Unravelling the Supramolecular Driving Forces in the Formation of CO-Responsive Pseudopeptidic Low-Molecular-Weight Hydrogelators.

A new family of C-symmetric pseudopeptides with a high functional density for supramolecular interactions has been synthetized through the attachment of four amino acid subunits to a diamino aliphatic spacer. The resulting open-chain compounds present remarkable properties as low-molecular-weight hydrogelators. The self-assembled 3D networks were characterized by SEM analyses, observing regular nanofibres with 80-100 nm diameters. Spectroscopic and molecular modelling experiments revealed the presence of strong synergic effects between the H-bonding and π-π interactions, with the best results obtained for the homoleptic tetra-pseudopeptide derived from l-Phe. In addition, these bioinspired hydrogels possessed pH- and CO-responsive sol-gel transitions. The formation of ammonium carbamate derivatives in the presence of carbon dioxide led to a detrimental change in its adequate self-assembly. CO desorption temperatures of ca. 70 °C were assigned to the thermodynamically favoured recovery of the supramolecular gel.