Deuterium REDOR: Principles and Applications for Distance Measurements

✍ Scribed by I. Sack; A. Goldbourt; S. Vega; G. Buntkowsky

• Publisher: Elsevier Science
• Year: 1999
• Tongue: English
• Weight: 161 KB
• Volume: 138
• Category: Article
• ISSN: 1090-7807
• DOI: 10.1006/jmre.1999.1710

✦ Synopsis

The application of short composite pulse schemes (90°x-90°y-90°x and 90°x-180°y-90°x) to the rotational echo double-resonance (REDOR) spectroscopy of X-2 H (X: spin 1 2 , observed) systems with large deuterium quadrupolar interactions has been studied experimentally and theoretically and compared with simple 180°pulse schemes. The basic properties of the composite pulses on the deuterium nuclei have been elucidated, using average Hamiltonian theory, and exact simulations of the experiments have been achieved by stepwise integration of the equation of motion of the density matrix. REDOR experiments were performed on 15 N-2 H in doubly labeled acetanilide and on 13 C-2 H in singly 2 H-labeled acetanilide. The most efficient REDOR dephasing was observed when 90°x-180°y-90°x composite pulses were used. It is found that the dephasing due to simple 180°deuterium pulses is about a factor of 2 less efficient than the dephasing due to the composite pulse sequences and thus the range of couplings observable by X-2 H REDOR is enlarged toward weaker couplings, i.e., larger distances. From these experiments the 2 H-15 N dipolar coupling between the amino deuteron and the amino nitrogen and the 2 H-13 C dipolar couplings between the amino deuteron and the ␣ and ␤ carbons have been elucidated and the corresponding distances have been determined. The distance data from REDOR are in good agreement with data from X-ray and neutron diffraction, showing the power of the method.