Understanding the Effects of Cholesterol and Ethanol on the Stability and Morphology of Bicellar Mixtures

Abstract

Elucidating the stability and morphology of bicellar mixtures is of great importance in the biomedical field. In this report, self-assembly cholesterol (CHOL)-containing bicellar mixtures were investigated, that were composed of long chain hydrogenated soybean phospholipids (HSPC), short chain 1, 2-diheptanoyl-sn-glycero-3-phosphocholine (DHPC) phospholipids, negatively charged dipalmitoyl phosphatidylglycerol (1, 2-dipalmitoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (DPPG), and polyethylene glycol conjugated (1, 2-dimyristoyl-sn-glycero-3-phosphoethano-lamine-N-[methoxy (polyethylene glycol)-2000] (PEG2000-DSPE) lipid. Analytical techniques like; Dynamic Light Scattering (DLS), Small Angle X-Ray Scattering (SAXS), and Transmission Electron Microscopy (TEM) were used to investigate the stability and morphology changes of these bicellar mixtures. The effects of CHOL and ethanol on the morphology and stability of these bicellar mixtures under 50ºC were also studied. The transition happened from nanodiscs to nanovesicles when the CHOL molar ratio was 40% in pure water. However, adding ethanol could improve CHOL solubility when the ethanol weight ratio was 20 wt% (ethanol/lipid) that favored nanodiscs-nanovesicle transition. Additionally, the ammonium sulfate maybe another factor that could affect the morphology of these bicellar mixtures form high order d-spacing structure.