DNA Condensation Triggered by the Synergistic Self-Assembly of Tetraphenylethylene-Viologen Aggregates and CT-DNA

Abstract

Development of small organic chromophores as DNA condensing agents, which explore supramolecular interactions and absorbance or fluorescence-based tracking of condensation and gene delivery processes, is in the initial stages. Herein, we report the synthesis and electrostatic/groove binding interaction–directed synergistic self-assembly of the aggregates of two viologen-functionalized tetraphenylethylene (TPE-V) molecules with CT-DNA and subsequent concentration-dependent DNA condensation process. TPE-V molecules differ in their chemical structure according to the number of viologen units. Photophysical and morphological studies have revealed the interaction of the aggregates of TPE-V in Tris buffer with CT-DNA, which transforms the fibrous network structure of CT-DNA to partially condensed beads-on-a-string-like arrangement with TPE-V aggregates as beads via electrostatic and groove binding interactions. Upon further increasing the concentration of TPE-V, the “beads-on-a-string”-type assembly of TPE-V/CT-DNA complex changes to completely condensed compact structures with 40–50 nm in diameter through the effective charge neutralization process. Enhancement in the melting temperature of CT-DNA, quenching of the fluorescence emission of ethidium bromide/CT-DNA complex, and the formation of induced CD signal in the presence of TPE-V molecules support the observed morphological changes and thereby verify the DNA condensation abilities of TPE-V molecules. Decrease in the hydrodynamic size, increase in the zeta potential value with the addition of TPE-V molecules to CT-DNA, failure of TPE-V/cucurbit(8)uril complex to condense CT-DNA, and the enhanced DNA condensation ability of TPE-V2 with two viologen units compared to TPE-V1 with a single viologen unit confirm the importance of positively charged viologen units in the DNA condensation process. Initial cytotoxicity analysis on A549 cancer and WI-38 normal cells revealed that these DNA condensing agents are non-toxic in nature and hence could be utilized in further cellular delivery studies.