Intermediate motions as studied by solid-state separated local field NMR experiments

Abstract

Second-order dipolar order in magic-angle spinning nuclear magnetic resonance J. Chem. Phys. 135, 154507 (2011) Single crystal nuclear magnetic resonance in spinning powders J. Chem. Phys. 135, 144201 (2011) Resistive detection of optically pumped nuclear polarization with spin phase transition peak at Landau level filling factor 2/3 Appl. Phys. Lett. 99, 112106 (2011) High-resolution 13C nuclear magnetic resonance evidence of phase transition of Rb,Cs-intercalated singlewalled nanotubes J. Appl. Phys. 110, 054306 (2011) Introduction of the Floquet-Magnus expansion in solid-state nuclear magnetic resonance spectroscopy J. Chem. Phys. 135, 044109 (2011) Additional information on J. Chem. Phys. In this report, the application of a class of separated local field NMR experiments named dipolar chemical shift correlation ͑DIPSHIFT͒ for probing motions in the intermediate regime is discussed. Simple analytical procedures based on the Anderson-Weiss ͑AW͒ approximation are presented. In order to establish limits of validity of the AW based formulas, a comparison with spin dynamics simulations based on the solution of the stochastic Liouville-von-Neumann equation is presented. It is shown that at short evolution times ͑less than 30% of the rotor period͒, the AW based formulas are suitable for fitting the DIPSHIFT curves and extracting kinetic parameters even in the case of jumplike motions. However, full spin dynamics simulations provide a more reliable treatment and extend the frequency range of the molecular motions accessible by DIPSHIFT experiments. As an experimental test, molecular jumps of imidazol methyl sulfonate and trimethylsulfoxonium iodide, as well as the side-chain motions in the photoluminescent polymer poly͓2-methoxy-5-͑2Ј-ethylhexyloxy͒-1,4-phenylenevinylene͔, were characterized. Possible extensions are also discussed.

Oligomerization state and supramolecular structure of the HIV‐1 Vpu protein transmembrane segment in phospholipid bilayers

“…Attempts to obtain equivalent information from a series of 1D 13 C spectra did not succeed because of spectral overlap with strong naturalabundance 13 C NMR signals from phospholipids. DIPSHIFT experiments at lower sample temperatures (20-40 C range) did not produce data consistent with the rapid uniaxial rotation of Vpu oligomers required for proper analysis of the data (i.e., the data showed monotonic signal decays indicative of slower motion, as discussed by Deazevedo et al 56 ). We attribute the temperature dependence of DIPSHIFT data to temperature-dependent rotational diffusion rates, primarily due to the lower membrane viscosity at higher temperatures 56 .…”

“…DIPSHIFT experiments at lower sample temperatures (20-40 C range) did not produce data consistent with the rapid uniaxial rotation of Vpu oligomers required for proper analysis of the data (i.e., the data showed monotonic signal decays indicative of slower motion, as discussed by Deazevedo et al 56 ). We attribute the temperature dependence of DIPSHIFT data to temperature-dependent rotational diffusion rates, primarily due to the lower membrane viscosity at higher temperatures 56 . 2D NMR spectra were processed and crosspeak volumes were extracted with NMRPipe software.…”

“…DIPSHIFT experiments were performed at 50 C. rapid rotational diffusion, in which limit the signals at s LG ¼ 0 and s LG ¼ 2s R are equal. Experimental data in Figure 10 were corrected for an overall decay of 20-30%, attributable to deviation from the veryrapid-motion limit as previously described in detail, 56 by multiplication with an increasing exponential function. For comparison, uncorrected data are shown in Figure S10 of the Supporting Information.…”

“…1 H-13 C dipolar-shift correlation (DIPSHIFT) measurements 53,56,68 were performed in a quasithree-dimensional manner with the rf pulse sequence in Supporting Information Figure S1c, using a Varian InfinityPlus spectrometer and Varian 5.0 mm MAS NMR probe operating at 150.7 MHz 13 C NMR frequency (14.1 T magnetic field). Sample volumes were 160 lL and contained $20 mg of Vpu , with the larger volume and higher field being required for adequate signal-to-noise.…”

Molecular relaxations in polyfluorene based cast films

“…Motions with rates between 10 3 and 10 7 Hz average the 13 C-1 H coupling, changing the shape of the DIPSHIFT curves and making possible to distinguish rigid from mobile groups [10]. Although, motions with rates of about 1 kHz can be already detected by DIPSHIFT, the analysis of DIPSHIFT curves when motions with rates between 10 3 and 10 6 Hz (intermediate regime) take place involves more elaborated approaches [11], which includes dynamic spins dynamics simulations to describe the motion effect in the quantum evolution of the 13 C nuclear spins under homonuclear decoupling of the 1 H nuclei [12]. In contrast, for motions in the so called fast limit (motional rates higher than 10 6 Hz) the analysis is much simpler since the DIPSHIFT curves become dependent of only geometrical aspects of the motion, for example, reorientation angles or if the motion is isotropic or anisotropic [10].…”