Relaxation lanthanide-induced shifts

NMRD nuclear magnetic relaxation dispersion LIS lanthanide induced shifts ... 

The simultaneous least-squares fits of lanthanide induced relaxation (LIR, 7j) according to eq. (18) and lanthanide induced shifts (LIS) according to eq. (47) with the crystal structures of [R(L6)(N03)](N03)2 as starting molecular models display only minor shift of Will) from its original location. For the lighter lanthanides (R = Ce-Eu), the best fit shows a slight shift... 

Peters, J.A., Huskens, J., and Raber, D.J. (1996) Lanthanide induced shifts and relaxation rate enhancements. Progress in Nuclear Magnetic Resonance Spectroscopy, 28, 283-350. 

Solution structure determination essentially relies on NMR data, via either a classical analysis of the number of signals and of their chemical shifts with the help of two-dimensional COSY, NOESY, and NOEDIF measurements, or the more sophisticated investigation of both lanthanide-induced shifts (LIS) and relaxation times (LIR). When the major species in solution is the heterobimetallic helicate, analysis of the... 

The hydration number q-. this parameter influences strongly the IS contribution (equations (3) and (4)). If this number increases from 1 to 2, the relaxivity increases by about 30%, but most of the Gd-complexes have a q number equal to one. This number can be measured by fluorescence study of europium or terbium complexes or by NMR measuring the lanthanide induced shift (LIS). 

Information on the hydration state of the Gd(III) chelate in solution is indispensable for the analysis of its proton relaxivity Several methods exist to determine q, though they are mostly applicable for other lanthanides than Gd(III). In the case of Eu(III) and Tb(III) complexes, the difference of the luminescence lifetimes measured in D20 and H20 can be related to the hydration number [15, 16]. For Dy(III) chelates, the lanthanide induced 170 chemical shift of the bulk water is proportional to the hydration number [17]. Different hydration states of the same chelate may also coexist in solution giving rise to a hydration equilibrium. Such an equilibrium can be assessed by UV-Vis measurements on the Eu(III) complex [18-20]. These techniques have been recently discussed [21]. 

Detailed solution structures have been obtained thanks to the analysis of the paramagnetic NMR lanthanide-induced relaxation and chemical shifts (Piguet and Geraldes, 2003, see Section 3.4) combined with high-resolution emission spectra recorded for the Eu helicates (Bunzli and Piguet, 2005 see Section 3.5). In all cases, the crystal structures represent... 

Solution structures deduced from LIS data. - Andre et a/." have prepared new ditopic trihelicate lanthanide (La-La -L3) complexes, which they consider of potential utility as biomedical probes. The solution structures of these species were determined by analyses of lanthanide-induced chemical shifts and proton spin relaxation data of mixed complexes containing one diamagnetic Lu + ion and one paramagnetic lanthanide ion. 

In principle, paramagnetic ions also may be used to induce hyperfine shifts in nucleic acids to aid detection of binding sites. Ions with high relative magnetic anisotropy and short unpaired electron relaxation times (i.e., Co Fe and trivalent lanthanide ions except for Gd ) are candidates for such studies. Indeed, Tb and Eu ions have been used as fluorescent probes of nucleic acid structures it is expected that NMR studies also would be informative. " ... 

These comparisons should be taken into account when substituting lanthanide ions for first-row transition-metal ions in order to induce chemical shifts or change the relaxation behavior of a n.m.r. spectrum to elicit ion sequestering and structural information (see later). 

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