Abstract
Heptamethine cyanine dyes are a class of near infrared fluorescence (NIRF) probes of great interest in bioanalytical and imaging applications due to their modifiability, allowing them to be tailored for particular applications. Generally, modifications at the meso-position of these dyes are achieved through Suzuki-Miyaura C-C coupling and SRN1 nucleophilic substitution of the chlorine atom at the meso-position of the dye. Herein, a series of 15 meso phenyl-substituted heptamethine cyanines was synthesized utilizing a modified dianil linker. Their optical properties, including molar absorptivity, fluorescence, Stokes shift, and quantum yield were measured. The HSA binding affinities of two representative compounds were measured and compared to that of a series of trimethine cyanines previously synthesized by our lab. The results indicate that the binding of these compounds to HSA is not only dependent on hydrophobicity, but may also be dependent on steric interferences in the binding site and structural dynamics of the NIRF compounds.
Highlights
Heptamethine cyanine dyes are a class of near infared fluorescence (NIRF) probes that have shown great potential in numerous applications due to their versatility, low toxicity, narrow absorption band, and high extinction coefficients [1,2,3,4,5,6]
As shown in Scheme 1, the synthesis began with a Fischer indole cyclization by refluxing 4After cooling to room temperature, the reaction mixture was neutralized and the substituted indoles 2 substituted phenylhydrazines 1 overnight with 3-methyl-2-butanone in glacial acetic acid
Various quaternary ammonium salts 3 and dianil dianil compound 5 are condensed in a 2:1 ratio in acetic anhydride to yield the final phenyl compound 5 are condensed in a 2:1 ratio in acetic anhydride to yield the final phenyl substituted substituted heptamethine cyanines
Summary
Heptamethine cyanine dyes are a class of near infared fluorescence (NIRF) probes that have shown great potential in numerous applications due to their versatility, low toxicity, narrow absorption band, and high extinction coefficients [1,2,3,4,5,6]. These dyes are comprised of two terminal nitrogen-containing heterocycles linked together by a conjugated polymethine chain. The most common method of carbon-coupling at the meso-position far has been done by first synthesizing a heptamethine cyanine dye containing a chlorine atom at the Molecules 2018, 23, 226; doi:10.3390/molecules23020226 www.mdpi.com/journal/molecules
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