Control of specific attachment of proteins by adsorption of polymer layers

This study concerns the design of protein-resistant polymer adsorbed layers for the control of surface binding of biospecific recognition entities. Polymer surface layers were prepared using the adsorption of poly(allylamine hydrochloride) (PAH), poly(l-lysine) (PL), and branched and linear polyethyleneimine (PEI) and further modified by the covalent attachment of biotin for specific avidin attachment. The adsorption of PAH, PL, and PEI on silicon substrates was studied as a function of pH and ionic strength using ellipsometry. Average dry layer thicknesses of approximately 10, approximately 5, approximately 9, and approximately 3 A (+/-1 A) were obtained when polymer adsorption occurred from solutions at pH 9.5 that contained 0.5 M NaCl for PAH, PL, branched PEI, and linear PEI, respectively. These polymers showed significant differences in their efficiency to suppress nonspecific avidin adsorption. At low ionic strength, avidin adsorption occurred on all polymer-coated surfaces at basic pH values, despite the same positive electrostatic charge for protein globules and the surface. Though the net electrostatic repulsion between avidin molecules and branched PEI was efficiently screened in a protein solution of pH 7 and 0.15 M NaCl, branched-PEI coatings of high molecular weight were unique in their ability to provide avidin-resistant surfaces as a result of steric hindrance from the branched architecture of adsorbed polymer chains. All polymers studied were effective in suppressing avidin adsorption at pH 3 as a result of protonation of the avidin surface functional groups at this pH. Branched-PEI-coated surfaces were also effective for the suppression of smaller positively charged proteins such as lysozyme and ribonuclease A at pH 7 and 0.15 M NaCl. They were also resistant to the adsorption of negatively charged proteins such as BSA and fibrinogen at pH 7 and 0.75 M NaCl. Furthermore, by using PEI-modified protein-repellent surfaces, selective binding of avidin was achieved to surface-bound silver nanoparticles, which should provide a promising application for the label-free detection of biological species using surface-enhanced Raman scattering (SERS).     

Characterization of the cell surface and cell wall chemistry of drinking water bacteria by combining XPS, FTIR spectroscopy, modeling, and potentiometric titrations

Aquabacterium commune, a predominant member of European drinking water biofilms, was chosen as a model bacterium to study the role of functional groups on the cell surface that control the changes in the chemical cell surface properties in aqueous electrolyte solutions at different pH values. Cell surface properties of A. commune were examined by potentiometric titrations, modeling, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectroscopy. By combining FTIR data at different pH values and potentiometric titration data with thermodynamic model optimization, the presence, concentration, and changes of organic functional groups on the cell surface (e.g., carboxyl, phosphoryl, and amine groups) were inferred. The pH of zero proton charge, pH(zpc) = 3.7, found from titrations of A. commune at different electrolyte concentrations and resulting from equilibrium speciation calculations suggests that the net surface charge is negative at drinking water pH in the absence of other charge determining ions. In situ FTIR was used to describe and monitor chemical interactions between bacteria and liquid solutions at different pH in real time. XPS analysis was performed to quantify the elemental surface composition, to assess the local chemical environment of carbon and oxygen at the cell wall, and to calculate the overall concentrations of polysaccharides, peptides, and hydrocarbon compounds of the cell surface. Thermodynamic parameters for proton adsorption are compared with parameters for other gram-negative bacteria. This work shows how the combination of potentiometric titrations, modeling, XPS, and FTIR spectroscopy allows a more comprehensive characterization of bacterial cell surfaces and cell wall reactivity as the initial step to understand the fundamental mechanisms involved in bacterial adhesion to solid surfaces and transport in aqueous systems.     

Adsorption of L-lysine on Cu(110): a RAIRS study from UHV to the liquid phase

The adsorption of L-lysine on a Cu(110) surface has been investigated under UHV conditions from the sublimation of a crystalline phase. The adsorption was characterized by Fourier transform reflection absorption infrared spectroscopy (FT-RAIRS) during exposure and Auger electron spectroscopy (AES). At room temperature, the lysine molecules' adsorption geometry varies as a function of the exposure. At low coverage, the molecules are adsorbed via the oxygen atoms of the deprotonated carboxylate group and the nitrogen atom of the amino group. At high coverage, close to the monolayer, the molecules reorient to be anchored to the surface via one oxygen of a sideways-tilted carboxylate moiety. This first step is followed by the growth of multilayers of nonoriented molecules. In contrast, adsorption on an oxygen-modified copper surface leads to a rather disordered layer. The results are compared with the adsorption carried out on a polycrystalline copper surface after immersion in solutions of lysine at various pH values. The adsorption was monitored by polarization modulation infrared spectroscopy (PM-IRRAS). The chemistry of the adsorbed molecules is function of the starting chemical form of the lysine molecules imposed by the pH of the solution. The combination of the two techniques and various sets of adsorption conditions will give important insight into the adsorption of biomolecules on metal surfaces and the influence of water and surface oxygen.     

聚丙烯酰吡咯作为蛋白质吸附材料的研究

近些年, 具有电活性的聚合物在生物分子吸附材料方面的应用越来越广. 而导电聚合物的前聚体化合物的合成(如带吡咯基团的聚合物)对于生物分子的吸附研究非常重要. 详细研究了牛血清白蛋白(BSA)在导电聚合物前聚体—聚丙烯酰吡咯(PAP)表面上的吸附规律. 首先, 采用自由基聚合方法合成PAP, 通过spin-coating方法将PAP涂覆到50 nm厚的金膜上, 制备出均匀聚合物薄膜. 然后, 采用傅立叶转换红外光谱(FT-IR)和X射线光电子能谱(XPS)对PAP的化学结构及元素构成进行了分析, 同时考察了PAP膜在不同pH值的生物缓冲液环境中的水接触角. 在详细研究了聚合物膜的化学结构和表面性质之后, 采用表面等离子体谐振仪(SPR)原位监测BSA在PAP上的吸附动力学过程, 发现其吸附行为主要受缓冲液的pH值和BSA浓度的影响. 在不同生物缓冲液环境下, 蛋白质和聚合物膜之间的各种作用力会发生变化, 最终导致蛋白质吸附行为以及吸附量的不同, 这为以后制备更加敏感的导电蛋白质芯片奠定了基础.     

Two-dimensional correlation analysis of continuous online in situ ATR-FTIR on the adsorption of butyl xanthate at the surface of a-PbO

The adsorption behavior of butyl xanthate on the surface of lead oxide was investigated using continuous online in situ attenuated total reflectance Fourier transform infrared（ATR-FTIR） spectroscopy technique and two dimensional（2D） correlation analysis.The adsorbed layer studied was prepared by coating α-PbO particles onto the surfaces of the ZnSe crystal.The appearance of spectral peaks at 1203 cm^-1,1033 cm^-1 and their red shift indicated the formation and aggregation of xanthate at the surface of α-PbO.According to 1R intensity changes after rinsing with deionized water and a NaOH solution,the adsorption was proved to be a chemisorption type.The competition between xanthate and OH for the surfaces leads to desorption of xanthate at higher pH.The technique of 2D correlation ATR-FTIR spectroscopy was used to evaluate the changing order of spectral intensities in the adsorption process,and the results indicated that xanthate micelles were formed at the surfaces.The adsorption kinetics of butyl xanthate was found to be a pseudo-second-order reaction model and the adsorption capacity of butyl xanthate at α-PbO was as high as 281 mg g^-1 after 150 min.     

Labelling and binding of poly-(L-lysine) to functionalised gold surfaces. Combined FT-IRRAS and XPS characterisation

We compare herein the interfacial reactivity of self-assembled monolayers (SAMs) of 11-mercaptoundecanoic acid (MUA), 1-undecanethiol (UDT) and 11-mercaptoundecanol (MUD) on gold surfaces towards aqueous solutions of poly-(L-lysine) (PL). Liquid-phase labelling of PL with the alkyne dicobalt hexacarbonyl cluster 1 combined with analysis of the substrates by Fourier transform infrared reflection-absorption spectroscopy (FT-IRRAS) and X-ray photoelectron spectroscopy (XPS) revealed that irreversible binding of PL occurred in all cases. However, the mechanism of binding involved differed markedly from one monolayer to the other. The main mode of interaction of PL to MUA SAM was of electrostatic nature between the terminal carboxylate of MUA and the ammonium groups of PL. For a similar number of bound thiolate molecules, the UDT adsorbed layer was found less continuous than the MUA one, allowing a higher fraction of PL to directly bind to the gold surface. As for MUD, very little thiolate molecules were adsorbed, leaving bare gold surface areas for non specific adsorption of PL.     

Quartz crystal microbalance with dissipation monitoring and surface plasmon resonance studies of carboxymethyl cellulose adsorption onto regenerated cellulose surfaces

Adsorption of anionic polyelectrolytes, sodium salts of carboxymethyl celluloses (CMCs) with different degrees of substitution (DS = 0.9 and 1.2), from aqueous electrolyte solutions onto regenerated cellulose surfaces was studied using quartz crystal microbalance with dissipation monitoring (QCM-D) and surface plasmon resonance (SPR) experiments. The influence of both calcium chloride (CaCl(2)) and sodium chloride (NaCl) on CMC adsorption was examined. The QCM-D results demonstrated that CaCl(2) (divalent cation) caused significantly greater CMC adsorption onto regenerated cellulose surfaces than NaCl (monovalent cation) at the same ionic strength. The CMC layers adsorbed onto regenerated cellulose surfaces from CaCl(2) solutions exhibited greater stability upon exposure to flowing water than layers adsorbed from NaCl solutions. Both QCM-D and SPR results showed that CMC adsorption onto regenerated cellulose surfaces from CaCl(2) solutions increased with increasing CaCl(2) concentration up to the solubility limit (10 mM). Voigt-based viscoelastic modeling of the QCM-D data indicated that the CMC layers adsorbed onto regenerated cellulose surfaces had shear viscosities of η(f) ≈ 10(-3) N·s·m(-2) and elastic shear moduli of μ(f) ≈ 10(5) N·m(-2). Furthermore, the combination of SPR spectroscopy and QCM-D showed that the CMC layers contained 90-95% water. Adsorption isotherms for CMCs in CaCl(2) solutions were also obtained from QCM-D and were fit by Freundlich isotherms. This study demonstrated that CMC adsorption from CaCl(2) solutions is useful for the modification of cellulose surfaces.     

Assembly of layer-by-layer films of electroactive hemoglobin and surfactant didodecyldimethylammonium bromide

When a solid substrate with negative surface charges was placed in an aqueous didodecyldimethylammonium bromide (DDAB) vesicle dispersion, the cationic surfactant DDAB with two hydrocarbon chains could be assembled into the biomembrane-like tail-to-tail double-layer structure on the solid surface with the positively charged head groups toward outside, making the surface charge reverse from negative to positive. After the solid substrate with DDAB was immersed in a hemoglobin (Hb) solution at pH 9.0, the negatively charged Hb was adsorbed on the surface of DDAB layer by electrostatic attraction, forming a DDAB/Hb film. By repeating this adsorption cycle, the {DDAB/Hb}(n) layer-by-layer films were assembled on solid surfaces, which was confirmed by UV-vis spectroscopy, quartz crystal microbalance (QCM), and cyclic voltammetry (CV). The stable {DDAB/Hb}(n) films assembled on pyrolytic graphite (PG) electrodes showed two pairs of nearly reversible redox peaks at about -0.22 and -1.14 V vs SCE in pH 7.0 buffers, characteristic of the Hb heme Fe(III)/Fe(II) and Fe(II)/Fe(I) redox couples, respectively. The direct electrochemistry of Hb in the films could be used to electrocatalyze reduction of various substrates. UV-vis and IR spectroscopic results and comparison experiments with {DDAB/hemin}(n) films indicate that Hb in the {DDAB/Hb}(n) films essentially retains its native structure. Atomic force microscopy (AFM) was used to characterize the morphology of the films with different outermost layers.     

Mucin at solution/air and solid/solution interfaces

In this paper the surface activity of protein mucin at solution/air interface has been studied. The experiments of the adsorbed protein at solution/air interface have been carried out with a range of protein concentrations at a defined pH. The adsorption of the protein to solid surfaces and the degree of hydrophobicity at solid/solution interface of mucin have been evaluated at different pH and in the presence of Hofmeister electrolyte. The results from these studies have been further substantiated by surface potential measurements of mucin covered surface on stainless steel. Quartz crystal microbalance (QCM) has been used to follow the protein adsorption kinetics from solution to solid surface. The results from these measurements show that the adsorption behavior has a remarkable dependence on the degree of maximum coverage and is almost independent of the ionic strength. Other characteristic features such as maximum adsorption values at the protein isoelectric point (IEP4.7) and low-affinity isotherms that showed surface saturation even under unfavorable electrostatic conditions have been observed. The amount of mucin adsorbed in the presence of electrolytes has been estimated using electron spectroscopy for chemical analysis (ESCA). The study clearly shows that there exists an inverse relationship between the hydrophobicity and surface tension of the protein and also on the hydrated radius of Hofmeister electrolyte used.     

Mechanism of water photooxidation reaction at atomically flat TiO2 (rutile) (110) and (100) surfaces: dependence on solution pH

The mechanism of water photooxidation reaction at atomically flat n-TiO(2) (rutile) surfaces was investigated in aqueous solutions of various pH values, using photoluminescence (PL) measurements. The PL bands, which peaked at around 810 and 840 nm for the (110) and (100) surfaces, respectively, were assigned to radiative transitions between conduction-band electrons and surface-trapped holes (STH), [Ti-O=Ti(2)](s)+, formed at triply coordinated (normal) O atoms at the surface lattice. The PL intensity (I(PL)) decreased stepwise with increasing solution pH, namely, it sharply decreased at around pH 4, near the point of zero charge of TiO(2) (about 5), and then rapidly decreased to zero near pH 13. The first sharp decrease around pH 4 is attributed to the increased rate of nucleophilic attack of a water molecule to a hole at a site of surface bridging oxygen (Ti-O-Ti), the density of which increases with increasing pH. The nucleophilic attack is regarded as the main initiating step of the water oxidation reaction in low and intermediate pH. The high PL intensity at low pH is ascribed to slow nucleophilic attack owing to a very low density of Ti-O-Ti by its protonation at the low pH. The second sharp decrease near pH 13 is attributed to formation of surface anionic species like Ti-O- which can be readily oxidized by photogenerated holes. Interrelations between reaction intermediates proposed in this work and those reported by time-resolved laser spectroscopy are discussed.     

Labelling and binding of poly-( -lysine) to functionalised gold surfaces. Combined FT-IRRAS and XPS characterisation

We compare herein the interfacial reactivity of self-assembled monolayers (SAMs) of 11-mercaptoundecanoic acid (MUA), 1-undecanethiol (UDT) and 11-mercaptoundecanol (MUD) on gold surfaces towards aqueous solutions of poly-( -lysine) (PL). Liquid-phase labelling of PL with the alkyne dicobalt hexacarbonyl cluster 1 combined with analysis of the substrates by Fourier transform infrared reflection–absorption spectroscopy (FT-IRRAS) and X-ray photoelectron spectroscopy (XPS) revealed that irreversible binding of PL occurred in all cases. However, the mechanism of binding involved differed markedly from one monolayer to the other. The main mode of interaction of PL to MUA SAM was of electrostatic nature between the terminal carboxylate of MUA and the ammonium groups of PL. For a similar number of bound thiolate molecules, the UDT adsorbed layer was found less continuous than the MUA one, allowing a higher fraction of PL to directly bind to the gold surface. As for MUD, very little thiolate molecules were adsorbed, leaving bare gold surface areas for non specific adsorption of PL.     

Chemical composition and acid-base properties of the surface of GaAs-CdS solid solutions

Chemical composition and acid-base properties of the surfaces of GaAs-CdS solid solutions and the constituent binary compounds exposed to air, vacuum, CO, and NH₃ were analyzed using mass spectrometry, IR spectrometry, isoelectric-point pH (pH_iso) analysis, and mechanochemical methods. Powders and films were prepared from the solid solutions by isothermal diffusion and discrete vacuum evaporation, respectively. XRD and Raman analysis revealed that a solid solution has a sphalerite or wurtzite structure, depending on its composition. The initial surface of all the systems studied exhibited acidic properties: the pH value ranged from 4.9 to 6.45. The surfaces contained Lewis (electron accepting) and Brönsted (adsorbed H₂O and CO₂ molecules, OH^? groups) sites. The acidity of the surface increased upon treatment with CO and decreased upon treatment with NH₃. For all types of treatment, the concentration dependence of the acid-base properties of the surface exhibited an extremum. The strongest acidic sites were revealed on the surface of the (GaAs)_0.95 (CdS)_0.05 solid solution. The adsorption activity of this solution, a promising material for manufacturing gas sensors, was evaluated.     

Adsorption and conformation of carboxymethyl cellulose at solid-liquid interfaces using spectroscopic, AFM and allied techniques

Carboxymethyl cellulose (CMC) is a polysaccharide which is widely used in many industrial sectors including food, textiles, paper, adhesives, paints, pharmaceutics, cosmetics and mineral processing. It is a natural organic polymer that is non-toxic and biodegradable. These properties make it ideal for industrial applications. However, a general lack of understanding of the interaction mechanism between the polysaccharides and solid surfaces has hindered the application of this polymer. In this work, adsorption of CMC at the solid-liquid interface is investigated using adsorption and electrophoretic mobility measurements, FTIR, fluorescence spectroscopy, AFM and molecular modeling. CMC adsorption on talc was found to be affected significantly by changes in solution conditions such as pH and ionic strength, which indicates the important role of electrostatic force in adsorption. The pH effect on adsorption was further proven by AFM imaging. Electrokinetic studies showed that the adsorption of CMC on talc changed its isoelectric point. Further, molecular modeling suggests a helical structure of CMC in solution while it is found to adsorb flat on the solid surface to allow its OH groups to be in contact with the surface. Fluorescence spectroscopy studies conducted to investigate the role of hydrophobic bonding using pyrene probe showed no evidence of the formation of hydrophobic domains at talc-aqueous interface. Urea, a hydrogen bond breaker, markedly reduced the adsorption of CMC on talc, supports hydrogen bonding as an important factor. In FTIR study, the changes to the infrared bands, associated with the CO stretch coupled to the CC stretch and OH deformation, were significant and this further supports the strong hydrogen bonding of CMC to the solid surface. In addition, Langmuir modeling of the adsorption isotherm suggests hydrogen bonding to be a dominant force for polysaccharide adsorption since the adsorption free energy of this polymer was close to that for hydrogen bond formation. All of the above results suggest that the main driving forces for CMC adsorption on talc are a combination of electrostatic interaction and hydrogen bonding rather than hydrophobic force.     

The influence of the structure of the surface of functional organosilicas on the adsorption of cholic acid

High-dispersity silica was modified by functional groups capable of protonating or carrying a constant positive charge. IR and UV spectroscopy, temperature-programmed thermogravimetry, pH metry, and quantitative analysis of grafted compounds were used to determine the structure of the surface of functional organosilicas. The adsorption of primary bile (cholic) acid on silica adsorbents and cholestiramine was studied. The adsorption of cholic acid from solutions with pH 2–8 was substantially higher on adsorbents with positively charged surfaces. The silica adsorbents synthesized were shown to have higher cholic acid adsorption parameters compared with adsorbents used in medicine.     

Non-linear vibrational sum frequency spectroscopy of atmospherically relevant molecules at aqueous solution surfaces

Surface vibrational sum frequency spectroscopy has been shown to be a powerful surface probe of molecules adsorbed at solid and liquid surfaces. Studies described herein apply this method to studying heterogeneous air/aqueous solution interfaces to understand surface adsorption and structure of several solute molecules adsorbed at aqueous surfaces. The molecules examined at aqueous solution surfaces include Dimethyl sulfoxide (DMSO), methane sulfonic acid (MSA) and acetone. These results reveal that small soluble molecules such as these organize in different ways at the surface of aqueous solutions. This surface organization has implications for atmospheric chemical processes since adsorption at the surface of atmospheric aerosols affects bulk chemical concentrations.     

In-situ infrared spectroscopic studies of adsorption processes on boehmite particle films: exchange of surface hydroxyl groups observed upon chelation by acetylacetone

Adsorption processes on poorly crystalline boehmite (PCB) particle films have been studied using attenuated total reflection infrared spectroscopy. This method allows the in-situ investigation of wet surface chemical processes. Thin films of aggregated particles of PCB that are stable between pH 4 and 11 have been prepared by drying aqueous PCB dispersions. Carbonate adsorbs to the PCB films during the film formation process but can be removed without impact on the film by washing with alkali at pH 10. The adsorption of acetylacetone (acac) to the surface of PCB has been studied at the solid/liquid and solid/gas interfaces. The concomitant changes in the OH deformations of hydroxyl groups present on the surface has been observed. The IR absorption of surface hydroxyl groups involved in adsorption of a bidentate chelating ligand have been spectroscopically isolated through their interaction with acac.     

Quantitative SNIFTIRS studies of (bi)sulfate adsorption at the Pt(111) electrode surface

Subtractively normalized interfacial Fourier transform infrared reflection spectroscopy (SNIFTIRS) was applied to study (bi)sulfate adsorption on a Pt(111) surface in solutions of variable pH while maintaining a constant total bisulfate/sulfate ((bi)sulfate) concentration without the addition of an inert supporting electrolyte. The spectra were recorded for both the p- and s-polarizations of the IR radiation in order to differentiate between the IR bands of the (bi)sulfate species adsorbed on the electrode surface from those species located in the thin layer of electrolyte. The spectra recorded with p-polarized light consist of the IR bands from both the species adsorbed at the electrode surface and those present in the thin layer of electrolyte between the electrode surface and ZnSe window whereas the s-polarized spectra contain only the IR bands from the species located in the thin layer of electrolyte. A new procedure was developed to calculate the angle of incidence and thickness of the electrolyte between the Pt(111) electrode surface and the ZnSe IR transparent window. By combining these values with the knowledge of the optical constants for Pt, H(2)O and ZnSe, the mean square electric field strength (MSEFS) at the Pt(111) electrode surface and for thin layer of solution were accurately calculated. The spectra recorded using s-polarization were multiplied by the ratio of the average MSEFS for p- and s-polarizations and subtracted from the spectra recorded using p-polarization in order to remove the IR bands that arise from the species present within the thin layer cavity. In this manner, the resulting IR spectra contain only the IR bands for the anions adsorbed on the Pt(111) electrode surface. The spectra of adsorbed anions show little change with respect to the pH ranging from 1 to 5.6. This behavior indicates that the same species is predominantly adsorbed on the metal surface for this broad range of pH values and the results suggest that sulfate is the most likely candidate for this adsorbate.     

Thermoanalytical study of acid-treated clay containing amino acid immobilized on its surface

The aim of this study is to investigate the incorporation of amino acid molecules in an acid-activated montmorillonite by means of solid characterization after the incorporation of these biomolecules. The acid activation procedure was carried out for the purpose of increasing the acid sites in the clay as well as the impurity elimination in the mineral. Cysteine, aspartic, and glutamic acids were adsorbed on montmorillonite K10 which was previously treated with a hydrochloric acid solution. The clay was put in contact with amino acid solutions at two different concentrations. Each amino acid was adsorbed at identical conditions, with the pH fixed to ensure the charge of molecules and surface clay. The solid was characterized by means of X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, and nitrogen adsorption at 77 K. After the amino acid adsorption, the powders showed changes in their characteristics as well as in their thermal behavior, which depended on both the concentration and the nature of the adsorbed amino acid. The thermal decomposition and elimination of cysteine occurred at a higher temperature than the aspartic and glutamic acid; the complete removal of glutamic acid molecules was not observed at 850 °C. The differences observed in the solid characteristic after the adsorption of each amino acid were discussed. Both the thermoanalytical study and characterization of materials after the interaction with amino acid molecules can be useful to understand the adsorption mechanism of biomolecules on solid surfaces.     

Adsorption of bisulfate on the Ru(0001) single crystal electrode surface

Adsorption of anions from sulfuric acid solutions has been studied on Ru(0001) single crystal and polycrystalline surfaces by electrochemical techniques and in-situ Fourier transform infrared spectroscopy. Infrared spectroscopy shows that bisulfate is the anion adsorbed on the Ru(0001) surface. The bisulfate adsorption is detected at the H₂ evolution potential and extends into the potential region where the Ru surface is oxidized. A method for extracting unipolar bands from bipolar bands has been presented. The tuning rate of adsorbed bisulfate in the double layer potential region of Ru(0001) was found to be significantly smaller than those observed for other platinum metals. This has been ascribed to a small change in bisulfate coverage on Ru(0001) in this potential range. Bisulfate vibration frequencies are higher on this surface than at any face-centered cubic metal with the (111) orientation. Oxidation of the Ru(0001) surface is limited to one electron per Ru atom, distinctly different from the high degree of oxidation seen in polycrystalline surfaces. For oxidized polycrystalline Ru, only solution phase sulfates and bisulfates are observed in the IR spectra.     

Nature identification and morphology characterization of cation-exchange membrane fouling during conventional electrodialysis

The aim of this work was to study the effect of a concentrate solution pH value and of the composition in calcium, carbonate, and protein of a diluate solution to be treated by conventional electrodialysis on the fouling of cation-exchange membranes (CEM). It appeared that after demineralization of solutions containing CaCl(2) and CaCl(2)+Na(2)CO(3) using a concentrate solution maintained at a pH of 12, mineral fouling appeared on both sides of the CEM. The nature of the deposits was identified as calcium hydroxide and/or carbonate on both surfaces. The mineral fouling presented an aggregation-like crystal following a carnation-like pattern of aggregates of small rhombohedral crystals with CaCl(2) added alone, while CaCl(2)+Na(2)CO(3) yielded a smoother spherical crystal. Protein fouling was detected only on the CEM surface in contact with the diluate after demineralization of a solution containing CaCl(2)+Na(2)CO(3) using a concentrate pH value of 2.