Cholesterol increases the magnetic aligning of bicellar disks from an aqueous mixture of DMPC and DMPE-DTPA with complexed thulium ions.
Aqueous mixtures of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine-diethylenetriamine pentaacetate (DMPE-DTPA) with complexed thulium ions (Tm(3+)), and cholesterol with varying molar ratio were studied at different temperatures in the presence and absence of a magnetic field. For mixtures without cholesterol weakly magnetically alignable small disks, so-called bicelles, are formed at temperatures below the phase transition temperature (5-22 °C), as shown by cryo-transmission electron microscopy (cryo-TEM) and small-angle neutron scattering (SANS). In presence of 16 mol % cholesterol the disk size and the magnetic alignability were larger within the entire temperature range studied (5-40 °C). Cholesterol acts as a spacer between DMPE-DTPA with complexed Tm(3+), allowing these molecules to integrate more frequently into the planar part of the bicelles. Replacing DMPC partially by cholesterol thus lead to an increase in magnetic aligning by a higher amount of the magnetic handles (Tm(3+) complexed to DMPE-DTPA) in the plane and by an increased number of phospholipids in the enlarged bicelles. The magnetic aligning was most pronounced at 5 °C. The temperature-dependent structural changes of the DMPC/cholesterol/DMPE-DTPA/Tm(3+) aqueous mixtures are complex, including the transient appearance of holes in the disks at intermediate temperatures.
Laboratory of Food Process Engineering, ETH Zurich, Schmelzbergstrasse 9, 8092 Zurich, Switzerland.
Marianne
M
Liebi
Joachim
J
Kohlbrecher
Takashi
T
Ishikawa
Peter
P
Fischer
Peter
P
Walde
Erich J
EJ
Windhab
D002784:Cholesterol / Q000737:chemistry*; D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry*; D007477:Ions / Q000737:chemistry; D060526:Magnetic Fields; D008958:Models, Molecular; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D010316:Particle Size; D004369:Pentetic Acid / Q000737:chemistry*; D013499:Surface Properties; D013696:Temperature; D013932:Thulium / Q000737:chemistry*; D014867:Water / Q000737:chemistry
D007477:Ions; D009942:Organometallic Compounds; D014867:Water; D004369:Pentetic Acid; D013932:Thulium; D002784:Cholesterol; D004134:Dimyristoylphosphatidylcholine