Evaluation of interaction between imidazolium-based chloride ionic liquids and calf thymus DNA.

With ionic liquids (ILs) being widely used, the toxicity of many ILs has been studied and verified. However the mechanism underlying the interaction between ILs and DNA needs to be investigated. In this study, the interaction of three imidazolium-based ILs ([C8mim]Cl, [C12mim]Cl, and [C16mim]Cl) with calf thymus DNA (ctDNA) was investigated by UV absorption spectroscopy and fluorescence spectroscopy. An intense interaction between [Cnmim]Cl and ctDNA was observed, involving a hypochromic effect or even a hyperchromic effect, in the UV absorption spectrum of ctDNA at 260nm. The Tm of ctDNA increased over 10°C after binding with [Cnmim]Cl, and the KSV values of [Cnmim]Cl-ctDNA quenched by potassium iodide (KI) were lower than those of [Cnmim]Cl. The fluorescence intensity of ctDNA-ethidium bromide (EB) was gradually quenched as the [Cnmim]Cl concentration increased. The results indicated that ctDNA interacted with [Cnmim]Cl through an intercalation binding mode. The mechanism of fluorescence quenching of [Cnmim]Cl with ctDNA involved static quenching. The binding constant between [Cnmim]Cl and ctDNA were 1443, 11169, and 67189, and the number of binding sites were 0.89, 1.10, and 1.27 at 298K, for [C8mim]Cl, [C12mim]Cl, and [C16mim]Cl, respectively. The results indicated that the intercalation binding between the three [Cnmim]Cl and ctDNA increased with increasing IL-alkyl chain length. These results will aid in the understanding of the mechanism of toxicity and of the biologically mediated environmental processes of ILs.