Phase behavior of single DNA in mixed solvents
Phase behavior of single DNA in mixed solvents
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DOI：
10.1021/ja981491e
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发表时间：
1999-02-17
影响因子：
15
通讯作者：
Jönsson, B
中科院分区：
文献类型：
--
作者：
Mel'nikov, SM;Khan, MO;Jönsson, B
在存在伯醇、丙酮和乙二醇的水溶液中，单大dsDNA链的压实已经用荧光显微镜技术进行了实验研究。我们发现，在所有被研究的有机溶剂存在下，单个DNA分子表现出从一个细长的线圈的离散相变。变成紧密的球状构象。有趣的是，DNA相变发生在水溶液中不同质量分数的有机溶剂中，但所有研究的伯醇和丙酮的混合溶剂的介电常数相似。另一方面，乙二醇-水混合物的介电常数对应于单个DNA的坍塌跃迁，与其他所研究的体系不同。对这一现象的解释是考虑到水溶液中存在不同极性的乙二醇构象。因此，溶剂的介电常数是决定DNA在溶液中构象行为的关键因素。当介电常数降低时，单个DNA分子的压实被认为是离子-离子相关性增加的线索。对单个聚电解质链的蒙特卡罗模拟也表明，当静电耦合增加时，即通过降低介电常数，链的尺寸减小。实验结果可以用平衡反离子熵和离子-离子相关能的简单自由能模型来合理化。
Compaction of single large dsDNA chains in aqueous solution in the presence of primary alcohols, acetone, and ethylene glycol has been studied experimentally with the use of a fluorescence microscopy technique. It is found that in the presence of all studied organic solvents single DNA molecules exhibit a discrete phase transition from an elongated coiled. to a compacted globular conformation. interestingly, DNA phase transition occurred at various weight fractions of organic solvents in aqueous solution, but at similar dielectric constants of mixed solvent for all studied primary alcohols and acetone. On the other hand, the dielectric constant of ethylene glycol-water mixtures corresponding to the collapsing transition in single DNA differed from that for the other studied systems. The explanation of this phenomenon comes through consideration of the existence of ethylene glycol conformers with various polarities in aqueous solution. Thus, the dielectric permittivity of the solvent is a key factor that determines the conformational behavior of DNA in solution. The compaction of a single DNA molecule when the dielectric permittivity constant is lowered is thought to be clue to the increased importance of ion-ion correlation. Monte Carlo simulations for a single polyelectrolyte chain also show that the dimensions of the chain diminish when the electrostatic coupling is increased, i.e., by decreasing the dielectric constant. The experimental result can be rationalized with a simple free energy model balancing the counterion entropy and the ion-ion correlation energy.