The study of molecule-DNA binding interactions are vital as they are the principle components behind drug action, transcription and replication. Optical spectroscopic techniques are often used to study these interactions. However, the existing techniques cannot differentiate different binding motifs of intercalation and minor-grove binding. In the present study, we present a novel approach based on the two-photon absorption (2PA) cross-sections of chromophores to differentiate the intercalation and minor-grove binding interactions. The investigations are carried out using three cyanine derivatives Diethylthiacyanine iodide (DTI), 3,3'-Diethylthiacarbocyanine iodide  (DTCI) and 3,3'-Diethylthiadicarbocyanine iodide  (DTDCI). The chromophores were chosen as they are similar series of dye molecules but with different carbon chain lengths. As the chain length increases, the chromophores start to bind to minor-grove than intercalate. The results show that the 2PA cross-sections of DTI bound to salmon-sperm DNA are unchanged or slightly decreased with increase in DNA concentration. On the other hand, the 2PA cross-sections of DTDCI have increased by 6-fold with increase in DNA concentration. The results show that DTI binds to DNA via intercalation while DTDCI binds with DNA via minor-grove. The results are rationalized based on the DNA backbone's electric field. Additional results of fluorescence lifetimes, anisotropy and circular dichroism will be presented.

Two-photon absorption spectroscopy to differentiate chromophore-DNA binding interactions

247th National Meeting (2014)

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