Mishra Arpit, Ekka Mary Krishna, Maiti Souvik
CSIR-Institute of Genomics and Integrative Biology , Mall Road, New Delhi 110 007, India.
Academy of Scientific and Innovative Research (AcSIR) , Anusandhan Bhawan, 2 Rafi Marg, New Delhi 110001, India.
J Phys Chem B. 2016 Mar 17;120(10):2691-700. doi: 10.1021/acs.jpcb.5b11823. Epub 2016 Mar 4.
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.
离子液体（ILs）是离子配位较弱的盐，因此在低于100°C时仍保持液态，有些甚至在室温下也能保持液态。已知离子液体能为许多生物酶促反应提供有利环境，但它们与生物大分子的相互作用却知之甚少。在本研究中，我们以小牛胸腺DNA（ctDNA）-溴化乙锭（EB）为模型系统，研究了各种离子液体对DNA-小分子相互作用的影响。通过圆二色性（CD）、紫外熔解、荧光排斥和等温滴定量热法等一系列技术研究了各种离子液体对这些相互作用的影响。有趣的是，我们观察到离子液体的存在增加了ctDNA的稳定性，而不改变其结构。在300 mM离子液体存在下，EB与ctDNA结合的结合亲和力Kbs比不存在离子液体时的Kbs小约半个数量级，且对应于较不利的自由能。我们注意到，当调整到相应的缓冲条件时，ctDNA-EB相互作用的ΔG的不利变化在离子液体的情况下归因于熵的降低，而NaCl的相同作用则是由于焓的增加。
