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Low‐load rotor‐synchronised Hahn‐echo pulse train (RS‐HEPT) 1 H decoupling in solid‐state NMR: factors affecting MAS spin‐echo dephasing times
Author(s) -
Griffin John M.,
Tripon Carmen,
Samoson Ago,
Filip Claudiu,
Brown Steven P.
Publication year - 2007
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.2145
Subject(s) - chemistry , decoupling (probability) , spin echo , solid state nuclear magnetic resonance , dephasing , nuclear magnetic resonance , analytical chemistry (journal) , alanine , magnetic resonance imaging , condensed matter physics , physics , chromatography , medicine , biochemistry , amino acid , control engineering , engineering , radiology
Transverse dephasing times T 2 ′ in spin‐echo MAS NMR using rotor‐synchronised Hahn‐echo pulse‐train (RS‐HEPT) low‐load 1 H decoupling are evaluated. Experiments were performed at 300 and 600 MHz for 13 CH‐labelled L ‐alanine and 15 NH(δ)‐labelled L ‐histidine·HCl·H 2 O, together with SPINEVOLUTION simulations for a ten‐spin system representing the crystal structure environment of the 13 CH carbon in L ‐alanine. For 30 kHz MAS and ν 1 ( 1 H) = 100 kHz at 300 MHz, a RS‐HEPT T 2 ′ value of 17 ± 1 ms was obtained for 13 CH‐labelled L ‐alanine which is ∼50% of the XiX T 2 ′ value of 33 ± 2 ms. Optimum RS‐HEPT decoupling performance is observed for a relative phase of alternate RS‐HEPT π–pulses, Δϕ = ϕ′− ϕ, between 40 and 60° . For experiments at 600 MHz and 30 kHz MAS with 13 CH‐labelled L ‐alanine, the best RS‐HEPT (ν 1 ( 1 H) = 100 kHz) T 2 ′ value was 3 times longer than that observed for low‐power continuously applied sequences with ν 1 ( 1 H) ⩽40 kHz, i.e. corresponding to the same average power dissipated in the probe. A marked improvement in RS‐HEPT 1 H decoupling is observed for increasing MAS frequency: at 55.6 kHz MAS, a best RS‐HEPT T 2 ′ value of 34 ± 5 ms was recorded for 13 CH‐labelled L ‐alanine. Much improved RS‐HEPT broadband performance was also observed at 55.6 kHz MAS as compared to 30 kHz MAS. Copyright © 2007 John Wiley & Sons, Ltd.