Chiral imprinting

There exists the possibility that one can imprint a chiral arrangement on a catalytic surface. Although chiral imprinting is now occurring on silica surfaces14 and in polymers,15 it has not been used to induce chirality in metal surfaces. This is difficult to explore. 

Figure 1.21 Schematic representation of the strategy of molecular chiral imprinting of a sol-gel matrix using a chiral template and suitable achiral silanes. (Reproduced from ref. 48, with permission.)...

ORMOSIL are chemical sponges they adsorb and concentrate reactants at their surface, thereby enhancing reaction rates and sensitivity (in sensing applications). ORMOSIL-imprinted materials with a suitable chiral template such as a surfactant or a protein selectively adsorb (and detect) external reactants. A remarkable example is provided by thin materials that are generally enantioselective, namely where the chirally imprinted cavities can discriminate between enantiomers of molecules not used in the imprinting process, and completely different from the imprinting ones. 

Memory of chirality is demonstrated by a simple experiment addition of an excess of A-[Ru(phen)3]2+ (15 pM) to J aggregates preformed in the presence of A-[Ru(phen)3]2+ (10 pM) does not cause inversion of the CD bands in the visible region (where the absorption features of porphyrins dominate) but only in the UV region (the spectroscopic region where absorption of the inorganic complex occurs). This straightforward experiment (Fig. 26) shows that this type of J aggregates remembers the chirality imprinted at the very onset of their formation [51]. 

The imprinting of polymer supports is an exciting development in the immobilization of transition metal complexes. The process involves the copolymerization of an inorganic or an organic template into a crosslinked polymer network. In a subsequent step, the template is chemically removed leaving an imprint of molecular dimensions in the resin. Ideally, the imprint retains chemical information related to the size and shape of the template. This approach has been used to prepare chiral imprints in otherwise achiral polymer networks. The method is outlined in Scheme... 

Keywords. 3-Functionalized ketones, a-Keto acid derivatives. Cinchona modified Pt catalysts. Chiral imprints. Chiral metal surfaces. Chiral polymers. Cyanohydrin formation. Cyclic Dipeptides, Epoxidation catalysts. Heterogeneous catalysts. Hydrogenation catalysts. Modified metal oxides. Polypeptides, Tartrate-modified Nickel catalysts... 

Chiral imprints. The imprinting of organic [50] and inorganic materials [51] with transition state analog templates should, at least in principle, lead to what could be called artificial catalytic antibodies. Up to now, either the chiral recognition and/or the catalytic properties of such materials are still very poor. Some examples are a zeolite p, partially enriched in polymorph A [51], chiral footprints on silica surfaces [52], or several imprinted polymers [50]. 

Fireman-Shoresh S, Avnir D, Marx S (2003) General method for chiral imprinting of sol-gel thin films exhibiting enantioselectivity. Chem Mater 15( 19) 3607—3613... 

Matsuishi T., Shimada T. and Morihara K. (1992) Definite evidence for enantioselective catalysis over "Molecular Footprint" catalytic cavities chirally imprinted on a Sibca (alumina), Chem. Lett., 1921-1924. 

Gomez-caballero, A., Guerreiro, A., Karim, K., Piletsky, S., Goicolea, M. A., Barrio, R. J. (2011). Chiral imprinted polymers as enantiospecific coatings of stir bar sorptive extraction devices,... 

Chiral stationary phases that are currently available can be classified into those containing cavities (cellulose derivatives, cyclodextrins, synthetic polymers, crown ethers, and chiral imprinted gels), affinity phases (bovine serum albumin, human serum albumin, a-glycoprotein, enzymes), multiple hydrogen-bond phases, Ti-donor and Ti-acceptor phases, and chiral ligand exchange phases. This classification scheme was used in a review that gave numerous pharmaceutical examples of separation by... 

This technique is based on the preparation of synthetic polymers with specific selectivity by using chiral imprinting molecules mixed with functional and cross-linking monomers (usually methacrylic acid and ethylene glycol dimethacrylate, respectively), capable of interacting with such molecules. 

Similar impressive results for the imprinting of 1 and d-dopa (3,4-dihydroxy-l,d-phenylalanine) in 5 1 TMOS-PTMOS (dissolved in ethoxyethanol) derived silicate have been reported [313]. They showed over 20 times preferred uptake of the imprinted dopant. TMOS-PTMOS mixture also gave successful chiral imprinting of A,A -dimethylferrocenyl ethylamine (Figure 4.17). 

Matsuishi T, Shimada T, Morihara K. Definitive evidence for enantioselective catalysis over molecular footprint catalytic cavities chirally imprinted on a silicat(alumina) gel surface. Chem Lett 1992 1921-1924. 

Qiu, H., Inoue, Y., and Che, S. (2009) Supramolecular chiral transcription and recognition by mesoporous silica prepared by chiral imprinting of a helical micelle. Angew. Chem., Int Ed., 48, 3069-3072. 

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