Photocytotoxicity of Oligothienyl-Functionalized Chelates That Sensitize Ln Luminescence and Generate O.

Three new compounds containing a heptadentate lanthanide (Ln ) ion chelator functionalized with oligothiophenes, nThept(COOH) (n=1, 2, or 3), were isolated. Their Ln complexes not only display the characteristic metal-centered emission in the visible or near-infrared (NIR) but also generate singlet oxygen ( O ). Luminescence efficiencies (ϕ ) for [Eu1Thept(COO) ] and [Eu2Thept(COO) ] are ϕ =3 % and 0.5 % in TRIS buffer and 33 % and 3 % in 95 % ethanol, respectively. 3Thept(COO) does not sensitize Eu emission due to its low-lying triplet state. Near infra-red (NIR) luminescence is observed for all NIR-emitting Ln and ligands with efficiencies of ϕ =0.002 %, 0.005 % and 0.04 % for [YbnThept(COO) ] (n=1, 2, or 3), and ϕ =0.0007 %, 0.002 % and 0.02 % for [NdnThept(COO) ] (n=1, 2, or 3) in TRIS buffer. In 95 % ethanol, quantum yields of NIR luminescence increase and are ϕ =0.5 %, 0.31 % and 0.05 % for [YbnThept(COO) ] (n=1, 2, or 3), and ϕ =0.40 %, 0.45 % and 0.12 % for [NdnThept(COO) ] (n=1, 2, or 3). All complexes are capable of generating O in 95 % ethanol with ϕ efficiencies which range from 2 % to 29 %. These complexes are toxic to HeLa cells when irradiated with UV light (λ =365 nm) for two minutes. IC values for the Ln complexes are in the range 15.2-16.2 μm; the most potent compound is [Nd2Thept(COO) ] . The cell death mechanisms are further explored using an Annexin V-propidium iodide assay which suggests that cell death occurs through both apoptosis and necrosis.