The Aggregation Behavior and Antioxidative Activity of Amphiphilic Surfactants Based on Quinuclidin-3-ol

The self-aggregation and thermodynamic properties of three cationic quaternary ammonium surfactants were investigated. The physicochemical properties of compounds containing quinuclidin-3-ol with even number of carbon atoms (10, 12, and 14) in the hydrophobic tail were measured by conductivity, dynamic light scattering (DLS), and Zeta-potential measurements. DLS and Zeta-potential measurements show a similar size distribution for all surfactants with excellent uniformity, and Zeta-potential increases significantly with increase in the size of hydrocarbon tail. The critical micelle concentration (CMC) and the degree of micelle ionization (beta) were determined using conductivity measurements. The CMC values of surfactants were found to be between 3.4 and 23.8 x 10(-3) M. The standard Gibbs free energy (Delta Gmico) was derived from conductivity measurements and suggests that surfactants containing longer chains spontaneously form micelles. The antioxidative properties of these cationic surfactants were evaluated using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) and oxygen radical absorbance capacity (ORAC) assays. Among the tested samples, N-tetradecyl-3-hydroxyquinuclidinium bromide (QOH-C14) exhibited the highest antioxidative potential (388.30 nmol (TE) equivalents mL(-1)), which was further investigated by the DNA nicking assay.