Spectroscopic separation of 13C NMR spectra of complex isomeric mixtures by the CSSF‐TOCSY‐INEPT experiment |
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| Authors: | Lu Yang Aitor Moreno Wolfgang Fieber Robert Brauchli Horst Sommer |
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| Affiliation: | 1. R&D Division, Firmenich SA, Geneva 8, Switzerland;2. Bruker Biospin AG, F?llanden, Switzerland |
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| Abstract: | Isomeric mixtures from synthetic or natural origins can pose fundamental challenges for their chromatographic separation and spectroscopic identification. A novel 1D selective NMR experiment, chemical shift selective filter (CSSF)‐TOCSY‐INEPT, is presented that allows the extraction of 13C NMR subspectra of discrete isomers in complex mixtures without physical separation. This is achieved via CSS excitation of proton signals in the 1H NMR mixture spectrum, propagation of the selectivity by polarization transfer within coupled 1H spins, and subsequent relaying of the magnetization from 1H to 13C by direct INEPT transfer to generate 13C NMR subspectra. Simple consolidation of the subspectra yields 13C NMR spectra for individual isomers. Alternatively, CSSF‐INEPT with heteronuclear long‐range transfer can correlate the isolated networks of coupled spins and therefore facilitate the reconstruction of the 13C NMR spectra for isomers containing multiple spin systems. A proof‐of‐principle validation of the CSSF‐TOCSY‐INEPT experiment is demonstrated on three mixtures with different spectral and structural complexities. The results show that CSSF‐TOCSY‐INEPT is a versatile, powerful tool for deconvoluting isomeric mixtures within the NMR tube with unprecedented resolution and offers unique, unambiguous spectral information for structure elucidation. Copyright © 2014 John Wiley & Sons, Ltd. |
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| Keywords: | NMR 1H 13C chemical selective filter CSSF‐TOCSY‐INEPT analysis of complex mixtures |
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