Supramolecular catalysis and enzyme mimics

We have previously seen that calix[4]arenes and cyclodextrins have been used as host molecules for the recognition of various guest molecules (Sections 2.3-2.6) As a consequence of their hydrophobic cavity in conjunction with reactive functional groups, both calix[4]arenes and cyclodextrins, in particular, (3-cyclodextrin, have been used in many catalytic applications, for example, ester hydrolysis, oxidation reactions, hydroformylation, hydrogenation and cross-coupling reactions. 

The use of supramolecular catalysfs has achieved the conversion of 1-octene to its corresponding ketone (2-octanone), using (3-cyclodextrin 2.145 in 2-4 h. 

Higher generations of dendrimer (larger and more branched) lead to high catalytic activity and stability of the encapsulated Pd complex. For example, the 5th-generation dendrimer-Pd complex used for the Heck coupling between an 

We have previously described how versatile P-cyclodextrins are as host molecules (Section 2.6.6). If a single hydroxyl group is deprotonated, a nucleophilic centre is generated in close proximity to the hydrophobic cavity, hence resulting in enzymelike activity.  

Miguel, D. and Alvarez, C., Cationic fac-tris(pyrazole) complexes as anion receptors, Chem. Commun., 2005,546-548. 

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CDs are cyclic oligosaccharides comprised of a-l,4-linked glucopyr-anose units (37- 0). The following properties make CDs attractive components in organic chemistry and supramolecular catalysis/ enzyme mimics in particular (i) CDs are water soluble (ii) their hydrophobic cavity can host a variety of lipophilic guest molecules ... 

The purpose of synthesising hemoprotein model compounds is twofold. First, it gives an understanding into the nature and operation of those criteria in natural systems. Secondly, by constructing models that mimic the supramolecular ability of enzymes for binding, recognition, and catalysis, the models themselves may find practical application, e.g. in he oxidation of organic compounds. ... 

The imidazolyl group, a constituent of histidine, provides some crucial catalytic sites for enzymatic catalysis. The investigations on enzyme mimics constitute a major contemporary research area in supramolecular chemistry. The synthetic designs of enzyme mimics should necessarily possess a hydrophobic cavity and suitably preorganized functional... 

Overall, the earlier described reactions of terpene derivatives mediated by the capsule really represents important examples of how, with simple self-assembled nanometric containers endowed with a few functionalities, it is possible to mimic some of the fundamental properties of enzymes. This demonstrates that the way opened by the development of supramolecular catalysis will soon reward the scientists with better and better catalytic systems. 

Biological systems are fundamentally supramolecular in nature and provide much of the underlying inspiration for supramolecular synthesis in terms of the desire to mimic biological process such as enzyme catalysis, self-assembly and ion transport. 

Reactions in micelles and in the double layers of vesicles are analogous to natural membrane systems and in special cases are comparable with the function of an enzyme (cf. Section 3.2.1). In contrast to macromolecular enzymes, amphiphile aggregates with linked catalytic centers have a less rigid supramolecular structure. The preorganization of an enzyme is highly selective and as a consequence enzyme catalysis is much more effective than micellar catalysis, a type of artifical mimic [6]. 

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