title: Novel type of bicellar disks from a mixture of DMPC and DMPE-DTPA with complexed lanthanides.
abstract: We report on the formation of bicelles from a mixture of dimyristoylphosphatidylcholine (DMPC) and the chelator-lipid dimyristoylphosphatidylethanolamine-diethylenetriaminepentaacetate (DMPE-DTPA) with complexed lanthanides, either thulium (Tm(3+)) or lanthanum (La(3+)). The two phospholipids used have the same acyl-chain length but differ in headgroup size and chemical structure. The total lipid concentration was 15 mM, and the molar ratio of DMPC to DMPE-DTPA was 4:1. The system was studied with small angle neutron scattering (SANS) in a magnetic field, cryo-transmission electron microscopy (cryo-TEM), and (31)P NMR spectroscopy. We found that, after appropriate preparation steps, that is, extrusion through a polycarbonate membrane followed by a cooling step, monodisperse small unilamellar disks (flat cylinders called bicelles) are formed. They have a radius of 20 nm and a bilayer thickness of about 4 nm and are stable in the investigated temperature range of 2.5-30 degrees C. Fitting of SANS data with a form factor for partly aligned flat cylinders shows that the bicelles are slightly orientable in a magnetic field of 8 T if DMPE-DTPA is complexed with Tm(3+).
authors.affiliation: Laboratory of Food Process Engineering, ETH Zurich, Schmelzbergstrasse 9, 8092 Zurich, Switzerland.
authors.forename: Paul
authors.initials: P
authors.lastname: Beck
authors.forename: Marianne
authors.initials: M
authors.lastname: Liebi
authors.forename: Joachim
authors.initials: J
authors.lastname: Kohlbrecher
authors.forename: Takashi
authors.initials: T
authors.lastname: Ishikawa
authors.forename: Heinz
authors.initials: H
authors.lastname: Rüegger
authors.forename: Peter
authors.initials: P
authors.lastname: Fischer
authors.forename: Peter
authors.initials: P
authors.lastname: Walde
authors.forename: Erich
authors.initials: E
authors.lastname: Windhab
mesh_terms: D020285:Cryoelectron Microscopy; D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry*; D028581:Lanthanoid Series Elements / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008823:Micelles; D046529:Microscopy, Electron, Transmission; D008962:Models, Theoretical; D004369:Pentetic Acid / Q000737:chemistry*; D010714:Phosphatidylethanolamines / Q000737:chemistry*
chemical_list: D028581:Lanthanoid Series Elements; D008823:Micelles; D010714:Phosphatidylethanolamines; D004369:Pentetic Acid; D004134:Dimyristoylphosphatidylcholine; C018525:1,2-dimyristoylphosphatidylethanolamine