Novel asymmetric monomethine cyanine dyes derived from sulfobetaine benzothiazolium moiety as potential fluorescent dyes for non-covalent labeling of DNA

•Synthesis of novel asymmetric monomethine cyanine dyes and structural analysis.•Absorption and fluorescent studies – potential markers for nucleic acid detection.•Evaluation of binding constants to dsDNA.

Four novel monomethine cyanine dyes derived from a condensation reaction between N-quaternary 2-thiomethylbenzothiazolic, and 4-methylquinolinuim choromophores have been synthesized and characterized by 1H NMR, APT carbon NMR, ESI mass spectrometry, IR, absorption and fluorescence spectroscopy. The main synthetic approach for the target cyanines involves variations on both the substituent on the aromatic ring of the benzothiazolium derivative, as well as the size of the component yielding the additional positive charge linked to the quinolinium moiety. The interaction between novel fluorophores and dsDNA has been studied. The dyes were found to have negligible fluorescence in the buffer solution, but exhibited a significant emission increase upon binding to dsDNA. The binding parameters of cyanine dyes have been determined by fluorescence titration using the McGhee & von Hippel site-excluded model. The results obtained are consistent with an intercalative binding mode between cyanines and DNA.

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