Topology-Controlled Selective Fe3+ Binding in Water by δ-Peptides with a Dihydropyrimidinone-Containing Amino Acid

Abstract

The effect of topology on the structure, self-assembly, and selective Fe3+ binding of δ-peptides has been investigated. A series of δ-peptides with an amino acid containing dihydropyrimidinone and o-, m-, and p-aminobenzoic acids have been designed to study the structure–function relationship. A new amino acid containing dihydropyrimidinone was synthesized by the Biginelli reaction of ethyl acetoacetate, urea, and o-nitrobenzaldehyde followed by reduction with iron powder and acetic acid. X-ray crystallography sheds some light on the conformations, self-assembly, and the diverse degrees of π–π stacking of adjacent δ-peptide molecules. Peptides with o- or m-aminobenzoic acid form eight-membered intramolecular hydrogen-bonded turn conformations and self-assemble through intermolecular hydrogen bonds between dihydropyrimidinone units to form a butterfly-like structure. However, the δ-peptide containing p-aminobenzoic acid forms a water-mediated cage-like structure. Irrespective of the presence of the same functional groups, only the δ-peptide with o-aminobenzoic acid can selectively bind Fe3+ in methanol as well as in water. The topology plays a crucial role in the selective Fe3+ ion binding by the δ-peptide.