title: Tuning chelation by the surfactant-like peptide A6H using predetermined pH values.
abstract: We examine the self-assembly of a peptide A6H comprising a hexa-alanine sequence A6 with a histidine (H) "head group", which chelates Zn(2+) cations. We study the self-assembly of A6H and binding of Zn(2+) 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 Zn(2+) 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 Zn(2+) 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.
authors.affiliation: School of Chemistry, Food Science and Pharmacy, University of Reading , Whiteknights, Reading RG6 6AD, United Kingdom.
authors.forename: V
authors.initials: V
authors.lastname: Castelletto
authors.forename: I W
authors.initials: IW
authors.lastname: Hamley
authors.forename: M D
authors.initials: MD
authors.lastname: Segarra-Maset
authors.forename: C Berdugo
authors.initials: CB
authors.lastname: Gumbau
authors.forename: J F
authors.initials: JF
authors.lastname: Miravet
authors.forename: B
authors.initials: B
authors.lastname: Escuder
authors.forename: J
authors.initials: J
authors.lastname: Seitsonen
authors.forename: J
authors.initials: J
authors.lastname: Ruokolainen
mesh_terms: D000409:Alanine / Q000737:chemistry; D002614:Chelating Agents / Q000737:chemistry*; D006639:Histidine / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D010316:Particle Size; D010455:Peptides / Q000138:chemical synthesis / Q000737:chemistry*; D013499:Surface Properties; D013501:Surface-Active Agents / Q000737:chemistry*; D015032:Zinc / Q000737:chemistry*
chemical_list: D002614:Chelating Agents; D010455:Peptides; D013501:Surface-Active Agents; D006639:Histidine; D015032:Zinc; D000409:Alanine