title: The effects of temperature, salinity, concentration and PEGylated lipid on the spontaneous nanostructures of bicellar mixtures.
abstract: The self-assembling morphologies of low-concentration (mostly 1 and 10mg/mL) bicellar mixtures composed of zwitterionic dipalmitoyl (di-C16) phosphatidylcholine (DPPC), dihexanoyl (di-C6) phosphatidylcholine (DHPC), and negatively charged dipalmitoyl (di-C16) phosphatidylglycerol (DPPG) were investigated using small angle neutron scattering, dynamic light scattering and transmission electron microscopy. A polyethylene glycol conjugated (PEGylated) lipid, distearoyl phosphoethanolamine-[methoxy (polyethyleneglycol)-2000] (PEG2000-DSPE), was incorporated in the system at 5mol% of the total lipid composition. The effects of several parameters on the spontaneous structures were studied, including temperature, lipid concentration, salinity, and PEG2000-DSPE. In general, nanodiscs (bicelles) were observed at low temperatures (below the melting temperature, TM of DPPC) depending on the salinity of the solutions. Nanodisc-to-vesicle transition was found upon the elevation of temperature (above TM) in the cases of low lipid concentration in the absence of PEG2000-DSPE or high salinity. Both addition of PEG2000-DSPE and high lipid concentration stabilize the nanodiscs, preventing the formation of multilamellar vesicles, while high salinity promotes vesiculation and the formation of aggregation. This study suggests that the stability of such nanodiscs is presumably controlled by the electrostatic interactions, the steric effect induced by PEG2000-DSPE, and the amount of DHPC located at the disc rim.
authors.affiliation: Department of Chemical and Biomolecular Engineering, University of Connecticut, Storrs, CT 06269, USA.
authors.forename: Ying
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Polymer Program, Institute of Materials Science, University of Connecticut, Storrs, CT 06269, USA.
authors.forename: Ming
authors.initials: M
authors.lastname: Li
authors.affiliation: Polymer Program, Institute of Materials Science, University of Connecticut, Storrs, CT 06269, USA.
authors.forename: Yongkun
authors.initials: Y
authors.lastname: Yang
authors.affiliation: Department of Chemical and Biomolecular Engineering, University of Connecticut, Storrs, CT 06269, USA.
authors.forename: Yan
authors.initials: Y
authors.lastname: Xia
authors.affiliation: Department of Chemical and Biomolecular Engineering, University of Connecticut, Storrs, CT 06269, USA; Polymer Program, Institute of Materials Science, University of Connecticut, Storrs, CT 06269, USA; Department of Biomedical Engineering, University of Connecticut, Storrs, CT 06269, USA. Electronic address: mu-ping.nieh@ims.uconn.edu.
authors.forename: Mu-Ping
authors.initials: MP
authors.lastname: Nieh
mesh_terms: D008055:Lipids / Q000737:chemistry*; D049329:Nanostructures / Q000737:chemistry*; D010713:Phosphatidylcholines / Q000737:chemistry; D010715:Phosphatidylglycerols / Q000737:chemistry; D011092:Polyethylene Glycols / Q000737:chemistry*; D054712:Salinity; D013696:Temperature
chemical_list: D008055:Lipids; D010713:Phosphatidylcholines; D010715:Phosphatidylglycerols; D011092:Polyethylene Glycols
keywords: Bicelle; PEG effect; SANS; Salt effect; Structural transition; Thermodynamic stability; Unilamellar vesicle (ULV)