Avoiding Bias Effects in NMR Experiments for Heteronuclear Dipole–Dipole Coupling Determinations: Principles and Application to Organic Semiconductor Materials

Abstract

Carbon-proton dipole-dipole couplings between bonded atoms represent a popular probe of molecular dynamics in soft materials or biomolecules. Their site-resolved determination, for example, by using the popular DIPSHIFT experiment, can be challenged by spectral overlap with nonbonded carbon atoms. The problem can be solved by using very short cross-polarization (CP) contact times, however, the measured modulation curves then deviate strongly from the theoretically predicted shape, which is caused by the dependence of the CP efficiency on the orientation of the CH vector, leading to an anisotropic magnetization distribution even for isotropic samples. Herein, we present a detailed demonstration and explanation of this problem, as well as providing a solution. We combine DIPSHIFT experiments with the rotor-directed exchange of orientations (RODEO) method, and modifications of it, to redistribute the magnetization and obtain undistorted modulation curves. Our strategy is general in that it can also be applied to other types of experiments for heteronuclear dipole-dipole coupling determinations that rely on dipolar polarization transfer. It is demonstrated with perylene-bisimide-based organic semiconductor materials, as an example, in which measurements of dynamic order parameters reveal correlations of the molecular dynamics with the phase structure and functional properties.

Overcoming Prohibitively Large Radiofrequency Demands for the Measurement of Internuclear Distances with Solid-State NMR under Fast Magic-Angle Spinning

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Integration of Cell-Free Expression and Solid-State NMR to Investigate the Dynamic Properties of Different Sites of the Growth Hormone Secretagogue Receptor

“…Either direct excitation or cross polarization (CP) with contact times of 20, 700, or 2000 µs was used for the excitation of the 13 C nuclei. For the short contact time of 20 µs, the RODEO DIPSHIFT pulse sequence was used to minimize the distortions in the dephasing curves ( Kurz et al, 2013 ). For heteronuclear decoupling, the spinal sequence ( Paëpe et al, 2003 ) with an rf field strength of 65 kHz was used.…”

Expression, Functional Characterization, and Solid-State NMR Investigation of the G Protein-Coupled GHS Receptor in Bilayer Membranes

“…Excitation of 13 C nuclei was either accomplished by direct excitation or applying CP with contact times ranging from 20 μs to 2 ms. While using a short contact time of 20 μs the RODEO DipShift experiment64 was used to avoid distortion effects in the dephasing curves. Dephasing signals were acquired over one rotor period for all resolved isotropic chemical shift signals.…”