Quenching echo modulations in NMR spectroscopy. |
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Authors: | Jens Dittmer Geoffrey Bodenhausen |
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Institution: | Center for Insoluble Protein Structure (inSPIN) and Interdisciplinary Nanoscience Center (iNANO), Department of Chemistry, University of Arhus, Langelandsgade 140, 8000 Arhus C, Denmark. dittmer@chem.au.uk |
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Abstract: | In NMR spectroscopy, homonuclear scalar couplings normally lead to modulations of spin echoes that tend to interfere with the accurate determination of transverse relaxation rates by Carr-Purcell-Meiboom-Gill (CPMG) multiple refocusing experiments. Surprisingly, the echo modulations are largely cancelled when the refocusing pulses applied to the coupling partner deviate slightly from ideal pi rotations due to tilted effective radio-frequency (RF) fields, even at offsets that are much smaller than the radio-frequency amplitude. Experiments and simulations illustrate these effects for two-spin IS systems containing donor and acceptor (15)N nuclei I=N (D) and S=N(A) in RNA Watson-Crick base pairs with homonuclear scalar couplings J(IS)=(2h)J(N(D), N(A)) across the hydrogen bonds. |
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Keywords: | homonuclear scalar couplings nitrogen NMR spectroscopy RNA spin echoes |
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