Binding of a hemoregulatory tetrapeptide by a bis-guanidinium crown ether

A synthetic receptor for the molecular recognition of a tetrapeptide in aqueous buffer was obtained by combining a luminescent crown ether with two pyrrole-guanidinium moieties. The compound interacts with ammonium carboxylates of complementary geometry and binds the hemoregulatory peptide Ac-Ser-Asp-Lys-Pro with K=7×103 M−1 at physiological pH. Shorter fragments and other tetrapeptides show no or significant reduced affinity. The binding of the target peptide to the functionalized crown ether is signalled by an increase of its emission intensity.