Three adipic dihydrazide-based receptors functionalized with a pyridine moiety were synthesized by varying the positions of "pyridine -N", while one more receptor was fabricated as a control compound appended with phenyl moieties in the two arms instead of pyridine. The positional isomeric effects on the metallogelation behavior were investigated. Receptors ADH-Py-p and ADH-Py-m, having pyridine -N at the para and meta positions, respectively, were found to display selective metallogelation behavior in the presence of Ag+ (P-Ag-G) and Cd2+ (M-Cd-G), respectively, out of all the metal ions undertaken for our study. Interestingly, the metallogel P-Ag-G, formed in the presence of Ag+, eventually led to the spontaneous in situ formation of AgNPs inside the gel matrix. P-Ag-G and its gel nanocomposite were further utilized for an antibacterial study. The idea of selective metallogelation behavior of the receptor ADH-Py-m in the presence of toxic Cd2+ was then exploited for the detection of Cd2+ in the presence of other competitive metal ions in different real water samples through the naked eye, thus circumventing the need for any sophisticated instrumentation.
Moral et al. (Thu,) studied this question.