Solid proton spin-lattice relaxation

Quantitative solid state 13C CP/MAS NMR has been used to determine the relative amounts of carbamazepine anhydrate and carbamazepine dihydrate in mixtures [59]. The 13C NMR spectra for the two forms did not appear different, although sufficient S/N for the spectrum of the anhydrous form required long accumulation times. This was determined to be due to the slow proton relaxation rate for this form. Utilizing the fact that different proton spin-lattice relaxation times exist for the two different pseudopolymorphic forms, a quantitative method was developed. The dihydrate form displayed a relatively short relaxation time, permitting interpulse delay times of only 10 seconds to obtain full-intensity spectra of the dihydrate form while displaying no signal due to the anhydrous... 

Fig. 1. Magnetic field dependences of the proton spin-lattice relaxation time of water in Bioran B30 and Vycor glasses at temperatures above 27°C and below the temperature where the non-surface water freezes ( —25°C and —35°C). The solid lines represent the power law in the Larmor frequency with an exponent of 0.67 (34).

Fig. 2. Water proton spin-lattice relaxation dispersion in Cab-O-Sil M- samples with two different degrees of compression. The solid lines were computed using the model as in Ref. (45).

Fig. 18. The proton spin-lattice relaxation rate recorded as a function of the magnetic field strength plotted as the proton Larmor frequency for lysozyme samples. Dry ( ), hydrated to 8.9% ( ), 15.7% (O). 23.1% (A), and cross-linked in a gel ( ). The solid lines were computed from the theory. The solid lines are fits to the data using Eq. (4) with Rs given by Eq. (6). The two parameters adjusted are Rsl and b (97). The small peaks most apparent in the dry samples are caused by cross-relaxation to the peptide nitrogen spin (90,122).

Strong evidence of the dominant Influence of molecular conformation on the properties of coals Is Implicit In the several data sets which show an extremum In the measured property when plotted against carbon rank. Examples are the extrema which occur In the solid state properties of mass density (22,23) and proton spin-lattice relaxation rate (24) as well as In solvent swelling and extractablllty ( ). 

Mamniashvili G.I., Namoradze N.Z., Ratishvili I.G., Sharimanov Yu.G. Proton Spin-Lattice Relaxation Time in Ordering VHX alloys . J. Phys. Chem. Solids (2005), 66, 1192-1199. 

Regarding quantitation in the CP/MAS experiment, for peak areas to accurately represent the number of nuclei resonating, one of the conditions that must be met is that the time constant for cross polarization must be significantly less than the time constant for proton spin lattice relaxation in the rotating fi ame, Tch or Tnh TipH. Other factors affecting quantitation in CP/MAS have been discussed in several reviews (28-33). Since no analyses of the spin dynamics were performed in this study, the solid state spectra presented in this manuscript will be interpreted only semiquantitatively. 

The proton-spin-lattice relaxation time, T , in a diamagnetic sample is typically dominated by the dipole-dipole interactions among the protons, and is particularly sensitive to molecular motions therefore, T values have been used widely to derive information about domain uniformity or phase separation in solids. In single-phase solids with an abundance of protons, the protons are usually so strongly coupled by homonuclear dipolar interactions that possible differences in proton spin-lattice relaxation are averaged out by spin diffusion, and a single T will be observed in this case. In heterogeneous samples, different T values can be observed for different phases. 

Figure 26.16 The temperature dependence ofthe jump rates ry for deuterium in TaViDos and TaVjDu, as determined from the spin lattice relaxation data [72], The solid lines show the fits of Eq. (26.29) to the data. The dashed line represents the behavior of Ty (l) for H in TaVjHo jj, as derived from the fit of Eq. (26.29) to the proton spin-lattice relaxation data (Ref [54]).

Since the nuclei obtain their polarization from the spins, it is the proton spin-lattice relaxation time (T ) which determines the repetition rate of the CP experiment. This circumvents the problem of the long C values normally found in solids. In addition, the C signal shows an enhancement in its intensity, which can be as large as yn/yc = 4. The CP experiment results in both a time-saving and an improvement in the signal-to-noise ratio in the C NMR spectrscopy of solid samples. 

Solid-state spin-lattice relaxation rates in the rotating frame, Rip, contain useful information about slow motions with correlation times in the range of microseconds [146]. The measured Rjp data, however, contain the foUow-ing two relaxation pathways the spin-lattice contribution describing slow motions (Rip) and the interfering spin-spin contribution from a thermal coupling between Zeeman carbon (or nitrogen) and dipolar proton reservoirs (Rch)-... 

Figure 2. Proton spin-lattice relaxation time T, obtained by field cycling as a function of the Larmor frequency CO/2n for the smectic C phase of a biforked liquid crystal. The solid line is the best fit of a model taking into account collective movements, self diffusion, and molecular rotation. Reprinted with permission from [41].

Figure 8 Pressure dependence of the proton spin-lattice relaxation times, 7, of solid adamantane in its two phases at different temperatures. The open symbols denote values obtained in the compression run whereas the filled symbols give values for the decompression run.

The combining NMR techniques in the solid state permit the evaluation of the polymeric systems homogeneity. In polycarbonate-polyvinyl pyrrolidone blends, the response of proton spin-lattice relaxation time in the rotating frame was the determinant to obtain information on the transition when the quantity of polyvinyl pyrrolidone is close to 40 wt% and a better organisation of amorphous phase was detected. 13 refs. 

Different solid-state NMR techniques CPMAS NMR, the second moment of the signal, the spin-lattice relaxation time in the rotating frame T p) were combined to reach the conclusion that in the case of por-phine H2P the double-proton transfer is followed by a 90° rotation within the crystal (see Scheme 2). 

Figure 1 Schematic representation of the 13C (or 15N) spin-lattice relaxation times (7"i), spin-spin relaxation (T2), and H spin-lattice relaxation time in the rotating frame (Tlp) for the liquid-like and solid-like domains, as a function of the correlation times of local motions. 13C (or 15N) NMR signals from the solid-like domains undergoing incoherent fluctuation motions with the correlation times of 10 4-10 5 s (indicated by the grey colour) could be lost due to failure of attempted peak-narrowing due to interference of frequency with proton decoupling or magic angle spinning.

Fig. 13. The nuclear magnetic spin-lattice relaxation rate for water protons as a function of magnetic field strength reported as the proton Larmor frequency at 298 K for 5% suspensions of the particulate stabilized in a 0.5% agar gel presented as the difference plot (A) Zeolite 3A (B) Zeolite 13X (C) Zeolite NaY (D) kaolin with 7 s added to each point to offset the data presentation (E) Cancrinite with 9 s added to each point to offset the data presentation and (F) 0.5% agar gel profile with 10 s added to each point. The solid lines are fits to a power law (68).

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