Covalent coatings

An approach related to the covalent coating of porous silica by polymeric derivatives of vinylsilane has been recently taken by Kurganov et al. [43], A copolymer of the formula... 

Figure 13.3 The deposition of APTS on inorganic substrates results in the formation of a covalent coating containing primary amine groups.

Dissolve SPDP in dimethylformamide (DMF) at a concentration of 6.2 mg/ml (makes a 20 mM stock solution). Add 50 pi of the SPDP solution to the 1 ml particle suspension and mix to dissolve. Note The small quantity of DMF in a polymeric particle suspension should not affect particle stability, even if the polymer type is susceptible to swelling in pure DMF. Other particle types, such as metallic or silica based, usually are not affected by organic solvent addition, unless their surfaces are non-covalently coated with a dissolvable polymer. 

Qin, W., and Li, S.F.Y., Determination of ammonium and metal ions by capillary electrophoresis-potential gradient detection using ionic liquid as background electrolyte and covalent coating agent, ]. Chromatogr. A., 1048, 253-256,2004. 

Example of covalent coating that helps prevent protein from sticking to the capillary and provides reproducible migration times ... 

Figure 11.9 Schematic representation of the SiC>2 nanoparticles prepared by Greenway and coworkers64 for the detection of lipid peroxidation 15 nm Si02 nanoparticles covalently coated with the coumarin dye are embedded in a 100 nm silica protecting shell.

Due to the extra work involved in producing covalently coated capillary columns, various kinds of noncovalent coatings have been reported, such as anionic, polymeric, and nonionic/zwitterionic (Figure 2) [17]. During the dynamic... 

Quantitation of silica sol sizes is accomplished by means of a calibration plot. Theory predicts and experiments confirm a linear plot of the log of the particle diameter versus the retention (or elution) time of the colloid. This straight-line relationship is seen in the data in Figure 9 for a series of silica sols in the 8-25-nm range. Silica sols characterized by SdFFF were used as standards for this calibration plot. The column used for these separations contained porous spherical silica particles that had surfaces covalently coated with diol silane groups. 

Figure 3.2.6). Narrowly dispersed polystyrene (synthesized by atom transfer radical polymerization [polydispersity < 1.1]) was end fnnctionized with a phosphonate moiety that binds strongly to titanium oxide. The combination of narrowly dispersed titanium oxide and narrowly dispersed phosponate-terminated polystyrene generates a narrowly dispersed core-shell architecture as measured by dynamic light scattering, which can be spun into dielectric films. The covalent coating of polystyrene around titanium oxide is helpful at preventing aggregation of the nanoparticles in organic dispersion and in thin films.

EOF is eliminated in CIEF by covalent coating of the capillary wall, otherwise ampholytes and analytes would be wasted from the column before a pH gradient and analyte focusing was established. The technique has proved particularly successful for the separation of immunoglobulins and haemoglobulins. 

Non-covalent coating of cahx[4]arene-based glycocluster amphiphiles was used to bio functionalize CdSe QDs capped by TOPO. The alkyl chains of the glycocluster amphiphiles were inserted into the TOPO-coated QDs, and the terminal saccharide moieties (a- and P-glucoside, P-galactoside, and a-maltohexaoside) were exposed to bulk water to ensure solubility in aqueous buffers. Subsequently, gum arable and TOPO-QDs (CdSe/CdS) were used to produce non-toxic and biocompatible QD nanocolloids by non specific physical interactions. These glyco-QDs showed good photochemical stabilities and quantum yields. 

In the second group of CZE separations, many different approaches have been published. The main goal has been to avoid Tf adsorption to the capillary walls. This problem has been overcome by working with covalently coated capillaries, in some cases with hydroxyethylcellulose in the running buffer [79,89,191,202], or silica capillaries dynamically coated with DAB [185,196,200,202], spermine [185], DcBr [55], or diethylentriamine (DETA) [201], In general, the methods performed in uncoated capillaries with dynamic coatings are slower than the ones performed with the commercial buffers. On the other hand, the methods using covalently coated capillaries are as fast (usually in less than 10 min of analysis time) as the methods developed with the commercial buffers. 

On the basis of their differences in isoelectric point (pi), phosphorylated proteins can be separated in capillary isoelectric focusing (CIEF). Wei et al. employed a CIEF method using a capillary covalently coated with linear polyacrylamide and a pH gradient from 4 to 6.5 for the resolution of mono- and diphosphorylated ovalbumins. Proteins were detected by their UV absorbance at 280 nm. Additional ovalbumin variants within each of the mono- and diphosphoovalbumins, differing in their amount of glycosylation, were further analyzed by online CIEF-electrospray ionization (ESI)-MS. 

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