Self-assembled receptor

Ishi-i, T., Mateos-Timoneda, M.A., Timmerman, P., Crego-Calama, M., Reinhoudt, D.N., Shinkai, S. (2003) Self-assembled receptors that stereoselectively recognize a saccharide, Agnew. Chem., Int. Ed. 42, 2300-2305. 

Design, Synthesis, and Evaluation of Self-assembled Receptors... 

Since the term cryptand only refers to crown ether derived polycyclic receptors, polycyclic systems deriving from other structural motifs are commonly termed molecular cages or molecular capsules, although other names such as nanospheres, nanoflasks, temple-type receptors, etc., can also be found. The word cage well illustrates the overall architecture of many of these receptors, consisting of a floor and a roof connected by at least three bars.1 For self-assembled receptors, on the other hand, the term molecular capsule is often more appropriate. 

Figure 15 Synthesis of self-assembling receptors based on copper(l) complexes of phenanthroline... 

Other approaches to self-assembling receptors have been reported in recent years. A self-assembling, trimeric palladium complex based on the bis(benzimidazole) ligand (17) was designed by Williams and coworkers [4]. The complex contains a hydrophobic cavity that in the X-ray structure has included a molecule of acetonitrile. In a different context, Schepartz and McDevitt [70] have used the chelation of nickel(n) by A,7V -bis(salicylaldehy-de)ethylenediamine (salen) derivatives to control the position of K -binding glyme chains, and it has been shown that these self-assembled ionophores influence alkali metal transport across liquid membranes [71]. Also, Shinkai and coworkers [72] and Schneider and Ruf [73] have used metal chelation to induce an allosteric effect on binding at a second site. 

Evidence for ditopic binding by a self-assembled receptor (Figure 80) has been presented by Lee and Schwabacher [106]. They studied the binding of several indole and naphthalene derivatives bearing carboxylate sidearms. 1-Naphthyloxy acetate and the corresponding 1,5-diacetate showed the tightest binding (A p of 10 and 10 M, respectively). 

Figure 80 A self-assembled receptor for ditopic binding [106]...

Fig. 6 Examples of stable dimer (a) and pentamer (b) prepared by eoordinative assembly of free-base m so-pyridylporphyrins and metalloporphyrins (Refs. [52,53]). (e) A triple-decker complex with 4,4 -bipyridine (Ref. [56]). (d) The coordinatively self-assembled receptor exhibiting strong binding of terephthalic acid derivatives in chloroform (Ref. [57]).

For the approach detailed above to be successful, the metal binding domain must form robust complexes, yet retain synthetic flexibility. Although substituted phenanthroline and bipyridine easily form self-assembled receptors (12), the substitution stability of terpyridine (Fig. 2) makes this ligand more suited for the creation of libraries. The choice of metal also permits some flexibility in library creation. Iron complexes form easily through the addition of ammonium iron(II) sulfate hexahydrate, but can be cleaved by the addition of chelating guests (11,13), Cobalt complexes are also easily formed using cobalt(II)... 

Goodman, M. S., Weiss, J., and Hamilton, A. D. (1994) A self-assembling receptor for dicarboxylic acids. Tetrahedron Lett. 35, 8943-8946. 

Fig. 33.34 (a) The formation of the Ag" - assisted ternary self-assembled receptor of two molecules of 49 with Cgo or C70. (b) Formation of C6o 50 [Cu ] complex (Figures taken from Ref. [73] (/ ) Copyright 2000 and Ref. [74] right). Copyright 2001 with permission from Elsevier)... 

Van Anda H, Myles AJ, Rebek J Jr (2007) Charge transfer and encapsulation in a synthetic, self-assembled receptor. New J Chem 31(5) 631-633... 

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