Time proportional phase incrementation and order selective detection using 3D NMR

Time proportional phase incrementation and order selective detection using 3D NMR 

If the phase of the excitation radiation is incremented by A fi = AcoA each time that tx is incremented by At in the 2D NMR experiment i.e. time proportional phase incrementation (TPPI), the TV-quantum spectrum is offset by a frequency NA x from the transmitter in the 2D NMR spectrum. MQ orders are separated in frequency by Aco in the same fashion as if an offset had been employed. 

Syvitski et al43 reported a 3D sequence which uses TPPI to separate the spectra of different coherence orders. The pulse sequence employs a non-selective 2D excitation sequence (as in Fig. 2) but also systematically increments the phase of the first two pulses in the excitation sequence by A p at each value of t (Fig. 11). The number of phase increments (A / ) in the experiment is arbitrary but needs to be at least 2TV+ 1, where TV is the number of spins in the spin system. The 3D interferogram is then a function of t, fi and t2 and Fourier transformation over these dimensions6,30,44 affords MQ spectra of various orders cleanly separated in the pseudo-frequency  

The allowed transitions in the N and (N—l) quantum spectra of an. /V-spin system must belong to the highest symmetry class of the spin permutation group. By creating N or (N— 1) quantum coherence and then converting this into an observable IQ coherence, one obtains a symmetry-filtered lQ-spec-trum which contains only a subset of those transitions originating from the most symmetric class. The IQ spectra of solutes aligned in liquid crystalline 

This concept was extended by Carravetta et al46 to larger spin systems. Iterative analysis of the symmetry-selected, MQ-filtered single quantum spectra of spin systems up to eight spins (/ = 1/2) has been used to determine dipolar coupling constants of molecules aligned in liquid crystalline 

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