I-S dipolar coupling

Fig. 2. A 2D SLF pulse sequence (A) with S-spin magnetization evolution (B) subject only to heteronuclear dipolar couplings in the q period and detection of chemical shift spectrum in the 2 period. Various multiple pulse (MP) sequences can be used to suppress dipolar coupling among I spins in the laboratory frame during the h period, which enables line-narrowing in the I-S dipolar coupling dimension (i.e., the a>i frequency dimension of the 2D spectrum). This experiment under MAS can be used for separating I-S dipolar sideband patterns by isotropic chemical shifts the re-pulse and the start of the acquisition need to be synchronized with rotational echoes. Other aspects of this pulse sequence are similar to the SLF sequence in Fig. 1.

Fig. 7. A PISEMA pulse sequence for studies under a fast magic angle spinning condition. The modified SEMA pulse sequence in the tx period recovers I S dipolar couplings under MAS. Unlike other SLF pulse sequences, this pulse sequence does not require the synchronization of the tx period with the spinning speed of the rotor.

Figure 6. The proton(I)-carbon(S) dipolar coupling during a C-13 T,p and decoupled Tj experiment are compared. The relaxation rate is determined by the molecular fluctuation at the spin lock frequency u>,c or decoupling frequency a,a-...

Proton-driven spin diffusion (see also Appendix A) is the classical spin-diffusion experiment for low abundant spins. The line width of the one- and zero-quantum lines of the S-spins are mainly determined by the heteronuclear dipolar couplings while the homonuclear I-spin dipolar coupling makes the broadening of the levels homogeneous. Suter and Ernst [12] calculated an approximate value for the zero-quantum relaxation time... 

CP is an effective technique to significantly increase the sensitivity of nonabundant spins S dipolarly coupled with abundant spins I. The principle of the CP experiment is demonstrated in Fig. 5D. In this technique, an indirect excitation of dilute spins S (which are observed) by polarization transfer from abundant spins / (mostly H) is employed. The CP experiment consists of three steps (1) excitation of the I spins by n/2 pulse, (2) polarization transfer from Ito S spins by simultaneous irradiation of the rf fields and of the I and S spins... 

Within this framework, the dipolar coupling between two spins I and S may be described in terms of the Hamiltonian... 

The heteronuclear dipolar coupling between spin species I and S is given in Eq. (2) and rewritten below in different form ... 

Ru dihydride [in the absence of (CF3)2CHOH], and the Ti,min (RuH H) is a minimal relaxation time of the hydride ligand that is involved in dihydrogen bonding. The Ti min CRuH- H) value is calculated from eq. (4.11) as 0.0894 s. This time is remarkably shorter than that in the individual dihydride (0.178 s), due to an additional hydride-proton dipolar coupling. Then this additional relaxation rate, 1/ T i min (RuH- H), governed by the single hydride-proton dipolar contact, is expressed as... 

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