The refocused INADEQUATE MAS NMR experiment in multiple spin-systems: Interpreting observed correlation peaks and optimising lineshapes

• DOI: 10.1016/j.jmr.2007.05.016
• Publication Date: 2007-06-07T15:36:50Z
• Authors: Sylvian Cadars; Julien Sein; Luminita Duma; Anne Lesage; Tran N. Pham; Jay H. Baltisberger; Steven P. Brown; Lyndon Emsley
• Keywords: multispin systems; zero-quantum coherences; [CHIM.ORGA]Chemical Sciences/Organic chemistry; through-bond spectroscopy; 02 engineering and technology; INADEQUATE; solid-state; z-filter; magic angle spinning; solid-state NMR; scalar coupling; 0210 nano-technology

The robustness of the refocused INADEQUATE MAS NMR pulse sequence for probing through-bond connectivities has been demonstrated in a large range of solid-state applications. This pulse sequence nevertheless suffers from artifacts when applied to multispin systems, e.g. uniformly labeled (13)C solids, which distort the lineshapes and can potentially result in misleading correlation peaks. In this paper, we present a detailed account that combines product-operator analysis, numerical simulations and experiments of the behavior of a three-spin system during the refocused INADEQUATE pulse sequence. The origin of undesired anti-phase contributions to the spectral lineshapes are described, and we show that they do not interfere with the observation of long-range correlations (e.g. two-bond (13)C-(13)C correlations). The suppression of undesired contributions to the refocused INADEQUATE spectra is shown to require the removal of zero-quantum coherences within a z-filter. A method is proposed to eliminate zero-quantum coherences through dephasing by heteronuclear dipolar couplings, which leads to pure in-phase spectra.