Molecular footprint

In 1990, Choudary [139] reported that titanium-pillared montmorillonites modified with tartrates are very selective solid catalysts for the Sharpless epoxidation, as well as for the oxidation of aromatic sulfides [140], Unfortunately, this research has not been reproduced by other authors. Therefore, a more classical strategy to modify different metal oxides with histidine was used by Moriguchi et al. [141], The catalyst showed a modest e.s. for the solvolysis of activated amino acid esters. Starting from these discoveries, Morihara et al. [142] created in 1993 the so-called molecular footprints on the surface of an Al-doped silica gel using an amino acid derivative as chiral template molecule. After removal of the template, the catalyst showed low but significant e.s. for the hydrolysis of a structurally related anhydride. On the same fines, Cativiela and coworkers [143] treated silica or alumina with diethylaluminum chloride and menthol. The resulting modified material catalyzed Diels-Alder reaction between cyclopentadiene and methacrolein with modest e.s. (30% e.e.). As mentioned in the Introduction, all these catalysts are not yet practically important but rather they demonstrate that amorphous metal oxides can be modified successfully. 

More studies on Dickey s system — molecular footprints ... 

Morihara K, Kurosawa M, Kamata Y, Shimada T (1992) Enzyme-like enantioselective catalysis over chiral molecular footprint cavities on a silica (alumina) gel surface. J Chem Soc Chem Commun 4 358... 

Morihara K, Takiguchi M, Shimada V (1994) Footprint catalysis 11. Molecular footprint cavities imprinted with chiralamines and their chiral molecular recognition. Bull Chem Soc Jpn 67 1078... 

Such investigations have been extended to the field of catalysis by Patrikeev et al. 294). Silica gel precipitated in a solution of dimcthyl-diketopiperazine and then carefully washed, catalyzes more condensation of the alanine esters into a cjmlic dimer than silica gel which was similarly formed in a solution of alanylglycylglycine and which catalyzes the condensation chiefly into a linear trimer. Evidently, this happens because of the formation of molecular footprints. 

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. 

Morihara K., Kurokawa M., Kamata Y. and Shimada T. (1992) Enzymelike enantioselective catalysis over chiral Molecular Footprint cavities on a silica (alumina) gel surface, J. Chem. Soc., Chem. Comm., 358-360. Davis M E., Katz A. and Ahmad W.R. (1996) Rational catalysts design via imprinted nanostructured materials, Chem. Mater., 8,1820-1839. 

The only nonlinear saturated fatty acid to receive any attention has been isostearic acid. Some patent literature describes the use of such adds, espedaUy for treating aluminum hydroxide [14], The molecular footprint area for isostearic add has been determined to be about 0.45 nm, considerably higher than for stearic add. This is because of its branched nature. 

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. 

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