Receptor polytopic macrocyclic

Polytopic macrocyclic receptors 1, 2 (Figure 10.1) are able to complex the zwitterionic form of the amino acids by a double non-covalent charge interaction [28,29]. The unsymmetrical benzocrown sulfonamide derivative, 2 which contains benzo-18-crown-6 and benzo-15-crown-5 moieties was used as a ditopic receptor for multiple molecular recognition of the amino acids, by combining two non-covalent interactions ammonium-crown hydrogen bonding and carboxylate- complexed Na+-benzo-15-crown-5 charge interactions [28,33]. 

Fig. 10.1 Multiple molecular recognition of the zwitterionic amino acids by macrocyclic polytopic receptors 1,2 [28,33],...

Still more complicated receptees, for example, [Co(NH3>J, [Co(NH2CH2CH2NH2)3], [Co(l,3,6,8,10,13,16,19-octaazabicyclo[6.6.6]eicosane)], (in lasalocid A) (22 3), and ferri- and ferrocyanide (with macrocyclic polyammonium hosts) (24,25), have been incorporated as central moieties in coordination entities. The use of complexes as receptors or receptees is, in principle, indefinitely extendable. Indeed NH3 is a complex molecule that is a ligand in the hexaammine complex that is the receptee in the lasalocid complex. Placement of [Co(NH3)J(LAS)3 in a membrane, as receptor, is very like a fourth level of complexation. The receptor for NH3-R-NH3 (Figure 2) is illustrative of ditopic compartmental receptors (14-16). In principle, there is no limit to the number and relative orientations of the receptee sites of polytopic compartmental ligands. 

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