Silica imprinting

In Pyun and Rhee s work,54 it should be emphasized that the pore diameter calculated from Ab is similar to the transition pore diameters between two groups of the carbonization-induced pores and the silica-imprinted pores in PSD. It is thus indicated that the... 

Waksmundzki et al. extensively examined the surface areas and microporosities of imprinted silica surfaces [44]. It was found that although the template itself had little effect on the total surface area, the sizes of the micropores were positively correlated to the size of the template. Subsequent studies on the sorption of template to silicas imprinted with pyridine [45-50], quinoline and acridine [45-47], and 2-picoline, 2,4-lutidine and 2,4,6-collidine [50], combined with thermodynamic studies on the heat of wetting of template or methanol/water sorption [47,51-53], led to the conclusion that these templates were adsorbed as multilayers to the silica. This observation supported the association mechanism hypothesis. The possibility of a footprint mechanism and an association mechanism coexisting in a concentration dependent fashion does not appear to have been considered. 

The group of Patrikeev prepared silicas imprinted against harmine and a derivative, and employed these materials as stationary phases for zonal liquid... 

In Dickey s 1949 paper [24], he presented the idea that specific catalysis, analogous to that of enzymes, was a possible application for silicas imprinted against selected reactants or products. This idea does not appear to have been realised until 1962, when the group of Patrikeev demonstrated what could be regarded as an early synthetic enzyme [27]. The reaction studied was the polycondensation of amino acid esters, a reaction known to yield both linear polypeptides (4%) and cyclic peptides (diketopiperazine, 96%) (Fig. 1.7). 

For imprinted mesoporous carbons, the overall fractal dimension, determined from gas adsorption data, indicate that these materials are composed of two groups of pores. The surface fractal dimension of the carbonization-induced pores surface and that of the silica-imprinted pores surface has been obtained from TEM image analysis [38]. 

The high specificity obtained for optical resolution shows that it was in fact possible to copy the shape of the template and the arrangement of the functional groups into the polymer by this imprinting method. It should be noted that this method of resolution of racemates is a novel one. In this case no interactionsof the racemate with molecular parts carrying asymmetric carbon centers take place, but the enantiomers are bound within a chiral environment. The stability of these inclusion complexes is apparently different for the two enantiomers. This type of optical resolution is somewhat analogous to urea inclusion compounds ( ) or to silica imprinted by chiral compounds (27-29). Certain aspects of our method have been reviewed by our group (30-34) and by others (35-39). 

Figure 8. (a) Schematic picture of a polymer coated silica imprinted by 1. 

Direct Imprinting in Silica. As already pointed out at the beginning Dickey (2A) used the imprinting procedure to produce selectively adsorbing silicas. Other research groups applied this technique to various substrates (106, 107). and it was also possible to prepare silicas imprinted by optically active substances and achieve some enantiomeric resolution (27-29 108). 

Molecular imprinting of microporous silica is an interesting idea, which could have new applications, particularly for bioseparation. The ease of polymerization of organosilanes (see Reactions 6.4 and 6.5) makes imprinting of nticroporous, amorphous silica possible. By this route, bulk silicas imprinted with desired... 

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