Distortionless enhancement pulse sequence

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

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. 

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. 

Distortionless Enhanced Polarization Transfer) A method of running several 13C experiments with different pulse sequences so that the carbon atoms appear differently depending on whether they are bonded to 0, 1, 2, or 3 protons, (p. 607)... 

An alternative pulse sequence that provides the same multiplicities as INEPT but with intensity ratios that follow the binomial theorem is DEPT (distortionless enhancement by polarization transfer).The pulse sequence, depicted in Fig. 12.3a, can be used, like refocused INEPT, for sensitivity enhancement but is usually employed as an editing technique. The three evolution periods T are chosen to approximate 1/2/, but the length of the pulse labeled 0 can be varied. As we show in the following, CH has maximum intensity at 0 = 90° CH2 has zero... 

NMR spectra. Chloroform was used as an internal standard for and C NMR spectra. All chemical shifts reported were externally referenced to tetramethylsilane (TMS). A DEPT (distortionless enhancement by polarization transfer) pulse sequence was used to obtain Si NMR spectra (6). 

A very useful pulse sequence in spectroscopy is employed in the experiment called Distortionless Enhancement by Polarization Transfer, better known as DEPT. The DEPT method has become one of the most important techniques available to the NMR spectroscopist for determining the number of hydrogens attached to a given carbon atom. The pulse sequence involves a complex program of pulses and delay times in both the and ehannels. The result of this pulse sequenee is that carbon atoms with one, two, and three attached hydrogens exhibit different phases as they are recorded. The phases of these hydrogens will also depend on the duration of the delays that are programmed into the pulse sequence. In one experiment, called a DEPT-45, only carbon atoms that... 

The NMR signals of insensitive nuclear spins can be enhanced by transferring polarization from a more sensitive species to which they are coupled. The well-known pulse sequences as the polarization transfer techniques are insensitive nuclei enhanced by polarization transfer (INEPT), distortionless enhancement by polarization transfer (DEPT), and reverse insensitive nuclei enhanced by polarization transfer (RINEPT) The INEPT sequence is an alternative to the nuclear Overhauser effect. The INEPT experiment does not require any particular relaxation mechanism and therefore a better enhancement factor can be obtained. Furthermore it is demonstrated that INEPT sequence can be used to determine the multiplicity of each signal in a NMR spectrum. More recently, the INEPT and DEPT experiments were used for the coherence transfer via heteronuclear J-coupling between spin-1/2 and quadrupolar nuclei in the solids. " Fyfe et showed that coherence transfer via the scalar coupling between spin-1/2 and quadrupolar nuclei can be obtained in the solid state by using INEPT experiment. 

Numerous multipulse and two dimensional experiments are used to identify unknown (co)polymers and these experiments are most useful in analyzing differences between copolymers or impurities in production problems. The Distortionless Enhancement via Polarization Transfer (DEPT) pulse sequence is frequently used to determine the carbon multiplicity (CH vs. CHj vs. CH3) of a carbon spectrum. Newmark showed excellent DEPT spectra could be obtained on sidechain groups in vinyl polymers or in typical polyesters and polyurethanes, but that it was difficult to observe good DEPT spectra (at 200 MHz) on backbone carbons, such as the ring carbons in cellulose acetate butyrate (CAB) with very short carbon spin-spin relaxation times (Tj) (8). 

Determination of the number of directly bound hydrogen atoms, called multiplicity assignment, is easy through application of editing pulse sequences, e.g., distortionless enhancement by polarization transfer (DEPT) or attached proton test (APT). 

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