Silica naked

In the preparation of 15 nm core-shell fluorescent silica particles, Ow et al. (2004) reported that the naked core (2.2 nm) alone produced a fluorescence intensity of less than the free dye in solution, presumably due to dye quenching. However, upon addition of the outer silica shell around the core, the brightness of the particles increased to 30 times that of the free dye (using tetramethylrhodamine-5-(and 6)-isothiocyanate (TRITC)). They speculate that shell may protect the core from solvent effects, as evidenced by a lack of spectral shift upon changing the solvent in which the particles are suspended. 

PEBBLEs are water-soluble nanoparticles based on biologically inert matrices of cross-linked polymers, typically poly(acrylamide), poly(decylmethacrylate), silica, or organically modified silicates (ORMOSILs), which encapsulate a fluorescent chemo-sensor and, often, a reference dye. These matrices have been used to make sensors for pH, metal ions, as well as for some nonionic species. The small size of the PEBBLE sensors (from 20 to 600 nm) enables their noninvasive insertion into a living cell, minimizing physical interference. The semipermeable and transparent nature of the matrix allows the analyte to interact with the indicator dye that reports the interaction via a change in the emitted fluorescence. Moreover, when compared to naked chemosensors, nanoparticles can protect the indicator from chemical interferences and minimize its toxicity. Another important feature of PEBBLEs, particularly valuable in intracellular sensing applications, is that the polymer matrix creates a separate... 

Stationary phases. Five stationary phases from Shandon (Runcorn, Cheslvie, GB) were used they were spherical microparticules of 5 pm mean diameter. The four bonded silicas were manufactured from the same parent silica (Hypersil) and possess a monolayer coverage of trimethylsilyl (SAS Hypersil), dimethyloctylsilyl (MOS Hypersil), octadecylsilyl (ODS Hypersil) and cyanopropylsllyl (CPS Hypersil) groups. Their physicochemical properties are listed in Table II. The elemental analysis of carbon (SIC), corrected for the SIC value of naked silica, enables to estimate the surface concentration of the substituent (r ) with ... 

With the exception of SDS on naked silica, all the curves are of the H type (6J i.e. the amount of adsorbed surfactant increases rapidly and reaches a plateau for surfactant concentrations higher than the CMC. Two remarks should be made here the first one is that the adsorption plateaus are, unexpectedly, very close to each other for Cl, C8 and C18 bonded phases. The second remark is that the maximum adsorption is obtained on SAS (Cl) Hypersil but not on the more hydrophobic ODS (C18) phase (Table III). 

The utility of silica supported guanidinium salts was also well established in reactions sensitive to reversal while heating. Thus, we discovered that treatment of aldehydes with oxalyl chloride in the presence of a naked catalyst [e.g., HBGCI) produces 1-chloroalkyl oxalyl chlorides in 60-97% yields (Ref. 12) [Scheme 14] ... 

The molecular cluster [Ph4P]2[Ru5PtC(CO)i5] was used as a precursor for nanoparticle catalysts [14], The substrates with the layer of mesoporous silica were dried at 200°C in vacuum. The deposition of bimetallic clusters was achieved by immersing the substrates in ether-dichloromethane or ether-THF suspension (3 ml) containing 5 mg (2.8 pmol) of the precursor. This process was carried out for two days after which the plates were washed with diethylether and dried in vacuum. The impregnated plates were subsequently heated (either in vacuo or in air) at 200°C to decarbonylate the molecular cluster leading to the formation of anchored naked metallic nanoparticles. 

The surface of porous silica is covered by hydroxyl groups called surface silanols (Si-OH) [1,4]. Silanol groups are responsible for the polarity of the silica surface. They can ionize, the silanol pKa being 9.8. They are responsible for the silica dissolution in basic (pH>8) solutions. Naked silica packings are too polar to be used in RPLC. They are used in normal phase LC with apolar mobile phases. To obtain less polar packings for RPLC, it is necessary to derivatize the polar silanol groups. 

In cases where these assumptions are not valid, deviations from the expected behavior can be found. In fact, the three latter assumptions are only reasonable at a limited range of low surfactant concentration. For instance, adsorption of SDS does not occur on naked silica until 0.1 M concentration is reached. Therefore, the model should fail with silica as the stationary phase. In fact, it was observed that the change on the silica surface due to SDS adsorption caused a variation in the K s values of several nonionic and ionic solutes, so that the plots of 1/k vs. SDS micellar concentration were no longer linear [10]. 

Microcrystalline silica is similar to crystalline, except that the fine particles are from 1 (xm to as large as 74 p.m (200 mesh). Much microcrystaUine silica is difficult to detect with the naked eye. Pulverized and air-classified microcrystalfine silica is available as quartzite sand, sandstone, tripoli, and microcrystaUine novacuUte. Depending on the degree of fineness, reinforcing is possible. However, microcrystalline silica is usually used for rheological adjustments of resins from low viscosity to thixotropic. These fillers are compatible with thermosets and thermoplastics. They are also used with silicone rubbers. 

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