Proton dipolar spin-lattice

The interpretation of carbon Tip data is complicated by the fact that spin-spin (cross-relaxation) processes as well as rotating frame spin-lattice processes may contribute to the relaxation. This arises because the proton dipolar state is strongly coupled to the lattice. During the period in which carbon magnetization decays with H] h off, carbon polarization can decay by motional processes (Tjp) or by polarization transfer to the proton dipolar state (T p ), then to the lattice via the proton dipolar spin-lattice process Schaefer et al., ... 

Figure 8. During the C-13 T,p experiment, the protonated (primed) and unpro-tonated (unprimed) carbons are in contact with not only the lattice but also the proton dipolar reservoir. Here T,n (frot) indicates a dipolar spin-lattice process which depends on spinning speed and orientation.

This simple theoryis based on the expectation that, to a reasonable degree of approximation, proton-proton, dipolar contributions to the measured spin-lattice relaxation-rate are pairwise additive and decrease as a simple sixth power of the interproton distance. The simplified version of the dipole-dipole mechanism is summarized in the following two equations for spin i coupled intramolecularly with a group of spins j... 

Jonas et al. measured the proton rotating frame spin-lattice relaxation time (Tip) at pressures from 1 bar to 5000 bar and at temperatures of 50 to 70 °C for DPPC and at 5 to 35 °C for POPC. If intermolecular dipolar interactions modulated by translational motion contribute significantly to the proton relaxation, the rotating frame spin-lattice relaxation rate (1/Tip) is a function of the square root of the spin-locking field angular frequency... 

Self diffusion coefficients of deuterated toluene were measured, rather than protonated toluene in order to minimize the experimental difficulties associated with very long proton spin lattice relaxation times (T- ). Since the value of the T1 determines the length of time between pulse sequences, a long relaxation time leads to prohibitively long measurement times. Previous measurements (36-38) of proton and deuterium relaxation times in liquid toluene have been made as a function of temperature and pressure. The relaxation is due to dipolar interactions in protonated toluene and quadrupolar interactions in toluene-dg. Therefore, the relaxation times can be expected to increase with increasing temperature. However, the quadrupolar relaxed deuterium T. values are smaller than the proton T1... 

If the cross-relaxation to the dipolar reservoir is longer than the proton spin-lattice relaxation, T p, then the T p for the CH carbon will be ca. 1.7-2.Ox that of the CH2 carbon for spin-spin domination of the rotating-frame relaxation. This is roughly the result observed in the data displayed in Figure 13. The explanation is based on the approximate two-fold difference in the CH second moments for the two types of carbons (for full details see Reference 40). 

Key Words Dipolar glasses, Ferroelectric relaxors, Conducting polymers, NMR line shape, Disorder, Local polarization related to the line shape, Symmetric/asymmetric quadrupole-perturbed NMR, H-bonded systems, Spin-lattice relaxation, Edwards-Anderson order parameter, Dimensionality of conduction, Proton, Deuteron tunnelling. 

For the partially deuterated benzoic acid (C6D5COOH), the solid state H NMR spectrum is dominated by the intra-dimer H- H dipole-dipole interaction. In a single crystal, both tautomers A and B are characterised by a well-defined interproton vector with respect to the direction of the magnetic field (Fig. 1). Proton motion modulates the H- H dipole-dipole interactions, which in turn affects the H NMR lineshape and the spin-lattice relaxation time. It has been shown that spin-lattice relaxation times are sensitive to the proton dynamics over the temperature range from 10 K to 300 K, and at low temperatures incoherent quantum tunnelling characterises the proton dynamics. A dipolar splitting of about 16 kHz is observed at 20 K. From the orientation dependence of the dipolar splitting, the... 

Determination of ET rate constants. The proton relaxation of the cyclopentadienyl (cp) ring of the present mixed-valence complex is caused by the magnetic dipolar interaction with the electron spin on the Fe(III) ion of the fetiicenium unit (S=l/2). Then the proton spin-lattice relaxation rate of bfc+, 1/Ti, is represented by ... 

In HRu3(CO)9C2 Bu, the proton relaxation times T are 0.2 s and 2.9 s for t-butyl and for the hydride resonance, respectively. The latter value is significantly shorter than that found for H20s3(CO)io and indicates that dipolar coupling between the methyl groups and the hydride ligand does provide an efficient spin-lattice relaxation pathway. 

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