1-Propanol Causes Reentrant Transition on DNA whereas 2-Propanol does not: Experimental Verification through Single Molecular Observation

Abstract

Nowadays, structural characterization of genomic DNA is one of the most important trends in medicine, biology and agricultural sciences. The indispensable procedure for the analysis of DNA in living cells is to isolate DNA molecules as precipitates from the crude mixture in rich variety of cellular components. According to the standard experimental protocol in molecular biology and medicinal chemistry, usage of 2-propanol is recommended, seemingly without any reasonable physic-chemical explanation why 2-propanol is desirable. In the present study, we have measured the change of the higher-order structure of genomic DNA molecules in the presence of alcohols by use of single DNA observation with fluorescence microscopy, by focusing our attention to unveil the different effect between 1-propanol and 2-propanol. We found that, with 1-propanol, the long-axis length exhibits minimum at 60% and then tends to increase with the increase of alcohol content. On the other hand, with 2-propanol the long-axis length exhibits almost monotonous decrease with the increase of alcohol content. These results indicate that DNA undergoes reentrant transition of coil-globule-coil with 1-propanol, whereas such reentrance phenomenon does not appear with 2-propanol. As a related phenomenon, we have recently reported that ethanol causes reentrant transition on DNA accompanied by the increase of its concentration.[1] We will discuss the mechanism of the reentrant transition in terms of the effect of none-sized clusters on the ethanol and 1-propanol solutions with high concentrations. [1] Y. Oda, et al., “Highly Concentrated Ethanol Solution Behaves as a Good Solvent for DNA as Revealed by Single-Molecule Observation”, ChemPhysChem, 17, 471(2016).