Lanthanide-induced relaxation time

It is difficult to use lanthanide-induced relaxation data to obtain accurate distances between various nuclei and the lanthanide ion. If it can be shown that the dipolar contribution to either Tj or Tj is dominant, then the difficulty is related to a means to determine accurate values of the electron-spin relaxation times. If the Curie contribution can be shown to dominate, then the problem is measuring accurate correlation times. However, the major difficulty is that the relative dipolar and Curie contributions to T] and Tj are generally not known. However, since both the Curie and dipolar contributions to Tj" and dependency on the R " -nucleus distance, ratios of Ti or... 

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. " ... 

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 decision as to which metal to choose for a particular experiment is also dictated by the fact that, in addition to shift changes, all of the lanthanides produce some change in the nuclear relaxation-times of the substrate, and thereby increase the line-widths of the n.m.r. transitions. The ratio of shift change to line broadening is optimal for such metals as europium (III) and praseodymium (III), which are, therefore, the most suitable for use as shift reagents. In contrast, gadolinium (III) is totally unsuited for this particular purpose, as it induces substantial... 

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