PISEMA experiment

Fig. 4. Pulse sequences for 2D PISEMA experiments on static or slow-spinning samples. It has been shown that the use of ramped rf pulses for S-spin-lock during the ti period makes the pulse more tolerant to experimental errors. The original PISEMA sequence (A) does not suppress the effects of phase transients. Incorporation of the modified SEMA sequences, (B) and (C), in the ti period of the PISEMA sequence (A) have been shown to suppress the effects of phase transients.

As discussed later, the application of the SEMA sequence is not limited to the 2D PISEMA experiment, but it can be used to design a variety of sophisticated pulse sequences. For example, the selective transfer of magnetization between strongly coupled heteronuclei by SEMA is the key feature of the sequence that can be utilized in experiments such as HETCOR, H-detected experiments," and experiments to selectively measure relaxation parameters of a proton bonded to S nuclei. 

PISEMA experiment utilizes the evolution under the H-A dipolar coupling to acquire the signal in the channel. Therefore, this new sequence eliminates the sensitivity-loss due to the reverse cross-polarization step and could be used to develop a variety of H-detected multi-dimensional solid-state NMR experiments. 

PISEMA experiment was enhanced by many fold as compared to the... 

PISEMA experiments yield the local dipolar field experienced by the or nucleus. Perhaps counter intuitively, it has been shown that better resolution is obtained by using experiments which detect the local dipolar field on protons [129,... 

A new pulse sequence has been described for the recoupling of heteronuclear dipolar interactions under MAS. " The method is similar to the PISEMA experiment, but employs a well-defined amplitude modulation of one of the two RF fields. The technique was used for measurements of dipolar couplings in... 

Solid-state NMR experiments on and "N labelled WLP23 and related membrane proteins have been applied to determine the alignment of the protein with bilayers." Two NMR approaches were compared H NMR quadrupolar and "N PISEMA experiments. 

A low RF power PISEMA pulse sequence, PITANSEMA, has been described for the measurement of heteronuclear dipolar couplings from solids." The method employs a time averaged nutation concept to significantly reduce the RF power required to spin-lock low frequency nuclear spins in PISEMA experiments. The efficacy of the 2D method is demonstrated on a single crystal of n-acetyl-L- N-valyl-L- N-leucine dipeptide to measure dipolar... 

Polarization Inversion Spin Exchange at the Magic Angle (PISEMA) Experiment... 

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