Effect of gemini surfactants on binding interactions of Coumarin 485 with calf thymus deoxyribonucleic acid in presence of nanotubes of β-cyclodextrin

Abstract

Present study is focused on the binding of a dye, Coumarin 485 (C-485) with Calf thymus deoxyribonucleic acid (ctDNA), explored using the spectroscopic tools such as UV–visible absorption, steady-state fluorescence and fluorescence anisotropy, and time-resolved fluorescence spectroscopy and dynamic light scattering measurements. The hyperchromic shifts in UV–visible absorption and fluorescence bands depict that the C-485 binds with the ctDNA. Absorption spectrum of C-485 in presence of ctDNA, ethidium bromide displacement assay and iodide ion quenching experiment confirm that C-485 binds with ctDNA through the groove binding mode. β-Cyclodextrin (β-CD) molecules (host) in presence of C-485 (guest) form the nanotubes and secondary aggregates of nanotubes which has been explored as the carriers of C-485 for ctDNA. The binding efficiency of C-485 with β-CD is reduced in presence of ctDNA. Gemini surfactants, m-4-m (m = 12, 14 and 16) induce the release of C-485 from the cavities of nanotubes of β-CD. After getting released from the cavities, C-485 molecules bind with ctDNA in the form of inclusion complexes with β-CD/un-complexed state at a low concentration range of a gemini surfactant. A gemini surfactant with comparatively longer hydrocarbon tails pushes the guest molecules (C-485) out of the nanotubular cavities of β-CD more efficiently due to greater extent of hydrophobic interactions between the cavities and tails.