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New DEFT sequences for the acquisition of one‐dimensional carbon NMR spectra of small unlabelled molecules
Author(s) -
Piotto Martial,
Bourdonneau Maryse,
Elbayed Karim,
Wieruszeski JeanMichel,
Lippens Guy
Publication year - 2006
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.1884
Subject(s) - pulse sequence , chemistry , heteronuclear molecule , spectral line , adiabatic process , fourier transform , nuclear magnetic resonance , relaxation (psychology) , sequence (biology) , analytical chemistry (journal) , molecular physics , nuclear magnetic resonance spectroscopy , physics , stereochemistry , thermodynamics , quantum mechanics , psychology , social psychology , biochemistry , chromatography
The acquisition time and quality of 1D 13 C{ 1 H} spectra can be improved substantially by using a modified driven equilibrium Fourier transform (DEFT) sequence, which is specifically designed to compensate for the effects of B 1 inhomogeneity, pulse miscalibration and frequency offsets. The new sequence, called uniform driven equilibrium Fourier transform (UDEFT), returns the carbon magnetization with a high accuracy along its equilibrium position after each transient is complete. Thus, the sequence allows the use of relaxation delays (RD), which are much shorter than the carbon T1 of the molecule, thereby speeding up the acquisition process of 1D 13 C{ 1 H} spectra. To achieve this level of performance, UDEFT employs a refocusing element constituted by a composite adiabatic carbon pulse surrounded by two 90° carbon pulses whose phases are designed to compensate for 90° pulse miscalibrations in an MLEV manner (90° + x − τ(FID)− 180 + y (Adia)− τ− 90° + x − 180° + x (Adia)). A version of the UDEFT sequence allows recording 1D 13 C{ 1 H} spectra devoid of heteronuclear NOE by using a matched adiabatic 1 H decoupling scheme where an even number of 180° adiabatic pulses is applied during the UDEFT module. Spectra of a solution of 300 m M camphor that contains some carbon nuclei with very long T1 relaxation times (90 s and 78 s) were acquired with 128 scans in 10 min using a 5 s relaxation delay. Copyright © 2006 John Wiley & Sons, Ltd.