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The international journal for inorganic, organometallic and bioinorganic chemistry
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Paper
Dalton Trans., 2007, 4998 - 5007, DOI: 10.1039/b705111e
How do HYNIC-conjugated peptides bind technetium? Insights from LC-MS and stability studies
Robert C. King, M. Bashir-Uddin Surfraz, Stefano C. G. Biagini, Philip J. Blower and Stephen J. Mather
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- or halide 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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