Fibronectin adsorption onto polyelectrolyte multilayer films

The Layer-by-layer deposition of positively and negatively charged macromolecular species is an ideal method for constructing thin films incorporating biological molecules. We investigate the adsorption of fibronectin onto polyelectrolyte multilayer (PEM) films using optical waveguide lightmode spectroscopy (OWLS) and atomic force microscopy (AFM). PEM films are formed by adsorption onto Si(Ti)O2 from alternately introduced flowing solutions of anionic poly(sodium 4-styrenesulfonate) (PSS) and cationic poly(allylamine hydrochloride) (PAH). Using OWLS, we find the initial rate and overall extent offibronectin adsorption to be greatest on PEM films terminated with a PAH layer. The polarizability density of the adsorbed protein layer, as measured by its refractive index, is virtually identical on both PAH- and PSS-terminated films; the higher adsorbed density on the PAH-terminated film is due to an adsorbed layer of roughly twice the thickness. The binding of monoclonal antibodies specific to the protein's cell binding site is considerably enhanced to fibronectin adsorbed to the PSS layer, indicating a more accessible adsorbed layer. With increased salt concentration, we find thicker PEM films but considerably thinner adsorbed fibronectin layers, owing to increased electrostatic screening. Using AFM, we find adsorbed fibronectin layers to contain clusters; these are more numerous and symmetric on the PSS-terminated film. By considering the electrostatic binding of a segmental model fibronectin molecule, we propose a picture of fibronectin adsorbed primarily in an end-on-oriented monolayer on a PAH-terminated film and as clusters plus side-on-oriented isolated molecules onto a PSS-terminated film.     

Ethane adsorption in slit-shaped micropores: influence of molecule orientation on adsorption capacity

Adsorption of ethane in a slit shaped micropore system has been studied by Monte Carlo molecular simulation by considering this hydrocarbon as a two interacting sites molecule. Ethane adsorption in pore sizes from 0.41 to 1.66 nm was simulated at 303 K. Microscopic characteristics of the adsorbed phase have been studied for pores of different size, comparing two density profiles: the molecule centre of mass profile and the molecular interaction site profile. Averaged angle distribution of molecule positions with respect to the slit plane across the pore width has been also obtained by simulation. These results were related to ethane molecule packing efficiency, which is also related to the adsorption capacity in terms of the adsorbed phase density. Packing efficiency presents an oscillation shape as the result of the adsorbate disorder inside the pore. Pressure influence on the adsorption has been studied by following pore filling by simulation. When pore condensation takes place and for pressures above condensation, fluid-fluid interactions are determinant in molecule disorder observed between the two adsorbed layers.     

Fibronectin adsorption on titanium surfaces and its effect on osteoblast precursor cell attachment

The objective of this study was to investigate the adsorption of fibronectin on titanium (Ti) surfaces and the effect of pre-adsorbed fibronectin on osteoblast precursor cell attachment in vitro. Two different concentrations of bovine fibronectin were used in this study. Protein adsorption on Ti surfaces was analyzed using the micro bicinchoninic acid (BCA) protein assay. Cell concentration on Ti and fibronectin pre-adsorbed Ti surfaces after 3 h incubation was analyzed using the Vybrant™ cell adhesion assay. Cell morphology on Ti and fibronectin pre-adsorbed Ti surfaces was observed using scanning electron microscopy (SEM). After 180 min incubation, maximum adsorption of bovine fibronectin on Ti surfaces was observed. Fibronectin adsorption on Ti surfaces was observed to be significantly dependent on the initial concentration and the amount of incubation time. In the presence of 1 mg/ml fibronectin pre-adsorbed on Ti surfaces after 15 min, osteoblast precursor cell attachment on Ti surfaces was observed to be enhanced compared with control Ti surfaces, Ti surfaces pre-adsorbed with 1 mg/ml fibronectin for 180 min, and Ti surfaces pre-adsorbed with 0.1 mg/ml fibronectin for 15 and 180 min. No significant difference in cell attachment was observed between control Ti surfaces, Ti surfaces pre-adsorbed with fibronectin for 180 min, and Ti surfaces pre-adsorbed with 0.1 mg/ml fibronectin for 15 and 180 min. In addition, no differences in cell morphology of the attached osteoblast precursor cells on control Ti surfaces and Ti surfaces pre-adsorbed with fibronectin were observed in this study. It was concluded that an optimum concentration of adsorbed fibronectin on Ti surfaces plays an important role in governing cell attachment.     

Retracted: Nanobubbles influence on BSA adsorption on mica surface

Retraction: The following article from the Surface and Interface Anlysis, 'Nanobubbles influence on BSA adsorption on mica surface' by Wu ZH, Zhang XH, Zhang XD, Li G, Sun J, Zhang Y, Li M and Hu J, published online on 1 September 2005 in Wiley InterScience ( www.interscience.com ) and in print Volume 37 Issue 10 pages 797‐801, 2005, has been retracted by agreement between the authors, the journal's Editor‐in‐Chief Professor John F. Watts and John Wiley & Sons, Ltd. The retraction has been agreed due to the article being subsequently published in Volume 38 Issue 6, pages 990‐995 of the journal as part of a Special Issue entitled 'Chinese‐German Forum on Fundamentals and Technological Perspectives of Nanoscience 26‐30 September 2004, Beijing, China.'     

Fibronectin and bovine serum albumin adsorption and conformational dynamics on inherently conducting polymers: a QCM-D study

Quartz crystal microbalance with dissipation monitoring (QCM-D) was employed to characterize the adsorption of the model proteins, bovine serum albumin (BSA) and fibronectin (FN), to polypyrrole doped with dextran sulfate (PPy-DS) as a function of DS loading and surface roughness. BSA adsorption was greater on surfaces of increased roughness and was above what could be explained by the increase in surface area alone. Furthermore, the additional mass adsorbed on the rough films was concomitant with an increase in the rigidity of the protein layer. Analysis of the dynamic viscoelastic properties of the protein adlayer reveal BSA adsorption on the rough films occurs in two phases: (1) arrival and initial adsorption of protein to the polymer surface and (2) postadsorption molecular rearrangement to a more dehydrated and compact conformation that facilitates further recruitment of protein to the polymer interface, likely forming a multilayer. In contrast, FN adsorption was independent of surface roughness. However, films prepared from solutions containing the highest concentration of DS (20 mg/mL) demonstrated both an increase in adsorbed mass and adlayer viscoelasticity. This is attributed to the higher DS loading in the conducting polymer film resulting in presentation of a more hydrated molecular structure indicative of a more unfolded and bioactive conformation. Modulating the redox state of the PPy-DS polymers was shown to modify both the adsorbed mass and viscoelastic nature of FN adlayers. An oxidizing potential increased both the total adsorbed mass and the adlayer viscoelasticity. Our findings demonstrate that modification of polymer physicochemical and redox condition alters the nature of protein-polymer interaction, a process that may be exploited to tailor the bioactivity of protein through which interactions with cells and tissues may be controlled.     

The influence of the preliminary adsorption of water on the adsorption of organic solvent vapors on fullerene materials

The preliminary adsorption of water considerably decreased the sorption capacity of fullerene-containing materials with respect to benzene. The effect grew stronger as the content of fullerenes in the adsorbent increased. The possibility of increasing adsorption capacity by treatment with water was studied. The dependence of the sorption capacity of fullerene materials with respect to benzene on the relative water vapor pressure and the sorption capacity with respect to water at the preadsorption stage was determined.     

Fibronectin adsorption on gold, Ti-, and Ta-oxide investigated by QCM-D and RSA modelling

The adsorption of fibronectin on gold, Ti-, and Ta-oxide surfaces is investigated by means of the quartz crystal microbalance with dissipation (QCM-D) technique. The surface chemistry (gold, Ti-, and Ta-oxide) is found to influence the frequency shift observed during adsorption of the fibronectin layer with the magnitude being Delta f Au>Delta f Ti-oxide approximately Delta f Ta-oxide. Corresponding variations in the dissipation change normalised to frequency change (Delta D/Delta f) for the layer are observed. The QCM-D data are further analyzed by the random sequential adsorption (RSA) model, and adsorption rate parameter ka and footprint (a) determined, which supported the trend seen in the Delta f and Delta D/Delta f values. The value of ka found by the RSA modelling of the QCM-D resonance frequency data is found to match the ratio between the mass measured by QCM-D and the mass reported by optical techniques in literature. We conclude that comparison of the adsorption rate parameter (ka) obtained by RSA modelling of the QCM-D data with ka values obtained from RSA modelling of data obtained using optical techniques can be a route to determine the degree of hydration of the adsorbed protein layer.     

The influence of electrostatic forces on protein adsorption

In this paper we investigate the importance of electrostatic double layer forces on the adsorption of human serum albumin by UV-ozone modified polystyrene. Electrostatic forces were measured between oxidized polystyrene surfaces and gold-coated atomic force microscope (AFM) probes in phosphate buffered saline (PBS) solutions. The variation in surface potential with surface oxygen concentration was measured. The observed force characteristics were found to agree with the theory of electrical double layer interaction under the assumption of constant potential. Chemically patterned polystyrene surfaces with adjacent 5 microm x 5 microm polar and non-polar domains have been studied by AFM before and after human serum albumin adsorption. A topographically flat surface is observed before protein adsorption indicating that the patterning process does not physically modify the surface. Friction force imaging clearly reveals the oxidation pattern with the polar domains being characterised by a higher relative friction compared to the non-polar, untreated domains. Far-field force imaging was performed on the patterned surface using the interleave AFM mode to produce two-dimensional plots of the distribution of electrostatic double-layer forces formed when the patterned polystyrene surfaces is immersed in PBS. Imaging of protein layers adsorbed onto the chemically patterned surfaces indicates that the electrostatic double-layer force was a significant driving force in the interaction of protein with the surface.     

The influence of electron-withdrawing substituents on the adsorption of CO on copper

The chemisorption of carbon monoxide on Cu(100) in the presence of either methyl chloride or formic acid results in an increase in the the C---O stretching frequency to above the gas-phase value and a simultaneous increase in the heat of adsorption of CO. We explain this behavior qualitatively in terms of the simple Lewis acid/base character of both the surface and the adsorbate.     

Matrix isolation spectroscopic and theoretical study of water adsorption and hydrolysis on molecular tantalum and niobium oxides

The reactions of molecular tantalum and niobium monoxides and dioxides with water were investigated by matrix isolation infrared spectroscopy. In solid neon, the metal monoxide and dioxide molecules reacted with water to form the MO(H(2)O) and MO(2)(H(2)O) (M = Ta, Nb) complexes spontaneously on annealing. The MO(H(2)O) complexes photochemically rearranged to the more stable HMO(OH) isomers via one hydrogen atom transfer from water to the metal center under visible light excitation. In contrast, the MO(2)(H(2)O) complexes isomerized to the more stable MO(OH)(2) molecules via a hydrogen atom transfer from water to one of the oxygen atoms of metal dioxide upon visible light irradiation. The aforementioned species were identified by isotopic-substituted experiments as well as density functional calculations.     

The influence of temperature on the adsorption of mellitic acid onto goethite

The adsorption of mellitic acid (benzene-1,2,3,4,5,6-hexacarboxylic acid) onto goethite was investigated at five temperatures between 10 and 70 degrees C. Mellitic acid adsorption increased with increasing temperature below pH 7.5, but at higher pH the effect of increasing temperature was to reduce the amount adsorbed. Potentiometric titrations were conducted and adsorption isotherms were measured over the same temperature range, and the data obtained were used in conjunction with adsorption edge data to develop an Extended Constant Capacitance Surface Complexation Model of mellitic acid adsorption. A single set of reactions was used to model the adsorption for the three different experiment types at the five temperatures studied. The adsorption reactions proposed for mellitate ion (L(6-)) adsorption at the goethite surface (SOH) involved the formation of two outer-sphere complexes: SOH + L(6-) + 3H+ <==> [(SOH2)+ (LH2)(4-)]3-, 2SOH + L(6-) + 2H+ <==> [(SOH2)2(2+) (L)(6-)]4-. This mechanism is consistent with recent ATR-FTIR spectroscopic measurements of the mellitate-goethite system. Thermodynamic parameters calculated from the temperature dependence of the equilibrium constants for these reactions indicate that the adsorption of mellitic acid onto goethite is accompanied by a large entropy increase.     

The influence of grafted functional groups on the adsorption properties of silica

The adsorption properties of silica gel with grafted aminopropyl and guanidinoethanethiol (GET) groups were studied by the techniques of adsorption under static conditions and gas chromatography. It was shown that molecules capable of forming hydrogen bonds are adsorbed on all modified samples more weakly than on the initial silica gel. The grafting of GET radicals on the surface results in a noticiable increase in the dispersion interaction with adsorbed molecules. Calculation of the contributions of molecular groups to the constant of adsorption equilibrium showed that the thermodynamic characteristics of adsorption on aminosilochromes and aminosilicas with a polymeric layer of the modifying agent have similar values. Such adsorbents can be used for investigation of polar compounds, including organic bases. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 452–457, March, 1997.     

Surface methylation of aerosil and its influence on the adsorption of water

Reversible adsorption isotherms at different temperatures have been used to study the system of water adsorbed on Aerosil and on Aerosil whose surface has been partially methylated with trimethylchlorosilane.The change in the shape of the isotherm upon surface methylation from type II to type III, according to Brunauer's classification, renders difficult the calculation of the capacity of the monolayer; however, in this case it can be obtained by Kaganer's method.The variation in the mobility of the monolayer on surface methylation can be shown by comparing the experimental and theoretical integral entropies, while the molecules adsorbed in the multilayer region always have a high degree of freedom.     

Direct electroplating of copper on tantalum from ionic liquids in high vacuum: origin of the tantalum oxide layer

In this paper, it is shown that high vacuum conditions are not sufficient to completely remove water and oxygen from the ionic liquid 1-ethyl-3-methylimidazolium chloride. Complete removal of water demands heating above 150 °C under reduced pressure, as proven by Nuclear Reaction Analysis (NRA). Dissolved oxygen gas can only be removed by the use of an oxygen scavenger such as hydroquinone, despite the fact that calculations show that oxygen should be removed completely by the applied vacuum conditions. After applying a strict drying procedure and scavenging of molecular oxygen, it was possible to deposit copper directly on tantalum without the presence of an intervening oxide layer.     

A DFT study of the adsorption and dissociation of CO on Fe(100): influence of surface coverage on the nature of accessible adsorption states.

In the present article, we report adsorption energies, structures, and vibrational frequencies of CO on Fe(100) for several adsorption states and at three surface coverages. We have performed a full analysis of the vibrational frequencies of CO, thus determining what structures are stable adsorption states and characterizing the transition-state structure for CO dissociation. We have calculated the activation energy of dissociation of CO at 0.25 ML (ML = monolayers) as well as at 0.5 ML; we have studied the dissociation at 0.5 ML to quantify the destabilization effect on the CO(alpha3) molecules when a neighboring CO molecule dissociates. In addition, it is shown that the number and nature of likely adsorption states is coverage dependent. Evidence is presented that shows that the CO molecule adsorbs on Fe(100) at fourfold hollow sites with the molecular axis tilted away from the surface normal by 51.0 degrees. The asorprton energy of the CO molecule is -2.54 eV and the C-O stretching frequency is 1156 cm(-1). This adsorption state corresponds to the alpha3 molecular desorption state reported in temperature programmed desorption (TPD) experiments. However, the activation energy of dissociation of CO(alpha3) molecules at 0.25 ML is only 1.11 eV (approximately 25.60 kcal mol(-1)) and the gain in energy is -1.17 eV; thus, the dissociation of CO is largely favored at low coverages. The activation energy of dissociation of CO at 0.5 ML is 1.18 eV (approximately 27.21 kcal mol(-1)), very similar to that calculated at 0.25 ML. However, the dissociation reaction at 0.5 ML is slightly endothermic, with a total change in energy of 0.10 eV Consequently, molecular adsorption is stabilized with respect to CO dissociation when the CO coverage is increased from 0.25 to 0.5 ML.     

Revealing structural effects, part II: the influence of molecular structure on the adsorption of butanol isomers on platinum

The nature of the adsorbates formed when butanol isomers interact with platinum electrodes in a perchloric acid medium was investigated by the application of on-line differential electrochemical mass spectrometry (DEMS) and cyclic voltammetry. In this way, the reactivity of the residues remaining on the electrode surface after a flow-cell experiment was established for the different molecules. It was found that the four isomers form strongly adsorbed species on the electrode, which undergo both electro-oxidation and electroreduction, depending on the potential applied at the electrode. Oxidative stripping of the adsorbates produces CO2 as the only oxidation product, whereas propane and the corresponding butane isomer are obtained on platinum in the hydrogen adsorption potential region. The yields of these hydrocarbons were found to depend strongly on the nature of the butanol isomer and on the adsorption potential. According to these results, it can be concluded that fragmentation of the butanol isomers occurs during adsorption and reduction reactions. C4 alkene and acetyl species are proposed as the adsorbed intermediates in all cases.