The selective ge-1D HSQC experiment permit to obtain high-quality 1D HSQC spectra only showing the protons directly bonded to an specific heteronucleus (for instance, 13C). Similar results can be obtained using the selective ge-1D HMQC experiment and the selective ge-1D inverse INEPT experiment.

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 HSQC experiment is exactly the same as the conventional ge-2D HSQC pulse train in which the following modifications have been included:

• One of the two 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 original sequences were published in 95MRC144 , 95JMRA32-114 and 97FRE470 . A doubly-refocused version was also proposed in which carbon excitation was achieved from the in-phase transverse carbon magnetization ( 95MRC827 ). Recently, it has been demonstrated that PEP methodology can be also incorporated in 1D HSQC pulse sequences achieving a sensitivity enhancement by a factor of 2 for IS systems ( 97JMR278-126 ) without change any acquisition and processing parameter.

A simple version allows to obtain spin-state selection:

The HSQC pulse train can be used as a starting block in nD experiment. An example is given for a 13C-resolved 2D COSY experiment in which COSY cross-peaks can be detected and evaluated in overcrowded regions ( 95MRC144 ). On the other hand, a double-selective version has been proposed ( 95JMRA32-114 ) to select magnetization of protons bound to a specific carbon atom which is in the alpha or beta spin state. The first selective pulse selects the carbon resonance of interest under proton decoupling, and the second selective pulse determines the spin state. Appending a TOCSY block to this experiment alllows to measure accurate long-range proton carbon coupling constants.

The selective ge-1D HSQC 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 HSQC 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.

The selective ge-1D HSQC experiment can be used as a starting building block in more sophisticated pseudo-3D experiments. See:

Selective ge-1D HSQC-COSY experiment
Selective ge-1D HSQC-RELAY experiment
Selective ge-1D HSQC-TOCSY experiment
Selective ge-1D HSQC-ROESY experiment
Selective ge-1D HSQC-NOESY experiment