Interaction of a Julolidine-Based Neutral Ultrafast Molecular Rotor with Natural DNA: Spectroscopic and Molecular Docking Studies.

Ultrafast molecular rotors (UMRs) are reported to be one of the best fluorescent sensors to study different microenvironments, including biomolecules. In the present work, we have explored the possibility of application of a julolidine-based neutral UMR, 9-(2,2-dicyano vinyl) julolidine (DCVJ), as a DNA sensor and studied its mode of binding with DNA in detail using spectroscopic and molecular docking techniques. Our spectroscopic studies indicate that association of DCVJ with DNA leads to a very large enhancement in its emission intensity. Detailed investigation reveals that, despite being a neutral molecule, binding of DCVJ with DNA is largely modulated in the presence of salt. Such an unusual salt effect has been explained by invoking the ion-dipole interaction between DCVJ and the phosphate backbone of DNA. The ion-dipole interaction has also been established by studying the interaction of DCVJ with nucleosides. Detailed time-resolved studies show that the twisting motion around the vinyl bond in DCVJ gets retarded to a great extent because of its association with DNA molecules. Through competitive binding studies, it has also been established that DCVJ also binds to DNA through intercalation. Finally, quantum chemical calculations and molecular docking studies have been performed to confirm the mode of binding of DCVJ with DNA.