pH-responsive, bolaamphiphile-based smart metallo-hydrogels as potential dye-adsorbing agents, water purifier, and vitamin B12 carrier

A protein amino acid, phenylalanine-based bolaamphiphile 1 containing a centrally located oligomethylene group has been found to be a hydrogelator at nearly physiological pH (pH 6.5-7.2) in the presence of divalent metal salts (such as MnCl2, CoCl2, CuSO4, and NiCl2) on sonication. Other structurally related synthetic bolaamphiphiles 2-4 do not form hydrogels under similar conditions. The metallo-hydrogels have been characterized using transmission electron microscopic (TEM) studies and FT-IR studies. TEM study of these metallo-hydrogels indicates a network of nanofibrilar morphology that might be responsible for gelation. The pH sensitivity of these metallo-hydrogels can be potentially utilized for entrapment and slow release of biologically important molecules. It has been demonstrated that one of these gels entraps and slowly releases vitamin B-12 molecules depending upon the pH of the medium. Moreover, these metallo-hydrogels can efficiently adsorb various toxic dyes including Crystal Violet and Naphthol Blue Black from water and this property can be utilized for the removal of different types of toxic dye molecules from wastewater.