title: Electron transfer in peptides: on the formation of silver nanoparticles.
abstract: Some microorganisms perform anaerobic mineral respiration by reducing metal ions to metal nanoparticles, using peptide aggregates as medium for electron transfer (ET). Such a reaction type is investigated here with model peptides and silver as the metal. Surprisingly, Ag(+) ions bound by peptides with histidine as the Ag(+)-binding amino acid and tyrosine as photoinducible electron donor cannot be reduced to Ag nanoparticles (AgNPs) under ET conditions because the peptide prevents the aggregation of Ag atoms to form AgNPs. Only in the presence of chloride ions, which generate AgCl microcrystals in the peptide matrix, does the synthesis of AgNPs occur. The reaction starts with the formation of 100 nm Ag@AgCl/peptide nanocomposites which are cleaved into 15 nm AgNPs. This defined transformation from large nanoparticles into small ones is in contrast to the usually observed Ostwald ripening processes and can be followed in detail by studying time-resolved UV/Vis spectra which exhibit an isosbestic point.
authors: Department of Chemistry, University of Fribourg, Chemin du Musée 9, 1700 Fribourg (Switzerland).
authors: Sonja
authors: S
authors: Kracht
authors: Matthias
authors: M
authors: Messerer
authors: Matthieu
authors: M
authors: Lang
authors: Sonja
authors: S
authors: Eckhardt
authors: Miriam
authors: M
authors: Lauz
authors: Bernard
authors: B
authors: Grobéty
authors: Katharina M
authors: KM
authors: Fromm
authors: Bernd
authors: B
authors: Giese
mesh_terms: D004579:Electron Transport; D053768:Metal Nanoparticles; D046529:Microscopy, Electron, Transmission; D010455:Peptides / Q000737:chemistry*; D012834:Silver / Q000737:chemistry*
chemical_list: D010455:Peptides; D012834:Silver
keywords: Ag@AgCl nanocomposites; electron transfer; isosbestic point; silver nanoparticles; silver-peptide