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Transient NOE driven signal enhancement of INADEQUATE solid-state NMR spectroscopy for the structural analysis of
Zhiwei Yan1, Yue-Qi Ye2,3, Rongchun Zhang1,4
1South China Advanced Institute for Soft Matter Science and Technology (AISMST), School of Emergent Soft Matter (SESM), South China University of Technology, Guangzhou, 510640, China.
Abstract:
INADEQUATE (Incredible Natural Abundance DoublE QUAntum Transfer Experiment) is one of the most important techniques in revealing the carbon skeleton of organic solids in solid-state NMR spectroscopy. Nevertheless, its use for structural analysis is quite limited due to the low natural abundance of 13C-13C connectivity (∼0.01%) and thus low sensitivity. Particularly, in semi-solids like rubbers, the sensitivity will be further significantly reduced by the inefficient cross polarization from 1H to 13C due to molecular motions induced averaging of 1H-13C dipolar couplings. Herein, in this study, we demonstrate that transient nuclear Overhauser effect (NOE) can be used to efficiently enhance 13C signals, and thus enable rapid acquisition of two-dimensional (2D) 13C INADEQUATE spectra of rubbers. Using chlorobutyl rubber as the model system, it is found that an overall signal-to-noise ratio (SNR) enhancement about 22% can be achieved, leading to significant time-saving by about 33% as compared to the direct polarization-based INADEQUATE experiment. Further experimental results on natural rubber and ethylene propylene diene monomer (EPDM) rubber are also shown to demonstrate the robust performance of transient NOE enhanced INADEQUATE experiment.
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