DEPT experiments distortionless enhanced polarization

Of the multitude of ID 13C NMR experiments that can be performed, the two most common experiments are a simple broadband proton-decoupled 13C reference spectrum, and a distortionless enhancement polarization transfer (DEPT) sequence of experiments [29]. The latter, through addition and subtraction of data subsets, allows the presentation of the data as a series of edited experiments containing only methine, methylene and methyl resonances as separate subspectra. Quaternary carbons are excluded in the DEPT experiment and can only be observed in the 13C reference spectrum or by using another editing sequence such as APT [30]. The individual DEPT subspectra for CH, CH2 and CH3 resonances of santonin (4) are presented in Fig. 10.9. 

The carbon and DEPT (distortionless enhanced polarization transfer) spectra are shown in Figure 10. The HETCOR (heteronuclear two-dimensional proton-carbon correlation) spectrum is shown in Figure 11. The carbon assignments are listed in Table 5. Long-range HETCOR experiments were used to make the assignments for the thiophene carbons. 

The DEPT experiment, or distortionless enhanced polarization transfer, is a carbon selectivity experiment.29-35 Based on the pulse length selected, one... 

HSQC) or heteronuclear multiple quantum correlation (HMQC). The combined experiments such as 2D HSQC(HMQC)-TOCSY experiments are powerful tools for the assignment of the 13C and 11 resonances belonging to the same sugar residue providing enhanced dispersion of TOCSY correlations in the carbon dimension. More recendy, different carbon multiplicity editing methods, for example, DEPT (distortionless enhanced polarization transfer)-HMQC and E-HSQC, have been developed to reduce the complexity of proton-carbon correlation spectra and to enhance the resolution by narrowing the applied spectral window.11... 

The distortionless enhanced polarization transfer (DEPT) experiment is a carbon selectivity experiment.HO-116 Depending on the pulse length selected, one can selectively observe different types of carbon entities. We recommend setting the DEPT proton pulse length to 135°. In this case, quaternary carbons are suppressed, methylenes are inverted, and methine and methyl carbons... 

The DEPT experiment, or distortionless enhanced polarization transfer, is a carbon selectivity experiment. ° ° ° Depending on the pulse length selected, one can selectively observe different types of carbon entities. We recommend setting the DEPT proton pulse length to 135°. In this case, quarternary carbons are suppressed, methylenes are inverted, and methine and methyl carbons appear upright. Methines and methyls are distinguished based on chemical shift and 2D proton correlations. Methines usually appear downfield of methyls. Alternatively, if time permits, the entire series of DEPT experiments can be performed to conclusively distinguish methine from methyl resonances. One second is a reasonable default value for the recycle time. The spectrum should be set to capture the resonances of interest with 32-64 K data points and four dummy scans. While this is an easily interpreted data set, the multiplicity edited HSQC provides much more robust information, both multiplicity as well and the one-... 

The DEPT (distortionless enhanced polarization transfer) pulse sequence is probably one of the most widely used of all NMR experiments. It produces subspectra edited according to the number of protons bonded to each The DEPT pulse... 

The zero sum of intensities in a multiplet in these differential polarization transfer experiments means that any decoupling that causes all the lines to coalesce results in exact cancellation of intensities. Several methods have been devised to avoid this problem when decoupling is required. One is pulse-interrupted precession,which results in a net polarization transfer, as does the insertion of a properly chosen delay period in the INEPT sequence (as in Figure 12) so that all members of a multiplet appear positively enhanced, i.e., INEPT with refocusing (INEPTR). The DEPT (Distortionless Enhancement Polarization Transfer) sequence gives undistorted relative intensities of the multiplet components. 

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. 

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. 

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. 

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. 

Figure 13.6 is the proton-decoupled carbon-13 NMR distortionless enhancement of polarization transfer (DEPT) spectra of poly(methyl-l-pentene) [29]. This experiment, after data manipulation, separates the methine, methylene, and... 

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... 

NMR spectra have been used frequently to elucidate and/or confirm the structures of these heterocycles, but little or no systematic study had been done. A detailed study of l3C NMR spectra by distortionless enhancement by polarization transfer (DEPT), inverse H-I3C coherence transfer experiments (HMQC and HMBC) and by INADEQUATE of factor F0 has been reported <91JBC9622>. The 13C NMR spectra of a series of pyrido[4,3-J]pyrimidines were interpreted on the basis of a detailed study of other analogues <91JCS(P2)1559>. Carbon-13 NMR spectroscopy has been used to indicate the site of alkylation of pyrido[2,3-c]pyridazin-4-ones <90CPB3359>. 

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) 13C spectrum is designed to display separate subspectra for CH, CH2, and CH3 carbon signals. And like an INEPT spectrum, signal intensity (i.e., sensitivity) arises by polarization transfer. 

One-dimensional subspectra also may be obtained by combining selective excitation and broadband homonuclear Hartmann mixing with het-eronuclear polarization-transfer steps like INEPT, DEPT (distortionless enhancement by polarization transfer), or heteronuclear Hartmann-Hahn transfer (Doss, 1992 Gardner and Coleman, 1994 Willker et al., 1994). Related experiments with multiple-step selective Hartmann-Hahn mixing in combination with heteronuclear coherence transfer were used by Kupce and Freeman (1993a). 

More modem one-dimensional (ID) sequences such as INEPT (Insensitive Nuclei Enhanced by Polarization Transfer) or DEPT (Distortionless Enhancement by Polarization Transfer) [6,13-15] have not been used extensively [16]. This type of experiment seems to be more powerful than the old INDOR technique. 

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