The influence of herbicidal anions on chemical shifts in NMR, phytotoxicity and surface properties of pyrrolidinium surface-active ionic liquids

Six surface-active ionic liquids (SAILs) with herbicidal anions were synthetized (with a yield of ≥ 88 %) and their structure was confirmed by NMR spectra. Subsequently, their surface properties, phytotoxicity and bulk aggregation behavior in aqueous solution investigated. The compounds studied have an amphiphilic structure and, due to the presence of two long alkyl chains in the cation, they displayed surface activity (CMC values, ranging from 0.13 mmol L−1 to 1.36 mmol L−1). Our results provide explanations for the role of counterions in the physical and chemical properties of SAILs. Indeed, the aromatic anion affects the hydrophilic charge of the surface-active compounds. The SAILs containing the [MCPA]− and [MCPP]− anions were the most phytotoxic to representatives of dicotyledonous plants compared to the other compounds. By analysis of the structure of SAILs, we demonstrate that counterions play an important role in self-assembly and adsorption processes in aqueous solutions, and therefore, in the potential biological application of these compounds.