DEPT pulse sequence

Figure 2.17 Application of the reverse DEPT pulse sequence to monitor C-labeled glucose by mouse liver-cell extract. (A) Normal FT spectrum. (B) Reverse DEPT spectrum showing the a- and )3-anomeric proton resonances. (C) Two different CH2 proton resonances, a and b, appear after 1.5 h of metabolism. (D) Edited H spectrum confirming that the CH2 resonances arise from metabolic products. (Reprinted from J. Magn. Resonance 56, Brooks et al., 521, copyright 1984, Academic Press.)...

Applying the reverse DEPT pulse sequence to monitor C-labeled glucose by mouse liver-cell extract is shown in Fig. 2.17. The a- and /3-anomeric proton resonances are shown in the starting material these are transformed to CH.2 proton resonances in the metabolite. 

Fig. 5.5.13 Spatially resolved 13C DEPT pulse sequence. This provides signal enhancement for 13C observation without need for using isotropically enriched materials. The signal is acquired under conditions of ]H decoupling.

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. 

In the case of isoorientin 6"-0-caffeate isolated from Gentiana arisanensis, the C NMR spectrum was assigned by H-decoupled spectra, DEPT pulse sequence, H- C COSY spectrum, long-range C- H COSY, and NOESY experiments the H NMR spectrum was analyzed with the aid of H- H COSY and H- C COSY. 

A schematic representation of how the double-phase encoded DEPT pulse sequence achieves spatial and spectral resolution within the fixed bed of ion-exchange resin is shown in Fig. 45. Typical data acquired in this experiment are shown in Fig. 46. The data were recorded from a vertical section through the center of the bed. The direction of superficial flow was from the bottom to the top of the bed. The spectra shown were recorded at regular intervals along the length of the bed, with a spatial separation of approximately 2.5 mm. With reference to Fig. 46, the... 

APT distinguishes between two groups of signals, methyl/methine (normally shown in positive phase) and methylene/quaternary (negative). DEPT is similar, except that quaternary carbons are not detected by this sequence. There may be cases where it is necessary to distinguish between methyl and methine, and this can be done by adjusting the DEPT pulse sequence (known as editing ) the standard experiment is known as DEPT-135, and requires, like APT, short measurement times. 

Theoretical values of parameters a, b and c are 1.00, 0.707 and 0.00, respectively however, experimental values are determined by obtaining the optimum cancellation of unwanted signals in the subspectra 254). The DEPT pulse sequence has several advantages, such as insensitivity to JCH and smaller sensitivity to rf-pulse inhomogeneities as compared to other analogous techniques. However, very accurate experimental conditions are generally required in order to obtain the final spectra, which are created from the three subspectra by a co-addition of the pure spectra. In the case of admixture of the subspectra, some additional linear combinations are usually required to produce the clean spectra. 

Vlahov, G., Schiavone, C., and Simone, N. (2001). Quantitative 13C NMR method using the DEPT pulse sequence for the determination of the geographical origin (DOP) of olive oils. Magn. Resort. Chem. 39, 689-695. 

FIGURE 4.11 DEPT pulse sequence. The 1/2 J is for CH coupling constants typically 145 Hz. 6 is a variable pulse angle.-R,/ is a relaxation delay, 6 is a variable pulse angle, f2 is the acquisition time. 

Figure 13 Pulse sequences of -detected IPAP DEPT-INADEQUATE.The insert is used when in-phase doublets are acquired. The filled and open rectangles represent 90° and 180° rectangular pulses, respectively, applied from the x-axis unless stated otherwise. The dashed rectangles of the DEPT pulse sequence represent rectangular pulses with flip angle 6 = 90° or 45°. The 180° BIBOP pulses are indicated as wide rectangles with a sine wave. The 13C adiabatic inversion pulses are designated by an inclined arrow. The following delays were used t = 0.5/Vch> At = 0.25/VCo A2 = 0.25/ycc. For other parameters see Ref. 31. Reproduced by permission of Elsevier.

Bardet M, Foray MF, Robert D (1985) Use of the DEPT pulse sequence to facilitate the nC NMR structural analysis of lignins Makromol Chem 186 1495-1504... 

Figure 12.15. Pictorial depiction of the DEPT pulse sequence.

Along with the DEPT pulse sequence, a useful complement is the QUAT sequence, which detects only quaternary carbons (S4)- As illustrated in Figure... 

The DEPT pulse sequence is depicted in Figure 12.15. The key addition is the inclusion of a H pulse y with a variable tip angle that controls the relative intensity of carbon signals of different multiplicity according to the equations... 

In a continuing study(20), these experiments were applied to five fulvic and humic samples. In addition, the DEPT pulse sequence was used. This technique allows for a further discrimination between singly and doubly protonated nuclei. They found that all five samples react in the same manner. Reaction products of hydroxylamine with esters were observed. Other resonances discovered were attributable to the tautomeric forms of the nitrosophenol and monooxime derivatives of quinones. Thus, this study provides indirect evidence for the presence of quinones in humic material and also suggests the possible presence of cyclic... 

In another study, ammonia fixation of N-labeled ammonium hydroxide with Suwannee River fiilvic acid, IHHS peat and leonardite humic acid were examined by solution NMR with the application of INEPT and DEPT pulse sequences.(23) Similar reaction of ammonia with all three samples is reported. Most of the nitrogen incorporated seems to be in the form of indole and pyrrole followed by pyridine, pyrazine, amide and aminohydroquinone nitrogen. The authors also suggest a possible reaction mechanism to explain the formation of the heterocyclic compounds identified in the spectra. They also claimed that these results need to be substantiated through further work with model compounds and experiments with the reaction conditions, i.e., in which phenols will undergo oxidation to quinones when reacted with ammonia. 

Another milestone in Ge NMR was made by the introduction of high field instruments coupled with the advancement of software technology. Use of high field instruments is particularly advantageous for low frequency nuclei such as Ge. Observation of the Ge resonance of larger and less symmetric compounds became possible in certain cases. Use of advanced software has also widened the scope of Ge NMR spectroscopy. Thus, INEPT and DEPT pulse sequences achieved several fold signal enhancement (and hence corresponding reduction in machine time). Application of 2D techniques to Ge NMR spectroscopy has also been reported. 

The DEPT pulse sequence is illustrated in Fig. 4.31. To follow events during this, consider once more a H- C pair and note the action of the two 180 pulses is again to refocus chemical shifts where necessary. The sequence begins in a similar manner to INEPT with a 90 (H) pulse after which proton magnetisation evolves under the influence of proton-carbon coupling such that after a period 1 /2J the two vectors of the proton satellites are antiphase. The application of a 90 (C) pulse at this point produces a new state of affairs that has not been previously encountered, in which both transverse proton and carbon magnetisation evolve coherently. This new state is termed heteronuclear multiple quantum coherence (hmqc) which, in general, cannot be visualised with the vector model, and without recourse to mathematical formalisms it is... 

The DEPT pulse sequence, applied to the square-planar silver(III) [Ag(CF2H)4 ] ion, reveals a beautifully symmetric 109Ag resonance pattern resulting from seven of the nine signals expected for coupling to eight equivalent fluorines (Figure 3)9. Each component is... 

Check it 5.2.6.10 (1) shows the differences between the DEPT and the DEPTQ experiment by converting the standard DEPT pulse sequence into the DEPTQ sequence. The spin system used to illustrate these differences is a reduced spin system similar to caffeine. 

Two new polarization transfer techniques have recently been reported INEPT (2) and DEPT (3,4). These pulse sequences lack the limitations of previous polarization transfer methods, and allow the routine collection of 29Si-NMR data. The principal virtues of both the INEPT and DEPT pulse sequences are that the polarization transfer enhancements are substantial (five- to ninefold) (12) and relatively nonselective and that they can easily be used by chemists familiar with normal FT-NMR spectroscopy on available commercial multinuclear FT-NMR instruments. 

Several modified INEPT and DEPT pulse sequences have recently been introduced (IS) (see Fig. 1). The new INEPT+, DEPT +, and DEPT + + sequences differ from the original INEPT and DEPT sequences only in that they employ additional refocusing and purging pulses. These serve to reduce or eliminate distortions inherent in the parent pulse sequences. The fundamental polarization transfer mechanism however remains unchanged. 

The INEPT and DEPT pulse sequences shown in Fig. 1 (IS, 14) are all multinuclear pulse sequences in which proton and/or silicon pulses are separated by free precession periods. However, INEPT and DEPT differ in both the number and duration of precession periods. In the INEPT pulse sequences, there are two precession periods of duration t, and one of duration A [a refocusing pulse (15) bisects the A period]. Both t and A are parameters set by the user to optimize enhancements, although t is routinely set to a constant (4J) 1 (where J is the H-29Si coupling constant). The A parameter can be set according to Eq. (5) (Section IV,A) to obtain optimal enhancement, or may be set to selectively invert or suppress specific silicon resonances as shown by Figs. 8-10 (Section III,D). 

The single most important consideration in choosing between INEPT and DEPT is the length of the pulse sequence relative to the silicon spin-spin relaxation time, T2, which is fairly constant (about 160 msec) for most silanes. The DEPT pulse sequence is about three times longer than an equivalent INEPT pulse sequence (Section II,B). The length of INEPT or... 

DEPT pulse sequences is determined by the length of the r precession times, which are inversely proportional to J. For large J values (J > 50 Hz) INEPT and DEPT sequences are both short relative to T2 and give similar enhancements. For small J values (J < 10 Hz) the INEPT sequence is still short relative to T2, but the DEPT sequence length becomes comparable to T2. Consequently, the DEPT enhancements are poorer due to relaxation during the pulse sequence. 

Signal enhancement from INEPT and DEPT pulse sequences differs substantially from nuclear Overhauser enhancement. While polarization transfer enhancements are dependent on the number of protons coupled to... 

Through the mathematical manipulation of the results of each of the different DEPT pulse sequences, it is also possible to present the results as a series of subspectra in which only the CH carbons appear in one trace, only the CH2 carbons appear in the second trace, and only the CH3 carbons appear in the third trace. Another eommon means of displaying DEPT results is to show only the result of the DEPT-135 experiment. The spectroscopist generally can interpret the results of this spectram by applying knowledge of likely chemical shift differences to distinguish between CH and CH3 carbons. 

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