Luminescent Cell-Penetrating Pentadecanuclear Lanthanide Clusters

A novel pentadecanuclear lanthanide hydroxy cluster [{Ln15(μ3-OH)20(PepCO2)10(DBM)10Cl}­Cl4] (Ln = Eu (1), Tb (2)) featuring the first example with peptoids as supporting ligands was prepared and fully characterized. The solid-state structures of 1 and 2 were established via single-crystal X-ray crystallography. ESI-MS experiments revealed the retention of the cluster core in solution. Although OH groups are present, 1 showed intense red fluorescence with 11(1)% absolute quantum yield, whereas the emission intensity and the quantum yield of 2 were significantly weaker. In vitro investigations on 1 and 2 with HeLa tumor cells revealed an accumulation of the clusters in the endosomal–lyosomal system, as confirmed by confocal microscopy in the TRLLM mode. The cytotoxicity of 1 and 2 toward the HeLa cells is moderate.