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/T1Z and 1/T1Q 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/T1i= a0i+a2iP2(cos β)+a4iP4(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 api 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.
Techniques such as NMR, ESR, fluorescence depolarization, and neutron scattering are commonly used to investigate the physical properties of membranes. Oriented membrane bilayer systems (single crystals) are often employed in these investigations. It is important to know and be able to control the level of hydration in these samples. In particular, one must have confidence that a sample is in fact "fully hydrated" and remains so during the course of the experiment. Full hydration is difficult to obtain by hydrating oriented samples using water-saturated vapor. An alternative method for hydrating oriented samples is to surround the oriented sample by a polymer solution. Higher hydration levels are achieved using this method. Three nuclear magnetic resonance studies using headgroup deuterated 1,2-dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC) were done to compare the hydration level of oriented headgroup samples surrounded by a polymer/water solution and fully hydrated multibilayer dispersions. Transition temperatures, quadrupolar splittings (at 50 degrees C) and spin-lattice relaxation times (at 50 degrees C) were measured. The simple tests of the transition temperature and quadrupolar splitting to determine full hydration, as my results show, are not sufficient. In this paper I demonstrate that more fully hydrated samples can easily be achieved by surrounding the oriented sample with a 5 wt% polyethylene glycol/water solution than by hydrating in water saturated vapor.
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