Synthesis and Antibacterial Evaluation of Three Quaternary Ammonium Surfactants Based on Isatin

Abstract

In present study, several isatin-derived quaternary ammonium surfactants with different carbon chain lengths were designed and synthesized. They were synthesized by alkylation of indoline-2,3-dione with various dibromo-alkanes, then quaternization with trimethylamine. Nuclear magnetic resonance (1H NMR, 13C NMR) and mass spectroscopy were employed to examine their chemical structures. Further, the critical micelle concentrations (CMC) value of surfactants synthesized was determined in an aqueous solution using electrical conductivity. The synthesized surfactants had CMC ranging from 0.01 to 0.012 mol/L. The antibacterial activity of the titer compounds (3a-3c) was evaluated against Gram-negative bacteria (Pseudomonas aeruginosa and Escherichia coli), as well as Gram-positive bacteria (Staphylococcus aureus). The surfactant with a long hydrocarbon chain (12 carbons) showed activity against all bacteria tested (minimum inhibitory concentration = 1.25-2.5 mg/mL), whereas those with a short hydrocarbon chain proved to be inactive.