The ge-2D semi-selective COSY experiment is a gradient-enhanced band-selective version of the 2D COSY experiment. By the use of some band-selective excitation method, only part of the 1H spectrum is evolving during the conventional variable t1 period or/and the proton acquisition period. In this way, a conventional 2D COSY spectrum is partially recorded with improved resolution and t1-noise.

Easy implementation on any AVANCE spectrometer equipped with pulsed field gradients (PFGs) and selective excitation using shaped pulses.

The most simple way to convert the classical 2D COSY pulse sequence to a F1-semi-selective 2D COSY pulse sequence is replacing the initial 90º 1H pulse by a SPFGE  or DPFGE scheme ( 96MRC807 ). In the original paper, the SPFGE block is prefered because minimizes sensitivity losses due short transverse relaxation times without sacrify selectivity.

Band-selective excitation of the F2 dimension can be equally performed by replacing the mixing 90º 1H pulse of the COSY experiment by another SPFGE block. Both band-selective excitation schemes can be combined in a same experiment as demonstrated in the original article. The first SPFGE block was applied on the alpha proton region of an small peptide in H2O and the second SPFGE block was applied on the amide proton region. The result is a ultra-clean high-resolved phase-sensitive 2D COSY map of only the fingerprint region (F1=alpha and F2=amide). In modern spectrometers equipped with digital filters, automatic selection on the F2 dimension could be accomplished without the need to include the second SPFGE block. It is important to choose a shaped selective pulse giving excelent selective inversion profile as, for instance, a RE-BURP sequence.

Magnitude-mode ge-2D semi-selective COSY spectra could be acquired incorporating the SPFGE block in the regular ge-2D COSY pulse sequence as described above.

The experiment is acquired an processed using the same experimental conditions as described for its phase cycle counterpart. The only difference is the presence of gradients. Thus, the user needs to define the strength, duration, shape of the gradients and the recovery delay. In the original experiment, PFGs are not used for coherence selection and, therefore, clean phase-sensitive spectra can be obtained using a eigth-step phase cycle without sensitivity losses. The inversion profile of the selected SPFGE scheme migth be checked on the same sample.

Tutorials: 2D homonuclear experiments

Tutorials: 2D gradient-based homonuclear experiments

Tutorials: 2D gradient-based homonuclear experiments in H₂O

Data is processed and analyzed as in a conventional 2D COSY experiment.

Related experiments:

2D homonuclear experiments

2D gradient-based homonuclear experiments