A series of linear peptide based anion receptors, in which the distance between the bis[zinc(II)dipicolylamine]
binding sites and the peptide backbone was varied systematically, was prepared and their anion
binding ability was investigated using indicator displacement assays. Shortening the distance between the
binding site and the peptide backbone was found to enhance both the receptor affinity and selectivity for
pyrophosphate over other organic polyphosphate anions in Krebs buffer with the maximum selectivity
and affinity observed with a spacer length of two methylene units. The suitability of these receptors for
the determination of pyrophosphate concentrations in Krebs buffer and in artificial urine was examined.