吸附量高于MAPTMS修饰芯片,但吸附层厚度一致,表明DAPTMS表面上BSA存在聚集现象;AFM扫描结果与DPI分析结果一致,证明了配基密度和种类不仅影响界面上蛋白质吸附量,而且影响蛋白质吸附密度和表面聚集行为。     

Adsorption and synergism of cellobiohydrolase I and II of Trichoderma reesei during hydrolysis of microcrystalline cellulose

Hydrolysis of microcrystalline cellulose (Avicel) by cellobiohydrolase I and II (CBH I and II) from Trichoderma reesei has been studied. Adsorption and synergism of the enzymes were investigated. Experiments were performed at different temperatures and enzyme/substrate ratios using CBH I and CBH II alone and in reconstituted equimolar mixtures. Fast protein liquid chromatography (FPLC) analysis was found to be an accurate and reproducible method to follow the enzyme adsorption. A linear correlation was found between the conversion and the amount of adsorbed enzyme when Avicel was hydrolyzed by increasing amounts of CBH I and/or CBH II. CBH I had lower specific activity compared to CBH II although, over a wide concentration range, more CBH I was adsorbed than CBH II. Synergism between the cellobiohy-drolases during hydrolysis of the amorphous fraction of Avicel showed a maximum as a function of total enzyme concentration. Synergism measured as a function of bound enzyme showed a continuous increase, which indicates that by decreasing the distance between the two enzymes the synergism is enhanced. The adsorption process for both enzymes was slow. Depending on the enzyme/substrate ratio it took 30-90 min to reach 95% of the equilibrium binding. The amount of bound enzyme decreased with increasing temperature. The two enzymes compete for the adsorption sites but also bind to specific sites. Stronger competition for adsorption sites was shown by CBH I. (c) 1994 John Wiley & Sons, Inc.     

Yeast alcohol dehydrogenase bound to membranes: surface and microenvironment effects on activity and stability.

The enzyme, yeast alcohol dehydrogenase, was adsorbed to porous nitrocellulose and nylon membranes. The two membranes provide different surface chemistries as indicated by the results of the streaming potential, enzyme adsorption, and fluorescein isothiocyanate adsorption experiments. The stability of the enzyme, as determined by continually measuring the extent of coenzyme reduction as a function of time, appeared to be much less for the enzyme adsorbed to the positively charged membrane surface. Moreover, the enzyme adsorbed to the positively charged membrane was the least responsive to pulses of the reducing agent, dithiothreitol, and appeared to exhibit the highest transition temperature when subjected to differential scanning calorimetry analysis. These results indicate that the entropically spreading process observed for other adsorbed proteins may be occurring and the process is more rapid and extensive when enzyme is adsorbed to the nylon than the nitrocellulose membrane. In addition to the relative stability of the enzyme on two different surfaces being examined, the effect of the microenvironment on modulating the activity of the enzyme was investigated by using the reversibility of the enzyme-catalyzed reaction as a probe of the average local environment of the enzyme. It was found that a threshold buffer concentration existed that, once exceeded, the effect of proton production by the reaction could be suppressed.     

Computational investigation of the adsorption of carbon dioxide onto zirconium oxide clusters

A theoretical investigation of the adsorption of CO(2) onto ZrO(2) is presented. Various cluster models were used to mimic different basic and acidic sites on the surface. The method used was the density functional theory with the generalized gradient approximation and including Grimme's empirical model in order to properly describe the weak interactions that may occur between the adsorbate and the surface. We found that the adsorption at sites exhibiting two adjacent unsaturated zirconium atoms led to either the exothermic dissociation of CO(2) or to a strongly physisorbed state. By contrast, on a single unsaturated zirconium, CO(2) was adsorbed in an apical manner. In this case, the molecule is highly polarized and the adsorption energy amounts to -64.6?kJ?mol(-1). Finally, the weakest adsorption of CO(2) occurred on the basic OH sites on the surface.     

Membrane fluidity changes of liposomes in response to various odorants. Complexity of membrane composition and variety of adsorption sites for odorants.

Three kinds of liposomes prepared from phosphatidylcholine (PC), azolectin, and azolectin-containing membrane proteins of the canine erythrocytes were used as models for olfactory cells. To explore properties of the adsorption sites of odorants, membrane fluidity changes in response to various odorants were measured with various fluorescence dyes which monitor the fluidity at different depths and different regions of the membranes. (a) Application of various odorants changed the membrane fluidity of azolectin liposomes. The patterns of membrane fluidity changes in response to odorants having a similar odor were similar to each other and those in response to odorants having different odors were different from each other. These results suggested that odorants having a similar odor are adsorbed on a similar site and odorants having different odors are adsorbed on different sites. (b) Such variation of the pattern was not seen in liposomes of a simple composition (PC liposome). (c) In the proteoliposomes whose composition was more complex than that of azolectin liposomes, the patterns of membrane fluidity changes varied among odorants having a similar odor. It was concluded that liposomes of complex membrane composition have the variety of adsorption sites for odorants.     

Adsorption of coliphages T1 and T7 to clay minerals.

Coliphages T1 and T7 of Escherichia coli were absorbed by kaolinite (K) and montmorillonite (M). Maximum adsorption of T7 (96%) to M was greater than that of T1 (84%), but the adsorption of both coliphages to K was the same (99%). Positively charged sites (i.e., anion exchange sites) on the clays appeared to be primarily responsible for the adsorption of T1 to K but only partially responsible for the adsorption of T1 to M; equilibrium adsorption isotherms of T1 to K and M did not show a correlation between adsorption and the cation exchange capacity of the clays, and the reduction in adsorption caused by sodium metaphosphate (a polyanion that interacts with positively charged sites on clay) was more pronounced with K than with M. The equilibrium adsorption isotherms of T7 to K and M suggested a correlation between adsorption and the cation exchange capacity of the clays. However, studies with sodium metaphosphate indicated that T7 also adsorbed to positively charged sites on the clays, especially on K. Adsorption of the coliphages to positively charged sites was greater with K than with M, probably because the ratio of positively charged sites to negatively charged sites was greater on K than on M.     

Biocatalyst-adsorbant systems: a viable alternative to proteolytic processes in solution

Proteolytic biocatalysts were adsorbed and stabilized using alumina as a support medium. Two biocatalyst-adsorbant systems were prepared with different physical characteristics of the adsorbant: alumina powder and alumina pearls. Direct adsorption onto the support medium has the main advantage, over other fixation methods, that preliminary steps are not required for a good interaction between the support and the biocatalyst. Proteases were adsorbed and stabilized without modifying or sterically hindering their active sites. Parameters affecting adsorption (pH, temperature, ionic strength) were varied so as to optimize adsorption conditions. Operational viability of the immobilized biocatalysts was demonstrated, taking into account the rate of desorption, resistance to microbial attack, and stability during storage. Desorption in water was studied in batch and continuous-flow processes, at various flow rates. The systems also proved to be resistant to microorganisms. Tests for stability during storage found the systems' activity remained constant after 60 days, and they performed better than biocatalysts in solution. Proteolysis of a solution of g per litre of azocasein was carried out in continuous-flow and batch modes, using our biocatalyst-adsorbant systems we prepared. In all cases, free amino group concentrations were around 2.5 times greater after treatment with biocatalyst-adsorbants than they were in the starting solution.     

Enzyme adsorption on SO2 catalyzed steam-pretreated wheat and spruce material

Lignocellulose is widely recognized as a sustainable substrate for biofuels production, and the enzymatic hydrolysis is regarded as a critical step for the development of an effective process for the conversion of cellulose into ethanol. One key factor affecting the overall conversion rate is the adsorption capacity of the cellulase enzymes to the surface of the insoluble substrate. Pretreatment has a strong impact on hydrolysis, which could be related to both chemical changes and morphological changes of the material. In the current work, the accessibility of four differently pretreated wheat straw substrates, two differently pretreated spruce materials, and Avicel cellulose was investigated. Adsorption isotherms (at 4 °C and 30 °C) for a cellulase preparation were obtained, and the rates of hydrolysis were determined for the different materials. Furthermore, the surface area and pore size distribution of the various materials were measured and compared to adsorption and hydrolysis properties, and the structures of the pretreated materials were examined using scanning electron microscopy (SEM).The results demonstrated a positive correlation between enzyme adsorption and the substrate specific surface area within each feedstock. Overall, the amount of enzyme adsorbed was higher for pretreated spruce than for the pretreated wheat straw, but this was not accompanied by a higher initial rate of hydrolysis for spruce. Also, the difference in the measured endoglucanase adsorption and overall FPU adsorption suggests that a larger fraction of the enzyme adsorbed on spruce was unproductive binding. The SEM analysis of the material illustrated the structural effects of pretreatment harshness on the materials, and suggested that increased porosity explains the higher rate of hydrolysis of more severely pretreated biomass.     

Interaction of calcium ions and salivary acidic proline-rich proteins with hydroxyapatite. A possible aspect of inhibition of hydroxyapatite formation.

The relationship between Ca2+- and hydroxyapatite-binding sites in salivary acidic proline-rich phosphoproteins A and C was investigated. Coating of hydroxyapatite with protein before adsorption had no effect on Ca2+ binding to the mineral, but simultaneous adsorption of Ca+ and protein to hydroxyapatite caused additional Ca2+ binding to the solid. The additional amount of Ca2+ adsorbed, measured in mol of Ca2+/mol of protein adsorbed to hydroxyapatite, was approx. 2 for protein C, 4 for protein A, 9 for the N-terminal tryptic peptide and 2 for dephosphorylated protein A. It is suggested that the ability of the proteins to inhibit hydroxyapatite formation is related to the binding of the proteins to crystal growth sites on the mineral, which prevents access of Ca2+ from the surrounding liquid.