Amide-bonded silica

Yoshida [37] has examined amide-bonded silica for peptide separations in HILIC mode. Amide-bonded silica phases such as the TSKgel Amide-80 (Tosoh Bioscience, Tokyo, Japan) are hydrophilic phases containing a carbamoyl group on a short aliphatic spacer. 

LC-DAD, amide-bonded silica column at 25°C and gradient MeCN 25 mM phosphate buffer containing 0.1% sodium heptanesulphonate... 

Carboxylic acid-terminated organosilanes were used in the early studies on chemically bonded glycopeptides to immobilize vancomycin and thiostrepton via then-amino groups, leading to the formation of stable amide bonds between antibiotics and modified silica [7]. In a typical reaction, 4 g of dry silica gel is slurried on 50 mL of dry toluene. Two grams of [l-(carbomethoxy)ethyl]methyldichlorosilane or [2-(carbomethoxy)ethyl]trichlorosilane is dissolved in 15 mL of dry toluene contained in a dropping flask. The organosilane solution is added dropwise over 30 min... 

Figure 6. Formation of a single or double amide bond by reaction of site-isolated or otherwise aminopropyl functionalized mesoporous silica with isopthaloyl chloride [20].

In situ amine-impregnated silica gel Amine- or amide-bonded phases Diol- and polyol-bonded silica gel Anion exchangers Cation exchangers... 

Several new phases applied to maltosaccharide analysis that seem to be promising have been described in the literature, for instance, a silica-phase covered with polymeric polyamine resin, and an entirely polymeric resin containing an amide function (35). In any case, partition chromatography is restricted mainly to the utilization of polar-bonded phases, as already described. Nevertheless, there have been a certain number of applications of reversed-phase chromatography that permit relatively simple separations to be achieved. Octadecyl-bonded silica phases are the most widely used, although few applications involve carbohydrate analysis. Their interest lies rather in the analysis of derivated sugars, where the selectivity increases (36). 

A general lack of effectiveness has been noted for several MCAs in the suppression of GI-uptake of cadmium in mice. In this study the MCAs, the metal-binding capacity was 2-6.8 mM g 1, ranged from DTPA immobilized via amide bond formation to finely divided aminopropyl-silica, xanthates of polyvinylalcohol and various polysaccharides, and a dextran bearing ethylthiol moieties produced by action of ethylenesulphide on dextran209. ... 

Fig. 34 Example of mechanized mesoporous silica nanoparticles (MSNPs). SEM (a) and TEM (b) images show the structure and morphology of the MSNP platform [238]. (c) Structural formula of the a-cyclodextrin-based snap-top rotaxane that blocks the pores of an enzyme-cleavable mechanized MSNP. The stopper is connected to the stalk (dumbbell) by an ester or an amide bond [254]. (d) Release profile of rhodamine B from the snap-top MSNP. The addition of an esterase enzyme cleaves the ester bond, releasing the stopper, a-cyclodextrin, and cargo from the nanoparticles, which is monitored by the fluorescence intensity of rhodamine B. Controls employing an amide bond snap-top or deactivated enzyme do not release significant amounts of cargo...

This type of bonding between the chiral moiety and the silica is obviously far more stable although it has been reported that the amide bond is vulnerable to extremes of pH and high salt concentrations. 

Figure 12 Imprinting of a theophylline derivative immobilized on silica. The template (a carboxypropyl-derivative of theophylline) was immobilized on porous and spherical amino-functionalized silica gel via formation of an amide bond. This construct is then imprinted with traditional imprinting monomers (TFMAA and DVB). Following polymerization, the composite material is treated with HF to dissolve and remove the silica gel, leaving spherical porous MIP particles which mirror the original silica in size, shape, and porosity.

Efficiency of amide -bonded SEC columns as a function of flow rate. Column, amide-bonded Grace 250 A silica, 10 um, 25 cm x 4.1 mm mobile phase, 0.1 M Iris, pH 7, -I- 0.4 M sodium chloride detection, 280 nm, UV elution order, thyroglobulin, alcohol dehydrogenase, conalbumin, myoglobin, cytochrome c, and dinitrophenylglutamic acid. 

The starting material is a compound that contains a deoxynucleoside covalently joined to silica gel (g) through an amide bond ... 

Silica surface was treated with APS and modified with poly(acrylic acid), using the reaction illustrated in Scheme 1. The carboxyl groups on poly(acrylic acid) reacted with the APS amine functional groups to form salt bonds on the surface of silica. The salt-modified beads were heated in DMF at 140°C to form amide bonds. The FTIR spectrum of the APS-modified silica exhibited a peak at about 1600 cm due to the amino group in addition to the original silica peak. Treatment with poly(acrylic acid) produced new peaks at 1710 cm" and 1660 cm", indicating the carboxyl groups of poly(acrylic acid) and the amide bond formation between the poly(acrylic acid) and the bound APS, respectively. ... 

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