Alloxazine-Based Ligands and Their Ruthenium Complexes as NADH Oxidation Catalysts and G4 Binders

Flavin-like ligands (<b>L-1</b> and <b>L-2</b>) with extended π-conjugation were synthesized using microwave-assisted techniques. An <i>N</i>,<i>N</i>-chelating fragment was integrated into alloxazine units, providing binding sites for metal ions while retaining redox activity. The complexation capability of <b>L-1</b> and <b>L-2</b> with two prototypical Ru-scaffolds was examined to design Ru(II) complexes (<b>M-1</b> and <b>M-2</b>), whose electronic properties were studied and compared with their corresponding ligands via absorption and emission spectroscopy, computational analysis (density functional theory (DFT) and time-dependent DFT (TD-DFT)), and cyclic voltammetry (CV). The ability of <b>L-1</b> and <b>M-1</b> to undergo alloxazine/isoalloxazine tautomerization was demonstrated to play a crucial role in the photocatalytic oxidation of NADH, including under green and red wavelengths. Moreover, the interaction of <b>M-1</b> and <b>M-2</b> with B-DNA and G-quadruplex structures was investigated. <b>M-2</b> showed high stabilization of Kit1 and h-Telo oligonucleotides. Meanwhile, <b>M-1</b> demonstrated switchable emissive properties with B-DNA and induced conformational changes in the h-Telo G-quadruplex structure.