Zwitterionic betaine transition from micelles to vesicles induced by cholesterol

Abstract

Vesicle formation by self-assembly in an aqueous mixture of zwitterionic carboxylate betaine surfactant and cholesterol was studied as a potential drug delivery nanocarrier. In this study, pyrene and 1,6-Diphenyle1-1,3,5-hexatrine (DPH) were applied as fluorescence probes that provides information on polarity and fluidity of the microenvironment, and used to monitor the transition of zwitterionic betaine from monomers to micelles, and to vesicles promoted by addition of cholesterol to micellar solutions through the variation of vibronic peak intensity ratio I1/I3 of the pyrene and solubilization with intensity quenching I428 of (DPH). In addition, the steady-state and time-resolved fluorescence anisotropy measurements of the (DPH) probe provides information on the effect of cholesterol on the dynamic properties vesicle membrane and vesicular distribution accompanied by dynamic light scattering (DLS), transmission electron microscopy (TEM), and turbidity measurements. Our results show an abrupt change of the ratio I1/I3 of pyrene and fluorescence intensity I428 of (DPH) in the transition from monomer to micelle with increasing betaine concentration, as well as fluorescence anisotropy results thought the transition from micelle to vesicle promoted by cholesterol and confirmed by TEM result. Furthermore, the fluorescence anisotropy measurements shows that addition of small amount of cholesterol to zwitterionic betaine micelle have a significant influence on the molecular packing leading to vesicle formation and increasing bilayer rigidity with increasing cholesterol concentration up to χchol=0.25.