Luminescent Eu III and Tb III Complexes Containing Dopamine Neurotransmitter: Biological Interactions, Antioxidant Activity and Cellular‐Imaging Studies

Two luminescent water‐soluble lanthanide(III) complexes, [Ln(DTPA‐DOPA)(H 2 O)] ( 1–2 ) where Ln = Eu III ( 1 ), Tb III ( 2 ), formed by reaction with diethylenetriaminepentaacetic acid (DTPA) carrying the neurotransmitter dopamine with catechol functional groups [i.e., DTPA‐bis(3‐hydroxytyramide)], are characterized and their photophysical properties are studied. Strong characteristic red and green luminescence is observed for 1 and 2 upon photoexcitation, followed by efficient energy transfer from dopamine to Ln III , leading to intraconfigurational f – f transitions. They show distinguishable sharp emission bands due to intraconfigurational 5 D 0 → 7 F J transitions in Eu III and 5 D 4 → 7 F J transitions in Tb III . They exhibit long excited‐state lifetimes [ τ = 0.52 ms ( 1 ) and 0.33 ms ( 2 )] and calculated quantum yields, Φ overall , of 0.022 ( 1 ) and 0.038 ( 2 ). The luminescent complexes are studied for their antioxidant activity, ability to interact with calf‐thymus DNA (CT‐DNA) and bovine serum albumin (BSA), hydrolytic cleavage of pUC19 supercoiled plasmid DNA and as cellular‐imaging probes for both cancer cells and neuroblastoma cells. Both the Eu III and Tb III complexes exhibit potent antioxidant activity. These complexes show moderate binding affinity towards CT‐DNA ( K b ≈ 10 4 m –1 ) and BSA ( K BSA = 10 3 m –1 ). The complexes at 200 µ m exhibit good hydrolytic cleavage of supercoiled pUC19 DNA. The non‐cytotoxic nature of these complexes makes them efficient candidates for cellular‐imaging probes. Cytosolic localization is observed for both of the complexes in HeLa cells and mouse neuroblastoma (Neuro‐2a) cells. The present systems, with advantageous antioxidant activity, may have potential application in the tracking and delivery of dopamine, which is important for dopamine replacement therapy in various neurodegenerative disorders.