Alumina multiple bonds

Various types of surface-anchor interactions are responsible for the adsorption of a dispersant to the particle surface. These include ionic or acid/base interactions sulphonic acid, carboxylic acid or phosphate with a basic surface (e.g., alumina) amine or quaternary with an acidic surface (e.g., silica) H-bonding surface esters, ketones, ethers, hydroxyls multiple anchors-polyamines and polyols (H-bond donor or acceptor) or polyethers (H-bond acceptor). Polarizing groups (e.g., polyurethanes) can also provide sufficient adsorption energies and, in nonspecific cases, lyophobic bonding (via van der Waals attractions) driven by insolubility (e.g., PMMA). It is also possible to use chemical bonding, for example by reactive silanes. 

Another approach in taxoid preparative separation included solid-phase extraction (alumina, silica, or RP-8 cartridges) followed by preparative TLC on silica gel plates with quaternary mobile phase consisting of dichloromethane-dioxane-acetone-methanol (83 5 10 2, v/v). In this way, 10-DAB III, paclitaxel, and cephalomannine as well as two further taxoids could be easily isolated with relatively high efficiencies from yew materials (Fig. 2). Multiple development technique or fiuther separation of the isolated taxoid fractions (especially less polar ones) on RP-2 silica bond stationary phase with methanol-water mixtures as mobile phases was applied for purification of the compounds isolated. 10-DAB III isolated in this way was relatively pure, as was shown in reversed-phase (RP)-HPLC analysis (Fig. 3). 

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