ИСТИНА

Long-lived 99Tc has the spin of the nucleus 9/2, so it is an NMR active isotope. Thus, 99Tc- NMR can be applied to investigations in chemistry and nuclear medicine. Some recent advances are summarized in an excellent review by Farnan and Berthon [1]. Here we present new results on Tc speciation and analyses. Tc speciation was investigated the in H2SO4 from 2 M to 18 M, and the resulting complexes were characterized by NMR exchange spectra and EXAFS spectroscopy [2]. According to NMR, the TcO4 - species transformation is complete at 12 M.When KTcO4 is dissolved in 12 M H2SO4, EXAFS measurements on the resulting yellow solution indicated the presence of the [TcO3(H2O)3]+ cation. NMR was applied to recognition receptor design and characterization. The reverse NMRtitration method, in which concentration of pertechnetate was kept constant, showed [3] good reproducibility (Fig.2). Binding constants of 4 for TcO4 - were found to be logK = 3.00. Another application is based on the interaction of 99Tc nucleus spins with the spins of surrounding nucleus. 99Tc NMR has been suggested as an original method of evaluating the content of oxygen isotopes in oxygen O18-enriched water, a precursor for the production of radioisotope fluorine-18 used in positron emission tomography. To this end, solutions of NH4TcO4 or NaTcO4 (up to 0.28 mol/L) with natural abundance of oxygen isotopes in virgin or recycled 18O-enriched water have been studied by 99Tc NMR.The method is based on 16O/17O/18O intrinsic isotope effects in the 99Tc NMR chemical shifts, and the statistical distribution of oxygen isotopes in the coordination sphere of TcO4 - and makes it possible to quantify the composition of enriched water by measuring the relative intensities of the 99Tc NMR signals of the Tc16O4−n 18On − isotopologues. TcO4 - ion was selected as a probe due to its high stability in aqueous solutions and the significant 99Tc NMR shift induced by a single 16O→18O substitution (−0.43 ± 0.01 ppm) in TcO4 - and spin coupling constant 1J(99Tc– 17O) (131.46 Hz), favorable for the observation of individual signals of Tc16O4−n 18On− isotopologues.