In photocatalytic H 2 formation, tertiary amines are commonly used as sacrificial electron donors, thereby limiting the pH range for studies in water and the concentration of free protons. We found that ascorbate rapidly reductively quenches the excited state of [Re(CO) 3 (bipy)(py)] + (bpy = 2,2Ј-bipyridyl; py = pyridine). In combination with the water reduction catalyst (WRC) [Co{(DO)(DOH)pn}Br 2 ] [(DO)(DOH)pn =

H 4 octox, a versatile new octadentate acyclic chelating ligand, has been investigated as an alternative to the acyclic DTPA and the macrocyclic DOTA for trivalent metal ions useful in diagnostic medical imaging or therapeutic applications (Y 3+ , In 3+ , La 3+ , Gd 3+ , Lu 3+ ). The synthesis of H 4 octox is straightforward in less steps and thus more economical than those of most previously reported chelators. Complex formation equilibria in the presence of Y 3+ , In 3+ , La 3+ , Gd 3+ , and Lu 3+ revealed fast chelation and high metal-sequestering capacity. Quantitative labeling with 111 In 3+ was achieved within 15 min at room temperature at ligand concentrations as low as 10 −7 M, exactly the properties required for the development of kit-based radiopharmaceuticals. In vitro serum stability studies and in vivo SPECT imaging confirmed excellent complex stability of [ 111 In-(octox)] − . Moreover, it is more lipophilic than most of the multidentate carboxylate-or picolinate-based chelators; it therefore shows more liver clearance and provides a complementary choice in the design of metal-based pharmaceuticals and in the tuning of their pharmacokinetic properties. Finally, H 4 octox showed a large fluorescence enhancement upon complexation with different metals, in particular, with Y 3+ and Lu 3+ , which could be useful for non-radioactive fluorescent stability and cell studies as well as bimodal imaging. Excellent in vitro stability of [Y(octox)] − against transferrin and Fe 3+ was confirmed employing this fluorescence.

The first octadentate 3-hydroxy-4-pyridinone chelator was prepared and its monometallic 89Zr(iv)-complex was studied in vitro and in vivo.