Adsorption Of Calcium Ions Research Articles

Investigating the Mechanical Effects of Adsorption of Ca2+ Ions on a Silicon Nitride Microcantilever Surface

Adsorption characteristics of calcium ions on silicon nitride surfaces have been investigated using microcantilevers. Both resonance frequency and cantilever bending undergo variation due to calcium ion adsorption. The adsorption behavior was found to fit a Langmuir isotherm. From the linearized form of the isotherm, the binding constant of adsorption, K, was found to be 116 M-1 and the stress change at maximum coverage, Δσmax, was 0.46 N m-1. The Gibbs free energy change was estimated to be −11.8 kJ mol-1. A calcium-binding protein, calmodulin, was used to check for the presence of adsorbed Ca2+ ions on the cantilever surface. Fluorescence measurements with Alexa Fluor 488 conjugated calmodulin gave confirmatory evidence of the presence of Ca2+ ions on the silicon nitride side of the cantilever surface. These results indicate that the presence of Ca2+ ions and probably other cations in the solution can cause cantilever resonance frequency shifts and bending. It is therefore critical to correct for these ...

In situ detection of calcium ions with chemically modified microcantilevers

We report a novel technique of micromechanical detection of trace amounts of calcium ions by using microcantilevers modified with ion-selective self-assembled monolayers (SAMs). The SAM-modified microcantilevers undergo bending due to selective adsorption of calcium ions. Experiments conducted under flow conditions show that the modified cantilevers respond sensitively to calcium ions (Ca 2+); a Ca 2+ concentration of 10 −9 M can be detected with this technique. Other cations, such as Na + and K +, do not have any effect on the deflection of these cantilevers. We demonstrate two different kinds of SAMs having selectivity for calcium ions.

Effect of Reversible Cross-linker, N,N‘-Bis(acryloyl)cystamine, on Calcium Ion Adsorption by Imprinted Gels

Imprinted gels incorporating two different breakable cross-linkers, a PbMAA2 complex and a disulfide (S−S) bond, were prepared by radical polymerization. After the lead ions were removed by washing, these gels showed a high affinity for calcium ions. Breakage and subsequent reconnection of the S−S bonds in the absence of Ca2+ decreases the Ca2+ binding affinity of the gel. This indicates that random reconnection of the S−S bonds produces a frustration in the adsorption of Ca2+ by the carboxyl groups. However, if the S−S bonds were reconnected in the presence of Ca2+ and the Ca2+ was subsequently removed (the post-imprinting technique), the resulting gels showed a higher binding affinity for Ca2+. This indicates that the post-imprinting technique creates a more favorable conformation for Ca2+ binding in the polymer network. We interpret our data to mean that “memory” of target-binding sites was encoded effectively into the polymer network by the initial imprinting technique and then enhanced by the post-im...

Reversible adsorption of calcium ions by imprinted temperature sensitive gels

With the aim of developing polymeric gels sensitive to external stimuli and able to reversibly adsorb and release divalent ions, copolymer gels of N-isopropylacrylamide (NIPA) and methacrylic (MAA) monomers were prepared. We chose calcium as a target divalent ion. Two MAAs form a complex with a calcium ion, and the NIPA component allows the polymers to swell and shrink reversibly in response to temperature. The adsorbing site develops an affinity to target ions when the adsorbing molecules come into proximity, but when they are separated, the affinity diminishes. To enhance the affinity to calcium, an imprinting technique was applied using Ca2+ and Pb2+ ions as templates in methylsulfoxide and dioxane media, respectively. The adsorption capacity of the imprinted gels was compared with that of the nonimprinted gels, and the effects of the templates, the solvents, and the amount of methacrylic monomers used in the synthesis and the medium temperature over the Ca2+ adsorption capacity of the gels from aqueous solutions were evaluated. The analysis of the adsorption revealed that (a) the adsorption can be described by the Langmuir isotherms; (b) there is an approximately linear relationship between saturation and methacrylic monomer concentration; (c) the affinity depends on the degree of gel swelling or shrinkage that can be switched on and off by temperature; (d) in the shrunken state, the affinity depends approximately linearly on the MAA concentration in the imprinted gels, whereas in the nonimprinted gels it is proportional to the square of MAA concentration; (e) the imprinted gels adsorb more than the nonimprinted gels when MAA concentration is less than that of permanent cross linkers. The success of imprinting of CaMAA2 and PbMAA2 complex is evidence for memory of such complex onto the weakly cross-linked gel.

Effect of clays and calcium ions on bitumen extraction from athabasca oil sands using flotation

AbstractA novel approach, based on the doping of rich estuarine oil sands with calcium and/or clays, was developed to study bitumen extraction. The batch flotation tests showed that the addition of either calcium ions up to 40 p.p.m., or kaolinite, illite and montmorillonite clays at 1 wt% of oil sands processed had marginal effect on bitumen recovery from the estuarine ores. A sharp reduction in bitumen recovery was observed only when calcium ions greater than 30 p.p.m. and 1 wt% montmorillonite clays were added together. While bitumen recovery correlated well with changes in water/air/bitumen contact angle, no correlation was found between bitumen recovery and measured zeta potential of clays or surface tension of the supernatants from the flotation slurry. The wettability of bitumen was identified as a key element in determining bitumen recovery. The aqueous solution analysis for calcium ions showed that most of the added calcium ions disappeared from the solution when montmorillonite clays were present. The addition of illite or kaolinite clays changed the calcium ion concentration in the slurry only marginally. Stronger adsorption of calcium ions on montmorillonite than on either kaolinite or illite is considered to be responsible for the increased bitumen wettability, and hence reduced bitumen recovery.

Influence of surface modifications to titanium on oral bacterial adhesion in vitro.

The influence of surface modifications to titanium on the initial adherence of Porphyromonas gingivalis ATCC33277 and Actinobacillus actinomycetemcomitans ATCC43718 was evaluated. Surface modifications were performed with dry processes including ion implantation (Ca(+), N(+), F(+)), oxidation (anode oxidation, titania spraying), ion plating (TiN, alumina), and ion beam mixing (Ag, Sn, Zn, Pt) with Ar(+) on polished pure titanium plates. Comparatively large amounts of P. gingivalis and A. actinomycetemcomitans adhered to polished titanium plates. The degree of P. gingivalis adhesion showed a positive correlation with surface energy and the amount of calcium-ion adsorption. Adherence of both P. gingivalis and A. actinomycetemcomitans increased on calcium-implanted surfaces compared with polished titanium surfaces, whereas adherence of P. gingivalis was remarkably decreased on alumina-coated surfaces. These findings indicate that titanium implants exposed to the oral cavity require surface modification to inhibit the adherence of oral bacteria, and that surface modification with a dry process is useful in controlling the adhesion of oral bacteria as well as ensuring resistance against wear.

Characterisation of surface properties of ceramic ultrafiltration membranes by studying diffusion-driven transport and streaming potential

The knowledge of the electrokinetic properties of the filtering layer of membranes is useful to predict and understand their filtration performances. Streaming potential allows the characterisation of these properties during the filtration process. This technique coupled with permeation flux measurements was carried out with different multi-layered ceramic membranes composed of distinct alumina, titania and zirconia layers in order to determine the true streaming potential and isoelectric point of each metal oxide layer composing the membrane. The apparent transport number of ions in the different structures and the permselectivity have been determined by imposing a concentration gradient across these membranes. The isoelectric point of the two finest pore layers were deduced from the pH dependence of the membrane permselectivity. The specific adsorption of calcium ions onto the surface of these amphoteric membranes was shown from permselectivity values as well as from streaming potential measurements.

Surface functional group dependence on apatite formation on self‐assembled monolayers in a simulated body fluid

Self-assembled monolayers (SAMs) of alkanethiols having CH3, PO4H2, COOH, CONH2, OH, and NH2 terminal groups formed on a gold surface via sulfur attachment were soaked in a simulated body fluid (SBF), whose ion concentrations were nearly equal to those of human blood plasma, at 37°C for up to 40 days. The effect of their terminal functional groups on apatite formation was assessed using X-ray photo-electron spectroscopic (XPS) measurement and a quartz crystal microbalance (QCM) technique. The Ca and P atoms were detected, of which element intensities increased with time, on SAMs except for the alkanethiol having the methyl terminal group. The Ca/P atomic ratios of the apatites formed on the SAMs ranged from around 1.0 to around 1.3. The most potent inducer for apatite formation, judged from the growth rate (micrometers per day) calculated from the weight change during QCM measurement, was the SAM of the alkanethiol with the PO4H2 group, followed by that of the alkanethiol with the COOH group. The SAMs of the alkanethiols with the CONH2, OH, and NH2 groups possessed much weaker inducing powers than the former two SAMs. Little weight change was observed for the methyl-group-terminated alkanethiol SAM. The growth rates increased with time, irrespective of the terminal group species among apatite formation-inducing groups. During the experimental observation period, the following relationship held. The growth rate decreased in the order PO4H2 > COOH ≫ CONH2 ≃ OH > NH2 ≫ CH3 ≃ 0. Since negatively charged groups strongly induced apatite formation but the positively charged group did not, it can be said that the apatite formation initiated via calcium ion-adsorption upon complexation with a negative surface-charged group may be dominant in biomaterial calcification where ionic species directly contact the biomaterial surface in body fluids. © 1997 John Wiley & Sons, Inc.

Surface functional group dependence on apatite formation on self-assembled monolayers in a simulated body fluid.

Self-assembled monolayers (SAMs) of alkanethiols having CH3, PO4H2, COOH, CONH2, OH, and NH2 terminal groups formed on a gold surface via sulfur attachment were soaked in a simulated body fluid (SBF), whose ion concentrations were nearly equal to those of human blood plasma, at 37 degrees C for up to 40 days. The effect of their terminal functional groups on apatite formation was assessed using X-ray photo-electron spectroscopic (XPS) measurement and a quartz crystal microbalance (QCM) technique. The Ca and P atoms were detected, of which element intensities increased with time, on SAMs except for the alkanethiol having the methyl terminal group. The Ca/P atomic ratios of the apatites formed on the SAMs ranged from around 1.0 to around 1.3. The most potent inducer for apatite formation, judged from the growth rate (micrometers per day) calculated from the weight change during QCM measurement, was the SAM of the alkanethiol with the PO4H2 group, followed by that of the alkanethiol with the COOH group. The SAMs of the alkanethiols with the CONH2, OH, and NH2 groups possessed much weaker inducing powers than the former two SAMs. Little weight change was observed for the methyl-group-terminated alkanethiol SAM. The growth rates increased with time, irrespective of the terminal group species among apatite formation-inducing groups. During the experimental observation period, the following relationship held. The growth rate decreased in the order PO4H2 > COOH >> CONH2 approximately equal to OH > NH2 >> CH3 approximately equal to 0. Some negatively charged groups strongly induced apatite formation but the positively charged group did not, it can be said that the apatite formation initiated via calcium ion-absorption upon complexation with a negative surface-charged group may be dominant in biomaterial calcification where ionic species directly contact the biomaterial surface in body fluids.

Adsorption of calcium ions by graft copolymer of acrylic acid on biopolymer chitin

The graft copolymer of acrylic acid on biopolymer chitin, with 45% grafting efficiency, was used to study the effect of the carboxylic group of the graft copolymer on the metal binding ability of calcium ions in aqueous solution as a function of pH, contact time and metal concentration. The adsorption equilibrium data correlate well with the Langmuir isotherm equation. The maximum adsorption capacities of graft copolymer and chitin were found to be 0.500 ± 0.013 and 0.195 ± 0.005 mmol Ca 2+ g −1 , respectively, suggesting the effective participation of the carboxylic group in Ca 2+ adsorption. The poly(acrylic acid)- grafted chitin is promising as a polymeric matrix to be used in the preparation of new glass ionomer cements.

Coal oxidation and calcium loading on oxidized coal

Abstract A Pittsburgh No. 8 coal, and two IBC (Illinois Basin Coal) 101 and 112 coals were oxidized in a 2 1 Parr Stirred Bench Top Reactor. The oxidation time was varied up to 5 h; the temperature from 150°C to 225°C, the oxygen pressure from 100 to 600 psi, and coal dosage from 15 to 60 g in 600 ml of distilled water. The oxidation of coal was evaluated by measuring total acidic group formed on the coal surface as well as by measuring adsorption of calcium ion on the oxidized coal from a solution in a separate system. It was found that upon oxidation of coal, acidic groups were formed on the coal surface and were responsible for the adsorption of calcium ion. The oxidation increased with increasing oxygen pressure without much leveling-off effect. However, the oxidation increased sharply with increase in temperature from 150°C to 180°C and then tended to level off above 180°C. The optimum oxidation conditions were determined by considering BTU loss and Ca/S molar ratio where S is the total sulfur in coal. The optimum oxidation conditions of Pittsburgh No. 8 coal were 170°C and 500 psi O 2 with 60 g of coal for 3 h, while those of IBC 112 coal were 150°C and 500 psi O 2 with 60 g of coal for 3 h. Under these conditions, the Ca/S molar ratio reached approximately 1.3 and the BTU loss was less than 20%. This value of Ca/S molar ratio may be high enough to capture sulfur during fluidized combustion and coal gasification. Thus, it is concluded that the present method has the potential to be used in a commercial process for preparation of a feed stock for fluidized-bed combustion and coal gasification.

Mechanism of Action of Adsorbed Fluoride Ions on the Dissolution Kinetics of Apatite Powder

The kinetics of dissolution of calcium hydroxyapatite powder (HAP) is studied at 37°C at a constant pH 5 or 6 in the presence of 1 or 10 ppm fluoride ions. Experiments were carried out with an automatic setup which recorded continuously the proton uptake and the concentrations of calcium and fluoride in solution, using specific electrodes. We demonstrate that fluoride ions have a dual action. Their presence at the interface reduces the apatite solubility, and, as a consequence, the equilibrium is attained earlier. However, the adsorption of fluoride ions onto the apatite surface accelerates the initial dissolution process. Both processes are fully interpreted using the quantitative model recently proposed for HAP dissolution. According to this model, apatite dissolution is autoinhibited by the adsorption of calcium ions at the solid interface, thus forming a cationic semipermeable layer. Fluoride ions interact with this layer and decrease its autoinhibiting ability, especially in the case of higher fluoride concentrations where interfacial CaF 2 is formed.

Adsorption of Neutral and Anionic Polyacrylamides on Hydroxyapatite and Human Enamel: Influence on the Dissolution Kinetics

The adsorption of polyacrylamide fractions of different molecular weights and degrees of hydrolysis on hydroxyapatite and dental enamel, as well as their influence on the kinetics of dissolution of the latter, are studied at a constant pH under well controlled conditions. It is shown that the adsorbed polymers can slow down the dissolution process. The intensity of the inhibition effect follows the characteristics of the adsorption layer. The inhibition increases with the molecular weight of the polymers and their degree of hydrolysis. These behaviors are well interpreted with the model of apatite dissolution recently proposed, which supposes the formation of a cationic semipermeable layer, formed by the adsorption of calcium ions at the apatite interface.

Inhibition of dissolution of hydroxyapatite powder by adsorbed anionic polymers

The effect of the presence in solution of neutral or anionic hydrosoluble polymers on the kinetics of dissolution of hydroxyapatite powder (HAP) is analysed at a constant pH of 5 and under well-controlled conditions. Four polymers are studied. It is shown that the polymers that are able to be adsorbed induce a decrease in the rate of dissolution which strongly depends on the chemical structure of the polymers. Chemical groups with the ability to bind calcium ions, such as phosphate and phosphonate groups, are particularly efficient. The results are interpreted with the use of a recently proposed apatite dissolution model which assumes the formation, at the apatite interface, of an ionic semipermeable layer produced by the adsorption of calcium ions. According to this model, adsorbed polymers increase the ionic capacity of the interface.

メタクリル酸樹脂のカルシウム吸着能とエナメル質吸着性

ジメタクリレートで橋かけしたポリメタクリル酸によるカルシウムイオンの吸着は, Langmuir式に従い, 膨潤した樹脂での飽和吸着量から組成 [-COO-] 2Ca2+での結合と大きな安定度定数 (104l/mol) 示された. 樹脂のカルボキシル基はエナメル質のカルシウムとも結合し, 樹脂はエナメル質を良好に吸着した.

Calcium Ion Adsorption on Phospholipid Bilayers Theoretical Interpretation

A theoretical approach to phase transition enthalpy change as a function of calcium ion concentration was studied in terms of calcium ion adsorption on a phospholipid surface. The phospholipids used in this study were dipalmitoylphosphatidylcholine (DPPC), dipalmitoylphosphatidylethanolamine (DPPE), and dipalmitoylphosphatidylglycerol (DPPG). The theory used here is based on the DLVO theory, taking into account electrostatic interaction caused by calcium ion adsorption on the membrane surface. Calcium ion effects on DPPC and DPPG phase behavior can be explained by Helmholtz free energy change. Experimental enthalpy change is dependent on the electrical contribution in the free energy equation. This contribution is related to the binding constant K and effective surface area a'. Binding parameters, binding constant K and effective surface area a' were K=100 M-1 and a'=60, 000 m2/g for DPPG, and K=40 M-1 and a'=750 m2/g for DPPC as optimal values. These values for DPPE could not be determined owing to the absence of enthalpy change.

Quantitative Model for the Dissolution of Calcium Hydroxyapatite with a Permselective Ionic Interface

A model for the dissolution of calcium hydroxyapatite (HAP) is proposed using the current theory of ionic transport through a permselective membrane. In order to describe the experimentally observed self-inhibiting dissolution mechanism, the model includes an interfacial ionic layer formed at the apatite surface by the adsorption of calcium ions. It provides a quantitative explanation for the phenomenological rate reducing factor k introduced previously. In particular, the analysis shows that the experimental dependence of k with pH is well explained by the difference of permeability of the layer to HPO2-4 and H2PO-4 ions resulting from HAP dissolution. The values of the calcium adsorption parameters estimated from the comparison of the experiments with the model are in agreement with adsorption on phosphate and/or hydroxyl sites exposed on the apatite surface. The proposed theory may constitute a new approach to understanding the role of inhibitors of HAP dissolution and of the carious process.

Characterization of surface film formed on titanium in electrolyte using XPS

The surface film formed on titanium in a neutral electrolyte was characterized using XPS with an angular-dependent technique and argon-ion sputtering in order to predict the structure of the substance formed on titanium in a biological system. The results revealed that a calcium phosphate was naturally formed on titanium oxide, indicating that the surface layer of the titanium in the electrolyte consists of two parts: calcium phosphate and titanium oxide (essentially TiO 2). The calcium phosphate contained phosphate in the form of PO 3− 4, HPO 2− 4 and H 2PO − 4. The proportion of PO 3− 4 was the largest among the phosphates and approximately 60% of the phosphate was PO 3− 4. The calcium phosphate also contained hydroxyl groups and bound water. The formation and growth of the calcium phosphate was caused by the adsorption of hydrated phosphate ions by the titanium surface, the release of protons from the phosphate ions, and the adsorption of calcium ions by the phosphate.

Calcium ion as a cofactor in Na channel gating.

Calcium ions in the external medium stabilize the resting state of voltage-dependent channels, including Na channels. This effect of calcium on channel gating is usually explained in terms of the surface charge hypothesis, which proposes that local adsorption of calcium ion to the outside of the membrane alters the intramembranous electric field, thus influencing channel behavior indirectly. Calcium ion has also been shown to block Na channels, most strongly at negative voltage. We have examined these two apparently separate effects of calcium, the gating effect and Ca block, and find the two are closely correlated. We propose that calcium (or a suitable substitute) is an essential cofactor in normal gating and that it produces gating and blocking effects by binding within the channel.

Electrochemical investigation of lead-calcium alloys in sulphuric acid

The hydrogen evolution reaction from, and the cycle life (Pb /ar PbSO 4) of, a series of lead-calcium alloys (0 - 0.2 wt.% Ca) in sulphuric acid hav The exchange current density and Tafel slope for the H.R.E. increase with Ca content up to 0.05 wt.% then decrease to a value approaching that of pure The observed results are explained by: (i) preferential adsorption of calcium ions at the electrode surface; (ii) incorporation of Ca, to form a supersaturated solution, with alloys containing < 0.075 wt.% Ca; (iii) formation of an insoluble, non-conducting layer of calcium sulphate on the high content alloy.