Nuclear relaxation in paramagnetic lanthanide

Nuclear relaxation in paramagnetic lanthanide complexes for extracting R-nucleus distances... 

For any nucleus i of a paramagnetic lanthanide complex in the absence of significant chemical exchange, the experimental longitudinal (l/7 p) and transversal (1 /7 xp) nuclear relaxation rates are given by eqs. (4), (5) in which 7]dia corresponds to the characteristic relaxation times of the same nucleus i in the analogous diamagnetic complex (R = La, Y, Lu) and 7)para are... 

In order to characterize the active site structure of Ca ATPase from sarcoplasmic reticulum, we have employed Gd + as a paramagnetic probe of this system in a series of NMR and EPR investigations. Gadolinium and several other lanthanide ions have been used in recent years to characterize Ca + (and in some cases Mg2+) binding sites on proteins and enzymes using a variety of techniques, including water proton nuclear relaxation rate measurements (35,36,37), fluorescence (38) and electron spin resonance (39). In particular Dwek and Richards (35) as well as Cottam and his coworkers (36,37) have employed a series of nuclear relaxation measurements of both metal-bound water protons and substrate nuclei to characterize the interaction of Gd + with several enzyme systems. 

The exponential dependence on inverse temperature, predicted by eqs. (186) and (187), is characteristic of the spin-lattice relaxation of nuclei of lanthanide ions in the VV paramagnets in a certain temperature region. Some experimental results on nuclear relaxation, induced by hyperfine magnetic field fluctuations, are given in table 15. 

Five reviews have appeared Nuclear magnetic resonance of paramagnetic compounds , Advances in single- and multi-dimensional NMR spectroscopy of paramagnetic metal complexes , NMR and spin relaxation in dimers , Liquid-liquid extraction and NMR , which contains the use of lanthanide and actinide ions to determine distances, and Lanthanide(III) chelates for NMR biomedical applications . ... 

Similarities exist between the chemical characteristics of the actinides and those of the lanthanides. The metal ions are generally considered to be relatively hard Lewis acids, susceptible to complexation by hard (i.e., first row donor atom) ligands and to hydrolysis. Both actinide and lanthanide ions are affected by the lanthanide contraction, resulting in a contraction of ionic radius and an increasing reluctance to exhibit higher oxidation states later in the series. Most species are paramagnetic, although the electron spin-nuclear spin relaxation times often permit observation of NMR spectra, and disfavor observation of ESR spectra except at low temperatures. The elements display more than one accessible oxidation state, and one-electron redox chemistry is common. 

Relaxivity A measure of the effect of a paramagnetic ion, such as gadolmium(lll) on the nuclear excited state lifetime of any adjacent nucleus, that of the proton being most important in current applications of the lanthanides. 

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