Various lanthanide complexes have been shown to promote phosphodiester hydrolysis. Distribution of the available coordination sites of the lanthanides between the ligand and the labile water molecules has proved to be critical in determining the activity and stability of the complex in water at neutral pH. Since the final goal is to conjugate such hydrolytically active molecules to DNA oligomers, the design must include a functionality that can be made reactive in standard conjugation protocols. To that end, we have synthesized a nitrophenyl-derivatized TCMC-La3+ complex, and it is as active as the unmodified TCMC-La3+ in the transesterification of an RNA model substrate. (C) 1998 Elsevier Science Ltd. All rights reserved.