Proton nuclear magnetic relaxation time

Fig. 3. Illustration of the origin of proton nuclear magnetic relaxation induced by a super-paramagnetic crystal. The water molecule (symbolized by a bee) experiences a magnetic field which fluctuates because of the translational diffusion and because of Neel relaxation. The bottom curve represents a typical time evolution of this field.

The transition of polyethylene from the orthorhombic to the hexagonal phase was observed at very high pressures (3000-5000 bar) by proton NMR and nuclear magnetic relaxation time measurements the phase diagram derived from this spectroscopy is in substantial agreement with DSC data. According to these results (see Fig. 1), the hexagonal phase can be observed above the triple point at 490 K and 3000 bar [13,14]. 

In protein solutions the water protons may be considered to reside in two different environments, i.e. the bulk water, and the hydration spheres of the protein molecules. If there is fast exchange of protons between these environments a single proton nuclear magnetic resonance will be observed, which corresponds to the average of the resonances in the different environments. Following McConnell (74) the observed longitudinal relaxation time is to a good approximation... 

B. D. Sykes, W. E. Hull, and G.H. Snyder, Biophys. /, 21, 137 (1978). Experimental Evidence for the Role of Cross-relaxation in Proton Nuclear Magnetic Resonance Spin Lattice Relaxation Time Measurements in Proteins. 

The proton spin-lattice relaxation times for solvent water are strongly perturbed if the water is in rapid exchange with a paramagnet. In particular, Mn is a strong relaxer for water protons and thus nuclear magnetic resonance (NMR) spectroscopy provides a sensitive probe for the presence of exchangeable water molecules bound to Mn in Mn proteins. 

Roose et al. (1996) studied the magnetic-field dependence of the proton spin-lattice relaxation time Tj (referred to as nuclear-magnetic-relaxation dispersion) in aqueous colloidal silica containing paramagnetic Mn + ions (Figure 1.112). The experimental relaxation rate of solvent protons in aqueous colloidal silica suspensions containing Mn + ions can be expressed as a weighted mean of several contributions ... 

Note also that the finite time needed to encode the NMR magnetization in fe-space requires that the nuclear spin relaxation time, T2, be sufficiently long. T2 is determined predominantly by internuclear interactions, which in turn are motionally averaged by molecular tumbling. This means in effect that molecules in the liquid state have long proton T2 values (10-1000 ms) while those in the solid state may have relaxation times as short as 10 ps. This results in a sharp discrimination of the signal in which the solid state component is entirely filtered out, unless special... 

Diamagnetic electrolyte solutions Intermolecular nuclear magnetic relaxation rate of proton in water molecules correlation times for molecular rotation in free water and hydrated water self diffusion coefficients of water molecules 84, 85... 

The diffusion of hydrogen atoms in ternary hydrides can be most conveniently studied by means of proton nuclear magnetic resonance (see for instance Barnes et al., 1976). By applying different pulse sequences, experimental information can be obtained about the spin-lattice relaxation time T and the spin-spin relaxation time By means of the relation Tjf = — Tf it is possible to derive the dipolar... 

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