Aminosilica

Comparison of electronic absorption spectra of BPR and PR in solution with electronic absolution spectra of BPR and PR on NH -S and en-S surfaces has been made. In contrast to aqueous solutions, where shift of the absolution maximum of dyes is occurred when pH is changed, significant shift of maxima is not observed on aminosilica gels surface during pH changing. Both reagents BPR and PR have an absolution maximum in the field of 17900-18100 cm at different pH values. However use of BPR is more preferable than that of PR as qualitative soi ption of BPR occurs at wider pH range. 

Solution processes of complexes of Mo(VI), W(VI) and V(V) with BPR as well as these complexes in the presence of dodecylpyridiniy chloride from aqueous solutions on aminosilica gels surfaces have been considered. The presence of dodecylpyridiniy chloride increases significantly the sorption degree of metals and broadens pH range of their quantitative extraction. 

Kutsuna, H., Ohtsu, Y., and Yamaguchi, M., Synthesis and characterization of highly stable polymer-coated aminosilica packing material for high-performance liquid chromatography, ]. Chromatogr., 635, 187, 1993. 

Aminosilicas have been widely studied for use in catalysis, either as a base catalyst or as a support for metal complexes (12). For example, amine functionalized silica can be used to catalyze the Knoevenagel condensation, an important C-C bond forming reaction. Also, the amine sites on the silica can be further functionalized to form supported imines, guanidine, and other species... 

When combined with the isolation and reactivity studies of the patterned aminosilica (7), the increased activity of the patterned catalysts provide further evidence that the patterning technique developed allows for the synthesis of aminosilicas which behave like isolated, single-site materials (although a true single site nature has not been proven). As the olefin polymerization catalysts supported by the patterned materials show a marked improvement over those materials supported on traditional aminosilicas, these patterned materials should be able to improve supported small molecular catalysis as well. Future improvements in catalysis with immobilized molecular active sites could be realized if this methodology is adopted to prepare new catalysts with isolated, well-defined, single-site active centers. 

Yu, K., McKittrick, M. W. and Jones, C. W. Role of amine structure and site isolation on the performance of aminosilica-immobilized zirconium CGC-inspired ethylene polymerization catalysts, Organometallics, 2004, 23, 4089 4096. 

This may be explained as follows the SDS interacts with the maximum of partially protonated aminopropyl groups, by electrostatic interactions between dodecylsulfate anion and and sodium cation neutralization. The remaining amino groups are entrapped into the silica network. The amount of P-CD moieties incorporated depend on the initial molar ratio of P-CD APS, and not of the presence or not of SDS. P-CD groups may not interact with SDS. We can say, that for these hybrid materials, the templated mechanism is a S P one (S for anionic surfactant, P for cationic aminosilica species). 

Considerable attention has been given to the LC separation of AEO and APEO. Both reversed-phase and normal-phase LC have been apphed. In reversed-phase LC, the use of methanol as modifier is preferred over the use of acetonitrile. A separation based on different alkyl chains irrespective of the EO-number can be achieved [36]. In normal-phase LC, the EO-number is more important than the alkyl chain length. Aminosilica columns are more successful than bare silica, especially with a acetonitrile-water-dichloromethane mobile phase [36]. 

To test the performance of the trityl-spaced aminosilica, Ti, Zr, and Hf constrained-geometry-inspired catalysts (CGCs) were grafted to the amine sites (Fig. 20.3) [14-18]. 

The synthesis of these materials starts with the reaction of chlorodimethyl-(2,3,4,5-tetramethyl-2,4-cyclopentadien-l-yl)silane (Cp -silane) with the snrface amine groups. It was shown that the percentage of amine sites reactive toward the Cp -silane was significantly better for the trityl-spaced material than traditionally prepared aminosilica (77% reacted amines vs. 29% reacted amines) [19]. Also, once the Cp -silane moiety was reacted with the trityl-spaced amines, the percentage... 

The benzyl-spaced aminosilica was also used as a scaffold on which to anchor CGC-inspired catalysts [19]. As in the trityl-spaced study, the aminosilica was first reacted with Cp -silane. For the benzyl-spaced materials, complete conversion of the amine groups through reaction with the Cp -silane did not occur however, the amine conversion for this material was twice the amine conversion for the traditionally grafted material (63% reacted amines vs. 29% reacted amines) [19]. When the grafted, metallated catalyst was tested for polymerization of ethylene, the benzyl-spaced catalyst again outperformed the traditionally grafted material, although it was somewhat less active than the trityl-spaced immobilized catalyst. 

As previously mentioned, one of the primary motivations for the development of site-isolated aminosilicas is to construct a better molecular-level understanding of immobilized catalysts through the use of a more uniformly reactive surface. Within the area of a-olefin polymerizations, another parameter that negatively affects the ability to study well-defined surfaces is the use of methylaluminoxane (MAO) as a catalyst activator. The exact structure of the MAO species has been postulated to exist in a number of different forms, which makes it difficult to elucidate the exact nature of its interactions with the surface [21]. To address this issue, a well-defined sulfonic acid organic/inorganic hybrid material was developed to serve as both a support and a catalyst activator for homogeneous a-olefin polymerization catalysts [22]. 

The sorption activity of polyaminosiloxane sorbents prepared by Parish and coworkers was demonstrated by the absorption of protons [2]. It was found that the majority (over 90 %) of the amino groups were accessible, provided that the contact with acid was maintained not shorter than 15 h. The content of amino groups ( 3.0 mmol/g) on the surface of such sorbents was 3-5 times as much as that, for example, on aminosilicas prepared according to standard procedures [2,28,29]. Saturation with salts of 3d-metals... 

Fullerene Ceo and aminosilica react in toluene or p-xylene solutions at heating with formation of brown adsorbent. Specific surface area of silica gel and Silasorb Amin containing fullerene Ceo after reaction of modification is increased a little in compared with the specific surface area of initial adsorbents. The values of C constant of BET equation for both adsorbents are practically the same. So the adsorption properties of these modified adsorbents are similar as well as the degree of modification by fullerene molecules. 

Figure 4. Arrangement of bonded Ceo fullerene molecules on the surface of aminosilica.

Figure 5. The isotherms of nitrogen adsorption at 77 K on aminosilica gel (filled dots) and on Silasorb Amin (open dots) with bonded fullerene Ceo-...

Stationary phases" for affinity chromatography can be prepared by the user, often starting from diol- or aminosilica. However, it is much simpler to buy an activated gel which allows the desired ligand to be bound according to well known methods. A possible example for activation and binding is shown in Figure 16.3. For separation problems that require common ligands, ready-to-use stationary phases... 

The complexity of the sample dictates the number of isolation steps necessary before the final analysis. For instance, ambient air particulate extracts usually contain predominantly neutral organic compounds that greatly simplify the sample cleanup. In more complex samples, e.g., crude oil, the procedure involves removal of waxes, separation on a silica column, normal-phase preparative LC on an aminosilica column, and elution through a Sephadex LH-20 column. 

Besides silica, other direct phase supports such as alumina, diatomaceous earth, cellulose, MgO-diatomaceous earth, and sucrose layers were employed for the separation of various pigment mixtures. Mixed-mode supports (cyano, diol, and aminosilica layers) were also employed in both the direct and reversed-phase elution modes for the separation of natural pigments, but their performance was markedly lower that those of traditional silica layers. Reversed-phase supports (polyamide, octadecylsilica, alumina, sihca, and diatomaceous earth impregnated with paraffin oil) were also applied for the separation of color pigments (carotenoids from Capsicum annuum, anthocyanins from red wines) and it was found that their separation... 

A similar analysis where both alkyl chain and ethoxamer separations are demonstrated, but without derivatisation, is described in [19]. The columns used were LiChrosorb RP8 for alkyl chain length and Hypersil aminosilica for ethoxamer distribution. Detection used absorption or indirect fluorescence. 

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