The selective ge-1D inverse INEPT experiment is a simple modification of the selective ge-1D HSQC experiment in which the initial proton-to-carbon INEPT pulse train is substituted by a single selective 90º carbon pulse. In this experiment, sensitivity improvement is achieved by proton decoupling during the relaxation period (heteronuclear NOE enhancement).

Easy implementation on AVANCE spectrometers equipped with pulsed field gradients, selective excitation using shaped pulses and inverse probehead.

The basic pulse sequence of the selective ge-1D inverse experiment experiment is exactly the same as the conventional ge-2D inverse INEPT pulse train in which the following modifications have been included:

• The first 90º 13C pulses is made selective on a specific heteronucleus. In order to improve the selectivity, proton decoupling is simultaneously applied during the long selective 13C pulse.
• The variable evolution period of the 2D version is fixed to a  minimum delay (3 microseconds).
• Carbon decoupling during proton acquisition is optional. In the coupled version, the two satellites will appear as in-phase multiplet, allowing the accurate measurement of the 1J(CH). In the decoupled version, these satellites collapse in a single signal, improving the signal-to-noise by a factor of two.
• Gradients are usually applied for coherence selection purposes in natural abundance samples to obtain efficient suppression of 1H-12C magnetization.

The sequence can be designed from the HSQC analog (see 95JMRA32-114 ). Recently, it has been demonstrated that PEP methodology can be also incorporated in 1D inverse INEPT pulse sequences achieving a sensitivity enhancement by a factor of 2 for IS systems ( 97JMR278-126 ) without change any acquisition and processing parameter.

The same sequence has been used to measure long-range proton-carbon coupling constants ( 96MRC377 ). The interpulse delay is optimized to 5-10 Hz, the refocusing period is omitted, a BIRD pulse train is inserted at the middle of the defocusing period to remove direct responses, and the resulting antiphase multiplets are analyzed as in the selective ge-1D HMBC experiment.

The selective ge-1D inverse INEPT experiment can be run with minor changes from a predefined parameter set. Important parameters to consider are:

Selectivity of the selective excitation 13C pulse: the user must define the offset, the shape, the duration and the power level needed for a defined excitation profile.

Optimization of the J-coupling delay as a function of 1/(4*J(CH)), in order to get in-phase magnetization of the directly-bonded protons.

In a selective 1D inverse INEPT spectrum, only protons directly attached to an specific carbon will be present. The use of gradients allows to obtain a clean, artefact-free spectrum in a short time in which perfect suppression of undesired 1H-12C magnetization is achieved with a single two-step phase cycle. In the long-range optimized experiment, only long-range coupled protons showing antiphase pattern with respect to the selected carbon are present.

Selective ge-1D HSQC experiment
Selective ge-1D HMQC experiment