Interaction between glyphosate pesticide and amphiphilic peptides for colorimetric analysis

The large-scale use of glyphosate pesticides in food production has attracted attention due to environmental damage and toxicity risks. Several regulatory authorities have established safe limits or concentrations of these pesticides in water and various food products we consume every day. The irreversible inhibition of acetylcholinesterase (AChE) activity is one of the strategies used for pesticide detection. Herein, we found that lipopeptide sequences can act as biomimetic microenvironments of the AChE, showing higher catalytic activities than natural enzymes in an aqueous solution, based on IC50 values. These biomolecules contain in the hydrophilic part the amino acids L-proline (P), L-arginine (R), L-tryptophan (W), and L-glycine (G), covalently linked to a hydrophobic part formed by one or two long aliphatic chains. The obtained materials are referred to as compounds 1 and 2, respectively. According to fluorescence assays, the system composed only by 2 is more hydrophobic than the other composed only by 1. The circular dichroism (CD) data present a significant difference in the ellipsometry values, likely related to distinct conformations assumed by the proline residue in the lipopeptides' supramolecular structure in solution. The morphological aspect was further characterized using small-angle X-ray scattering (SAXS) and cryogenic transmission electron microscopy (Cryo-TEM), which showed the compounds 1 and 2 self-assembly into cylindrical and planar core-shell structures, respectively. The mimetic AchE behavior of lipopeptides was confirmed by Ellman’s hydrolysis reaction, where the proline content of the peptides acts as nucleophilic scavengers of organophosphate pesticides. Moreover, the isothermal titration calorimetry (ITC) experiments revealed that host-guest interactions in both systems were dominated by enthalpically-driven thermodynamics. The UV-Vis kinetic experiments were performed to assess the inhibition of the lipopeptide catalytic activity and the IC50 values, where we found that the detection limit correlated with the increase in hydrophobicity of the lipopeptides, implying the micellization process to be more favorable.