Lumos: A β-Diketone-Derived Artificial Nucleobase Forming Inter-Strand Complexes in DNA that Promote Lanthanoid Ion Luminescence

A novel artificial nucleobase, 1-(3-(hydroxymethyl)phenyl)-3-phenylpropane-1,3-dione (Hdbm^OR), containing a β-diketone designed to form inter-strand complexes that resemble metal-mediated base pairs, was synthesized and characterized towards its lanthanoid ion binding properties. Based on UV/vis spectra, a (labile) coordination of Eu^III and Sm^III by the benzyl-functionalized model ligand is proposed, allowing the detection of distinct luminescence patterns upon coordination under alkaline conditions. The compatibility of the nucleoside analog with automated solid-phase DNA synthesis was proven by the generation of a dinucleotide. NMR spectroscopic characterization of this dinucleotide revealed a temperature-dependent equilibrium of two conformers, which likely involve hydrogen bonding of the β-diketone moiety and the deoxyribose and/or phosphate moieties. The antenna effect of the new ligand promoting the luminescence of Eu^III is retained upon incorporation into DNA. Modification of a parallel-stranded DNA duplex with a terminal homo base pair of Hdbm^OR allows, despite natural fraying of DNA, a thermal stabilization of about 3 °C upon coordination of Eu^III or Sm^III. Temperature-dependent luminescence spectroscopy demonstrates a direct correlation between the thermal stability of the duplex and its luminescence intensity. The ligand extends the library of artificial nucleobases for lanthanoid-mediated base pairs, combining the luminescence properties of lanthanoid complexes with the self-assembly properties of DNA.