Tuning Chelation by the Surfactant-Like Peptide A(6)H Using Predetermined pH Values

[Image: see text] We examine the self-assembly of a peptide A(6)H comprising a hexa-alanine sequence A(6) with a histidine (H) “head group”, which chelates Zn(2+) cations. We study the self-assembly of A(6)H and binding of Zn(2+) ions in ZnCl(2) solutions, under acidic and neutral conditions. A(6)H self-assembles into nanotapes held together by a β-sheet structure in acidic aqueous solutions. By dissolving A(6)H in acidic ZnCl(2) solutions, the carbonyl oxygen atoms in A(6)H chelate the Zn(2+) ions and allow for β-sheet formation at lower concentrations, consequently reducing the onset concentration for nanotape formation. A(6)H mixed with water or ZnCl(2) solutions under neutral conditions produces short sheets or pseudocrystalline tapes, respectively. The imidazole ring of A(6)H chelates Zn(2+) ions in neutral solutions. The internal structure of nanosheets and pseudocrystalline sheets in neutral solutions is similar to the internal structure of A(6)H nanotapes in acidic solutions. Our results show that it is possible to induce dramatic changes in the self-assembly and chelation sites of A(6)H by changing the pH of the solution. However, it is likely that the amphiphilic nature of A(6)H determines the internal structure of the self-assembled aggregates independent from changes in chelation.