In Vitro Imaging and Human Serum Albumin Responsive Dimeric Lanthanide DO3A Complex

Two series of dimeric DO3A (1,4,7,10-tetraazacyclodecane-1,4,7-triacetate) lanthanide complexes (LnL 1 –LnL 2 , Ln = Eu, Gd, and Tb) have been synthesized with two different bridged chromophores. The X-ray structures of dimeric LnL 1 (Ln = Gd and Tb) complexes show that each metal ion has nine coordination numbers with eight directly bound donor atoms of the ligand and one oxygen donor from the water molecule. Photophysical measurements indicate that the bridged antenna in LnL 2 gives a higher efficiency than that of LnL 1 and is responsive to the protein Human Serum Albumin (HSA), giving an f–f luminescence signal enhancement with a binding constant log K = 4.84. In vitro imaging of EuL 1 and EuL 2 in HeLa cells has been recorded, and EuL 2 has demonstrated a higher rate of cellular uptake and low cytotoxicity (IC50 = 3 mM).