Biphenyl bicelle disks align perpendicular to magnetic fields on large temperature scales: a study combining synthesis, solid-state NMR, TEM, and SAXS

Biophys J. 2007 Jun 1;92(11):3949-59. doi: 10.1529/biophysj.106.097758. Epub 2007 Feb 16.

Abstract

A phosphatidylcholine lipid (PC) containing a biphenyl group in one of its acyl chains (1-tetradecanoyl-2-(4-(4-biphenyl)butanoyl)-sn-glycero-3-PC, TBBPC) was successfully synthesized with high yield. Water mixtures of TBBPC with a short-chain C(6) lipid, dicaproyl-PC (DCPC), lead to bicelle systems formation. Freeze-fracture electron microscopy evidenced the presence of flat bilayered disks of 800 A diameter for adequate composition, hydration, and temperature conditions. Because of the presence of the biphenyl group, which confers to the molecule a positive magnetic anisotropy Delta chi, the disks align with their normal, n, parallel to the magnetic field B(0), as directly detected by (31)P, (14)N, (2)H solid-state NMR and also using small-angle x-ray scattering after annealing in the field. Temperature-composition and temperature-hydration diagrams were established. Domains where disks of TBBPC/DCPC align with their normal parallel to the field were compared to chain-saturated lipid bicelles made of DMPC(dimyristoylPC)/DCPC, which orient with their normal perpendicular to B(0). TBBPC/DCPC bicelles exist on a narrow range of long- versus short-chain lipid ratios (3%) but over a large temperature span around room temperature (10-75 degrees C), whereas DMPC/DCPC bicelles exhibit the reverse situation, i.e., large compositional range (22%) and narrow temperature span (25-45 degrees C). The two types of bicelles present orienting properties up to 95% dilution but with the peculiarity that water trapped in biphenyl bicelles exhibits ordering properties twice as large as those observed in the saturated-chains analog, which offers very interesting properties for structural studies on hydrophilic or hydrophobic embedded biomolecules.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Biphenyl Compounds / chemical synthesis
  • Biphenyl Compounds / chemistry*
  • Magnetic Resonance Spectroscopy*
  • Magnetics*
  • Microscopy, Electron, Transmission*
  • Phosphatidylcholines / chemical synthesis
  • Phosphatidylcholines / chemistry*
  • Scattering, Small Angle*
  • Temperature*
  • X-Ray Diffraction*

Substances

  • Biphenyl Compounds
  • Phosphatidylcholines