Molecular recognition by synthetic receptors

Abstract

Aza crown ethers are effective hosts for primary alkylammonium cations and the stereoselectivity of complexation depends upon the size of the crown ether macrocycle. Metalloporphyrins form complexes with electron rich ligands and anions. Ditopic receptors have been designed which incorporate two of these synthetic receptor molecules in a face-to-face relationship. The rigid face-to-face diaza crown ethers are highly selective hosts for bis-primary alkylammonium cations H3N+(CH2)xNH+3 and the selectivity can be rationalised in terms of a simple model. The crown-capped metalloporphyrins are suitable hosts for both components of primary alkylammonium and metal salts, and preliminary experiments show that face-to-face metalloporphyrins will form inclusion complexes with suitable bidentate ligands.