Tuning chelation by the surfactant-like peptide A6H using predetermined pH values

We examine the self-assembly of a peptide A6H comprising a hexa-alanine sequence A6 with a histidine (H) “head group”, which chelates Zn2+ cations. We study the self assembly of A6H and binding of Zn2+ ions in ZnCl2 solutions, under acidic and neutral conditions. A6H self-assembles into nanotapes held together by a β-sheet structure in acidic aqueous solutions. By dissolving A6H in acidic ZnCl2 solutions, the carbonyl oxygen atoms in A6H chelate the Zn2+ ions and allow for β-sheet formation at lower concentrations, consequently reducing the onset concentration for nanotape formation. A6H mixed with water or ZnCl2 solutions under neutral conditions produces short sheets or pseudocrystalline tapes, respectively. The imidazole ring of A6H chelates Zn2+ ions in neutral solutions. The internal structure of nanosheets and pseudocrystalline sheets in neutral solutions is similar to the internal structure of A6H nanotapes in acidic solutions. Our results show that it is possible to induce dramatic changes in the self-assembly and chelation sites of A6H by changing the pH of the solution. However, it is likely that the amphiphilic nature of A6H determines the internal structure of the self-assembled aggregates independent from changes in chelation

Tuning Chelation by the Surfactant-Like Peptide A₆H Using Predetermined pH Values

We examine the self-assembly of a peptide A₆H comprising a hexa-alanine sequence A₆ with a histidine (H) “head group”, which chelates Zn²⁺ cations. We study the self-assembly of A₆H and binding of Zn²⁺ ions in ZnCl₂ solutions, under acidic and neutral conditions. A₆H self-assembles into nanotapes held together by a β-sheet structure in acidic aqueous solutions. By dissolving A₆H in acidic ZnCl₂ solutions, the carbonyl oxygen atoms in A₆H chelate the Zn²⁺ ions and allow for β-sheet formation at lower concentrations, consequently reducing the onset concentration for nanotape formation. A₆H mixed with water or ZnCl₂ solutions under neutral conditions produces short sheets or pseudocrystalline tapes, respectively. The imidazole ring of A₆H chelates Zn²⁺ ions in neutral solutions. The internal structure of nanosheets and pseudocrystalline sheets in neutral solutions is similar to the internal structure of A₆H nanotapes in acidic solutions. Our results show that it is possible to induce dramatic changes in the self-assembly and chelation sites of A₆H by changing the pH of the solution. However, it is likely that the amphiphilic nature of A₆H determines the internal structure of the self-assembled aggregates independent from changes in chelation

Selfassembly of a peptide amphiphile: transition from nanotape fibrils to micelles Self-assembly of a peptide amphiphile: transition from nanotape fibrils to micelles †

A thermal transition is observed in the peptide amphiphile C 16 -KTTKS (TFA salt) from nanotapes at 20 C to micelles at higher temperature (the transition temperature depending on concentration). The formation of extended nanotapes by the acetate salt of this peptide amphiphile, which incorporates a pentapeptide from type I procollagen, has been studied previously [V. Castelletto et al., Chem. Commun., 2010, 46, 9185]. Here, proton NMR and SAXS provide evidence for the TFA salt spherical micelles at high temperature. The phase behavior, with a Krafft temperature separating insoluble aggregates (extended nanotapes) at low temperature from the high temperature micellar phase resembles that for conventional surfactants, however this has not previously been reported for peptide amphiphiles