Modulation of ligand fluorescence by the Pt(II)/Pt(IV) redox couple
Author(s)Wilson, Justin Jeff; Lippard, Stephen J.
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The dangling carboxylic acid moiety of the known platinum(II) complex, [Pt(edma)Cl2] (edma = ethylenediaminemonoacetic acid), was functionalized via amide coupling chemistry with benzyl amine and dansyl ethylenediamine to afford the derivatives [Pt(edBz)Cl2] (1) and [Pt(edDs)Cl2] (2). Subsequent oxidation of these platinum(II) complexes with iodobenzene dichloride in DMF yielded the respective platinum(IV) analogs, [Pt(edBz)Cl4] (3) and [Pt(edDs)Cl4] (4). All four platinum complexes were characterized by multinuclear NMR spectroscopy, IR spectroscopy, electrospray ionization mass spectrometry, and elemental analysis. In addition, compounds 1 and 3 were structurally characterized by X-ray crystallography. The photophysical properties of the compounds bearing the fluorescent dansyl moiety, 2 and 4, were evaluated. The emission quantum yields of 2 and 4 in DMF are 27% and 1.6%, respectively. This large difference in emission efficiency indicates that the platinum(IV) center in 4 is more effective at quenching the dansyl-based fluorescence than the platinum(II) center in 2. Time-dependent density functional theory calculations indicate that 4 has several low-lying singlet excited states that energetically lie below the primary radiation-accessible excited state of the dansyl fluorophore. These low-energy excited states may offer non-radiative decay pathways that lower the overall emission quantum yield. Treatment of 4 with biologically relevant reducing agents in pH 7.4 phosphate-buffered saline induces a 6.3-fold increase in emission intensity. These results demonstrate that 4 and future derivatives thereof may be useful for imaging the reduction of platinum(IV) complexes in living systems, chemistry of importance for evolving platinum-based anticancer drug strategies.
Dedicated to Professor Jon Zubieta on the occasion of his 65th birthday.
DepartmentMassachusetts Institute of Technology. Department of Chemistry
Inorganica Chimica Acta
Wilson, Justin J., and Stephen J. Lippard. “Modulation of Ligand Fluorescence by the Pt(II)/Pt(IV) Redox Couple.” Inorganica Chimica Acta 389 (July 2012): 77-84.
Author's final manuscript