LAUSR

Abstract With their hydrolytic, optical and magnetic properties, lanthanide ions (Ln 3+ ) are versatile probes for nucleic acids. In addition, nucleotide-coordinated Ln 3+ ions form useful nanoparticles. However, the thermodynamic basis of their interaction is still lacking. In this work, isothermal titration calorimetry (ITC) is used to study the binding between nucleotides and 14 different Ln 3+ ions. Ln 3+ interacts mainly with the phosphate of cytidine and thymidine monophosphate (CMP and TMP), while the nucleobases in adenosine and guanosine monophosphate (AMP and GMP) are also involved. Phosphate binding is fully entropy driven since the reactions absorb heat. Nucleosides alone do not bind Ln 3+ and the purines need the phosphate for chelation. With increasing atomic number of Ln 3+ , the binding reaction with GMP goes from exothermic to endothermic. The entropy contribution starts to increase from Gd 3+ , explaining the ‘gadolinium break’ observed in many Ln 3+ -mediated RNA cleavage reactions. This study provides fundamental insights into the Ln 3+ /nucleotide interactions, and it is useful for understanding related biosensors, nanomaterials, catalysts, and for lanthanide separation.