Longitudinal NMRD profiles

Evolution of the longitudinal NMRD profile during the agglomeration of particles coated by a polyelectrolyte. 

Fig. 15. Longitudinal NMRD profile of ferritin ( ) and apoferritin ( ) aqueous solutions at 37°C. The contribution of the ferrihydrite core to the relaxation ( ) is obtained by the subtraction of the profiles. Ferritin solution has an iron concentration of 100 mM, while the protein concentration of both samples is 0.058 mM. Longitudinal NMRD profile of akaganeite particles (O) with an iron concentration of 100 mM.

Akaganeite particles Both Ti and T2 are strongly pH-dependent (Pigs. 17 and 19). The amplitudes of the longitudinal NMRD profiles drastically decrease when the pH increases from 3.35 to 9.45. The correlation time associated with the first dispersion is only weakly pH dependent, consistent with its former interpretation as an electron relaxation time. However, T2, the correlation time characteristic of the second dispersion, increases from 30 8 ns at pH 3.35 to 280 32 ns at pH 9.45, which eliminates its interpretation as a diffusion time T2 can be identified as a proton exchange time. 

Fig. 18. Contribution of the ferrihydrite core to the longitudinal NMRD profile of ferritin solutions for different pH values at 37°C. The iron concentration is 100 mM.

Fig. 21. Longitudinal NMRD profile of gadolinium-loaded apoferritin at pH 7 and 25°C. Reproduced with permission from Ref. (60).

The NMRD profile of Mn(H20)g in water solution shows two dispersions (Fig. 10) in the 0.01-100 MHz range of proton Larmor frequency one, at about 0.05 MHz, due to the contact relaxation, and a second, at about 7 MHz, due to the dipolar relaxation (39). The correlation time for contact relaxation is the electron relaxation time, whereas the correlation time for dipolar relaxation is the reorientational time (ir = 3.2 x 10 , in accordance with the value expected for hexaaquametal(II) complexes). This accounts for the different positions of the two dispersions in the profile. From a best fit of longitudinal and transverse proton relaxation profiles, the electron relaxation time is described by the parameters A = 0.02-0.03 cm and... 

The NMRD profiles of water solution of Ti(H20)g" have been shown in Section I.C.7 and have been already discussed. We only add here that the best fit procedures provide a constant of contact interaction of 4.5 MHz (61), and a distance of the twelve water protons from the metal ion of 2.62 A. If a 10% outer-sphere contribution is subtracted from the data, the distance increases to 2.67 A, which is a reasonably good value. The increase at high fields in the i 2 values cannot in this case be ascribed to the non-dispersive term present in the contact relaxation equation, as in other cases, because longitudinal measurements do not indicate field dependence in the electron relaxation time. Therefore they were related to chemical exchange contributions (see Eq. (3) of Chapter 2) and indicate values for tm equal to 4.2 X 10 s and 1.2 X 10 s at 293 and 308 K, respectively. 

The longitudinal relaxation rate inversely decreases with the residence time of water molecules inside the agglomerate. This effect was demonstrated thanks to a controlled and chemically induced process of agglomeration amongst ferrite nanomagnets coated by polyelectrolyte polymers. The NMRD profile becomes flatter on increasing agglomeration (Pig. 10). 

Fig. 20. Longitudinal and transverse NMRD profiles of magnetoferritin at 37°C. Reproduced with permission from Ref. 58).

Fig. 5.3. Water proton longitudinal relaxivity as a function of proton Larmor frequency ( H NMRD profiles) for solutions of Fe(OH2) + at ( ) 278 K, ( ) 288 K, (A) 298 K, ( ) 308 K. High field transverse relaxivity data at 308 K >) are also shown. The lines represent the best fit curves using the Solomon-Bloembergen-Morgan equations (Eqs. (3.11), (3.12), (3.16), (3.17), (3.26) and (3.27)) [4],...

The mobility of proton containing molecules in foods can be investigated by the acquisition of Nuclear Magnetic Resonance Dispersion (NMRD) profiles that report about the changes in the H-spin-lattice or longitudinal relaxation rate (Ri=l/Ti) as function of the applied magnetic field strength. 

The NMRD profiles for TBVM samples showed much higher longitudinal relaxation rate values with respect to the BVM samples over the whole proton Larmor fi-equency... 

Fig. 10. Water NMRD longitudinal ( ) and transverse (O) profiles for Mn(H20)g" solutions at 298 K (39).

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