6-Aryl-Substituted Harmanium Derivatives as Light-Up Probes for Fluorimetric DNA Detection and Staining of Eukaryotic Cells

Abstract

Nine 6-aryl-substituted harmanium derivatives were synthesized by Suzuki-Miyaura coupling of 6-bromoharmane with arylboronic acids and subsequent N2-benzylation. Depending on the substitution pattern of the aryl group the emission maxima cover a range between λ_fl=445 and 529 nm with quantum yields of Φ_fl=<0.01–0.92. The interactions with duplex DNA were investigated by photometric and fluorimetric titrations as well as CD and LD spectroscopy. These ligands bind to DNA by intercalation with binding constants of K_b=1–3×10⁴ M⁻¹. It was demonstrated by fluorescence microscopy that the 2-benzyl-6-(3-methoxyphenyl)harmanium derivative operates as a fluorescent light-up probe in the complex biological environment of eukaryotic cells, namely in NIH 3T3 mouse fibroblasts, as it stains the perinuclear cytoplasm and distinct substructures of the nucleus preferentially as compared with the rest of the nucleoplasm.