Probing the inner cavities of hydrogels by proton diffusion

The reversible proton dissociation and geminate recombination of a photoacid was studied in peptide-based hydrogels over a large concentration range of the self-assembled peptide nanotube (PNT) network. 8-Hydroxypyrene-1, 3, 6-trisulfonate trisodium salt (HPTS) was used as the photoacid. We found that the proton transfer to the solvent rate is not affected by the presence of the fibrous structures. However, the proton geminate recombination process is affected by the PNT walls. We used the photoprotolytic reversible geminate recombination model to analyze the time-resolved emission data in the hydrogel samples. Our assumptions lead to the suggestion that the hydrogels form water nanopools of the order of 100 Å.