RESUMO
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 consumed daily. 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 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, 2 is more hydrophobic than 1. The circular dichroism (CD) data present a significant difference in the molar ellipticity values, likely related to distinct conformations assumed by the proline residue in the lipopeptide 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 that compounds 1 and 2 self-assembly into cylindrical and planar core-shell structures, respectively. The mimetic AchE behaviour of lipopeptides was confirmed by Ellman's hydrolysis reaction, where the proline residue in the peptides act as a nucleophilic scavenger of organophosphate pesticides. Moreover, the isothermal titration calorimetry (ITC) experiments revealed that host-guest interactions in both systems were dominated by enthalpically-driven thermodynamics. UV-vis kinetic experiments were performed to assess the inhibition of the lipopeptide catalytic activity and the IC50 values were obtained, and we found that the detection limit correlated with the increase in hydrophobicity of the lipopeptides, implying the micellization process is more favorable.
RESUMO
Four amphiphilic peptides were synthesized, characterized, and evaluated regarding their efficiency in the catalysis of direct aldol reactions in water. The lipopeptides differ by having a double lipid chain and a guanidinium pyrrole group functionalizing one Lys side chain. All the samples are composed of the amino acids l-proline (P), l-arginine (R), or l-lysine (K) functionalized with the cationic guanidiniocarbonyl pyrrole unit (GCP), l-tryptophan (W), and l-glycine (G), covalently linked to one or two long aliphatic chains, leading to surfactant-like designs with controlled proline protonation state and different stereoselectivity. Critical aggregation concentrations (cac) were higher in the presence of the GCP group, suggesting that self-assembly depends on charge distribution along the peptide backbone. Cryogenic Transmission Electron Microscopy (Cryo-TEM) and Small Angle X-ray Scattering (SAXS) showed a rich polymorphism including spherical, cylindrical, and bilayer structures. Molecular dynamics simulations performed to assess the lipopeptide polymorphs revealed an excellent agreement with core-shell arrangements derived from SAXS data and provided an atomistic view of the changes incurred by modifying head groups and lipid chains. The resulting nanostructures behaved as excellent catalysts for aldol condensation reactions, in which superior conversions (>99%), high diastereoselectivities (ds = 94 : 6), and enantioselectivities (ee = 92%) were obtained. Our findings contribute to elucidate the effect of nanoscale organization of lipopeptide assemblies in the catalysis of aldol reactions in an aqueous environment.
