Cationic Silica Research Articles

Rheology modification of montmorillonite dispersions by colloidal silica

We have studied the effect of additions of both anionic and cationic spherical silica colloids of different sizes on the rheology of dispersions of a well-characterised montmorillonite clay, SWy-2. The systems have been studied above and below the critical hydrodynamic overlap concentration, c*, of the clay. For dispersions at c c*, replacement of ∼10 % w/w of the clay content by silica leads to enhancements of all the rheological parameters characteristic of a gelling system, for the addition of both anionic and cationic silica. A simple tentative microstructural model for this complex behaviour is presented. This work, alongside our previous studies, confirms significant rheological modification by the addition of small quantities of nanoparticles as a general phenomenon of clay-colloid systems. It further suggests that viscosity enhancement and control of the rates of sol-gel transitions for product applications can be achieved using relatively low-cost, commercially available materials, such as silica nanoparticles and natural clays of different mineralogy.

Enhanced stability of curcumin in colloidosomes stabilized by silica aggregates

A novel approach to develop colloidosomes with enhanced barrier properties that can reduce the oxidation of encapsulated bioactive compound is described. These novel colloidosomes were stabilized using silica aggregates. Silica aggregates were prepared based on electrostatic complexation between anionic and cationic silica nanoparticles and were subsequently used to stabilize sub-micron scale oil-in-water colloidosomes. Control colloidosomes stabilized using negative charged silica nanoparticles were also prepared. Particle size and ζ-potential results confirmed the formation of silica aggregates. Curcumin was used as a model encapsulant. Fluorescence microscopy results showed that curcumin was encapsulated within the lipid core of the colloidosomes. Curcumin showed significantly higher stability in colloidosomes stabilized by silica aggregates as compared to those stabilized by negative charged silica nanoparticles (p < 0.05). Enhanced stability of curcumin in silica aggregate stabilized colloidosomes could be attributed to higher interfacial thickness of silica aggregates compared to silica nanoparticles. The proposed approach can be a simple and efficient alternative to layer-by-layer assembly of interfacial materials.

Positively charged functionalized silica nanoparticles as nontoxic carriers for triggered anticancer drug release

The aim of this study is the synthesis of pH-responsive cationic silica nanoparticles (NPs) by pyridinium-based ionic liquid for the improved sustained release formulations of methotrexate (MTX) as an anionic anticancer drug. Fanctionalized cationic silica NPs were successfully prepared via graft copolymerization of methacrylic acid (MAA) onto vinyl-bond-modified silica NPs. The prepared NPs were characterized using the scanning electron microscopy (SEM), the infrared spectroscopy (IR), and the thermogravimetric analysis. The resultant NPs were uniform spherical NPs with a mean diameter of approximately 160 ± 20 nm. We explored the ionic interaction of MTX NPs in order to generate pH-responsive controlled release system. The cumulative release of MTX-loaded composite microspheres shows a highly desirable precise pH-responsive drug release performance, i.e. loaded drug would not leak in physiological pH (7.4), but would release in a sustained way, where the pH value is lower (4). The protonation of carboxyl groups at mildly acidic condition resulted in a faster dissociation of copolymer/MTX complex, leading to an accelerated release of MTX at pH 4. Thus, complexation of MTX with NPs yielded a drug delivery system affording a pH-triggered release of MTX in an acidic environment. The in vitro cytotoxicity test by MTT assay against breast cancer cells, MCF7 indicates that NPs are nontoxic and suitable to use as drug carriers. Antitumor activity of the MTX-loaded nanocomposites against the cells was kept over the whole experiment process. The results showed that the MTX could be released from the nanocomposites without losing cytotoxicity.

Synthesis, characterization and pH-controllable methotrexate release from biocompatible polymer/silica nanocomposite for anticancer drug delivery

The objective of this study was to develop pH-responsive silica nanoparticles by imidazole-based ionic liquid for controlled release of methotrexate. In this article, we synthesized pH-responsive cationic silica nanoparticles by graft copolymerization of vinyl functionalized silica nanoparticles and methacrylic acid (MAA) monomer. Imidazole-based ionic liquid (Im-IL) was verified by 1HNMR and Fourier-transform infrared (FTIR) spectroscopy. The synthesized functionalized silica particles were characterized and confirmed by various technologies including the scanning electron microscopy (SEM), the infrared spectroscopy (IR) and the thermogravimetric analysis (TGA). SEM results reveal the uniformity in size/shape of silica particles. This nanosystem is modified for targeted delivery of an anticancer agent methotrexate. The nanocomposite-MTX complex was formed at physiological pH (7.4) due to the electrostatic interactions between anionic carboxylic group of MTX molecules and cationic rings in carrier, while, the release of which can be achieved through the cleavage of the nanocomposite-MTX complex by protonation of carboxyl groups in the MTX segment that are sensitive to variations in external pH at weak acidic conditions. FT-IR spectroscopy showed the presence of light interactions between the silicate silanols and the drug. MCF7 cells were incubated with the MTX-free nanocomposite and MTX-loaded nanocomposite at various concentrations for 24, 48 and 72 h, and the data showed that the nanocomposites themselves did not affect the growth of MCF7 cells. Antitumor activity of the MTX-loaded nanocomposites against the cells was kept over the whole experiment process. The results showed that the MTX could be released from the fibers without losing cytotoxicity.

Treatment of wood with silica sols against attack by wood-decaying fungi and blue stain

Abstract Pine sapwood was treated with various types of silica sols. Whereas alkaline sols were not able to penetrate deeper into wood, neutral and acidic sols showed good penetration. The weight percent gain of treated specimens amounted to 20–25%; bulking was negligible or even slightly negative. All silica sols in the treated specimens were stable against water leaching. A water submersion test revealed hydrophobation of the wood only after treatment with a cationic silica sol; all other silica sols increased the rate of water uptake. The addition of 2% cationic sol to a malt-agar growth medium caused growth inhibition of 40–50% of the wood decay fungi Coniophora puteana and Trametes versicolor, whereas the other silica sols did not inhibit growth. Pine sapwood and beech wood blocks treated with the cationic sol showed a strong reduction in mass loss compared to the control samples after incubation with C. puteana (pine) and T. versicolor (beech) according to EN 113 and CEN/TS 15083-1; all other silica sols did not inhibit fungal decay. The cationic silica sol reduced blue staining by Aureobasidium pullulans compared to the untreated control but did not fully prevent it; all other silica sols did not inhibit blue staining.

Fire resistance of wood treated with a cationic silica sol

Wood was treated with the cationic silica sol (CSS) Levasil 200S and dried at various temperatures (room temperature, 40, 60, 80 and 103 °C). A water leaching test revealed fixation of the silica in wood even after drying at room temperature. Maximum cross sectional swelling of the specimens decreased from 15.6 % (untreated control) to 13.0 %, when treated wood was dried at 103 °C; cell wall bulking values were also negative (−2.3 %), indicating a thermal degradation of the cell wall polymers catalyzed by the CSS. Penetration of the CSS into the cell wall did not occur. A simple flammability test revealed increased fire resistance of the treated wood. Mass loss and velocity of mass loss as well as burning time were reduced; glowing of the formed charcoal was completely prevented. The effectiveness increased with increasing weight percent gain of the CSS in the wood. Thermo gravimetric analysis under nitrogen atmosphere displayed only minor reduction in the initial temperature of thermal decomposition for wood treated with CSS as compared to the control. In the presence of oxygen the resulting charcoal showed comparable thermal behaviour to the control. The yield of charcoal after pyrolysis was increased to a minor extent (from 19.9 to 23.0 %), indicating that the release of combustible gases was hardly reduced. The mode of action of enhanced fire resistance due to CSS-treatment is discussed.

Construction of Dendritic-Linear Brushes on Silica Nanoparticles by Electrostatic Assembly

Using dendritic bromide poly (benzyl ether), G2-Br, as macroinitiator, dendritic-linear polymer (G2-PS-NHSO3Na) was obtained via atom transfer radical polymerization and nucleophilic substitution of G2-PS-Br. G2-PS-NHSO3Na was constructed on cationic silica by both electrostatic attraction and steric effort coming from dendritic block of G2-PS-NHSO3Na. 1H-NMR and differential scanning calorimetry were used to characterize the structure and thermal behavior of G2-PS-NHSO3Na; thermo-gravimetric analysis and TEM were applied to analysis the assembly amount of G2-PS-NHSO3Na and the dispersibility of silica before and after assembly. The results show that G2-PS-NHSO3Na can be synthesized successfully and has exact structure; it can be constructed on cationic silica with 27% assembly amount; the aggregation of silica can be prevented effectively by the dendritic-linear brushes, but the molecular weight of linear segment and the generation of dendritic block will influence the assembly behavior and the amount of the dendritic-linear brushes.

Use of polyelectrolyte complexes and multilayers from polymers and nanoparticles to create sacrificial bonds between surfaces

In this study, particle polyelectrolyte complexes (PPECs) were formed by mixing cationic polyacrylamide (CPAM) and silica nanoparticles using the jet mixing technique. Within certain limits, the size of the formed PPECs could be controlled. The aim was to prepare PPECs with embedded sacrificial bonds, similar to those found in bones. Examination of PPEC adsorption to silica model surfaces indicated that smaller PPECs adsorbed to a higher level than larger ones, due to the higher diffusion speed of smaller complexes. Adsorption studies of the same components as in the PPECs, but arranged in multilayers, that is, particle polyelectrolyte multilayers (PPEMs), indicated a stable, gradual build-up of material on the surface with smaller nanoparticles, whereas PPEMs comprising elongated nanoparticles appeared to be more loosely adsorbed onto the surface when the nanoparticles were in the outer layer, due to repulsive forces within the adsorbed layer. The AFM colloidal probe technique was used to study the interaction between surfaces treated with PPECs, multilayers, or polyelectrolyte complexes (PECs). The results showed that the expected long-range disentanglement could be achieved with PPECs but that the pull-off forces were generally low. Treatment with PPEMs comprising the same polymer and nanoparticle components produced higher pull-off values, together with disentanglement behaviour, possibly due to better contact between the surfaces. Adhesion experiments with polymer PECs showed significantly higher pull-off values than with the PPECs, probably due to polymer interdiffusion across the surface boundary.

Facile Control of DNA-Templated Inorganic Nanoshell Size

We elaborated a facile method to control the size of CdS nanoshells obtained by DNA assisted "double templating" approach. By changing the concentration of NaCl in solution to vary the extent of DNA electrostatic deposition on cationic silica beads, we succeeded to control the density of DNA adsorbed on the beads, and further the density of CdS material grown on DNA. Further dissolution of the silica core triggers shrinking of CdS shell to a different extent depending on the CdS shell density and results in formation of CdS nanoshells of different sizes from ca. 100 nm to ca. 400 nm. Therefore, the main advantage of the proposed method is that it can be used to synthesize hollow nanoshells of various sizes, from ca. 25% to ca. 75% size of the primary template (silica bead), by using only one single primary template.

Synthesis and characterization of positively charged, alumina‐coated silica/polystyrene hybrid nanoparticles via pickering miniemulsion polymerization

AbstractPositively charged, raspberry‐like hybrid nanoparticles, consisting of a polystyrene core and an alumina‐coated silica shell were successfully prepared in a surfactant free system via the radical copolymerization of styrene (St) and different comonomers (acrylic acid, methacrylic acid, and acrylamide) by using a cationic silica sol as the sole emulsifier in Pickering miniemulsion polymerization. The influence of different parameters like pH of the dispersion, comonomer content, and the amount and size of silica nanoparticles on the colloidal stability of the systems, prepared with different comonomers, was examined. The particles' morphology was observed via high‐resolution scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The removal of free silica particles via centrifugation was proved by TEM and SEM, and the content of free and adsorbed silica was quantified via thermogravimetric analysis (TGA). © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Coating cells with cationic silica–magnetite nanocomposites for rapid purification of integral plasma membrane proteins

This study developed a simple and rapid purification method for plasma membrane with high yields from adherent cells. The plasma membrane (PM) sheets could be absorbed specifically by the cationic silica-magnetite nanocomposites (CSMN) under acidic conditions, and recovered directly in cell-lysis-buffer with no need for precipitation. The binding between CSMN and PM sheets was confirmed by electron microscopy. Western blot analysis demonstrated a >10-fold relative enrichment factor. Up to 422 integral membrane proteins were identified from 10(7) Huh7 cells. Notably, we found 29 Ras family proteins by classification according to their biological functions. The whole enrichment procedure took <30 min. The CSMN-based procedure demonstrates a simple, economical and efficient enrichment of integral PM proteins in proteomic study.

Dip coating of charged colloidal suspensions onto substrates with patterned wettability: Coating regime maps

Aqueous dispersions of silica nanoparticles were dip coated onto Si substrates that contained patterned wettability. The patterns were prepared by photolithography and consisted of groups of hydrophilic lines (5-100μm wide) separated by hydrophobic areas (5-100μm wide). Coating were made from two aqueous silica dispersions: a cationic dispersion in which particles have positive surface charge, and an anionic dispersion in which particles have negative surface charge. Coating morphology, thickness, and pattern quality were characterized. For a pattern containing 25μm wide hydrophilic stripes separated by equally wide hydrophobic spaces, coating regime maps were created to show the effect of process variables on pattern features and morphology. Within the map there is a critical concentration for both dispersions, above which uniform stripes are formed and below which a segregated non-uniform structure results. Coatings prepared at withdrawal rates of 0.1mm/s or lower resulted in a monolayer of coatings in the case of cationic silica and no deposition in the case of anionic silica. A maximum withdrawal rate was also found; above a critical speed, excess liquid is entrained and results in nonuniformity in the bottom of the pattern. The physical origin of the regimes and differences between the two types of particles are discussed.

Involvement of endothelial Man and Gal-binding lectins in sensing the flow in coronary arteries

The coronary endothelial luminal membrane (CELM) glycocalyx has diverse molecules involved in blood flow signal transduction. Evidence suggests that some of these structures may be lectinic. To test this, we synthesized two monosaccharide polymers (Mon-Pols) made of Mannose (Man-Pol) or Galactose (Gal-Pol) covalently coupled to Dextran (70 kDa) and used them as lectin affinity probes. In situ intracoronary infusion of both polymers resulted in CELM-binding but only Man-Pol caused a reduction in flow-induced positive inotropism and dromotropism. To demonstrate that our lectinic probes could bind to CELM lectins, a representative CELM protein fraction was isolated via intracoronary infusion of a cationic silica colloid and either Mannose- or Galactose-binding lectins were purified from the CELM protein fraction using the corresponding Mon-Pol affinity chromatography resin. Resin-bound CELM proteins were eluted with the corresponding monosaccharide. 2D-SDS-PAGE (pH 4-7) revealed 9 Mannose- and approximately 100 Galactose-selective CELM lectins. In summary, the CELM glycocalyx contains Mannose- and Galactose-binding lectins that may be involved in translating coronary flow into a cardiac parenchymal response.

Sodium Polyacrylate Adsorption onto Anionic and Cationic Silica in the Presence of Salts

Sodium polyacrylate is well known for its application as a scale inhibitor in common household products, and the effects of both monovalent and divalent metal cations on its structure have been covered by a range of previous publications. In the present article, we extend this work by using solvent relaxation NMR to look at the adsorption of the polyelectrolyte onto both positively and negatively charged silica and how this is altered by calcium chloride. In the anionic case, we found that polyacrylate adsorption was predictably very weak, and interestingly, perhaps counterintuitively, it was further reduced by calcium ions. This is probably linked to NaPA-Ca2+ binding, which changes the conformation and charge of the polyelectrolyte. In contrast, NaPA adsorbs very strongly on cationic silica, to the point that precipitation often occurs, particularly on addition of salt.

Different glycosidic probes upon binding to coronary endothelial luminal lectins allow the isolation of these proteins

The coronary endothelial luminal membrane (CELM) has structures involved in blood flow transduction-physiological response; these flow-sensitive structures may be lectinic. We isolated the coronary endothelial luminal plasma membrane from various species. Lectinic proteins were identified using monosaccharide polymers (probes) formed either by Mannose, N-acetyl-Glucosamine or Galactose covalently linked to a 70kDa Dextran. We isolated CELM by coating with cationic silica, polymerizing with polyacrylic acid, homogenizing the tissue, and centrifuged in a density gradient. Proteins were solubilized by probe sonication in SDS, analyzed via polyacrylamide gel electrophoresis. Adherence of the silica colloid was assessed via electron microscopy and non-luminal coronary protein contamination during homogenization was discarded. A comparison of protein profiles obtained from guinea pig, rat and porcine hearts. The protein fraction purified in affinity columns made up by one of the probes and retained lectins were eluted with the corresponding free monosaccharide. From the guinea pig luminal coronary membrane protein extract we isolated one lectin using the mannose probe and two lectins using the galactose probe. Together with physiological studies these data suggest that these purified proteins may be involved in blood flow sensing. Funded by CONACyT SEP-42567, CONACyT-SALUD 2004-C01-156

Novel Retention System Based on (2,3-Epoxypropyl)trimethylammonium Chloride Modified Silica Nanoparticles and Anionic Polymer

This work investigated the synthesis, characterization, and evaluation of surface-modified cationic silica nanoparticles as part of retention or flocculation systems. Quaternary amine groups were introduced onto the fumed silica surface using the cationic reagent (2,3-epoxypropyl)trimethylammonium chloride under various reaction conditions. To characterize the surface properties of the modified silica particles, the ζ potential and charge density were determined. Dynamic flocculation experiments showed that, when used alone, the cationic silica nanoparticles contributed little to inducing clay flocculation. However, when the nanoparticles were used in conjunction with an anionic polymer of high Mw and low charge density, significant improvement in the flocculation of fine clay particles was achieved. The interaction between the cationic silica nanoparticles and anionic polymer, as well as the silica adsorption behavior on clay surfaces, was explored. The mechanism of flocculation induced by the dual-compo...

Cationic Silica Nanoparticles as Gene Carriers: Synthesis, Characterization and Transfection Efficiency &lt;I&gt;In vitro&lt;/I&gt; and &lt;I&gt;In vivo&lt;/I&gt;

The potential of cationic SiO2 nanoparticles was investigated for in vivo gene transfer in this study. Cationic SiO2 nanoparticles with surface modification were generated using amino-hexyl-amino-propyltri-methoxysilane (AHAPS). The zeta potential of the nanoparticles at pH = 7.4 varied from -31.4 mV (unmodified particles; 10 nm) to +9.6 mV (modified by AHAPS). Complete immobilization of DNA at the nanoparticle surface was achieved at a particle ratio of 80 (w/w nanoparticle/DNA ratio). The surface modified nanoparticle had a size of 42 nm with a distribution from 10-100 nm. The ability of these particles to transfect pCMVbeta reporter gene was tested in Cos-1 cells, and optimum results were obtained in the presence of FCS and chloroquine at a particle ratio of 80. These nanoparticles were tested for their ability to transfer genes in vivo in the mouse lung, and a two-times increase in the expression levels was found with silica particles in comparison to EGFP alone. Very low or no cell toxicity was observed, suggesting silica nanoparticles as potential alternatives for gene transfection.

Polyoxometalates on Cationic Silica Nanoparticles. Physicochemical Properties of an Electrostatically Bound Multi-Iron Catalyst

Reaction of a solution of the multi-iron polyoxometalate (POM) K9[(FeIII(OH2)2)3(A-α-PW9O34)2] (K91) with a colloidal suspension of cationic silica nanoparticles ((Si/AlO2)Cl) results in the production of a new heterogeneous oxidation catalyst (K81/(Si/AlO2)). Dynamic light scattering data, coupled with elemental analysis and streaming potential measurements suggests that there are 58 molecules of POM electrostatically bound to the surface of each silica particle on average. Transmission electron microscopy confirms the presence of the POM on the surface of the cationic silica and shows the diameter of the (Si/AlO2)Cl and of the K81/(Si/AlO2) nanoparticles to be ∼12 and ∼17 nm, respectively. Significantly, cryo-high-resolution scanning electron microscopy (cryo-HRSEM) shows that the POM retards the natural gelation process that colloidal silica is known to undergo upon aging. EPR and catalytic data collectively suggest that the exchange of the cationic silica for one of the nine K+ cations associated with...

Organic−Inorganic Nanoassembly Based on Complexation of Cationic Silica Nanoparticles and Weak Anionic Polyelectrolytes in Aqueous and Alcohol Media

Complexation of tertiary amine containing silica nanoparticles (diameter ≈ 3.0 nm) and a weak acidic polyelectrolyte, poly(acrylic acid), which has a characteristic pH-responsive property, was investigated under various environments. The salt- and temperature-induced association/transformation/dissociation behavior was studied in aqueous medium by following the turbidity as a function of time. Complex formation was observed in methanol, whereas no complexation was obtained in DMF. The size and density of the aggregate structures formed in methanol could be controlled by the temperature, as confirmed by TEM measurements. Characterization of the isolated complexes was conducted by elemental analysis, 1H NMR, and FT-IR measurements, suggesting that the silica composition in the complex isolated from water is the same as that obtained from methanol. On the contrary, the kind of solvent has a significant influence on the interaction between the components and the resulting aggregated structures. MALDI-TOF MS w...

Comparative proteomics of human endothelial cell caveolae and rafts using two‐dimensional gel electrophoresis and mass spectrometry

The human endothelial cell plasma membrane harbors two subdomains of similar lipid composition, caveolae and rafts, both crucially involved in various essential cellular processes like transcytosis, signal transduction and cholesterol homeostasis. Caveolin-enriched membranes, isolated by either cationic silica or buoyant density methods, were explored by comparing large series of two-dimensional (2-D) maps and subsequent identification of over 100 protein spots by matrix-assisted laser desorption/ionization (MALDI) peptide mass fingerprinting. Improved representation and identification of membrane proteins and valuable information on various post-translational modifications was achieved by the presented optimized procedures for solubilization, destaining and database searching/computing. Whereas the cationic silica purification yielded predominantly known endoplasmic reticulum residents, the cold-detergent method yielded a large number of known caveolae residents, including caveolin-1. Thus, a large part of this subproteome was established, including known (trans-)membrane, signal transduction and glycosyl phosphatidylinositol (GPI)-anchored proteins. Several predicted proteins from the human genome were isolated for the first time from biological samples, including SGRP58, SLP-2, C8ORF2, and XRP-2. These findings and various optimized procedures can serve as a reference to study the differential composition of endothelial cell caveolae and rafts, known to be involved in pathologies like cancer and cardiovascular disease.