Catalysis footprint

Of special interest is the eventuality of stabilizing transition states by imprinting their features into cavities or adsorption sites using stable transition state analogs as templates. Studies towards such TSA footprint catalysis have been performed by generating TSA complementary sites as marks on the surface [7.73a] or as cavities in the bulk [7.73b] of silica gel. These imprinted catalytic sites showed pronounced substrate specificity [7.74a,b] (namely in the case of cavities [7.73 b]) and chiral selectivity [7.74c,d]. 

Morihara K, Kurihara S, Suzuki J (1988) Footprint catalysis LA new method for designing tailor-made catalysts with substrate-specificity-silica (alumina) catalysts for butanolysis of benzoic anhydride. Bull Chem Soc Jpn 61 3991... 

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... 

Morihara s research group worked very intensively on preparing catalysts on the surface of silica gel (see, e.g., [113, 148]). In a process described as footprint catalysis , commercial silica gel is treated with Al ions and imprinted with a transition-state analogue. Similar accelerations to those of the foregoing examples were obtained. 

Morihara K., Nishihata E., Kojima M. and Miyake S. (1988) Footprint Catalysis. 11., Molecular recognition of footprint catalytic sites. Bull. Chem. Soc. Jpn. 61, 3999-4003. 

Most studies reported so far on footprint catalysis have come from Morihara and his collaborators in a series of papers starting from 1988 (Morihara et al., 1988a,b, 1989, 1992, 1993a,b,c Shimada et al., 1992, 1993, 1994 Matsuishi et al., 1992, 1994). Refer to them for further details. 

Cammidge, A.N. Baines, N.J. Bellingham, R.K. Synthesis of heterogeneous palladium catalyst assemblies by molecular imprinting. Chem. Commun. 2001, 2588-2589. Morihara, K. Kurihara, S. Suzuki, J. Footprint catalysis. I. A new method for designing tailor-made catalysts with substrate specificity silica (alumina) catalysts for butanolysis of benzoic anhydride. Bull. Chem. Soc. Jpn. 1988, 61, 3991-3998. Morihara, K. Nishihata, E. Kojima, M. Miyake, S. Footprint catalysis. II. molecular recognition of footprint catalytic sites. Bull. Chem. Soc. Jpn. 1988, 61, 3999-4003. Shimada, T. Makanishi, K. Morihara, K. Footprint catalysis. IV. structural effects of templates on catalytic behavior of imprinted footprint cavities. Bull. Chem. Soc. Jpn. 1992, 65, 954-958. 

The need for novel catalytic processes is clear and, as discussed in Chapter 9, combining catalytic steps into cascade processes, thus obviating the need for isolation of intermediate products, results in a further optimization of both the economics and the environmental footprint of the process. In vivo this amounts to metabolic pathway engineering [20] of the host microorganism (see Chapter 8) and in vitro it constitutes a combination of chemo- and/or biocatalytic steps in series and is referred to as cascade catalysis (see Chapter 9). Metabolic engineering involves, by necessity, renewable raw materials and is a vital component of the future development of renewable feedstocks for fuels and chemicals. 

The latest results on imprinted chiral footprints [154] have shown that enantioselective catalysis (hydrolysis) does occur, and based on kinetic measurement the authors believe that this is due to an enantioselective mechanism. Kaiser and Andersson also chose aluminium doped silica as a polymeric material to obtain phenanthrene imprints and their work has been discussed earlier [52]. No selectivity towards the template was observed when imprinted silica was used as stationary phase. Only relative retention and capacity factors increased. Furthermore, even after careful extraction in a Soxhlet, the polymer still leaked phenanthrene. They also found that diazomethane yields a side reaction forming long alkyl chains. Finally they attempted to rej at the work of Morihara et al. [150-155]. but were not able to detect any selectivity using dibenzamide as the template and instead found that the template decomposes into at least five different products when adsorbed on the silica. Clearly further work is required on these systems. 

The first use of imprinted metal oxides for catalysis was performed by Morihara et al. in the late 1980s [47,48]. Substrate selective catalytic sites for the esterification of anhydrides were prepared using an alumina sol-gel technique formed on silica gel. Template molecules, present during the final stages of alumina gel formation, are thought to leave footprint-like impressions on the gel surface after subsequent... 

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... 

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. 

Kaiser G.G. and Anderson J.T. (1992) Sorbents for liquid chromatography based on the footprint principle, Fresenius J. Analyt. Chem., 342, 834-838. Heilman J. and Maier W.F. (1994) Selective catalysis on silicon dioxide with substarte-specific cavities, Angew. Chem., Int. Ed. Engl, 33, 471-473. 

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. 

The following part of this work will be devoted to the use of these macroscopically shaped nitrogen-doped CNTs and mesoporous carbon for catalysis applications. It is worthy to note that reports that deal with the use of these macroscopic N-CNTs remain scarce nowadays despite their high potenhal. However, results obtained indicate that this new family of metal-free catalysts will play a key role in the relentless development race of future catalysts with better catalytic performance alongside with low carbon footprint. 

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