Abstract
The fact that a protein crystal can serve as a chemical reaction vessel is intrinsically fascinating. That it can produce an electron-dense tetranuclear rhenium cluster compound from a rhenium tri-carbonyl tri-bromo starting compound adds to the fascination. Such a cluster has been synthesized previously in vitro, where it formed under basic conditions. Therefore, its synthesis in a protein crystal grown at pH 4.5 is even more unexpected. The X-ray crystal structures presented here are for the protein hen egg-white lysozyme incubated with a rhenium tri-carbonyl tri-bromo compound for periods of one and two years. These reveal a completed, very well resolved, tetra-rhenium cluster after two years and an intermediate state, where the carbonyl ligands to the rhenium cluster are not yet clearly resolved, after one year. A dense tetranuclear rhenium cluster, and its technetium form, offer enhanced contrast in medical imaging. Stimulated by these crystallography results, the unusual formation of such a species directly in an in vivo situation has been considered. It offers a new option for medical imaging compounds, particularly when considering the application of the pre-formed tetranuclear cluster, suggesting that it may be suitable for medical diagnosis because of its stability, preference of formation and biological compatibility.
Highlights
The organometallic chemistry of the manganese group 7 triad involving the technetium-99m synthon continues to attract significant attention in the development of modern radiopharmaceuticals. 99mTc remains an important radionuclide for diagnostic nuclear medicine with $80% of current radiopharmaceuticals administered clinically containing this radioisotope (Liu, 2004; Kluba & Mindt, 2013)
For the sake of comparison, the IR of the pure starting mononuclear rhenium complex, fac[Et4N]2[Re(CO)3(Br)3] is as follows, IR: v(CO) = 1996, 1847. This suggests that the formation of the tetranuclear cluster in these structures involves a complex interplay of factors, which includes the presence of the protein and the salt buffer conditions
The application of tetranuclear complexes creates a window of opportunity for the development of mixed rhenium–technetium tetranuclear clusters for the development of theranostic agents (Frei et al, 2018), previously less explored due to the complexity of their synthesis
Summary
The organometallic chemistry of the manganese group 7 triad involving the technetium-99m synthon continues to attract significant attention in the development of modern radiopharmaceuticals. 99mTc remains an important radionuclide for diagnostic nuclear medicine with $80% of current radiopharmaceuticals administered clinically containing this radioisotope (Liu, 2004; Kluba & Mindt, 2013). The reactivity studies on manganese(I) tricarbonyl complexes have provided insight into the manner in which the nuclearities of rhenium(I) tricarbonyl complexes can be manipulated to form either mono- or dinuclear species (Mokolokolo et al, 2018). This has been followed by two strategies which can prepare multinuclear rhenium(I) and technetium(I) tricarbonyl complexes, either di- or tetranuclear clusters, in a one-pot reaction. It allows for a tetranuclear cluster containing both rhenium and technetium metal centres to be a model theranostic agent (Frei et al, 2018). The structures reveal a completed, very well resolved, tetranuclear rhenium(I) tricarbonyl cluster after two years and an intermediate state after one year
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
