Enhanced detection of pesticides: evaluating monocarbamoylcarboxylic acids modified with amines for glyphosate and dicamba sensitivity

In this work a series of monocarbamoylcarboxylic acids (MCCAs) N-functionalized with different amines were evaluated to detect the pesticides glyphosate (Gly) and dicamba (Dic). The MCCAs have molar absorptivity coefficients (ε) three orders of magnitude higher than pesticides facilitating the measurements under UV–Vis spectroscopy. These compounds have the isolectric point (IEP) in the range of pH 3.04–4.82 and beyond are negative charged. The absorption properties of the compounds are pH-dependent due to the protonation and deprotonation of their molecules, the adsorption band shifts to a longer wavelength as the pH increases and in some ligands a hyperchromic effect is observed. The titration of MCCAs with a pesticide generates a change in the adsorption band and the sensitivity of the response is also pH-dependent. The sensitivity of MCCAs towards pesticides decreased at pH 5.0 and increased at pH 7.0 and 9.0 which is clearly influenced by the acid-base equilibriums in water. The response was more sensitive towards dicamba than with glyphosate, exhibiting linear concentration intervals up to 100 µM with 1a at pH 4 and 85 µM in compounds 2b and 2c at pH 7.0. The ¹H NMR analysis in DMSO‑d₆ of compounds 2a and 2c in presence of glyphosate and dicamba showed changes in the hydrogen signals indicating the interaction of these MCCAs with the pesticides in specific sites of their molecules. These MCCAs, proved to be promising molecular platforms for the optical detection of glyphosate and dicamba due to their pH-adjustable sensitivity and their ability to show significant electrostatic interactions, enabling pesticide detection over a wide concentration range.