Proton magnetization, time dependence

In addition to measuring TCH for the polymorphic system in question, the proton T value must be determined since the repetition rate of a CP experiment is dependent upon the recovery of the proton magnetization. Common convention states that a delay time between successive pulses of 1-5 X T, must be used. Figure 10B outlines the pulse sequence for measuring the proton Tx through the carbon intensity. One advantage to solids NMR work is that a common proton Tx value will be measured, since protons communicate through a spin-diffusion process. An example of spectral results obtained from this pulse sequence is displayed in Fig. 12. 

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).

Sobol et al.8 have measured proton SLR time (7 ) in Rb1 x(NH4)xH2As04 systems in the range 100-4.2 K. Magnetization recovery was found to be non-exponential in the entire range of temperature. The MR data fit to a stretched exponential recovery and the exponent a was found to be temperature dependent implying broadening of the distribution of microscopic correlation times p(r ) with decreasing temperature. 

An extensive solid-state cp/mas study was undertaken to determine 7) time-constants of 13C nuclei in the crystalline methochloride salt (22), and the results are reported in Fig. 6.29 Local magnetic fields from the two sets of rapidly rotating methyl proton magnetic dipoles (estimated to revolve at ca. 109 rotations/s in the solid)34 provide a distance-dependent relaxation mechanism for the neighboring... 

The time dependence of the magnetization for the proton systems in a hydrated protein may be described heuristically by two coupled equations containing three relaxation rates R- , the longitudinal relaxation rate for the water in the absence of the protein proton interaction R]p, the longitudinal relaxation rate for protein protons in the absence of a relaxation path provided by water protons and Rt, a rate of magnetization transfer between the two spin systems. The equations then become... 

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