Separation and characterization of different signals from intermolecular three-spin orders in solution NMR.
In this paper, signals originating from a pure specific coherence of intermolecular three-spin orders were separated and characterized experimentally in highly polarized two-component spin systems. A modified CRAZED sequence with selective radio-frequency excitation was designed to separate the small signals from the strong conventional single-spin single-quantum signals. General theoretical expressions of the pulse sequence with arbitrary flip angle pulses were derived using dipolar field treatment. The expressions were used to predict the relaxation and diffusion properties and optimal experimental parameters such as flip angles. For the first time, relaxation and diffusion properties of pure intermolecular single-quantum, double-quantum, and triple-quantum coherences of three-spin orders were characterized and analyzed in one-dimensional experiments. All experimental observations are in excellent agreement with the theoretical predictions. The theoretical results show that the quantum-mechanical treatment leads to exactly the same predictions as the dipolar field treatment. The quantitative study of intermolecular multiple-quantum coherences of three-spin orders presented herein provides a better understanding of their mechanisms.
Chen
Zhong
Z
Departments of Physics and Chemistry, Xiamen University, and State Key Laboratory of Physical Chemistry of Solid Surface, Xiamen, Fujian 361005, PR China. Chenz@jingxian.xmu.edu.cn
Chen
Zhi-Wei
ZW
Hwang
Dennis W
DW
Zhong
Jianhui
J
Hwang
Lian-Pin
LP