Theory of Nuclear Overhauser Enhancement and C13–1H Dipolar Relaxation in Proton-Decoupled Carbon-13 NMR Spectra of Macromolecules

作者：David M. Doddrell, Victor Glushko, Adam Allerhand · 发表于：The Journal of Chemical Physics · 年份：1972 · DOI：10.1063/1.1677747 · 被引用次数：451 · 研究领域：Advanced NMR Techniques and Applications、Electron Spin Resonance Studies、NMR spectroscopy and applications

Expressions are presented for the nuclear Overhauser enhancement (NOE), the spin-lattice relaxation time (T1), and the spin-spin relaxation time (T2) of a 13C nucleus relaxing by a dipolar interaction with one proton under conditions of complete proton decoupling, and without assuming that the extreme narrowing limit applies. Specific equations are derived for a C–H group in a rigid molecule rotating isotropically and also for a C–H group with one degree of internal motion attached to a molecule undergoing isotropic rotational reorientation. Numerical results are presented for T1, T2, and the NOE of a C–H group in a rigid molecule (undergoing purely dipolar relaxation) as a function of the rotational correlation time (τR) and the resonance frequency (ωC). T1 goes through a minimum when τRωC ≈ 0.8. The NOE varies from the expected value of 2.988 in the extreme narrowing limit to 1.153 when 1/τR is much smaller than the resonance frequency. The numerical results indicate that the signal-to-noise ratio in proton-decoupled 13C Fourier transform spectra of macromolecules in solution may not improve significantly by going to very high magnetic field strengths (such as 51.7 kG), because the increase in basic sensitivity can be offset by a decrease in the NOE and the T2/T1 ratio. The magnitude of the latter two parameters is strongly dependent on τR and the magnetic field strength. Numerical results are also presented for a C–H group with one degree of internal motion. 1/T2 is a mono...