Nuclear Overhauser effect as a probe of molecular structure, dynamics and order of axially reorienting molecules in...

The location, orientation, order and dynamics of cholesterol in model membranes have been well characterized, therefore cholesterol is an ideal molecule for developing new methods for studying structured molecules undergoing rapid axially symmetric reorientation. The use of (13)C filtering via short contact cross polarization transfer to (1)H allows the recovery of the weak cholesterol (1)H magic angle spinning NMR signals from beneath the strong phospholipid background in bicelles composed of chain perdeuterated dimyristoyl phosphatidylcholine/dicaproyl phosphatidylcholine/[3,4-(13)C]-cholesterol. Measurements of the nuclear Overhauser enhancement for (1)H nuclei located in the first ring of cholesterol are interpreted in terms of a simple two motion model consisting of axial reorientation, with a correlation time τ∥, and a slower reorientation of the diffusion axis relative to the bilayer normal, with correlation time τ⊥. This approach can be extended to other molecules which undergo rapid axial reorientation such as small membrane associated peptides.