Dipolar Recoupling Technique In Solid State NMR And Its Application

In this dissertation, the basic principle of dipolar interaction in solid state NMR and the homonuclear and heteronuclear dipolar-recoupling methodologies were reviewed. Based on extensively used techniques, such as rotational resonance (RR) homonuclear recoupling and REDOR heteronuclear recoupling, we proposed several dipolar recoupling methods and combined them with other methods for resolving the problems in solid-state NMR.We improved the RR technique and proposed broadband rotational resonance (BBRR) method. The DARR irradiation is applied on proton spins during the mixing time, alternatively no RF field irradiation is applied. Reintroduced or partially residual heteronuclear I-S dipolar couplings modulate the homonuclear S-S dipolar couplings. The dipolar couplings of all spin pairs are reintroduced no matter whether the difference of the resonant frequencies of the coupled spins satisfies the RR conditions or not. Therefore, through-space homonuclear correlation in the whole system can be measured by the BBRR techniques.Quantitative cross polarization (QUCP) was proposed, which incorporates the conventional cross polarization with dipolar-assisted rotational resonance (DARR) broadband homonuclear recoupling technique. During the mixing time, the broadband S-S dipolar couplings were reintroduced by DARR irradiation, then polarization transfer among enhanced S spin magnetization is facilitated by the reintroduced S-S dipolar couplings. With this re-distribution of the polarization among the S spins, uniform enhancement of S spins can be achieved. QUCP can be used for the quantitative measurement in solid-state CP/MAS spectroscopy.In this dissertation, we brought forward the point of view that the recycle delay can be unlimited by the 5T1 requirment in quantitative experiments of solid-state NMR. We introduced the experimental schemes that are applicable for quantitative measurement in CP/MAS and SP/MAS spectra of solid state NMR, which are named as quantitative cross polarization (QUCP) and quantitative single pulse (QUSP), respectively. The improved pulse schemes combine the broadband homonuclear recoupling techniques (such as DARR, RFDR) into the conventional CP and SP experiments. In the mixing time, the non-uniformly enhanced or recovered spin magnetizations transfer under the reintroduced homonuclear interactions, reaches a quasiequilibrium state with uniform spin magnetization.A novel selectively heteronuclear recoupling method was introduced, which combines modulatory pulse technique with general REDOR heteronuclear recoupling approach, which is called M-REDOR. In the evolution period, MORE modulated continuous pulse rather than discontinuousπpulses is used for the RF field irradiation on S channel. M-REDOR can be used to selective measurement of weak heteronuclear I-S interaction in I-Sn systems. We demonstrated the feasibility and selectivity of M-REDOR experiments on 13C, 15N doubly labeled L-leucines.