ABSTRACT
Magnetic-resonance force microscopy is combined with cross-polarization and spin-decoupling NMR techniques to obtain double-resonance NMR signals of micrometer-scaled objects. The effective one-dimensional spatial resolution obtained in our experiments performed on a KPF6 single crystal sample is approximately 0.5 microm. The spectral linewidth of 900 Hz is sample limited. The described double-resonance techniques can introduce new chemical specificity to the magnetic-force sensor.
ABSTRACT
Model-membrane systems composed of liquid-crystalline bicellar phases can be uniaxially oriented with respect to a magnetic field, thereby facilitating structural and dynamics studies of membrane-associated proteins. Here we quantitatively characterize a method that allows the manipulation of the direction of this uniaxial orientation. Bicelles formed from DMPC/DHPC are examined by (31)P NMR under variable-angle sample-spinning (VAS) conditions, confirming that the orientation of the liquid-crystalline director can be influenced by sample spinning. The director is perpendicular to the rotation axis when Theta (the angle between the sample-spinning axis and the magnetic field direction) is smaller than the magic angle, and is parallel to the rotation axis when Theta is larger than the magic angle. The new (31)P NMR VAS data presented are considerably more sensitive to the orientation of the bicelle than earlier (2)H studies and the analysis of the sideband pattern allows the determination of the orientation of the liquid-crystal director and its variation over the sample, i.e., the mosaic spread. Under VAS, the mosaic spread is small if Theta deviates significantly from the magic angle but becomes very large at the magic angle.
