The DEPT (Distortionless Enhancement by Polarization Transfer) experiment was designed to improve the sensitivity of NMR experiments on low-abundant and low magnetogyric ratio nuclei, X , such as ¹³C or ¹⁵N. The net effect is the non-selective polarizarion transfer from protons to X nuclei with the appropriate ¹H-X coupling. Presently, DEPT experiments are largely used to determine carbon multiplicities.

Easy implementation on AVANCE spectrometer

The basic DEPT pulse sequence ( 81JACS4603 , 82JMR323-48 , 82JCP2745 , and 83JMR272-53 ) consists of the following steps (see DEPT block):

• Relaxation period (d1) to achieve a pre-equilibrium state.
• 90º ¹H pulse (p1) to create transverse ¹H magnetization (I_y).
• An evolution delay optimized to 1/2*J(XH) to achieve antiphase proton amgnetization (I_xS_z).
• Simultaneous 180º ¹H and 90 X pulses. The proton pulse will allow to refocus ¹H chemical shift evolution while the carbon pulse creates multiple quantum coherences.
• During a second delay (also optimized to 1/2*J(XH)) heteronuclear coupling is not evolving.
• Simultaneous Yº ¹H and 90 X pulses. The carbon pulse refocus ¹³C chemical shift evolution while the Y proton pulse creates a different functional dependence as a function of carbon multiplicity:

CH      2I_zS_ysin(Y)
CH₂    4I_zI´_zS_ysin(Y)cos(Y)
CH3    8I_zI´_zI´´_zS_ysin(Y)cos²(Y)
 
• A final evolution delay (also optimized to 1/2*J(XH)) to achieve in-phase ¹³C magnetization.
• ¹³C acquisition is performed under broadband proton decoupling.

Modified DEPT sequences:

• ¹H-coupled DEPT spectra can be obtained under the same consitions if the proton decoupling is not applied. The last evolution period can also be omitted if antiphase multiplets are required. A particular experiment is the DEPT++ experiment.
• Use of composite pulses or adiabatic pulses
• By incorporating a variable evolution period in the defocusing period, 2D DEPT-based HETCOR experiment results.
• A reverse DEPT sequence ( 83JMR520-51 ). Starting from X nuclei, magnetization is transferred to ¹H nuclei. The result is the acquisition of the satellites ¹H-¹³C resonances and the suppression by means of phase cycling of the large unwanted central ¹H-¹²C resonance. This block is referred as retro-DEPT building block in many multidimensional experiments.
• Compensated DEPT sequences over a range of ¹J(XH) values ( 91JMR45-92 ).
• A DEPTQ pulse sequence to observe quaternary carbons ( 98JMR529-135 ).

The DEPT experiments are usually recorded in a fully automated way. Minor changes from a predefined parameter set are required. Only the flip angle of the last ¹H pulse must be set according to the multiplicity-edited selection.

Combinations of these three spectra undergo CH_n-edited ¹³C spectrum. For further details on practical implementation of the DEPT experiment on AVANCE spectrometers Tutorial: DEPT experiment.

Some theoretical enhancement factors for NOE and DEPT(INEPT) experiments with X{¹H} pais of nuclei:
 

X	11B	13C	15N	29Si	57Fe	103Rh	109Ag	119Sn	183W
NOE	2.56	2.99	-3.94	-1.52	16.48	-16.89	-9.75	-0.41	13.02
DEPT	3.12	3.98	9.87	5.03	30.95	31.77	21.50	2.81	24.04

 

The DEPT experiment affords a ¹H-decoupled ¹³C spectrum in which the intensity of X resonances depends on the flip angle of the last ¹H pulse.

• With a 45º pulse, all protonated carbon resonances appear with positive intensity.
• With a 90º pulse, only CH systems will be displayed.

With a 135º pulse, CH and CH₃ groups appear positive while CH₂ are negative.

See DEPT Spectra

Similar polarization transfer effects is achieved using the 1D INEPT pulse train, and other sequences have been also used for 13C-multiplicity editing purposes

General search for DEPT