Binding Gibbs energy of ionic liquids to calf thymus DNA: a fluorescence spectroscopy study

The binding constants and binding Gibbs energies of [C(n)mim]Br (n = 4, 6, 8, 10, 12) and [C(4)mim][BF(4)] to calf thymus DNA-D1501 have been determined by the fluorescence measurements of the pyrene probe. It was found that values of the binding Gibbs energy decrease linearly with the increase of alkyl chain length of the ILs. Based on this observation, Gibbs energies for both the interaction between DNA and -CH(2)- of the ILs and the interaction between DNA and the cationic head group of the ILs have been reported. The result suggests that electrostatic interaction between DNA and the cationic head group of the ILs is predominant for the binding of the ILs with DNA although contribution from the non-electrostatic interaction between DNA and the alkyl chain of the ILs increases with increasing alkyl chain length of the ILs. The information obtained here may have application in the design of novel ILs-based DNA extraction/separation systems.