An Amino Acid-Based Self-Shrinking Supramolecular Bioactive Hydrogel - A Sustainable Platform for Wastewater Treatment and Water Purification.

This study investigates the unique syneresis (self-shrinking) behavior of N-Terminally Fmoc-protected amino acid, Fmoc-hPhe-OH (Fmoc-homo-L-phenylalanine, abbreviated in this work as hF)-based hydrogel, and its potential in environmental remediation applications. Fmoc-hPhe-OH (hF) forms a hydrogel in 50 mM phosphate buffer (PB) of pH 7.4. Interestingly, hF-based hydrogel shows syneresis behavior with controlled release of residual water from the hydrogel matrix. Moreover, this hydrogelator can form co-assembled hydrogels with various dyes, including Congo Red and Rhodamine B; natural water samples, including natural mud water and sea water; and heavy metal ions aqueous solutions, including Cd^II, Pb^II, and Hg^II separately in 50 mM PB of pH 7.4. Interestingly, after 2 to 3 hours for shake gel and 5-6 hours for nonshake gel, the released waters have been tested and it has been found that these co-assembled hydrogels are capable of retaining almost all the contaminants within the shrink hydrogels matrix and releasing almost pure water along with the presence of hydrogel nanofibers. Syneresis is augmented to purify the contaminated water with dyes, mud, dissolved salts, and toxic heavy metal ions. These co-assembled hydrogels, leading to distinct structural and functional changes, which have been characterized by using Fourier-Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), and Field Emission Scanning Electron Microscopy (FE-SEM), suggesting various supramolecular interactions including π-π stacking, hydrogen bonding, and electrostatic interactions are responsible for stable hydrogelations. The rheological study evaluates the hydrogel's mechanical and thixotropic properties and spectroscopic techniques, including UV-visible spectroscopy and fluorescence spectroscopy, to monitor structural transition. This novel class of amino acid-based hydrogel shows antibacterial activity against both Gram-positive and Gram-negative bacteria, likely through membrane-disruptive mechanisms, and also shows promising antioxidant properties. The native hF hydrogel is biocompatible and shows anticancer activity toward the pancreatic cancer cell line. The research finding bestows the biomedically relevant hydrogel's potential use in green and sustainable environmental remediation.