Highly Concentrated Ethanol Solutions: Good Solvents for DNA as Revealed by Single-Molecule Observation

• Published in: Chemphyschem Vol. 17; no. 4; pp. 471 - 473
• Main Authors: Oda, Yuki, Sadakane, Koichiro, Yoshikawa, Yuko, Imanaka, Tadayuki, Takiguchi, Kingo, Hayashi, Masahito, Kenmotsu, Takahiro, Yoshikawa, Kenichi
• Format: Journal Article
• Language: English
• Published: Germany Blackwell Publishing Ltd 16.02.2016; Wiley Subscription Services, Inc; John Wiley and Sons Inc
• Subjects: Circular Dichroism; Communication; Communications; Deoxyribonucleic acid; DNA; DNA - chemistry; DNA structures; Ethanol; Ethanol - chemistry; ethanol precipitation; Microscopy, Fluorescence; Nucleic Acid Conformation; phase transitions; single-molecule studies; Solvents - chemistry; water nanoclusters; phase transitions; ethanol precipitation; DNA structures; single-molecule studies; water nanoclusters
• ISSN: 1439-4235; 1439-7641
• DOI: 10.1002/cphc.201500988

We observed single DNA molecules at different ethanol concentrations by using fluorescence microscopy. Large single DNA molecules undergo reentrant conformational transitions from elongated coil into folded globule and then into elongated coil state, accompanied by the increase of the concentration of ethanol in a low‐salt aqueous environment. The second transition from globule into the coil state occurs at around 70 % (v/v) ethanol. From circular dichroism (CD) measurements, it is confirmed that the reentrant transition of the higher order structure proceeds together with the transitions of the secondary structure from B to C and, then, from C to A in a cooperative manner. The determined mechanism of the reentrant transition is discussed in relation to the unique characteristics of solutions with higher ethanol content, for which clathrate‐like nanostructures of alcohol molecules are generated in the surrounding water. More alcohol is the solution! As is well‐known, DNA molecules precipitate upon the addition of ethanol. From the observation of single DNA molecules, it is revealed that in 60 % ethanol the DNA structure changes from the higher order structure of a compact globule into an elongated state upon the addition of more ethanol. Based on the discovery of the reentrant transition of single DNA molecules, the solubility of DNA in higher ethanol concentrations is confirmed at the macroscopic level.