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Biphenyl Bicelle Disks Align Perpendicular to Magnetic Fields on Large Temperature Scales: A Study Combining Synthesis, Solid-State NMR, TEM, and SAXS

Cécile Loudet ^*, Sabine Manet ^*, Stéphane Gineste , Reïko Oda ^*, Marie-France Achard  and Erick J. Dufourc ^*

^* UMR 5248 CBMN, CNRS-Université Bordeaux 1-ENITAB, Institut Européen de Chimie et Biologie, Pessac, France; and UPR 8641, Centre de Recherche Paul Pascal, CNRS, Pessac, France

Correspondence: Address reprint requests to Erick J. Dufourc, UMR 5248 CBMN, CNRS-Université Bordeaux 1-ENITAB, IECB, 2 rue Robert Escarpit, 33607 Pessac, France. Tel./Fax: 33-5-4000-2218; E-mail: e.dufourc{at}iecb.u-bordeaux.fr.

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 C₆ lipid, dicaproyl-PC (DCPC), lead to bicelle systems formation. Freeze-fracture electron microscopy evidenced the presence of flat bilayered disks of 800 Å 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 , the disks align with their normal, n, parallel to the magnetic field B₀, as directly detected by ³¹P, ¹⁴N, ²H 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 B₀. 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°C), whereas DMPC/DCPC bicelles exhibit the reverse situation, i.e., large compositional range (22%) and narrow temperature span (25–45°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.