Scheme 1.

Chemical structures of (A) DS, and (B) MH. The Green boxes mark the chemical groups that can participate in hydrogen bonding, red boxes mark the metal ion chelating sites in MH, and the blue box marks the positively charged ammonium group in MH which can potentially participate in the electrostatic interaction with DS. (C) Schematic of complex formation. One MH molecule can bind to two or more chemical groups in DS simultaneously through metal ion binding, hydrogen bonding, and electrostatic interactions to induce intra and intermolecular crosslinking of DS molecules which leads to insoluble complex formation. M²⁺ denotes metal ions.