Spectral editing techniques

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. 

T vo approaches can be adopted for dealing with the overlap problem. Firstly, simple sample preparation such as centrifugal ultrafiltration can be used to remove the macromolecules. This results in a spectrum of all the nonprotein-bound metabolites contributing to the spectrum. Alternatively, to avoid s unple manipulation, a spectral editing technique can be applied. It has... 

HR-MAS NMR analysis of products attached to solid-phase resin beads is advantageous for several reasons. It is nondestructive, requires minimal sample preparation, and permits rapid analysis of small quantities (e.g., 1.6 nmol in 20 minutes) Special NMR hardware is required for the analysis, but the experimental setup is equivalent to a traditional liquids analysis. The polymer portion of the resin contributes a broad spectral background that can be minimized by detecting rather than For maximal sensitivity this requires a probe optimized for detection and labeled compounds. A more practical approach is to suppress the poljmier background with spectral editing techniques. 

Another method, based on relaxation phenomena, capable to probe internal molecular motion is dipolar-dephasing (DD) experiment [102], The main advantage of this method is that it rehes on very simple experimental setup and minimum hardware requirements. Moreover, this experiment is employed in high-resolution mode (i.e. under MAS and proton decoupling), with good sensitivity and selectivity essential for dynamic characterization. Furthermore, this method can be used as a spectral editing technique, too. In the simplest approach (Fig. 2.15) after CP, the decoupler is... 

For Zn, the heteronuclear dipole—dipole interaction is important for the sensitivity-enhancement/spectral editing techniques such as cross polarization (CP) and the methods designed for measuring the intemuclear distance involving zinc (see discussions later). 

Use one-dimensional spectral editing techniques such as selective spin decoupling experiments for the determination of the proton bonding of the carbons in the polymer molecule before and after photodegradation. In some cases, it is recommended to employ two-dimensional (2-D) NMR techniques [200,325,630,2222]. 

The other commonly seen spectral editing techniques used in carbon NMR involve the transfer of polarization from protons to carbons in particular ways. A good example of this type of experiment is the so-called DEPT (distortionless enhancement by polarization transfer) sequence (Figure 5). By careful choice of experimental parameters, one can obtain spectra that represent only the quaternary, only the methines, only the methylenes and only the methyl groups in the sample. This is done in this case by use of the sequence shown in Figure 5. Four spectra are obtained with <5 =7t/4, jtH, and 3 7r/4 in the sequence... 

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