Cui Shuxun, Albrecht Christian, Kühner Ferdinand, Gaub Hermann E
Lehrstuhl für Angewandte Physik and Centre for Nanoscience, Ludwig-Maximilians Universität München, Amalienstrasse 54, 80799 München, Germany.
J Am Chem Soc. 2006 May 24;128(20):6636-9. doi: 10.1021/ja0582298.
In this paper, we measure the single chain elasticity of an oligomer single-stranded DNA (ssDNA) in both aqueous and nonaqueous, apolar liquid environments by AFM-based single molecule force spectroscopy. We find a marked deviation between the force-extension relations recorded for the two conditions. This difference is attributed to the additional energy required to break the H-bond-directed water bridges around the ssDNA chain in aqueous solutions, which are nonexistent in organic solvents. The results obtained in 8 M guanidine-HCl solution provide more evidence that water bridges around ssDNA originate the observed deviation. On the basis of the results obtained by an ab initio quantum mechanics calculation, a parameter-free freely rotating chain model is proposed. We find that this model is in perfect agreement with the experimental force-extension curve obtained in organic solvents, which further corroborates our assumption. On the basis of the experimental results, it is suggested that the weak H-bonding between ssDNA and water molecules may be a precondition for stable double-stranded DNA to exist in water.
在本文中，我们通过基于原子力显微镜的单分子力谱技术，测量了寡聚物单链脱氧核糖核酸（ssDNA）在水性和非水性、非极性液体环境中的单链弹性。我们发现两种条件下记录的力-伸长关系存在显著偏差。这种差异归因于在水溶液中打破围绕ssDNA链的氢键导向水桥所需的额外能量，而在有机溶剂中不存在这种水桥。在8M盐酸胍溶液中获得的结果提供了更多证据，表明ssDNA周围的水桥导致了观察到的偏差。基于从头算量子力学计算得到的结果，提出了一个无参数的自由旋转链模型。我们发现该模型与在有机溶剂中获得的实验力-伸长曲线完全一致，这进一步证实了我们的假设。基于实验结果，有人提出ssDNA与水分子之间的弱氢键可能是稳定双链DNA在水中存在的先决条件。
