DONUT-HYSCORE

In the HYSCORE experiment only nuclear frequencies in different manifolds belonging to the same paramagnetic center are eorrelated with each other. For multinuclear spin systems the assignment of nuelear frequencies is often not straightforward, since some of the correlation peaks may not be observed in the HYSCORE speetrum due to the small intensity of the nuelear transitions in one of the two Ws manifolds. Additional information can be gained if correlations of nuclear frequencies within the same manifold can be obtained. Cross-peaks that represent such correlations can be created by replacing the nonselective transfer n pulse in the HYSCORE sequence by the double nuclear-coherence transfer (DONUT) mixer % - t - n [58]. This DONUT-HYSCORE experiment with the pulse sequence ji/2 -ti nil - echo results in crosspeaks and (twp i, copj). The presence of these cross-peaks in the DONUT-... 

HYSCORE spectrum is a proof that p and < j belong to the same paramagnetic center, and this information can support their unambiguous assignment. An experimental example for nitrogens that are close to the exact cancellation condition has been published for the complex Co(II)TPP(py) [59], where the DONUT-HYSCORE experiment revealed one of the NQR frequencies that was missing from the HYSCORE speetrum. 

Goldfarb D, Kofman V, Libman J, Shanzer A, Rahmatouline R, Van Doorslaer S, Schweiger A. 1998. Double nuclear coherence transfer (DONUT)-HYSCORE a new tool for the assignment of nuclear frequencies in pulsed EPR experiments. J Am Chem Soc 120 7020-7029. 

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