Novel synthetic approach to near-infrared heptamethine cyanine dyes and spectroscopic characterization in presence of biological molecules

• Novel synthetic approach to near-infrared heptamethine cyanine dyes.
• Evaluation of photophysical properties in organic solvents.
• Association of the dyes AK7 in presence of dsDNA.
• Binding of the dyes AK7 to Bovine Serum Albumine (BSA).
• Partition of the dyes AK7 with lipid membranes (PC).

Two near-infrared symmetric heptamethine cyanine dyes, containing integrated chlorosubstituted cyclohexenyl ring were obtained via a novel synthetic approach, using mild conditions at room temperature. UV–vis and fluorescence properties of the dyes were evaluated in organic solutions varying solvent polarity. Further spectral studies illustrating their application as potential labels for biological molecules, were reported in the presence of deoxyribonucleic acid (DNA), bovine serum albumin (BSA), and phospholipids (PC). The dyes undergo H-type intramolecular complexation between the two cyanine subunits when free in buffer. Absorption studies show that binding of cyanines to DNA, BSA and lipid membranes leads to the red shift in the H-aggregates peak with appearance of monomeric and dimeric dye species pointing to the disaggregation of the dyes under study in the presence of biological molecules. The fact that the decrease of liposome-induced cyanine aggregation was more pronounced in the zwitterionic phosphatidylcholine bilayer, suggests that the disruption of highly organized molecular arrangements are most likely electrostatically-controlled.

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