X-ray microscopy studies of protein adsorption on a phase segregated polystyrene/polymethylmethacrylate surface. 2. Effect of pH on site preference

X-ray photoemission electron microscopy (XPEEM) using synchrotron radiation illumination has been used to study the adsorption of human serum albumin (HSA) onto a phase segregated polystyrene/polymethylmethacrylate (PS/PMMA) blend surface from solutions of five different pH values. The absolute coverage of albumin on each of three chemically distinct components of the surface, PS domains, PMMA domains, and the interface between the domains, was determined from a quantitative analysis of C 1s image sequences. At all pH values, the preferred adsorption site is the interface. At neutral pH (7.0), albumin showed a slight preference for PS regions relative to PMMA. At strongly acidic pH (2.0) and strongly basic pH (10.0), similar amounts of albumin adsorb on the PS and PMMA regions. However, at pH 4.0, the amount of albumin adsorbed on PMMA domains is approximately 1.6 times greater than that on PS domains, while at pH 8.6 the amount of albumin adsorbed on PMMA is one-half that adsorbed on PS domains. The pH dependence of the site preference is rationalized in terms of the known changes of albumin conformation with pH [Peters, T., Jr. All About Albumin: Biochemistry, Genetics, and Medical Applications; Academic Press: New York, 1995]. We infer from our results that the site preference of albumin adsorption on PS/PMMA blends is related mainly to changes in hydrophobic interactions, which are driven by pH-dependent electrostatic effects, that is, changes to the protein surface structure as the charge on the protein changes. The results provide insight into changes in the secondary structure of albumin in acid and basic media.     

聚甲基丙烯酸甲酯在纳米氧化铝表面的吸附和氢键作用

研究了聚甲基丙烯酸甲酯(PMMA)在纳米氧化铝表面的吸附行为, 采用透射红外光谱研究了吸附的PMMA中的羰基和纳米氧化铝表面羟基之间的氢键作用. 结果表明, PMMA在纳米氧化铝表面的吸附曲线为典型的Langmuir曲线, 饱和吸附值为1.2 mg/m2, 受氢键作用影响, 键合羰基在红外光谱中的吸收峰向低波数方向移动. 根据计算, 羰基的最大键合值(即含键合羰基的甲基丙烯酸甲酯单元的总质量)为0.36 mg/m2, 其余为自由羰基. 随着吸附量的增加, 羰基的键合比例逐渐降低. 吸附达到饱和时, 羰基键合比例为0.30, 说明PMMA主要以平铺的方式覆盖在纳米氧化铝的表面.     

Bound carbonyls in PMMA adsorbed on silica using transmission FTIR

The fraction of directly‐bound carbonyls of surface‐adsorbed poly(methyl methacrylate) (PMMA) was determined using transmission Fourier‐transform infrared (FTIR) spectroscopy. The small size of the silica used allowed these measurements to be made directly in the transmission mode from dried casts deposited on KBr salt plates. Curve fitting of the carbonyl‐stretching region allowed the estimation of both the relative amounts and also the relative ratio of the absorption coefficients for the free and bound carbonyls. The bound‐carbonyl fractions were found to vary smoothly from 0.3 to 0.1 for adsorbed amounts from 0.5 to 1.8 mg of PMMA/m². The bound fractions depended primarily on the adsorbed amount of polymer. Only very small, perhaps even negligible, direct effects of the solvent composition (toluene vs. benzene/acetonitrile) or molecular mass (32 to 420 kg/mol) were observed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2071–2078, 2006     

Adsorption of bovine serum albumin onto poly(methyl methacrylate) stereocomplex films with a molecularly regulated nanostructure

Stereoregular poly(methyl methacrylate)s (PMMAs) were stepwise assembled on a quartz crystal microbalance (QCM) substrate after the immersion of the QCM into alternating acetonitrile solutions at ambient temperature. A quantitative QCM analysis at each step showed stereocomplex formation on the substrate surface. The adsorption of bovine serum albumin (BSA) onto stereocomplex films with a molecularly regulated nanostructure was analyzed quantitatively. The adsorption constant and the maximum adsorption amount, calculated by the assumption of Langmuir‐type adsorption, showed that BSA adsorbed with a relatively weak interaction onto the stereocomplex films. The BSA adsorption onto the stereocomplex films occurred in an end‐on manner, with a smaller adsorption constant than for that onto individual spin‐coated films. The amount of BSA adsorbed was significantly affected by the molecular weight of syndiotactic PMMA. Attenuated total reflection spectra indicated that BSA adsorbed onto the films with or without denaturing. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1807–1812, 2003     

Kinetics of conformational changes of fibronectin adsorbed onto model surfaces

Fibronectin (FN), a large glycoprotein found in body fluids and in the extracellular matrix, plays a key role in numerous cellular behaviours. We investigate FN adsorption onto hydrophilic bare silica and hydrophobic polystyrene (PS) surfaces using Fourier transform infrared spectroscopy-attenuated total reflection (FTIR-ATR) in aqueous medium. Adsorption kinetics using different bulk concentrations of FN were followed for 2h and the surface density of adsorbed FN and its time-dependent conformational changes were determined. When adsorption occurs onto the hydrophilic surface, FN molecules keep their native conformation independent of the adsorption conditions, but the amount of adsorbed FN increases with time and the bulk concentration. Although the protein surface density is the same on the hydrophobic PS surface, this has a strong impact on the average conformation of the adsorbed FN layer. Indeed, interfacial hydration changes induced by adsorption onto the hydrophobic surface lead to a decrease in unhydrated beta-sheet content and cause an increase in hydrated beta-strand and hydrated random domain content of adsorbed FN. This conformational change is mainly dependent on the bulk concentration. Indeed, at low bulk concentrations, the secondary structures of adsorbed FN molecules undergo strong unfolding, allowing an extended and hydrated conformation of the protein. At high bulk concentrations, the molecular packing reduces the unfolding of the stereoregular structures of the FN molecules, preventing stronger spreading of the protein.     

Design of silica microparticles with oligopeptide brushes and their interaction with proteins

Synthesis of small oligopeptide brushes (oligo(S-benzyl-l-cysteine)) onto polyelectrolyte functionalized silica microparticles was developed. Poly(vinyl amine) (PVAm) adsorbed from salt-free and KCl 10⁻¹ mol L⁻¹ aqueous solution onto silica microparticles was chemically and naturally cross-linked by epichlorohydrin and CO₂, respectively. After the adsorption of PVAm onto microporous silica particles and stabilization by cross-linking, five repeated coupling reactions of Boc-S-benzyl-l-cysteine were performed. To test the protein interactions with the newly designed surface, human serum albumin (HSA) has been selected as a model protein. X-ray photoelectron spectroscopy, total organic carbon, potentiometric and polyelectrolyte titrations, and electrokinetic analysis were employed to obtain information about the polyelectrolyte adsorption and the amount of the amino acid S-benzyl-l-cysteine that was covalently bound to the solid surface and for determination of the protein amount adsorbed onto functionalized surface. The amount of HSA adsorbed onto modified silica microparticles decreased in order: silica/PVAm-cross-linked (silica/PVAm-C) (8.00 mg g⁻¹) > silica/PVAm-C/S-benzyl-l-cysteine (6.34 mg g⁻¹) > silica (4.86 mg g⁻¹) > silica/PVAm-C/(S-benzyl-l-cysteine)₅ (1.86 mg g⁻¹).     

Effects of molecular mass and surface treatment on adsorbed poly(methyl methacrylate) on silica

The behavior of relatively monodisperse adsorbed poly(methyl methacrylate) (PMMA) samples, from 19 to 587 kDa on silica, was studied using modulated differential scanning calorimetry and FTIR. On untreated Cab? O? Sil silica, the glass transition temperatures (T_gs) were higher (by around 30 °C), and the transitions were significantly broader (by a factor of 5–6) than those for the corresponding bulk samples. While the T_gs for the bulk polymers showed the expected dependence on molecular mass, the polymers on untreated silica showed little dependence, i.e., at the same adsorbed amounts, the glass transitions were very similar. The FTIR spectra of the adsorbed PMMA (on untreated silica) showed the presence of at least two resonances, one for the bound (hydrogen bonded to surface silanols) and another for free carbonyls. Fitting of the spectra allowed the estimation of the bound fractions of carbonyls that were dependent on the adsorbed amount, but not molecular mass. On Cab? O? Sil treated with hexamethyldisilizane (HMDS), the adsorbed PMMA exhibited glass transition behavior with little molecular‐mass dependence; the T_gs for the different PMMA samples were very similar to those of the high‐molecular mass bulk polymer, but with additional broadening of about a factor of 2. FTIR spectra for the PMMA samples on the treated silica did not show significant amounts of any of the hydrogen‐bonded carbonyl groups. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 649–658, 2008     

Adsorption of Ethoxylated Alkyl Phenols on Silica Gel from Aqueous Micellar Solutions

Adsorption of ethoxylated nonylphenols (Neonols) from their micellar solutions on coarse-pore KSK silica gel was studied under static conditions. The energy of adsorption interaction between micelles and silica gel surface was determined using the Hill–de Boer isotherm. For the initial parts of the isotherms (from 1 to 6 CMC₁), it was equal to –15.8kT. The study of coadsorption of Neonols with dye methylene blue showed that the micellar adsorption layer is fragmentary and that the amount of the adsorbed surfactant is dependent on the conditions of the adsorption layer formation.     

Integral geometry analysis of fluorescence micrographs for quantitative relative comparison of protein adsorption onto polymer surfaces

Most methods developed to study protein binding to distinct surfaces can only determine the average amount of adsorbed protein or merely provide (qualitative) information on its spatial distribution. Both these features can be characterized rigorously by integral geometry analysis of fluorescence micrographs. This approach is introduced here to compare the relative protein adsorption onto various polymer surfaces: polystyrene (PS), poly(methyl methacrylate) (PMMA), poly( n-butyl methacrylate) (PnBMA), poly( tert-butyl methacrylate) (PtBMA), and PS(PETA) and cross-linked poly(ethylene oxide) (PEO*(PETA)), admixed with pentaerythritol triacrylate (PETA). The polymeric surfaces were incubated for 15 min in phosphate-buffered saline (pH 7.4) containing 125 mug/mL fluorescently labeled lectins, either lentil lectin (LcH) or concanavalin A (ConA). Fluorescence images were recorded at identical conditions (physiological buffer, same exposure time, magnification, gain). For each image, taken a few times for each polymer, the distribution and average value of the normalized intensity were determined. The results show that the binding of LcH to PS(PETA), PtBMA, PS, PnBMA, PMMA, and PEO*(PETA) can be expressed by the ratio of the following values (mean +/- 95% confidence interval): 0.356 +/- 0.022, 0.298 +/- 0.030, 0.241 +/- 0.014, 0.083 +/- 0.008, 0.039 +/- 0.008, and 0.010 +/- 0.006, respectively. In turn, the relative adsorption of ConA is described by the values 0.252 +/- 0.016, 0.217 +/- 0.014, 0.222 +/- 0.016, 0.046 +/- 0.006, 0.116 +/- 0.008, and 0.006 +/- 0.002, respectively. Low dispersions of fluorescence intensity around average values indicate homogeneous distribution of adsorbed proteins. The introduced approach enables a fast and easy way not only to quantify the relative amount of bound proteins but also to characterize quantitatively the organization of their surface distribution, as demonstrated for patchlike protein adsorption onto the polymer blend surface.     

Isotherm analysis of phenol adsorption on polymeric adsorbents from nonaqueous solution

Macroporous poly(methyl methacrylate-co-divinylbenzene) (PMMA), interpenetrating polymer adsorbent based on poly(styrene-co-divinylbenzene) (PS) and poly(methyl methacrylate-co-divinylbenzene) (PMMA/PS), and macroporous cross-linked poly(N-p-vinylbenzyl acetylamide) (PVBA) were prepared for the adsorption of phenol from cyclohexane. The sorption isotherms of phenol on the three polymeric adsorbents were measured and fitted to Langmuir and Freundlich isotherms. It is shown that the Langmuir isotherm, which is based on a homogeneous surface model, is unsuitable to describe the sorption of phenol on the adsorbents from nonaqueous solution and the Freundlich equation fits the tested three adsorption systems well. The isosteric enthalpy was quantitatively correlated with the fractional loading for the sorption of phenol onto the three polymeric adsorbents. The surface energetic heterogeneity patterns of the adsorbents were described with functions of isosteric enthalpy. The results showed that the tested three polymeric adsorbents exhibited different surface energetic heterogeneity patterns. The initial isosteric enthalpy of phenol sorption on polymeric adsorbent has to do with the surface chemical composition and is free from the pore structure of the polymeric adsorbent matrix. Forming hydrogen bonds between phenol molecules and adsorbent is the main driving force of phenol sorption onto PVBA and PMMA adsorbent from nonaqueous solution. When phenol is adsorbed on PMMA/PS, pi-pi interaction resulting from the stacking of the benzene rings of the adsorbed phenol molecules and the pendant benzene ring of adsorbent is involved.     

Nano-organized collagen layers obtained by adsorption on phase-separated polymer thin films

The organization of adsorbed type I collagen layers was examined on a series of polystyrene (PS)/poly(methyl methacrylate) (PMMA) heterogeneous surfaces obtained by phase separation in thin films. These thin films were prepared by spin coating from solutions in either dioxane or toluene of PS and PMMA in different proportions. Their morphology was unraveled combining the information coming from X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and water contact angle measurements. Substrates with PMMA inclusions in a PS matrix and, conversely, substrates with PS inclusions in a PMMA matrix were prepared, the inclusions being either under the form of pits or islands, with diameters in the submicrometer range. The organization of collagen layers obtained by adsorption on these surfaces was then investigated. On pure PMMA, the layer was quite smooth with assemblies of a few collagen molecules, while bigger assemblies were found on pure PS. On the heterogeneous surfaces, it appeared clearly that the diameter and length of collagen assemblies was modulated by the size and surface coverage of the PS domains. If the PS domains, either surrounding or surrounded by the PMMA phase, were above 600 nm wide, a heterogeneous distribution of collagen was found, in agreement with observations made on pure polymers. Otherwise, fibrils could be formed, that were longer compared to those observed on pure polymers. Additionally, the surface nitrogen content determined by XPS, which is linked to the protein adsorbed amount, increased roughly linearly with the PS surface fraction, whatever the size of PS domains, suggesting that adsorbed collagen amount on heterogeneous PS/PMMA surfaces is a combination of that observed on the pure polymers. This work thus shows that PS/PMMA surface heterogeneities can govern collagen organization. This opens the way to a better control of collagen supramolecular organization at interfaces, which could in turn allow cell-material interactions to be tailored.     

Prepation of poly(N-isopropylacrylamide)-grafted silica gel and its temperature-dependent interaction with proteins

Poly(N-isopropylacrylamide) oligomer was immobilized onto a silica gel surface. The gel adsorbed a hydrophobic protein γ-globulin (IgG) at 37°C, however, did not adsorb IgG at 24°C. The adsorbed IgG at 37°C was adsorbed by lowering the temperatue, No adsorption of a hydrophilic protein bovin serum albumin (BSA) onto this matrix was observed at 37°C nor 24°C.     

Quantitative analysis of protein adsorption on a planar surface by Fourier transform infrared spectroscopy: lysozyme adsorbed on hydrophobic silicon-containing polymer

The adsorption of hen egg white lysozyme onto a solid polytris(trimethylsiloxy)silylstyrene (pTSS) surface from a D(2)O solution at pD 7 containing 100 mM NaCl and 10 mM sodium deuterated phosphate was monitored at 25 degrees C by Fourier transform infrared spectroscopy using the attenuated total reflection (ATR) method. The infrared spectrum attributed to only the adsorbed lysozyme was derived from the observed spectrum, and the amount of adsorbed lysozyme was determined as a function of time and lysozyme concentration. The kinetics of adsorption could be decomposed into two components, one of which was a process with a time constant of larger than 4 h(-1) and the other was a process with one of about 0.1 h(-1). These spectra showed that the lysozyme adsorbed in the faster process had a higher beta-structure content than the dissolved lysozyme. It was also found that the slower adsorption induced some conformational change in the lysozyme adsorbed in the faster process and/or that adsorbed in the slower process. After adsorption for 24 h, the pTSS surface was rinsed out with lysozyme-free solution. The resultant spectra of the surface indicated that the lysozyme adsorbed in the faster process was bound irreversibly on the surface and was changed to a conformer with a higher beta-structure content during the slower process. The experimental procedures and the theoretical applications for such a quantitative analysis in the ATR spectroscopic method are presented in detail.     

Estimation of the adsorption state of nonionic emulsifier molecules onto styrene–methacrylic acid copolymer particles by in situ <Superscript>1</Superscript>H NMR measurements

The adsorption behavior of poly(oxyethylene) nonyl phenyl ether nonionic emulsifier molecules onto polystyrene (PS) and styrene-methacrylic acid copolymer [P(S-MAA)] particles dispersed in D₂O was evaluated by in situ ¹H NMR measurements at room temperature. The resonance due to the protons of the emulsifier molecules was only observed. Normalized NMR integrals of the resonance due to the protons of hydrophobic groups (nonyl and phenyl groups) and the hydrophilic group, poly(oxyethylene) chain, at a certain concentration of the emulsifier decreased with an increase in the total surface area of the PS particles dispersed in the system. The decrease for the hydrophobic groups was much larger than that for the hydrophilic groups. In the dispersion system of P(S-MAA) particles, ionized carboxyl groups at the particle surface decreased the amount of the emulsifier adsorbed.     

Adsorption of stereoregular poly(methyl methacrylates) on γ-alumina: Spectroscopic analysis

ABSTRACTS: Three poly(methyl methacrylates) (PMMA) with a racemic fraction ranging from 0.25 to 0.91 have been adsorbed from a chloroform solution on γ-alumina and studied by diffuse reflectance infrared spectroscopy (DRIFT) and solid-state ¹³C NMR spectroscopy. From DRIFT spectra, it is seen that the fraction of carbonyl groups bonded to the surface goes from 0.29 for s-PMMA to 0.41 for i-PMMA, but there is a larger amount of s-PMMA retained on the surface (at any given solution concentration). NMR spectroscopy indicates, from shifts of the methylene and α-methyl carbon peaks (due to the γ-gauche effect), that the adsorption is accompanied by changes in conformation, with an increase in the number of trans conformers, particularly with i-PMMA. These results indicate that s-PMMA adsorbs on γ-alumina in a brush-like configuration, with a relatively small number of groups attached to the surface, and tails and loops sticking out of the surface, whereas i-PMMA adsorbs in a sheet-like configuration, with a greater number of interacting groups. In both cases, the adsorption is accompanied with an increase in the number of trans conformers as compared to the bulk conformation. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2985–2995, 1999     

Controllable synthesis of silica nanoparticle size and packing efficiency onto PVP-functionalized PMMA via a sol–gel method

This study aimed to investigate synthesis and adsorption behavior of silica nanoparticles onto polyvinylpyrrolidone (PVP)-functionalized poly(methyl methacrylate) under various conditions such as methanol/water ratio, ammonium hydroxide concentration, polymer contents, tetraethylorthosilicate contents, and total volume of solvent via sol–gel method. First, the copolymerization of methyl acrylate as a comonomer and 1-dodecanethiol as a chain transfer agent increased the thermal stability of the product; however, the uniformity of the PMMA particles decreased because of the chain transfer reaction. Second, the adsorption behavior and size of silica nanoparticles could be controlled by adjusting the silica synthesis conditions. The adsorbed silica particle size was greatly influenced by the ammonium hydroxide concentration and the addition of water further enhanced the size increase. However, increasing the water content reduced the packing efficiency of the adsorbed silica particles. Increasing the PVP-functionalized PMMA content at a fixed TEOS content linearly decreased the silica particle size. But TEOS concentration did not significantly affect the silica particle size. © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 662–672     

Two different approaches to XPS quantitative analysis of polyelectrolyte adsorption layers

X-ray photoelectron spectroscopy (XPS) was employed to quantify adsorption of polyelectrolytes from aqueous solutions of low ionic strength onto mica, glass, and silica. Silica surfaces were conditioned in base or in acid media as last pre-treatment step (silica-base last or silica-acid last, respectively). Consistency in the determined adsorbed amount, Γ, was obtained independent of the choice of XPS mode and with the two quantification approaches used in the data evaluation. Under the same adsorption conditions, the adsorbed amount, Γ, varied as Γ_mica > Γ_{silica-base last} ≈ Γ_glass > Γ_{silica-acid last}. In addition, the adsorbed amount increased with decreasing polyelectrolyte charge density (100% to 1% of segments being charged) for all substrates. Large adsorbed amount was measured for low-charge density polyelectrolytes, but the number of charged segments per square nanometer was low due to steric repulsion between polyelectrolyte chains that limited the adsorption. The adsorbed amount of highly charged polyelectrolytes was controlled by electrostatic interactions and thus limited to that needed to neutralize the substrate surface charge density. For silica, the adsorbed amount depended on the cleaning method, suggesting that this process influenced surface concentration and fraction of different silanol groups. Our results demonstrate that for silica, a higher density and/or more acidic silanol groups are formed using base, rather than acid, treatment in the last step.     

Polystyrene-coated micro-sized particles by "in situ" surface initiated polymerization in accord with Langmuir model adsorption

This study describes the mechanism of adsorption of polystyrene chains PS "in situ" growth from micro-sized commercial silicate particles, i.e. Feldspar. The main aim is to derive adsorption isotherms from thermal gravimetric analysis (TGA) and size exclusion chromatography (SEC) data obtained during the direct polymerization of PS initiated by a pre-adsorbed radical initiator onto the inorganic surface. The adsorption isotherm plot indicates that the PS adsorption is in accord with the Langmuir Model. The amount of PS monolayer coverage increases with polymerization time, and it is highly dependent on the monomer diffusion to the surface during the hybrid inorganic/organic synthesis. Such behavior depends on the concentration gradient between monomer concentration in solution and that adsorbed by polymerization onto the micro-sized particles surface of Feldspar.     

Participation of electrolyte cations in albumin adsorption onto negatively charged polymer latices

The participation of electrolyte cations in the adsorption of bovine serum albumin (BSA) onto polymer latices was investigated. The latices used were hydrophobic polystyrene (PS), and hydrophilic copolymers, i.e., styrene (St)/2-hydroxyethyl methacrylate(HEMA) copolymer [P(St/HEMA)] and styrene/acrylamide (AAm) copolymer [P(St/AAm)]. Three kinds of electrolyte cations (Na⁺, Ca²⁺, Mg²⁺) were used as the chloride. The amount of BSA adsorbed in every cation medium showed a maximum near the isoelectric point (iep, pH about 5) of the protein. The amounts of BSA adsorbed onto copolymer latices (except in the acidic pH region lower than the iep) were considerably smaller than that onto PS latex because of the steric repulsion and the decrease in the hydrophobic interaction between BSA and copolymer latices. In the acidic pH region, there was little difference in the amount of BSA adsorbed in every cation medium. However, in the pH region higher than the iep, the amounts of BSA adsorbed (particularly onto PS latex) in divalent cations (Ca²⁺ and Mg²⁺) media were relatively greater compared with that in a monovalent (Na⁺) one. This result was interpreted on the basis of the differences in such effects of electrolyte cations as dehydration power, suppression of the electrostatic repulsion, and binding affinity to BSA molecule. Ion Chromatographic estimation of the amounts of electrolyte cations captured upon BSA adsorption (in pH > 5) revealed that divalent cations were incorporated into the contact interface between the latex and BSA molecule so as to prevent the accumulation of anion charge and facilitate the protein adsorption.