Lanthanides medical applications

Medical applications are so far limited in number, but gadolinium complexes of DTPA and other hgands have become highly important injectible MRI contrast agents (see Metal-based Imaging Agents). The luminescent properties of the lanthanides are becoming exploited in luminescent sensors and bioassays. 

The 2PA effect has been widely involved in numerous appheations as reviewed by Prasad et al. [25], such as frequency-up conversion lasing [26], optical power limiting [27,28], microfabrication [29,30], optical data storage and processing [31 ] and biological or medical applications [32]. As this chapter, which addresses 2PA of lanthanide complexes, will concern mainly biological applications, we will focus in this part on two-photon excited fluorescence microcopy in biology. 

Although nuclear magnetic resonance (NMR) spectroscopy has been used to study a variety of lanthanide based systems like contrast agents for medical imaging applications, only a handful of studies on lanthanide SMMs using NMR have been performed to date. These include the neutral [Ln(Pc)2]°(Ln = Dy or Tb)... 

For the application of lanthanide complexes in medical diagnosis and therapy, a general requirement is that the ion Ln3+ and the ligand should remain associated while the complex is in the body, i. e. their dissociation should be minimal, since the free ligand and Ln3+ are toxic. For the dissociation to be negligible, the complexes must be kinetically inert under physiological conditions. Since the complexation properties of the lanthanide ions and Y3+ are quite similar, it is of interest to compare the results obtained as concerns the kinetic behavior of Gd3+ complexes with those known for the complexes of other lanthanides and Y3+. 

The discussed examples clearly demonstrate the importance of azamacrocycles as structural element to create supramolecular function. Their rigid structure, the basicity and transition metal-ion coordinating ability make them suitable as scaffolds and binding sites. Lanthanide chemosensors containing azamacrocyclic ligands have already reached applications in medical diagnostics. Other applications of azamacrocyclic systems with supramolecular functions, particularly in biochemistry, will follow. 

So far in this section the examples discussed have comprised of hetero aromatic antenna receptors, which mainly function as pH sensors. The detection of metal cations in biological, medical and ecological applications is of major interest. However, this requires more elaborate receptors that can selectively bind a specific metal cation. Naturally, the more elaborate the receptor required, the more challenging its synthesis becomes. The synthesis of lanthanide-based sensors of 53 and 54 has been reported with each ligand incorporating an antenna/receptor selective for zinc(ll) [158,159]. In both cases the receptors are structurally similar, with 53 synthesised from benzylamine and 54 from aniline. 

Some uses of the lanthanides, such as in certain steel alloys or as cigarette lighter flints, require no separation of the metals as obtained from certain ores. In other applications, such as phosphors for television screens, medical immunoassays, X-ray photography, and, of course, the study of their chemistry, the individual elements must be separated.7... 

As mentioned earlier, the combination of the imique properties of lanthanide compounds and nanoscale objects has already found a wide range of commercial applications in many industries. New potential apphcations in medical diagnosis are also actively being pursued. In this section, brief descriptions of some common apphcations are given. 

The rare metal thulium has almost no practical applications. What it can provide is available -more cheaply - from other lanthanides. It has been suggested, however, that the metal could be incorporated in ceramics, making them magnetic. If so, this material could be used in microwave equipment The y-radiation from the radioactive isotope °Tm has been examined for use in materials testing and as a portable X-ray source for medical use. 

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