Spectral editing

2 Spectral Editing. - The use of NMR and inverse NMR in metabolic flux analysis has been reviewed.  

The simultaneous detection of water (as an internal standard) and brain 

Nuclear Magnetic Resonance, Volume 31 The Royal Society of Chemistry, 2002 

We saw in Section 12.1 that APT and DEPT provide straightforward methods for differentiating among CH3, CH2, CH, and quaternary carbons. This information is almost essential in interpreting the 13C spectrum, and in some instances it can best be obtained with APT or DEPT, where 13C is observed, especially when the proton spectrum is crowded. If HETCOR and/or indirect detection of 13C is needed, these one-dimensional editing techniques provide somewhat redundant information but may still be helpful. 

Recently, it has been shown that a Gaussian-shaped pulse can be used for selective excitation under the condition of MAS.34 This strategy has 

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Additionally, more sophisticated pulse sequences (the procedure is called spectral editing) enable one to obtain spectra, after addition or subtraction, where only the following are present (see, for example Bouquet, 1986) ... 

Spectral editing refers to any method which alters the appearance of the spectmm so that specific stmctural features become readily identifiable. 

A number of other, more sophisdcated, selective averaging tools (includli spin echo, double resonance and two-dimensional techniques) are available, both for spectral editing purposes and for obtaining quantitadve information about inter-... 

Figure 2.11 The behavior of CH, CH2, and CH, groups during spectral editing.

How can spectral editing in INEPT be used to generate separate spectra for CH, CH2, and CH3 groups, and how is it superior to the traditional off-resonance decoupled spectra ... 

DEPT (distortionless enhancement by polarization transfer) A onedimensional C-NMR experiment commonly used for spectral editing that allows us to distinguish between CH, CH2, CH, and quaternary carbons. Detectable magnetization The magnetization processing in the x y -plane induces a signal in the receiver coil that is detected. Only single-quantum coherence is directly detectable. 

INEPT (insensitive nuclei enhanced by polarization transfer) Polarization transfer pulse sequence used to record the NMR spectra of insensitive nuclei, e.g., C, with sensitivity enhancement may be used for spectral editing. 

Through a -based spectral editing procedure we found some pectic material spatially located near cellulose. This included some eggbox pectin. Pectic material was also located more than 2nm away from cellulose. 

Key Words NMR, Heteronuclear Long-range correlation, HMBC, CT-HMBC, ACCORD-HMBC, IMPEACH-MBC, BIRD-HMBC, G-BIRD-HMBC, CIGAR-HMBC, IMPACT-HMBC, TS-HMBC, Broadband-HMBC, H2BC, edited HMBC, 10-ppm HMBC, /CH artefacts suppression, Spectral editing... 

There are also reports of interesting / coupling effects in some magic angle spinning (MAS) spectra as well as new experiments for purposes such as spectral editing. 

In more advanced applications, the DEPT experiment can be used to separate the signals arising from carbons in CH3, CH2 and CH groups. This is termed spectral editing and can be used to produce separate i C sub-spectra of just the CH3 carbons, just the CH2 carbons or just the CH carbons. 

The INEPT (Insensitive Nuclei Enhanced by Polarization Transfer) experiment [6, 7] was the first broadband pulsed experiment for polarization transfer between heteronuclei, and has been extensively used for sensitivity enhancement and for spectral editing. For spectral editing purposes in carbon-13 NMR, more recent experiments such as DEPT, SEMUT [8] and their various enhancements [9] are usually preferable, but because of its brevity and simplicity INEPT remains the method of choice for many applications in sensitivity enhancement, and as a building block in complex pulse sequences with multiple polarization transfer steps. The potential utility of INEPT in inverse mode experiments, in which polarization is transferred from a low magnetogyric ratio nucleus to protons, was recognized quite early [10]. The principal advantage of polarization transfer over methods such as heteronuclear spin echo difference spectroscopy is the scope it offers for presaturation of the unwanted proton signals, which allows clean spec-... 

K. K. Dey, S. Prasad, J. T. Ash, M. Deschamps and P. J. Grandinetti, Spectral editing in solid-state MAS NMR of quadrupolar nuclei using selective satellite inversion. /. Magn. Reson., 2007,185,326-330. 

Tang, H. -R., Wang, Y. -L., Belton, P. S. (2000). C CPMAS studies of plant cell wall materials and model systems using proton relaxation-induced spectral editing techniques. Solid State Nucl Magn. Reson., 15,239-248. 

Both solution-state and solid-state NMR spectroscopy are important analytical tools used to study the structure and dynamics of polymers. This analysis is often limited by peak overlap, which can prevent accurate signal assignment of the dipolar and scalar couplings used to determine structure/property relationships in polymers. Consequently, spectral editing techniques and two- or more dimensional techniques were developed to minimize the effect of spectral overlap. This section highlights only a few of the possible experiments that could be performed to determine the structure of a polymer. 

The multiplication of the FID s(t) with a factor a is equivalent to a multiplication of the spectrum S(f) with the same factor. This equivalence may be exploited e.g. in spectral editing to obtain multiplicity selective C subspectra from the DEPT-45, DEPT-90 and the DEPT-135 data. The multiplication with the corresponding factors may be performed with the DEPT FIDs or the DEPT spectra. 

Adding or subtracting different FIDs is commonly used for a number of reasons. For unstable compounds, where the coaddition of blockwise acquired and separately stored ID FIDs allows the best compromise between signal-to-noise ratio and sample decomposition to be obtained and for spectral editing including ... 

Much of the power of MAS NMR has come from the ability of exploiting crosspolarization for facile signal detection and spectral editing for insensitive and rare-spin nuclei. To date, protons have almost invariably constituted the abundant-spin reservoir for cross-polarization experiments, although, most recently, 19F has found increasing use. 

Smernik, R. I, Skjemstad, J. O., and Oades, J. M. (2000). Virtual fractionation of charcoal from soil organic matter using solid state 13C NMR spectral editing. Aust. J. Soil Res. 38, 665-683. 

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