Synthesis and Characterization of a Water-Soluble Pentamethine Indocyanine Dye for Peptide Labeling

Abstract

: A water-soluble pentamethine cyanine dye was synthesized for further conjugation with peptides. The dye preparation was accomplished by solution-phase chemistry and the synthesized compounds were characterized by the usual techniques (nuclear magnetic resonance, UV-vis absorption and fluorescence spectroscopies and mass spectrometry). The photophysical properties of cyanine 4 were studied in aqueous media, namely in phosphate-buffered saline (PBS) at pH 7.4. Sulfo-Cy5 carboxylic acid 4 exhibited a narrow absorption band and a high molar extinction coefficient (log ε = 5.11) at 646 nm. The wavelength of maximum fluorescence was found in the near-infrared (NIR) region at 661 nm. Therefore, due to its excellent spectral proprieties, good water solubility and emission in the NIR region, dye 4 can be employed in the synthesis of fluorescence resonance energy transfer (FRET) probes for studying enzymatic hydrolysis in vitro.