Orientation dependence of 2H nuclear magnetic resonance spin-lattice relaxation in phospholipid and phospholipid:cholesterol systems

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Abstract
Structural and dynamic properties of phospholipids in the liquid crystalline phase were investigated using the general orientation dependence of spin‐lattice relaxation for spin‐1 nuclei, namely deuterium. Relaxation rates 1/T 1Z and 1/T 1Q for Zeeman and quadrupolar spin‐lattice relaxation, respectively, can be expressed as a sum of Legendre polynomials up to order 4 for axially symmetric motions: 1/T 1i = a 0i +a 2i P 2(cos β)+a 4i P 4(cos β), i=Z, Q, where β is the angle between the axis of symmetry of the motion (in this case the bilayer normal) and the static magnetic field. The coefficients a pi are functions of order parameters and reduced spectral densities. We explore the structural and dynamical information that can be obtained from the orientation dependence of relaxation without invoking detailed models. Some conformational models, such as the rotational isomeric model for the acyl chains, were investigated. We studied the acyl chains of 1‐palmitoyl‐2‐oleoyl‐sn‐glycero‐3‐phosphocholine, the influence of temperature and the addition of cholesterol, and two positions on the headgroup of dipalmitoyl‐sn‐glycerol‐3‐phosphocholine.