Total correlation spectroscopy spin assignment

Total correlation spectroscopy (TOCSY) also known as homonuclear Hartmann-Hahn (HOHAHA) experiment provides all relayed connectivities within a spin system [453, 454). The primary intention in TOCSY as in other relayed experiments is to establish connectivities in less crowded spectral regions to facilitate the assignment of spin systems. 

Complete assignment of a whole spin system may be limited because of severe spectral overlap. To overcome this, DQF-COSY data are often used in conjunction with total correlation spectroscopy (TOSCY). This experiment results in a transfer of magnetization across an entire spin system and consequently crosspeaks may be observed between each resonance of a spin system. Thus it is possible to determine whether a particular overlapped region of the spectrum contains all unidentified members of a chemical spin system. 

Mixing sequences for total through-bond correlation spectroscopy in solids (TOBSY) have been developed for fast MAS experiments. Possible sequences with the desired Hamiltonian (the homonuclear isotropic J interaction) have been identified using lowest order average Hamiltonian theory combined with numerical simulations as a function of the MAS frequency. An experimental TOBSY spectrum of a uniformly C-labelled decapeptide at 20 kHz MAS has been obtained using one of the new sequences. The spectrum allows to assign the resonances to the respective spin systems. 

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