Influence of Ionic Liquids on Thermodynamics of Small Molecule–DNA Interaction: The Binding of Ethidium Bromide to Calf Thymus DNA

Abstract

Ionic liquids (ILs) are salts with poor ionic coordination, resultantly remaining in liquid state below 100 °C and some may retain liquid state even at room temperature. ILs are known to provide a conducive environment for many biological enzymatic reactions, but their interaction with biomacromolecules are poorly understood. In the present study, we investigate the effect of various ionic liquids on DNA-small molecule interaction using calf thymus DNA (ctDNA)-ethidium bromide (EB) as a model system. The effect of various ionic liquids on these interactions is studied by an array of techniques such as circular dichroism (CD), UV melting, fluorescence exclusion and isothermal titration calorimetry. Interestingly, we observed that presence of IL increased the stability of ctDNA without altering its structure. The binding affinities Kbs for EB binding to ctDNA in the presence of 300 mM ILs are about half order of magnitude smaller than the Kbs in absence of ILs and correspond to a less favorable free energy. We noted that, when adjusted to corresponding buffer condition, the unfavorable shift in ΔG of ctDNA-EB interaction is attributed to decreased entropy in the case of ILs, whereas the same effect by NaCl was due to increased enthalpy.

Interaction studies of cholinium-based ionic liquids with calf thymus DNA: Spectrophotometric and computational methods

“…Combining these two, several articles have been published describing the interaction of DNA with imidazolium, morpholinium, etc. based ILs [21][22][23][24][25][26][27][28][29]. For example, Liu and co-workers studied the impact of alkyl chain length present on imidazolium-based ILs [23] towards ct-DNA through extensive photophysical methods.…”

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

“…Several reports described the mechanism of interaction between DNA and environmental pollutants such as polycyclic aromatic hydrocarbon metabolites (Wei et al, 2010) and herbicides (Li et al, 2014). The interaction of DNA with ILs has also been investigated by spectroscopic and molecular docking study (Pabbathi and Samanta, 2015;Mishra et al, 2016). However, the complicated mechanism of interaction between ILs and DNA remains poorly understood.…”

“…The ctDNA-ethidium bromide (EB) interaction has been well studied by UV absorption spectroscopy, fluorescence quenching, and molecular docking studies and, hence, is a good model system for monitoring IL-based changes (Mishra et al, 2016). EB has no any appreciable fluorescence emission in aqueous solutions.…”

Choline‐Based Ionic Liquids: Improvement of Antimicrobial Activity

“…These works illustrate the different practical uses of choline‐based ILs in health and life sciences. ILs have found use in enzymatic and whole‐cell biocatalysis, protein stabilisation and biodiesel production such as in biological enzymatic reactions in Protein (BSA) and enzyme (catalase) activity with antimicrobial ILs or ADME studies in particular, protein binding affinity of API‐ILs.…”