High-speed magic-angle spinning 13C MAS NMR spectra of adamantane:: Self-decoupling of the heteronuclear scalar interaction and proton spin diffusion

被引:46
作者
Ernst, M [1 ]
Verhoeven, A [1 ]
Meier, BH [1 ]
机构
[1] Univ Nijmegen, NSR Ctr Mol Struct Design & Synth, Phys Chem Lab, NL-6525 ED Nijmegen, Netherlands
关键词
solid-state NMR; spin-diffusion; MAS; self-decoupling;
D O I
10.1006/jmre.1997.1311
中图分类号
Q5 [生物化学];
学科分类号
071010 ; 081704 ;
摘要
We have investigated the carbon line shape of solid adamantane under high-speed magic-angle sample spinning (MAS) acquired without proton decoupling, The CH-group shows a spinning-speed-dependent line broadening while the CH2-group consists of a spinning-speed-independent sharp component and a spinning-speed-dependent broader part, These phenomena can be explained by self-decoupling of the J-interaction due to proton spin diffusion. Such a self-decoupling process can be described by a magnetization exchange process between the multiplet lines, Changing the spin-diffusion rate constant by off-resonance irradiation of the protons allows us to observe the full range from slow exchange to coalescence to fast exchange of the carbon spectra, One of the multiplet components in the CH2-group corresponds to a group spin of the protons of zero and therefore does not couple to the other protons, This gives rise to the sharp central line. The magnetization exchange rate constant between the different multiplet lines can be determined from the spectra and is a measure for the spinning-speed-dependent proton spin-diffusion rate constant, Even at an MAS speed of 30 kHz, proton spin diffusion is still observable despite the relatively weak intermolecular proton dipolar-coupling network in adamantane which results in a static proton line width of only 14 kHz (full width at half height). (C) 1998 Academic Press.
引用
收藏
页码:176 / 185
页数:10
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