Distortionless enhancement by polarization transfer

A relatively new pulse sequence, called DEPT (Distortionless Enhancement by Polarization Transfer) (80), has been devised to overcome some difficulties of INEPT. In this pulse sequence, the pulse 6 is varied to generate a series of subspectra, which are then combined in appropriate ratios to optimize spectral editing. 

Now we are prepared to combine the APT (Section 12.10) and INEPT (Section 12.11.2) experiments into one of the most useful experiments in modem NMR. Like an APT spectrum, a DEPT (distortionless enhancement by population transfer) spectrum is designed to display separate subspectra for CH, CH2, and CH3 carbon signals. And like an INEPT spec-tmm, signal intensity (i.e., sensitivity) arises by polarization transfer. 

The bottom spectrum is the normal decoupled C spectrum consisting of 15 signals. The top three subspectra reveal, respectively, which are the CH3, CH2, and CH signals. The fourth subspectrum is the sum of the first three any signals not present in this subspectrum but present in the normal C spectrum must belong to nonprotonated carbons. 

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Techniques developed in recent years make it possible to obtain large amounts of information from l3C NMR spectra. For example, DEPT-NMR, for distortionless enhancement by polarization transfer, allows us to determine the number of hydrogens attached to each carbon in a molecule. 

Population transfer experiments may be selective or nonselective. Selective population transfer experiments have found only limited use for signal multiplicity assignments (SSrensen et al, 1974) or for determining signs of coupling constants (Chalmers et al., 1974 Pachler and Wessels, 1973), since this is better done by employing distortionless enhancement by polarization transfer (DEPT) or Correlated Spectroscopy (COSY) experiments. However, nonselective population transfer experiments, such as INEPT or DEPT (presented later) have found wide application. 

The most widely used method for determining multiplicities of carbon atoms is DEPT (Distortionless Enhancement by Polarization Transfer). This has generally replaced the classical method of recording off-resonance C spectra with reduced CH couplings from which the multiplicity could be read directly. 

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. 

Multidimensional spectraas well as techniques including DEPT (distortionless enhancement by polarization transfer), COSY (correlated spectroscopy), and ROESY (rotating-frame overhauser enhancement spectroscopy) have been increasingly used. 

You may be told that your NMR laboratory does not routinely use APT spectra but provides DEPT spectra (Distortionless Enhancement by Polarization Transfer) instead. This is no problem, as DEPT spectra also provide you with the information you need just go back and read what we have said about the relative merits of APT and DEPT. 

The first of these tools is the distortionless enhancement by polarization transfer (DEPT) pulse sequence. There are a number of versions of this experiment which can be very useful for distinguishing the different types of carbons within a molecule. Of these, we have found the DEPT 135 sequence to be the most useful. In this experiment, the quaternary carbons are edited out of the spectrum altogether. 

DEPT Distortionless enhancement by polarization transfer. A useful one-dimensional technique which differentiates methyl and methine carbons from methylene and quaternary carbons. 

The most useful 1-D pulse sequence applied to 13C nuclei is known as distortionless enhancement by polarization transfer (DEPT). A decoupled... 

The 13C NMR spectrum of 64, an amide of 63, showed sixty-two carbon signals of which partial assignments, shown in Table 16, were made based upon distortionless enhancement by polarization transfer(DEPT), H-13C correlation experiments and literature data describing 13C NMR analysis of polyene macrolides. 

Deoxyepinephrine, chemiluminescence, 647 Deoxygenation, hydroperoxides, 153 DEPT (distortionless enhancement by polarization transfer), 725 -6 6,9-Desdimethylartemisinin, synthesis, 288 Desferrioxamine, PfATP6 enzyme inhibition, 1313... 

Distortionless enhancement by polarization transfer (DEPT), 725-6 Disubstituted alkenes, regioselectivity, 842-4 o-Ditoluidine, glucose determination, 632, 634 o,o -Dityrosine, low-density lipoprotein, 610 DMD see Dimethyldioxirane DMDO see Dimethyldioxirane DNA... 

The imaging of conversion within the fixed bed was achieved by using a distortionless enhancement by polarization transfer (DEPT) spectroscopy pulse sequence integrated into an imaging sequence, as shown in Fig. 44. In theory, a signal enhancement of up to a factor of 4 (/hZ/c 7i is the gyromagnetic ratio of nucleus i) can be achieved with DEPT. In this dual resonance experiment, initial excitation is on the H channel. Consequently, the repetition time for the DEPT experiment is constrained by Tih (< T lc) where Tn is the Ty relaxation time of... 

The distortionless enhancement by polarization transfer (DEPT) sequence 253) for the J-coupled heteronuclear spin system (J is 13C- H coupling, approximately 135 to 170 Hz) is shown in Fig. 48. The pulse sequence is based on a resolvable spin-spin coupling between two nuclei, one of them (lH) being the polarization source for the... 

Pulse sequences for non-selective polarization transfer, not only useful for signal enhancement but also for multiplicity selection, are referred to as INEPT [54], abbreviated from Insensitive Nuclei Enhanced by Polarization Transfer . An improved method denoted as Distortionless Enhancement by Polarization Transfer or DEPT" [55] permits the cleanest multiplicity selection known so far, with full enhancement and low sensitivity to individual CH coupling constants. In addition, fully enhanced and undistorted coupled spectra can be recorded. Finally, subspectra for CH, CH2 and CH3 groups can be generated. 

Furthermore, the allohimachalane (see Section 13.11.9.1) <1999T14623> as well as boletunones A and B, highly functionalized sesquiterpenes from the fruit body of the mushroom Boletus calopus <20040L823>, have been characterized by 2D-NMR (heteronuclear single quantum correlation (HSQC), HMBC, and 111-COSY). The structure of a drimen-ll,12-acetonide, isolated from Maya s herb, was deduced by means of 111 and 13C NMR, distortionless enhancement by polarization transfer (DEPT), COSY, NOESY, HSQC, and HMBC analyses <2005MRC339>. 

Olive oil samples coming from 13 PDO Italian areas of production were analyzed by 13C NMR DEPT (distortionless enhancement by polarization transfer), a particular pulse sequence used to improve the signal-to-noise ratio of13 C spectra (Vlahov et al., 2001). Olive oils were dissolved... 

Vlahov, G., Shaw, A. D., and Kell, D. B. (1999). Use of 13C nuclear magnetic resonance distortionless enhancement by polarization transfer pulse sequence and multivariate analysis to discriminate olive oil cultivars. JAOCS 76,1223-1231. 

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