Sharawy Mahmoud, Consta Styliani
Department of Chemistry, The University of Western Ontario, London, Ontario, Canada N6A 5B7.
Phys Chem Chem Phys. 2015 Oct 14;17(38):25550-62. doi: 10.1039/c5cp04331j.
We present the desolvation mechanism of a double-stranded oligodeoxynucleotide (dsDNA) from an aqueous nanodrop studied by using atomistic molecular dynamics methods. The central theme of this study is the stability of a non-covalently bound complex, in general, and that of a dsDNA in particular, in a droplet environment. Among the factors that may affect the stability of a complex in an evaporating droplet we examine the increase in ion concentration and the distinct droplet morphologies arising from the charge-induced instability. We explore in detail a large set of aqueous nanodrops with excess negative charge, which comprise a dsDNA and Na(+), Cl(-) ions at various concentrations. We find that for a square of the charge to volume ratio above that of the Rayleigh limit the droplet attains distinct "spiky" morphologies that disperse the charge in larger volume relative to that of the spherical drop. Moreover, it is found that it is possible for a non-covalent complex to remain associated in an unstable droplet as long as there is enough solvent to accommodate the instability. In the presence of Na(+) and Cl(-) ions, the Na(+) ions form adducts with the double helical DNA in the minor groove, which help stabilise the duplex state in the gas phase. The negative ions may be released from the droplet. In a DNA-containing droplet with a net charge that is less negative than 50% of the dsDNA charge, the DNA maintains a double-stranded state in the gas phase. Several of our findings are in good agreement with experiments, while the spiky droplet morphology due to the charge-induced instability calls for new experiments. The results shed light on the association properties of complexes of macromolecules in droplet environments, which are critical intermediates in electrospray ionisation experiments.
我们展示了通过原子分子动力学方法研究的双链寡脱氧核苷酸（dsDNA）从水性纳米液滴中的去溶剂化机制。本研究的核心主题是一般情况下非共价结合复合物的稳定性，特别是dsDNA在液滴环境中的稳定性。在可能影响蒸发液滴中复合物稳定性的因素中，我们研究了离子浓度的增加以及由电荷诱导不稳定性产生的不同液滴形态。我们详细探索了大量带过量负电荷的水性纳米液滴，其中包含不同浓度的dsDNA和Na⁺、Cl⁻离子。我们发现，对于电荷与体积比的平方高于瑞利极限的情况，液滴会呈现出独特的“尖刺状”形态，相对于球形液滴，这种形态会将电荷分散在更大的体积中。此外，研究发现只要有足够的溶剂来容纳不稳定性，非共价复合物就有可能在不稳定的液滴中保持结合状态。在存在Na⁺和Cl⁻离子的情况下，Na⁺离子在小沟中与双螺旋DNA形成加合物，这有助于在气相中稳定双链状态。负离子可能会从液滴中释放出来。在净电荷比dsDNA电荷少负50%的含DNA液滴中，DNA在气相中保持双链状态。我们的一些发现与实验结果高度一致，而由电荷诱导不稳定性导致的尖刺状液滴形态需要新的实验来验证。这些结果揭示了液滴环境中大分子复合物的缔合性质，而液滴环境是电喷雾电离实验中的关键中间体。
