The doubly-selective ge-1D TOCSY-ROESY (TORO) experiment permit to obtain high-quality artefact-free 1D ROESY spectra on a specific proton resonating in an overlapped region where typical on-resonance selective excitation is not feasible.

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

The basic scheme of the selective ge-1D TOCSY-ROESY experiment consists basically of a selective ge-1D TOCSY experiment followed by a selective ROESY experiment. As selective inversion pulse on the selected resonance is inserted between these blocks. The following steps must be considered:

Selective excitation of the selected resonance using the SPFGE block or the DPFGE block.

Mixing period to achieve in-phase polarization transfer to other spins. This is usually achieved applying some isotropic mixing sequence like MLEV, WALTZ or DIPSI pulse trains (see TOCSY Block).

Selective inversion on the relayed resonance.

Mixing period that in its basic form consists of a low-power continuous-wave irradiation block for in-phase polarization transfer to other spins via NOE in the transverse plane (see ROESY Block).

Proton detection as usual.

Gradients can be incorporated in this basic scheme in two different ways depending if a refocusing gradient is inserted before acquisition. If is is not incorporated, EXORCYCLE must be applied on a selective 180º pulse of the SPFGE or DPFGE scheme. If it is incorporated, ultra clean 1D spectra are obtained without need of phase cycling but sensitivity is lost with compared to a non-refocused experiment (selection of N- or P-type data as a function of the intensity of this refocusing gradient). Coherence selection was used in the original experiment ( 95JMRA124-113 ). However, excellent spectral quality without sensitivity losses can also be obtained using a four-step phase cycle ( 97JMR267-124 ).

The selective ge-1D TOCSY-ROESY experiment can be run with minor changes from a predefined parameter set. The best option is the version which uses a SPFGE or DPFGE scheme as a selective excitation and the refocusing gradient is omitted. Important parameters to consider are:

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

Optimization of the mixing time in the TOCSY block (as a function of 1/(J(HH)). When long mixing times are employed, magnetization is transferred to the whole spin subsystem.

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

Optimization of the mixing time in the ROESY block.

The final spectrum of a doubly-selective ge-1D TOCSY-ROESY experiment is a clean ROESY spectrum of a specific relayed resonance appearing in a overlapped region of a 1H spectrum. It is needed that this relayed proton is J-coupled to another well-isolated proton on which a previous selective 1D TOCSY experiment could be applied.