DNA aptamers are single-stranded oligonucleotides that bind to target molecules with high affinity and specificity. These interactions are governed not only by nucleotide sequence recognition but also by the presence of higher-order structures. The binding affinity of aptamers to target molecules may depend on various intermolecular interactions, such as electrostatic, hydrophobic, and hydrogen bond interactions. Water molecules are expected to affect the interactions between these molecules, considering that hydrogen bonding is essential for the formation of higher-order structures of both the DNA aptamers and target molecules. Furthermore, it has been reported that water activity affects the stability of DNA structures. Understanding the effect of water molecules on the structures and interactions of aptamers is, therefore, important for their further application. We have previously proposed ionic liquids (ILs) as potential candidates for controlling the state of water molecules.ILs are salts with melting points below 100 °C, and the solvent properties can be tuned to some extent by selecting the component ions. We have previously reported that the use of "hydrated ILs", in which the component ions are selected and a small amount of water is added, allows biomolecules such as proteins and nucleic acids to dissolve while maintaining their higher-order structure as in aqueous solution [1]. Furthermore, increased long-term and thermal stability of biomolecules have been reported after dissolution in hydrated ILs. When oligonucleotides forming quadruplex structure in buffer solution are dissolved in tuned hydrated IL, i.e., hydrated cholinium dihydrogen phosphate ([ch][dhp]), the original quadruplex structure is retained [2].Since it was found that oligonucleotides retain its original structure in hydrated ILs, the interaction of DNA aptamers with its target molecules has been investigated. As a first consideration, a thrombin-binding aptamer with an antiparallel G4 structure, namely 15-mer thrombin-binding aptamer (15TBA) and two different vascular endothelial growth factor 165 (VEGF) binding aptamers with parallel G4 structures, namely V7t1 and 3R02 were used [3]. Hydrated [ch][dhp] allowed the effective dissolution of these DNA aptamers while maintaining their G4 structure and binding affinity to the target molecule. On the other hand, change in the topology of DNA aptamers and the binding affinity were suggested in hydrated [ch][dhp] depending on the water contents. At the presentation, it will present the possibility of electrochemical detection of the binding between G4 and target molecules both in buffer solution and in hydrated ILs.Reference K. Fujita, H. Ohno, Chem. Rec., 23, e202200282 (2023).K. Fujita, H. Ohno, Chem. Commun., 48, 5751 (2012).K. Fujitta, T. Honda, K. Tsukakoshi, H. Ohno, K. Ikebukuro, J. Mol. Liq. 366, 120175 (2022).
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