Effect of terpene alcohol fragment and type of anion in the pyrrolidinium salts on the physicochemical properties and antibacterial activity

Pyrrolidinium salts containing in the cation chiral substituent derived from three terpene alcohols: (–)-menthol, (–)-borneol, and (+)-fenchol and consisting of six different anions: chloride [Cl]−, tetrafluoroborate [BF4]−, hexafluorophosphate [PF6]−, trifluoromethanesulfonate [OTf]−, bis(trifluoromethylsulfonyl)imide [NTf2]−, bis(pentafluoroethylsulfonyl)imide [NPf2]−, and perfluorobutanesulfonate [C4F9SO3]− were compared in terms of physicochemical properties and antimicrobial activity. The thermal properties including phase transition temperatures, thermal stability, specific rotation have been taken into consideration. Liquid pyrrolidinium salts with [NTf2]− and [NPf2]− anions, which can be classified as chiral ionic liquids, have also been compared in terms of density, dynamic viscosity, surface tension and contact angle on the surfaces of different polarity. The selected pyrrolidinium salts were evaluated for activity against nine bacterial strains using the agar well diffusion method. The zones of inhibition of bacterial growth were determined for pyrrolidinium salts used at different concentrations and depending on the structure of the cation and anion and compared with benzalkonium chloride as a positive control.