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  • Publisher:
    Royal Society of Chemistry
  • Publication Date:
    Apr 2007
  • Reference:
    Dalton Transactions, 2007, pp4998-5007
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How do HYNIC-conjugated peptides bind technetium? Insights from LC-MS and stability studies

Biagini S; Blower PJ; King R; Mather SJ; Surfraz B;

Hydrazinonicotinamide (HYNIC) is an established bifunctional complexing agent for technetium-99m (99mTc) but the structure of the technetium coordination sphere remains uncertain. To gain further insight into this, we have prepared conjugates of HYNIC and hydrazinobenzoic acid(HYBA) with a model peptide, and radiolabelled them with 99mTc using three well-established co-ligand systems: EDDA, tricine and tricine–nicotinic acid. The labelled peptides were studied by LC-MS and by subjecting them to serum stability and protein binding assays. For each co-ligand system, HYNIC conjugates formed fewer and more stable labelled species than the corresponding HYBA conjugates. LC-MS analysis showed that all conjugates contained one hydrazine moiety bound to Tc, that binding of Tc to HYNIC–peptide and co-ligand occurs with displacement of 5H+ indicating a Tc formal oxidation state of +5, and that the Tc has no oxo- orhalide ligands. LC-MS also shows that complexes formed with the HYNIC conjugate contain fewer coordinating co-ligand molecules than the HYBA conjugate indicating that HYNIC is able to more effectively satisfy the coordination requirement of technetium, perhaps by binding in chelating mode.

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