Silver Ion-Histidine Interplay Switches Peptide Hydrogel from Antiparallel to Parallel β-Assembly and Enables Controlled Antibacterial Activity.

Understanding the chemical absorption process of silver ions helps the rational design of functional materials for effective release to minimize unwanted toxicity. To this end, a histidine-containing aliphatic peptide (IH6) was designed to immobilize the silver ion (Ag+) through coordinate interaction. Using circular dichroism spectroscopy, Ag+ was found to dose-dependently induce parallel β-sheet conformation of IH6 to a saturation molar ratio of 1:2. A conformational switch of IH6 from antiparallel to parallel β-sheet assembly upon Ag + coordination was further revealed by Fourier transform infrared spectroscopy. The resultant Ag-IH6 hydrogel displayed substantially enhanced mechanical strength as well as controlled release of Ag+. Ag-IH6 hydrogel thus exhibited strong dose-dependent bactericidal activities that can be tuned selectively, sparing the cocultured human keratinocytes in normal. Overall, the study demonstrates an unusual silver ion-induced peptide conformational switch between β-structure subtypes and the bilateral effects on hydrogel-based chemical control of silver ion absorption and release, thus, revealing the potential in antibacterial applications.