Proton nuclear magnetic relaxation

The three different mechanisms which traditionally describe the ability of a CA to catalyze the water proton nuclear magnetic relaxation present themselves in different degrees of relative importance in determining the overall relaxivity. This latter attribute primarily depends on the structural properties of the CA, the temperature and the pH of the aqueous solution, and on the observation frequency. The CAs that are currently used in clinical practice are low molecular weight hydrophilic monoaqua Gd(III) complexes (Chart 2) that, at 25° C and 20 MHz, possess a relaxivity of about... 

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 pronounced increase above pH 9.3 of the proton nuclear-magnetic relaxation rates in aqueous solutions of (Cu",Zn )-BESOD at 295 K and 30 MHz was interpreted by the cleavage of His-61 from Cu and its replacement by an equatorial OH". The axial HjO on Cu remained unaffected... 

The proton nuclear magnetic relaxation dispersion profiles as well as the l70 temperature dependency were analysed. Best-fit parameters are given in Tables 7.18 and 7.19. 

P.-O. Westlund, N. Benetis, and H. Wennerstrdm, Paramagnetic Proton Nuclear Magnetic Relaxation in the Ni + hexa-aquo Complex. A Theoretical Study, Mol. Phys., 61 (1987), 177-194. 

Hershberg, R. D., Reed, G. H., Slotboom, A. J., and de Haas, G. H. (1976). Phospholipase A2 complexes with gadolinium (III) and interaction of the enzyme-metal ion complex with monomeric and micellar alkylphosphorylcholines. Water proton nuclear magnetic relaxation studies. Biochemistry 15,2268-2274. 

Haranczyk, H., Strzalka, K., Jasinski, G., and Mosna-Bojarska, K. 1996. The initial stages of wheat (Triticum aestivum, L.) seed imbibition as observed by proton nuclear magnetic relaxation. Colloid. Surf. A Physicochem. Eng. Aspects 115 47-54. 

Some recent papers permit an exciting outlook on the degree of sophistication of experimental techniques and on the kind of data which may be available soon. In the field of NMR spectroscopy, a publication by Hertz and Raedle 172> deals with the hydration shell of the fluoride ion. From nuclear magnetic relaxation rates of 19F in 1M aqueous solutions of KF at room temperature, the authors were able to show that the orientation of the water molecules in the vicinity of fluoride ions is such that the two protons are non-equivalent. A geometry is proposed for the water coordination in the inner solvent shell of F corresponding to an almost linear H-bond and to an OF distance of approximately 2.76 A, at least under the conditions chosen. 

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... 

Relaxation Measurements. Measurements of the magnetic fieldz dependence of the solvent water proton relaxation rate (T] l), i.e., nuclear magnetic relaxation dispersion (NMRD), were made by the field cycling method previously described (9,10). 

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. 

R272 E. E. Burnell, D. Capitani, C. Casieri and A. L. Segre, A Proton Nuclear Magnetic Resonance Relaxation Study of C12E6/D2O , J. Phys. Chem. B, 2000,104, 8782... 

The main mechanism for the relaxation of 15N nuclei with directly bonded protons is the hMH dipolar interaction. Under the extreme spectral narrowing condition, (coN + ooH) tc 1, where raN and raH are corresponding resonance frequencies, the nuclear magnetic relaxation is given by ... 

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