Chiral Glass Formation by Dipeptide Salts

A simple dipeptide WR (tryptophan-arginine) in the form of salts with organic acids tartaric acid or crotonic acid is shown to form glasses through a benign preparation route by evaporation of aqueous solution. The glasses have a remarkable range of properties including moldability, high transparency across a broad range of wavelengths, and fluorescence. The glasses show self-healing and adhesive properties, and have accessible glass transition temperatures. The glasses are shown to be amorphous via small-angle and wide-angle X-ray scattering (SAXS/WAXS) and scanning electron microscopy (SEM). Remarkably, the glasses are found to have a chiral structure, as shown by circular dichroism (CD) spectroscopy. Investigation of glass precursor dipeptide salt solutions shows that the glasses form from an initial unordered solution containing chiral peptide molecules. The diverse properties of the dipeptide glass materials points to a wide range of potential future applications.