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At an average uranium content of' 3.3 ppb the oceans can be considered as a very low-grade but practically unlimited source of uranium. Some essential chemical aspects of a large-scale sorptive recovery of uranium from seawater are discussed with special emphasis on required sorber properties such as high physical and chemical stability in seawater, fast and selective uptake of uranium, as well as a sufficient loading capacity. Systematic screening tests, including about 200 sorber materials on the basis of organic ion-exchange resins, identified cross-linked poly(acry1amidoximes) as the most promising candidate sorbers. Their uranium uptake closely approaches the uranium content of actually explored uranium ores.

Technetium-99m radiopharmaceuticals are increasingly finding application in nuclear medicine for scintigraphic and emission tomographic imaging, morphologic description and functional testing of organs. Over 80% of the radiopharmaceuticals currently clinically used are labeled with the short-lived, metastable nuclide 99mTc, whose nuclear properties are almost optimal with regard to a low radiation exposure of the patient and an effective detection of the emitted 7 quanta. yymTcOT can be easily prepared without the use of accelerator systems through generator columns. Most of the 99mTc radiopharmaceuticals are complexes which are synthesized by reduction of 9 9 m T~0 4 in the presence of suitable ligands. To achieve a high organ specificity. some understanding of the relationship between the structure of the diagnostic agent and its organ distribution is necessary. Structure analyses can be carried out on analogous compounds of the long-lived nuclide technetium99g; these compounds are obtainable in weighable quantities. The development of new 99mTc radiopharmaceuticals is a challenge to coordination chemists. The syntheses, molecular structures, and applications of the most important y9mTc radiopharmaceuticals will be described in this review. and current directions and tendencies of the development will be shown.

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