title: Phosphatidylcholine "wobble" in vesicles assessed by high-resolution 13C field cycling NMR spectroscopy.
abstract: High resolution (13)C NMR field cycling (covering 11.7 down to 0.002 T) relaxation studies of the sn-2 carbonyl of phosphatidylcholines in vesicles provide a detailed look at the dynamics of this position of the phospholipid in vesicles. The spin-lattice relaxation rate, R(1), observed down to 0.05 T is the result of dipolar and CSA relaxation components characterized by a single correlation time tau(c), with a small contribution from a faster motion contributing to CSA relaxation. At lower fields, R(1) increases further with a correlation time consistent with vesicle tumbling. The tau(c) is particularly interesting since it is 2-3 times slower than what is observed for (31)P of the same phospholipid. However, cholesterol increases the tau(c) for both (31)P and (13)C sites to the same value, approximately 25 ns. These observations suggest faster local motion dominates the dipolar relaxation of the (31)P, while a slower rotation or wobble dominates the relaxation of the carbonyl carbon by the alpha-CH(2) group. The faster motion must be damped with the sterol present. As a general methodology, high resolution (13)C field cycling may be useful for quantifying dynamics in other complex systems as long as a (13)C label (without attached protons) can be introduced.
authors.affiliation: Department of Chemistry and Biochemistry and the Rosenstiel Basic Medical Sciences Research Institute, Brandeis University, Waltham, Massachusetts 02454, USA.
authors.forename: V N
authors.initials: VN
authors.lastname: Sivanandam
authors.forename: Jingfei
authors.initials: J
authors.lastname: Cai
authors.forename: Alfred G
authors.initials: AG
authors.lastname: Redfield
authors.forename: Mary F
authors.initials: MF
authors.lastname: Roberts
mesh_terms: D008051:Lipid Bilayers; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D010713:Phosphatidylcholines / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D008051:Lipid Bilayers; D010713:Phosphatidylcholines