Handling the influence of chemical shift in amplitude-modulated heteronuclear dipolar recoupling solid-state NMR.
J Chem Phys
; 145(9): 094202, 2016 Sep 07.
Article
em En
| MEDLINE
| ID: mdl-27608995
ABSTRACT
We present a theoretical analysis of the influence of chemical shifts on amplitude-modulated heteronuclear dipolar recoupling experiments in solid-state NMR spectroscopy. The method is demonstrated using the Rotor Echo Short Pulse IRrAdiaTION mediated Cross-Polarization ((RESPIRATION)CP) experiment as an example. By going into the pulse sequence rf interaction frame and employing a quintuple-mode operator-based Floquet approach, we describe how chemical shift offset and anisotropic chemical shift affect the efficiency of heteronuclear polarization transfer. In this description, it becomes transparent that the main attribute leading to non-ideal performance is a fictitious field along the rf field axis, which is generated from second-order cross terms arising mainly between chemical shift tensors and themselves. This insight is useful for the development of improved recoupling experiments. We discuss the validity of this approach and present quaternion calculations to determine the effective resonance conditions in a combined rf field and chemical shift offset interaction frame transformation. Based on this, we derive a broad-banded version of the (RESPIRATION)CP experiment. The new sequence is experimentally verified using SNNFGAILSS amyloid fibrils where simultaneous (15)N â (13)CO and (15)N â (13)Cα coherence transfer is demonstrated on high-field NMR instrumentation, requiring great offset stability.
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1
Base de dados:
MEDLINE
Assunto principal:
Espectroscopia de Ressonância Magnética
/
Modelos Químicos
Idioma:
En
Revista:
J Chem Phys
Ano de publicação:
2016
Tipo de documento:
Article
País de afiliação:
Dinamarca