Efficient antimicrobial activity and reduced toxicity of 1-dodecyl-3-methylimidazolium tetrafluoroborate ionic liquid/β-cyclodextrin complex

• The inclusion complex of ionic liquid with β-cyclodextrin has been obtained.
• The structure of the complex was studied by DSC, FTIR and 1H NMR analysis.
• The long aliphatic tail of ionic liquid is included into β-cyclodextrin cavity.
• The complex of ionic liquid with β-cyclodextrin has high antimicrobial activity.
• The inclusion complex has considerably lower toxicity than pure ionic liquid.

Water immiscible ionic liquid 1-dodecyl-3-methylimidazolium tetrafluoroborate (DMIM-BF4) and its inclusion complex with β-cyclodextrin (β-CD) in molar ratio 1:1 have been synthesized. The formation of DMIM-BF4/β-CD complex was confirmed by FT-IR analysis, 1H NMR analysis, and differential scanning calorimetry data. Our results indicate that the aliphatic tail of DMIM-BF4 is included into β-CD inner cavity whereas imidazolium ring is located outside the torus. Moreover, the weak interaction between polar components of ionic liquid and hydrophilic outer surface of β-CD has also been detected. The standard agar disk diffusion method was performed to evaluate antimicrobial efficiency of the obtained compounds against Staphylococcus aureus (ATCC-25923), Escherichia coli (ATCC-25922) and Pseudomonas aeruginosa (ATCC-27853), Candida albicans (M 885 ATCC 10231) and its clinical isolate test-cultures. It has been found that both DMIM-BF4 and DMIM-BF4/β-CD complex possess high antimicrobial activity as revealed by similar zone inhibition values against all tested microorganisms. The acute toxicity studies on Danio rerio (zebrafish) model organism showed that the pure ionic liquid DMIM-BF4 is slightly toxic compound having LD50 value of 7 mg/L, whereas DMIM-BF4/β-CD complex has considerably reduced toxicity (LD50 = 100 mg/L) and therefore have potentially wider application areas.