Tritium labelled cholesterol, its synthesis and stability studies

By the detritiation of contaminated moderator from Cernavoda Nuclear Power Plant a raw material is obtained, with an economic value of ∼ 3 USD/Ci. It might be stored for long-term in order to be used in controlled fusion or, it might be immediately used in the synthesis of labelled compounds with an economic value up to 5 orders of magnitude higher than the raw material. Cholesterol-T-G was synthesized using the isotopic exchange technique in heterogeneous catalysis. Two methods were tested for: (a) labelling at neutral pH and b) labelling at acidic pH. Higher specific activities (54 Ci/mmol) were obtained when the second method was applied, similar to those obtained in the case of labelling through chemical synthesis. The stability test of the labelled synthesized compound consisted in two steps: one of theoretical analysis and quantum chemistry modelling of the decomposing processes and the second one of identification of critical storing parameters of the labelled compound. The quantum chemistry modelling of radiolytic processes made it possible highlighting radiolytic interaction zone (LUMO orbital) and of labile chemical bonds in the radiolytic process. The chromatographic analysis of cholesterol-T-G samples confirmed the major role of the secondary radiolytic processes. Accordingly, critical storing parameters of labelled cholesterol appear to be the radiochemical purity and the working temperature. (authors)