Charged Silanol Groups Research Articles

Mechanism of Apatite Formation Induced by Silanol Groups. TEM observation.

The essential requirement for an artificial material to bond to bone is formation of bonelike apatite on its surface in body environment. The formation of the apatite has been proposed to be induced by silanol groups on the surface of the material. In the present study, the mechanism of apatite formation induced by the silanol groups was investigated in a biomimetic process. A collodion film supported by a titanium grid which faced to a CaO-SiO2-based glass was soaked for various periods in an acellular simulated body fluid with ion concentrations nearly equal to those of the human blood plasma. The film was observed by a transmission electron microscope equipped with energy dispersive X-ray spectrometer. Silicate ions rich in silanol groups, which were released from the glass, were attached onto the collodion film. They first combined only with calcium ions in the fluid to form a calcium silicate. Later, the calcium ions in the calcium silicate combined with phosphate ions in the fluid to form an amorphous calcium phosphate with a low Ca/P atomic ratio. The amorphous calcium phosphate, increasing its Ca/P atomic ratio, eventually transformed into a crystalline apatite. This indicates that the silanol groups induce the apatite formation not directly but through the formation of calcium silicate and amorphous calcium phosphate with a low Ca/P atomic ratio. The formation of calcium silicate at the initial stage might be attributed to interaction between negatively charged silanol groups and positively charged calcium ions.

Comparison between wettability gradients made on gold and on Si/SiO 2 substrates

We have previously shown that wettability gradients on Si/SiO 2 can be used to analyze in detail the interactions of surfactants and proteins with the vast number of different surface properties that a gradient represents. We have also shown that the interactions of surfactants can be used to characterize the surface. In this report we discuss a new kind of wettability gradient that is composed from alkanethiols on gold. Surfactant and protein adsorption phenomena are investigated and compared with analogous experiments made on gradients prepared from chlorosilanes on Si/SiO 2 substrates. Surfactant adsorption studies were used to investigate the surface properties. Through their electrostatic interactions negatively charged groups on the surface could be detected and through their hydrophobic interactions defects in the surface layer resulting in hydrophobic groups could be detected. The alkanethiol gradient had at the extreme OH-side an advancing contact angle to water between 30 and 40°. Still this surface had a lower adsorbed amount of fibrinogen compared to a (completely wetting) silica surface covered with negatively charged and uncharged silanol groups, indicating that the fibrinogen molecules also interacts electrostatically through their positively charged amino acid residues. This shows that the amount of fibrinogen adsorbed is not solely dependent on the surface hydrophilicity.

Interaction mechanisms between insulin and N-acetylneuraminic acid in affinity chromatography.

Silica beads are coated with dextran carrying a calculated amount of positively charged diethylaminoethyl (DEAE) groups in order to neutralize negatively charged silanol groups at the silica surface and in this way to minimize non-specific interactions between silica and proteins in solution. Dextran-coated silica supports are potentially excellent stationary phases for high-performance liquid chromatography of proteins. These supports combine the advantages of polysaccharide phases with the excellent mechanical characteristics of silica. These supports [silica-dextran-DEAE (SID)] are easily functionalized by grafting N-acetylneuramic acid (NANA), extracted from edible birds' nests, using conventional coupling methods. The performance of supports bearing NANA was studied by high-performance liquid affinity chromatography of insulin, the hypoglycaemic peptide hormone of the human organism. The study showed that these supports exhibit a reversible and specific affinity towards insulin and allow separations with high purification yields. The influence of different physico-chemical parameters (pH, temperature and insulin concentration) on insulin retention on the support was studied. This allowed the optimization of the conditions of adsorption and a better understanding of the interaction mechanisms between insulin and NANA as a biospecific ligand.

Effective ion-pairing for the separation of basic proteins in capillary electrophoresis.

The addition of the sodium salt of phytic acid to the separation buffer (pH's 6.0-9.5) has allowed the analysis of a number of basic proteins (pI's > 9) by capillary electrophoresis. The method of analysis is simple and leads to considerable improvement in peak shape. Some very basic proteins, totally adsorbed onto the capillary fused silica surfaces in the presence of buffer only, can be analysed as sharp signals when this polyanionic species is included in the running electrolyte. These improvements in analysis are thought to arise as a result of the suppression of coulombic interactions between these positively charged proteins (ion-paired to phytic acid) and the negatively charged silanol groups on the inner wall of the capillary.

Synthesis and evaluation of epoxy polymer coatings for the analysis of proteins by capillary zone electrophoresis

This paper reports a diol-epoxy coating process to deactivate the inner surface of fused-silica capillaries for use in capillary zone electrophoresis. The most effective coating consists of an epoxy polymer covalently bonded to the silica surface through glycerylpropyl silane which eliminates a number of the negatively charged silanol groups. The epoxy polymer phase also further masks residual surface silanols and sterically limits interaction of proteins with the inorganic surface of the capillary. Application of the coating was a multi-step process. In the initial step, glycidylpropyltrimethoxy silane was used to derivatize the surface of fused-silica capillaries. This was followed by deposition at the capillary wall of a film of multifunctional oxirane. Polymerization was achieved by either boron trifluoride or tertiary amine. These coatings were of sufficient thickness and hydrophilicity to reduce protein adsorption but still allow sufficient electroosmotic pumping to carry both positive and negative species past the detector. The coatings provided capillaries with lifetimes exceeding 120 h. Proteins were resolved quickly and efficiently with high recovery of both cationic and anionic species between pH 5 to 10.

Immobilization of dermatan sulphate on a silica matrix and its possible use as an affinity chromatography support for heparin cofactor II purification

Dermatan sulphate (DS) is glycosaminoglycan which catalyses specifically thrombin inhibition by a plasmatic inhibitor, Heparin cofactor II (HCII). DS was insolubilized on a silica matrix to study its interaction with HCII. The immobilization of DS was performed with a yield on a silica previously coated with polysaccharides in order to neutralize the negatively charged silanol groups. The value of the affinity constant of insolubilized DS for HCII, measured by the adsorption isotherm, is consistent with the value obtained for soluble DS. The DS bound to the silica matrix was also tested as a chromatographic support for the purification of HCII from human plasma; the optimum conditions for HCII adsorption and desorption were determined. The eluted HCII was obtained with a good yield (21%) and with no contamination by antithrombin III, the other main plasmatic inhibitor of thrombin.

Coated silica supports for high-performance affinity chromatography of proteins

Polymer-coated silica supports are potentially good stationary phases for high-performance affinity chromatographic separations of proteins. Silica beads have been coated with a polysaccharide (dextran or agarose), substituted by a calculated amount of positively charged diethylaminoethyl functions in order to neutralize the negatively charged silanol groups of silica and to facilitate the formation of a hydrophilic polymeric layer on the inorganic surface. The silica-based supports were prepared in two steps. First. the silica was impregnated with a solution of diethylaminoethylated polymer, and then the coating polymer was crosslinked in order to avoid leakage of the polymeric layer. The supports present minimal non-specific interactions with proteins, as tested by high-performance size-exclusion chromatography. These coated silica supports were coupled with active ligands, such as protein A, concanavalin A and heparin, by conventional coupling methods. The resulting affinity stationary phases were tested by the elution of proteins in order to study their performance in high-performance affinity chromatography.

Dextran-coated silica packings for high-performance size-exclusion chromatography of proteins

Porous silica beads have excellent mechanical properties for the high-performance liquid chromatography of proteins. However, the importance of non-specific interations between silanols on the silica surface and the proteins requires a modification of these supports before they can be used as stationary phases for size-exclusion chromatography (SEC). Silica beads were coated with dextran bearing a small number of positive charges in order to neutralize the negatively charged silanol groups. Diethylaminoethyl-dextrans (DEAE-dextrans) with a relatively low percentage of dextran units bearing DEAE functions were layered on the silica beads. The influence of several characteristics of these packings on chromatographic performance were studied in order to determine the optimal conditions for the SEC of proteins.