Nuclear magnetic relaxation

If one perturbs a physical system from equilibrium and then removes the perturbing influence, the system will return to its original equilibrium condition. This does not happen instantaneously but occurs over some time, according to the equation 

Methods for measuring Ti and T2 are discussed in Chapter 5 of reference 21. Suffice it to say here that understanding the method for measuring T2 (the Carr-Purcell pulse sequence or spin-echo method) becomes important for discussing two-dimensional NMR spectra. When spin-spin coupling is present, a modulation of spin echoes is produced, and it is this fact that is important in 2-D NMR spectroscopy. Nuclear relaxation rates and mechanisms become important when discussing the effect of paramagnetic metal centers on NMR spectroscopy. 

One can distinguish three regions for such a relationship (i) an extreme narrowing limit 1) on the left of Fig. 9.3, for which the equality Ri = J 2 is valid, 

Nuclear relaxation rates have been used in studies of CyD complexes for the determination of correlation times, thus giving insight into the dynamics of the host and/or guest in the complex. H selective and nonselective longitudinal relaxation rates enable us to characterize the dynamics of the acridine-yS-CyD complex [9]. Proton longitudinal, Ri( H), and transverse, R2( H), relaxation rates were used to determine the motion of (+)camphor guest molecules in both diastereomeric complexes with a-CyD [10]. The Ri( C) rates were used as early as 1976 to obtain correlation times for guest and host molecules in complexes formed by a-CyD with three aromatic compounds [llj. The Ri( C) rates were also used for the determination of correlation times of constituents and complexes of several CyDs with azo dyes [12]. 

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Hertz, H. G. Nuclear Magnetic Relaxation, in Water — a Comprehensive Treatise, (ed. Franks, F.), Vol. 3, chapter 7, New York, Plenum Press 1973... 

Hubbard P. S. Theory of nuclear magnetic relaxation by spin-rotational interactions in liquids. Phys. Rev. 131, 1155-65 (1963). 

IL Claeys, FH Arnold. Nuclear magnetic relaxation study of hindered rotational diffusion in gels. AIChE J 35 335-338, 1990. 

McConnell, J. The Theory of Nuclear Magnetic Relaxation in Liquids 1987, Cambridge University Press Cambridge. 

Nuclear magnetic relaxation, recent problems and progress, 16,239... 

Nuclear Magnetic Relaxation Studies on Actinide Ions and Models of Actinide Complexes Jean F Desreux... 

Norbornyl cation reappraisal of structure, 11, 179 Nuclear magnetic relaxation, recent problems and progress, 16, 239 Nuclear magnetic resonance see NMR Nuclear motion, principle of least, 15, 1... 

Nozzle Beams, Supersonic (Anderson, Andres, Fenn). Nuclear Magnetic Relaxation Methods for the Study of 10 275... 

Study of Specific Molecular Interactions by Nuclear Magnetic Relaxation Methods (Jardetzky). ... 

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 this connection, attention should be paid to an unusual NMR technique called nuclear magnetic relaxation dispersion (NMRD). In contrast with NMR spectroscopy, the NMRD signal arises from the nuclei of the abundant solvent molecules and not from the dissolved substances. The relaxation properties of the solvent molecules are profoundly modified if the solvent contains paramagnetic particles (see a review by Desreux 2005). A solvent molecule sails in the vicinity of an ion-radical and finds itself in the local magnetic field of this paramagnetic particle. Then, induced magnetism of the solvent molecule dissipates in the solvent bulk. This kind of relaxation seems to be registered by NMR. NMRD is applicable to studies on ion-radical solvation/desolvation, ion-pair dynamics, kinetics of ion-radical accumulation/consumption, and so on. 

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.

NUCLEAR MAGNETIC RELAXATION STUDIES ON ACTINIDE IONS AND MODELS OF ACTINIDE COMPLEXES... 

The dependence of T (B) on the field B was soon nicknamed as the Ti dispersion curve or, more recently, as the Nuclear Magnetic Relaxation Dispersion (NMRD) profile. The first experimental curve of this type (Pig. 1) was published in 1950 by Ramsey and Pound (15,16). 

Bloembergen, N. Nuclear Magnetic Relaxation , Martinus Nijhoff The Hague, 1948, reprinted by Benjamin New York, 1961. 

Two-dimensional heteronuclear ( H- N) nuclear magnetic relaxation studies indicate that the dihydrofolate reductase-folate complex exhibits a diverse range of backbone fluctuations on the time-scale of picoseconds to nanoseconds To assess whether these dynamical features influence Michaelis complex formation, Miller et al used mutagenesis and kinetic measurements to assess the role of a strictly conserved residue, namely Gly-121, which displays large-amplitude backbone motions on the nanosecond time scale. Deletion of Gly-121 dramatically reduces the hydride transfer rate by 550 times there is also a 20-times decrease in NADPH cofactor binding affinity and a 7-fold decrease for NADP+ relative to wild-type. Insertion mutations significantly decreased both... 

The T2 spin-spin nuclear magnetization relaxation time values demonstrate that the Ti disorder above Tc is dynamic and not static (Fig. 6). 

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