A Molecular Sponge: pH-driven Reversible Squeezing of Stimuli-Sensitive Peptide Monolayers
March 13, 2019
The cyclic change of structure, thickness and density, with pH switching from acid (pH=3) to basic (pH=11) condition, has been revealed for chemisorbed monolayers of the peptide Lipo-Aib-Lys-Leu-Aib-Lys-Lys-Leu-Aib-Lys-Ile-Lol, a Trichogin GA IV-analog carrying Lys residues instead of Gly ones at positions 2, 5, 6, 9, while a homologous peptide non containing Lys residues does not show any response to pH changes. Experimental and theoretical results, obtained by means of Quartz Crystal Microbalance with Dissipation monitoring, Surface Plasmon Resonance, Nano Plasmonic Sensing technique, Fourier Transform Infrared – Reflection Attenuated Spectroscopy, Dynamic Force Spectroscopy, and Molecular Dynamics simulations provide detailed information on the overall monolayer structure changes with the pH, including the analysis of the intra- and inter-chain peptide dynamics, the structure of the peptide layer/water/solid interface as well as of the position and role of solvation and non-solvation water. The observed stimuli responsive behavior of L1 peptide monolayers is accounted in terms of the occurrence of a pH-induced wetting/dewetting process, due to the pH-induced switching of the hydrophilic character of charged lysine groups to hydrophobic one of the same uncharged groups, along the peptide chain. This behavior in turn promotes the collective change of the aggregation state of the peptides chains. The present results may pave the way to critically reexamine the mechanism of stimuli-responsive systems.
Grazia Maria Lucia Messina, Benedetta Di Napoli, Marta De Zotti, Claudia Mazzuca, Fernando Formaggio, Antonio Palleschi and Giovanni Marletta
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