Melamine-Based Molecularly Imprinted Monoliths Targeting Glyphosate in Aqueous Media: Synthesis and Binding Mechanism Elucidation

Cross-linked melamine imprinted monoliths targeting glyphosate were synthesized using 4-phosphonobutanoic acid (PBA) and <i>N</i>-(phosphonomethyl)-iminodiacetic acid (PMIDA) as templates. The binding capacities, evaluated in an aqueous medium, showed that both PMIDA and PBA promoted selective binding sites with imprinting factors of 2.5 and 1.7, respectively. Despite a relatively low imprinting factor, the polymer imprinted with PMIDA showed a noticeably higher binding efficiency in the presence of sodium chloride compared to the nonimprinted reference, demonstrating an ability to selectively target the desired analytes in real sample matrices. Spectroscopic investigations using Fourier transform infrared and ¹H nuclear magnetic resonance spectroscopy revealed the formation of "memory pockets" for glyphosate molecules in the imprinted melamine-formaldehyde scaffold promoted by simultaneous contributions from (i) hydrogen bonding with N-H/O-H moieties and (ii) electrostatic interaction toward the triazine ring.