The ge-2D COSY experiment allows to obtain a 2D COSY spectrum with a single scan per t₁ increment provided that the S/N ratio is adequate. The main advantage of such approach is the large reduction in the total acquisition time compared with a conventional 2D COSY experiment. The COSY experiment permits to trace out through-bond proton-proton connectivities via the homonuclear J_HH coupling constant.

Easy implementation on any AVANCE spectrometer equipped with pulsed field gradients.

The gradient-enhanced version of the 2D COSY experiment is easily made by incorporating two PFGs, just before and after the mixing pulse ( 91JMR423-93 and 92MRC768 ). When these gradients have the same duration and intensity, N-type data is selected in a single scan per t1 increment and, therefore, a magnitud-mode COSY spectrum can be quickly recorded in a few minutes. Weaker long-range 4JHH and 5JHH proton-proton connectivities have been observed in COSY spectra of oligosaccharides using long but weak gradients, equivalent to a delayed-COSY experiment optimized to observe small couplings ( 95JMRB194-109 ). In addition of the excellent reduction of t1 noise in gradient-based experiments, the use of corrective data processing techniques as reference deconvolution has been shown to dramatically reduce t1 noise by an extra factor of 60 in a gradient-enhanced COSY experiment, allowing to observe very small long-range correlations ( 96JMRA246-123 ).

Phase-sensitive spectra can be obtained using the SWAT technique ( 91JMR666-93 ) or the echo-antiecho approach. However, the gradient-enhanced version of the COSY-DQF experiments is used to obtain phase-sensitive data.

A simple variant of the COSY experiment has been used to readily observe surprising intermolecular multiple-quantum coherences in solution with at least one concentrated component ( 96JMRA94-122 , 93JCP6779 , 93SCI2005 , 95JCP1309 , 90JCP858 , 92JCP1659 , 96JCP874 , 95SCI654 , 96SCI92 , 95CPL207 , 95CPL639 , 96ENC1417 , 96CONC77 , and 97JMR114-128 ). In this so-called CRAZED experiment the two PFGs around the second RF pulse are optimized to a 1:n ratio in order to select n-quantum coherences. This experiment leads to observable multiple-quantum transitions in the F1 dimension and SQC in the directly F2 dimension. The basis of such outstanding results have been extensively studied and discussed for several groups.

The ge-2D COSY experiment is usually recorded in routine and automation modes using a single scan per increment t1 and minor changes are required if a predefined parameter set is available. This experiment is acquired an processed using the same experimental conditions as decsribed for its phase cycle version. The only difference is the presence of gradients. Thus, the user only need to define the strength, duration, shape of the gradients and the recovery delay. More details on practical implementation of ge-2D COSY experiments on AVANCE spectrometers can be found in

Tutorials: 2D homonuclear experiments

Tutorials: 2D gradient-based homonuclear experiments

Tutorials: 2D gradient-based homonuclear experiments in H₂O

List of available gradient-enhanced COSY pulse programs for AVANCE spectrometers.

The magnitude-mode spectrum resulting of the gradient-enhanced COSY version is a clean 2D map in which t1 noise has been efficiently reduced. As in the conventional COSY spectrum, cross-peaks correlate chemical shifts between J-coupled spins. Three main peaks can be present:

Diagonal or autocorrelated peaks.

Off-diagonal or cross-peaks. These peaks reveal J-coupling connectivity.

Axial peaks (appearing a F1=0) that are efficiently removed by using a two-step phase cycle.

Related experiments:

2D homonuclear experiments

2D gradient-based homonuclear experiments