Metal-Dependent Intramolecular Chiral Induction: The Zn^(2+) Complex of an Ethidium−Peptide Conjugate

Abstract

Ethidium bromide is an aromatic organic dye that for many years has been known to bind via intercalation to the minor groove of DNA. When the ethidium cation binds to DNA, the chirality of the right-handed double helix is imposed upon ethidium (Et), producing induced circular dichroism (ICD). Other examples of ICD have been observed in the heme group of hemoglobin and myoglobin as well as synthetic porphyrin assemblies, and in host−guest assemblies. In every case, an ICD spectrum is produced as a result of the close association of an achiral chromophore with a chiral moiety (e.g., a biopolymer). During the course of our ongoing research into artificial hydrolytic nucleases, we prepared an ethidium−peptide conjugate that displays metal-dependent ICD. Here we report the synthesis and spectroscopic characterization of a metal−peptide assembly which may represent a first example of metal-dependent intramolecular chiral induction.