Cationic silica

In the original James and Healy model, the magnitude of the adjustable chemical term usually swamped the other two terms. By using a much smaller value of the solvation energy as suggested by Levine [27], it was found that the adjustable chemical term could be eliminated in the simulation of a number of metal cation/silica systems [26],... 

Reaction of the sandwich-type POM [(Fc(0H2)2)j(A-a-PW9034)2 9 with a colloidal suspension of silica/alumina nanopartides ((Si/A102)Cl) resulted in the production of a novel supported POM catalyst [146-148]. In this case, about 58 POM molecules per cationic silica/alumina nanoparticle were electrostatically stabilized on the surface. The aerobic oxidation of 2-chloroethyl ethyl sulfide (mustard simulant) to the corresponding harmless sulfoxide proceeded efficiently in the presence of the heterogeneous catalyst and the catalytic activity of the heterogeneous catalyst was much higher than that of the parent POM. In addition, this catalytic activity was much enhanced when binary cupric triflate and nitrate [Cu(OTf)2/Cu(N03)2 = 1.5] were also present [148],... 

The direct interaction between surfactants and inorganic precursors was later found to be not the only pathway for the formation of mesophases. A major discovery following Mobil s work is the synthesis of mesophases through the assembly of cationic inorganic species with cationic surfactants in acidic solutions. Here, the interaction between cationic silica species and cationic surfactant headgroups is suggested to be mediated by halide anions. 

This mediated (S+X I+)-synthesis model is supported by the following evidence (i) the cationic silica species which are present at pH < 2 (ii) the near 1 1 surfactant-to-chlorine ratio in the hexagonal and lamellar products (iii) the easy removal of the surfactant with ethanol (iv) the observation that TEOS and SiC L hydrolyse and form mesophase products, while Cab-O-Sil, which does not readily hydrolyse in acidic conditions, forms no mesophase products and (v) the anion dependence of the synthesis, e.g., the different products obtained with Cl, Br, and oxyanions. 

Jang, H. M., and Fuerstenau, D. W., The nature of simple monovalent cation-silica interaction as reflected in the spin-lattice relaxation time of Na, Langmuir, 5, 1114 (1987). 

Ravi Kumar M N V, Samedt M, Mohapatra S S, et al. (2004). Cationic silica nanoparticles as gene carriers synthesis, characterization and transfection efficiency in vitro and in vivo. J. Nanosci. Nanotechnol. 4 876-881. 

Silica particles used in emulsion polymerization are of different origin and, consequently, their sizes and surface properties significantly vary. Although the large majority of works involve the use of anionic silica sols, cationic silica has also been used on some occasions. Silica particles are most often amorphous colloidal silicas of commercial origin with diameters in the range of 10-80 nm. Silica particles of larger diameters are prepared by controlled hydrolysis and precipitation... 

Baumann (154) collected data from other sources for comparison with the data of Alexander plotted in Figure 1.6 these data seem to confirm that the solubility reaches a minimum at pH 7-8, but the reason for the slightly higher solubility at lower pH is not known. However, Cherkinskii and Knyaz kova (160) verified the data (see Figure 1.6) and proposed that silica is amphoteric and is cationic below pH 7. They give equations assuming that all the soluble silica is actually polymeric and cationic at low pH. There is no experimental basis for such a tljeory all of the soluble silica has been shown to be monomeric, and there is no evidence for cationic silica above the isoelectric point of pH 2. 

The most commonly used method to exploit silica for gene delivery is by functionalizing the surface of the NPs with aminosi-lanes (either N-(2-aminoethyl)-3-aminopropyltrimethoxysilane or N-(6-aminohexyl)- 3-aminopropyltrimethoxysilane). The group of Lehr showed that commercially available silica NPs functionalized with N-(6-aminohexyl)- 3-aminopropyltrimethoxysilane were able to transfect efficiently Cos-1 cells with very low toxicity. Other cationic silica nanoparticles with surfaces modified by amino-hexyl-aminopropyltri- methoxysilane (AHAPS) were also reported recently to be successful transfection reagents. He et al used a similar approach but they directly synthesised positively charged amino-modified silica NPs. They showed that these NPs were able to protect pDNA from DNasel degradation in vitro in Cos-7 cells, thus evidencing a simple and efficient protection method. Zhu et also showed the successful delivery of antisense ODN with poly(L-lysine) functionalized silica nanoparticles in HNEI and HeLa cells. 

Fig. 51. Effects of R cation/silica pigment on the penetration of corrosion beneath an alkyd paint on mild steel (after Goldie and McCarroll 1983).

Bakerbond ABx Mixed mode Weak anion/cation Silica 10 X 7.75 J.T.Baker... 

Cocoamidopropyldimethy-lamine oxide and hexade-cyldimethylamine oxide detection in the presence of cationics Silica Gel 60 or aminopropyl-modified silica 70 20 10 2-BUOH/H2O/ HOAc (for silica) or 70 20 10 -PrOH/2-butanone/25% NHj (for aminopropyl-modified silica) Primulin fluorescence at 365 nm 19... 

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