A Dimethylaminophenyl‐Substituted Naphtho[1,2‐b]quinolizinium as a Multicolor NIR Probe for the Fluorimetric Detection of Intracellular Nucleic Acids and Proteins

Abstract

The dye 3‐(4‐(N,N‐dimethylamino)phenyl)naphtho[1,2‐b]quinolizinium was synthesized by means of a Suzuki–Miyaura reaction in good yield, and its binding properties with duplex DNA, quadruplex DNA (G4‐DNA), RNA, and bovine serum albumin (BSA) were investigated by photometric, fluorimetric and polarimetric titrations and DNA denaturation analysis. The compound intercalates into DNA and RNA, associates in binding site I of BSA, and binds to G4‐DNA by terminal π stacking. The ligand exhibits a fluorescence light‐up effect upon complexation to these biomacromolecules, which is more pronounced and blue shifted in the presence of BSA (Φfl=0.29, λfl=627 nm) than with the nucleic acids (Φfl=0.01–0.05, λfl=725–750 nm). Furthermore, the triple‐exponential fluorescence decay of the probe when bound to biomacromolecules in a cell enables their visualization in this medium and the differential labeling of cellular components.

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

“…In contrast, the nucleus exhibited lower fluorescence intensity, which might be caused by masking of 4 c binding sites or interception of 4 c already in the cytoplasm by cellular components with high binding affinity under the conditions after fixation ( cf . Supporting Information, Figure S12) [28] . It should be noted that this distribution of the probe 4 c within the cell may also be accompanied by association with RNA, because it is present in higher concentrations in the perinuclear region [32] .…”

“…Accordingly, the detected emission mainly results from the association of 4 c with DNA, which is consistent with the fluorescence light‐up effect observed in the in vitro fluorimetric DNA titration (Figure 3B). Moreover, higher fluorescence intensities of 4 c embedded in the cytoplasm within the perinuclear region might also be a result of an overall thicker cytoplasm around the nucleus as compared with the thickness in the cell periphery [28] …”

“…Supporting Information, Figure S12). [28] It should be noted that this distribution of the probe 4 c within the cell may also be accompanied by association with RNA, because it is present in higher concentrations in the perinuclear region. [32] However, at least in a control experiment, the compound 4 c even showed partial quenching of the emission intensity upon association with double-stranded RNA (cf.…”

“…Most importantly, this low intrinsic fluorescence intensity increases upon intercalation into DNA (Figure 3B). [28] To assess the suitability of this DNAsensitive fluorescent probe in biological samples, it was further examined in NIH 3T3 mouse fibroblasts by epifluorescence Surprisingly, very low background fluorescence was detected from 4 c in the cell medium, indicating that under these conditions the emission quantum yield is even lower than in aqueous BPE buffer solution. This effect may be attributed to additional quenching of the emission intensity of 4 c in the presence of chloride ions, which are found in high concentrations in cell culture media.…”

“…Moreover, higher fluorescence intensities of 4 c embedded in the cytoplasm within the perinuclear region might also be a result of an overall thicker cytoplasm around the nucleus as compared with the thickness in the cell periphery. [28] The fluorescence staining of the nucleus with the probe 4 c deserves special attention. Considering the DNA-binding properties of 4 c, as determined in the in vitro experiments, the fluorescence in the nucleus may be assigned to the light-up effect of the DNA-or RNA-bound ligand.…”