Rotational-resonance distance measurements in multi-spin systems
- 作者：Verhoeven ; Aswin ; Williamson ; Philip T.F. ; Zimmermann ; Herbert ; Ernst ; Matthias ; Meier ; Beat H.
- 刊名：Journal of Magnetic Resonance
- 出版年：2004
- 期刊代码：126_10907807
- 类别：ch
- 出版时间：June, 2004
- 卷：168
- 期：2
- 页码：314-326
- 文件大小：753 K
摘要
It is demonstrated that internuclear distances can be evaluated from rotational-resonance (RR) experiments in uniformly 13C-labelled compounds. The errors in the obtained distances are less than 10%without the need to know any parameters of the spin system except the isotropic chemical shifts of all spins. We describe the multi-spin system with a simple fictitious spin-1/2 model. The influence of the couplings to the passive spins (J and dipolar coupling) is described by an empirical constant offset from the rotational-resonance condition. Using simulated data for a three-spin system, we show that the two-spin model describes the rotational-resonance transfer curves well as long as none of the passive spins is close to a rotational-resonance condition with one of the active spins. The usability of the two-spin model is demonstrated experimentally using a sample of acetylcholine perchlorate with labelling schemes of various levels of complexity. Doubly-, triply-, and fully labelled compounds lead to strongly varying RR polarization-transfer curves but the evaluated distances using the two-spin model are identical within the expected error limits and coincide with the distance from the X-ray structure. Rotational-resonance distance measurements in fully labelled compounds allow, in particular, the measurement of weak couplings in the presence of strong couplings.