Bonded Phases - Synthesis of Bonded Phases by Surface Cross-Linking
The experimental procedure that was used is as follows.
The silica is first dried at 250oC to remove the majority of the strongly bound water from the surface (i.e. both physically and chemically adsorbed water). The silica is suspended in toluene that is contained in a flask fitted with a reflux condenser and then treated with an excess of dimethylchlorsilane (all the adsorbed water on the silica gel surface my not have been completely removed and the excess reagent will scavenge any residual water). The mixture is refluxed for about three hours and finally any remaining reagent or hydrochloric acid is removed by passing a stream of dry nitrogen through the hot reaction mixture. The surface is now covered with a layer of dimethylsilane groups. Squalene is then added to the suspension, accompanied by the catalyst chlorplatinic acid, and the mixture is next refluxed for a further 6 hours. Squalene contains six double bonds along its chain, each double bond being separated by two methylene groups and thus, in the presence of the catalyst, any double bond coming in contact with the silane hydrogen on the silica surface will open and attach the squalene chain to that silyl group. As a result, a single squalene chain will be attached to the silica at several points on the silica gel surface but at the same time the surface remains comparatively flat with no "brush-type" character. When the reaction is complete, the bonded phase is removed by filtration on a sintered glass filter, washed with toluene and then dried. The material may then be end capped if so desired.
So far it has been found that, from a chromatographic point of view, symmetrical peaks with good efficiencies have been obtained when eluting a-chymotrypsinogen and myoglobin from a column packed with such material. Further work by Fung (23) demonstrated that the bonded phase is also very useful for the separation of samples containing trypsin inhibitor, cyclosporin and human growth hormone (HGH).
Irrespective of the merit of the material for any particular biochemical application, the synthesis is a good example of another interesting approach to bonded phase synthesis.