Proton-detected local field

Fig. 3. Contour plot of the proton-detected local field (PDLF) spectrum of a static 5CB sample. The traces taken parallel to for each carbon site show distinct doublets that are related to individual C-H couplings. (Reproduced by permission of American Chemical Society.)...

Ramamoorthy and co-workers126 have recently reported proton-detected local field (PDLF) sequence to define the structure and dynamics of biological membranes. As was shown for this kind of laboratory-frame separated-local-field experiment, simple modification in the 2D PDLF sequence enables the measurement of remote 13C-31P and 1H-31P couplings in magnetically aligned bicelles. 

A novel MAS NMR approach has been presented for the determination of motionally averaged heteronuclear dipolar couplings in unoriented materials. The technique is based on the proton-detected local field protocol and achieves dipolar recoupling by R-type RF irradiation. The experiment, which is called R-PDLF spectroscopy, is demonstrated on solid and liquid-crystalline systems. For mobile systems, it is shown that the R-PDLF scheme provides better dipolar resolution as compared to techniques combining conventional separated local field spectroscopy with R-type recoupling. 

In separated local field experiments, the sites are separated in the Vj dimension of a 2D experiment according to their chemical shifts and correlated with their individual dipole-dipole couplings (their local fields) in the V2 dimension. The original C-detected local-field spectra are more complicated than the more recently introduced proton-detected local-field spectra [86]. When using C detection, each C... 

Ferreira et al. ° have reported cholesterol and POPC segmental order parameters in lipid membranes using solid state R-type proton-detected local field (R-PDLF) NMR with CP and INEPT as polarization... 

In the proton-detected local field (PDLF) [38-40] experiment (Figure 4-3b), magnetization evolves under the local field of rare spins during L and is subsequently transferred to spin for detection. Hence, PDLF dipolar spectrum is governed by two-spin dipolar interactions, which leads to a superposition of dipolar doublets. 

Figure 14.11 Basic 2D pulse sequence used for the measurement of residual dipolar local fields. After the excitation pulse the spins are allowed to evolve for some time tj (indirect dimension) under influence of the relevant spin interactions before crosspolarisation takes place. The direct detection during time t2 then takes place on the 13C side typically under proton dipolar decoupling (DD). The basic scheme can be extended by various spin manipulation techniques (not shown) during time tj. For instance, the heteronuclear dipolar contribution can be removed by a decoupling pulse...

Separated-local-field experiments are commonly used to measure the heteronuclear dipole-dipole interactions (called local-field in the molecule) in solids [2, 4, 30], These are two-dimensional pulse sequences as depicted in Figure 3-4 that consists of preparation, evolution and detection periods. A 90° pulse on the I nuclear spin (abundant nuclei like protons) channel followed by the cross-polarization sequence is the typical preparation period of the pulse sequence. This preparation step generates transverse magnetization of S nuclei (less sensitive nuclei like 13C) that evolves during the evolution period (tl) of the sequence under a suitably dressed Hamiltonian. There are a number of pulse sequences that differ in 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,... 

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