Photocytotoxicity of Thiophene- and Bithiophene-Dipicolinato Luminescent Lanthanide Complexes

New thiophene-dipicolinato-based compounds, K(2)nTdpa (n = 1, 2), were isolated. Their anions are sensitizers of lanthanide ion (Ln(III)) luminescence and singlet oxygen generation (O-1(2)). Emission in the visible and near-infrared regions was observed for the Ln(III) complexes with efficiencies (phi(Ln)) phi(Eu) = 33% and phi(Yb) = 0.31% for 1Tdpa(2-) and phi(Yb) = 0.07% for 2Tdpa(2-). The latter does not sensitize Eu-III emission. Fluorescence imaging of HeLa live cells incubated with K-3[Eu(1Tdpa)(3)] indicates that the complex permeates the cell membrane and localizes in the mitochondria. All complexes generate O-1(2) in solution with efficiencies (phi(1O2)) as high as 13 and 23% for the Gd-III complexes of 1Tdpa(2-) and 2Tdpa(2-), respectively. [Ln(nTdpa )(3)](3-) (n = 1, 2) are phototoxic to HeLa cells when irradiated with UV light with IC50 values as low as 4.2 mu M for [Gd(2Tdpa)(3)](3-) and 91.8 mu M for [Eu(1Tdpa)(3)](3-). Flow cytometric analyses indicate both apoptotic and necrotic cell death pathways.

Automated summary

New thiophene-dipicolinato-based compounds K(2)nTdpa (n = 1, 2) act as sensitizers for lanthanide ion (Ln(III)) luminescence and singlet oxygen generation (O-1(2)), permeating cell membranes and exhibiting phototoxicity to HeLa cells.