Abstract
Here, we report the syntheses of two pentamethine cyanine dyes containing quinolinium rings and substituted with either hydrogen (3) or bromine (4) at the meso carbon. The electron withdrawing bromine atom stabilizes dye 4 in aqueous buffer, allowing complex formation to occur between the dye and double-helical DNA. UV–visible, CD, and fluorescence spectra recorded at low DNA concentrations suggest that dye 4 initially binds to the DNA as a high-order aggregate. As the ratio of DNA to dye is increased, the aggregate is converted to monomeric and other low-order dye forms that interact with DNA in a non-intercalative fashion. The brominated dye 4 is relatively unreactive in the dark, but, under 707–759 nm illumination, generates hydroxyl radicals that cleave DNA in high yield (pH 7.0, 22 °C). Dye 4 is also taken up by ES2 ovarian carcinoma cells, where it is non-toxic under dark conditions. Upon irradiation of the ES2 cells at 694 nm, the brominated cyanine reduces cell viability from 100 ± 10% to 14 ± 1%. Our results suggest that 2-quinolinium-based carbocyanine dyes equipped with stabilizing electron withdrawing groups may have the potential to serve as sensitizing agents in long-wavelength phototherapeutic applications.
Highlights
Employed in photography to extend the wavelength range of silver halide emulsions, cyanine dyes are extensively used in diverse fields ranging from biotechnology to laser technology [1,2,3]
We showed that symmetrical 2-quinolinium pentamethine carbocyanine dyes substituted with hydrogen (3) or bromine (4) generate DNA cleavage when irradiated in the near-infrared wavelength range
UV–visible, circular dichroism, and fluorescence spectra of the brominated 2-quinolinium pentamethine cyanine (4) show that DNA has a major effect on dye aggregation
Summary
Employed in photography to extend the wavelength range of silver halide emulsions, cyanine dyes are extensively used in diverse fields ranging from biotechnology to laser technology [1,2,3]. Carbocyanines are typically composed of two nitrogen-containing heterocyclic aromatic rings that share a positive charge that is delocalized by the movement of electrons through a semi-flexible central polymethine bridge. These features make it possible for the monomeric and/or aggregated forms of many carbocyanine dyes to form stable complexes with double-helical DNA. For every two methine carbons added to the polymethine unit, absorption is red-shifted by ~100 nm [1].
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