Technetium chemistry of

Department of Chemistry, University of Cincinnati, Cincinnati, OH 45221 B. L. BARNETT 

Miami Valley Laboratories, Procter Gamble Company, Cincinnati, OH 45239 

The use and importance of technetium-99 m in nuclear medicine has been noted many times (1-4), and is further discussed by Marzilli et al. in this symposium (5). However, realization of the full potential of tech-netium-99m for diagnostic imagir of internal organs will require a much more extensive and detailed knowledge of technetium chemistry than is now available (1-5). This review covers some recent developments in the synthetic and structural aspects of technetium chemistry that may be relevant to the preparation, use, and understanding of the mode of action, of technetium radiopharmaeeuticals. 

Current Radiopharmaceutical Synthesis. The aqueous chemistry of technetium is dominated by the oxidizing power of soluble TcO , and the thermodynamic stability of insoluble TcOa. All technetium-99m radiopharmaceuticals, except pertechnetate itself, are prepared by the aqueous reduction of pertechnetate in the presence of a potential ligand to prevent Tc02 deposition (2). The most commonly employed reductant is stannous chloride, although many other reductants can, and have, been used (1,2). 

While widely used, this procedure is subject to several difficulties and limitations, (a) It allows introduction of only one type of ligand, or one distribution of ligands, into the technetium radiopharmaceuticaL (b) It does not allow specific control over the final oxidation state, coordination number, coordination geometry, etc. of the technetium in the Tc-L product, (c) The reductant, especially Sn, is often incorporated into the final product (1,6). (d) The excess reductant is injected into the patient tindl) has a long biological half-life (7) and causes several deleterious side effects (8). 

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