Magnetically aligned phospholipid bilayers in weak magnetic fields: optimization, mechanism, and advantages for X-band EPR studies

Investigating magnetically aligned phospholipid bilayers with EPR spectroscopy at Q-band (35GHz): optimization and comparison with X-band (9GHz)

“…A comparison with 2 H NMR phase transition studies of a Tm 3+ -doped bicelle sample indicated that the macroscopic reorientation of the bicelle starts in the liquid crystalline nematic phase (307 K). The alignment process continued to increase upon slowly raising the temperature and was well aligned in the liquid crystalline lamellar smectic phase (318 K) in the presence of an applied magnetic field [32]. The magnetic alignment of the bicelle system was well-aligned and stabilized by the smectic phase at 318 K. However, for Qband EPR experiments, the magnetic alignment of the bicelle system was stabilized even at a nematic liquid crystalline phase, i.e., 308 K. When the sample temperature was raised further from 308 to 318 K, the measured hyperfine splitting increased from 8.6 to 9.5 G. We attribute the increase in hyperfine splitting value to an enlargement in the amplitude of the random walk motion and a decrease in the overall alignment of the oriented bicelles caused by the increase in temperature.…”

“…However, only few Q-band EPR spectroscopic studies have been reported on the orientation of phospholipid bilayers on glass plate using cholestane as a spin label [22,36]. In our laboratory, previous studies have described the effect of lanthanide ions and experimental conditions necessary to magnetically align phospholipid bilayers in a static magnetic field for X-band EPR spectroscopic experiments [27,[29][30][31][32]. In this paper, for the first time we present the advantages of using Q-band to study magnetically aligned phospholipid bilayers.…”

“…In our laboratory, previous studies have extensively described the effect of lanthanide ions and experimental conditions necessary to macroscopically align phospholipid bilayers in the magnetic field of an X-band EPR spectrometer [27,[30][31][32]. However, bicelle alignment studies using X-band EPR have certain limitations.…”

The effects of cholesterol on magnetically aligned phospholipid bilayers: a solid-state NMR and EPR spectroscopy study

“…The magnetic alignment of bicelles depends on the magnetic susceptibility anisotropy tensor (Dv) of the phospholipid bilayers. The negative sign of Dv for bicelles dictates that they align with their bilayer normal oriented perpendicular to the direction of the static magnetic field (B 0 ) [28][29][30]. The degree of ordering of bicelles depends upon several factors, including the strength of the magnetic field, the sign and magnitude of the phospholipid bilayers magnetic susceptibility anisotropy tensor, the viscosity of the sample, the types of lanthanide ions used, and the temperature [3,[31][32][33].…”

A 2H solid-state NMR spectroscopic investigation of biomimetic bicelles containing cholesterol and polyunsaturated phosphatidylcholine

“…As the temperature is raised, the bilayer undergoes two thermal phase transitions leading to the lamellae liquid-crystalline phase (L ␣ ). In the liquid-crystalline phase, the phospholipid bilayer passes through many subphases characterized by different viscosities, hydrations, ordering, and motion, which can affect the formation and orientation of magnetically aligned phospholipid bilayers (Selig, 1976;Katsaras et al, 1997;Firestone et al, 1998;Bennett and Hess, 1999;Binnemans et al, 2000;Mangels et al, 2000;Raffard et al, 2000;Tiburu et al, 2001;Cardon et al, 2003). Kinks in the acyl chains cause the bilayer structure to become less tightly packed and more fluid increasing the rate of lateral diffusion of the phospholipids by two orders of magnitude (Dowhan, 1997).…”