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首页> 外文期刊>Biophysical Chemistry: An International Journal Devoted to the Physical Chemistry of Biological Phenomena >Electrostatic free energy of the DNA double helix in counterion condensation theory
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Electrostatic free energy of the DNA double helix in counterion condensation theory

机译：抗衡离子缩合理论中DNA双螺旋的静电自由能

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Polyelectrolyte theory based on counterion condensation is extended from the standard line charge model to helical and double helical charge arrays. The number of condensed counterions turns out to be the same as for a line charge with charge density equal to the axial charge density of the helix. Also, the logarithmic salt dependence of the electrostatic free energy is the same in the range of lower salt concentration, so that the limiting laws remain unchanged. However, the internal free energy of the condensed layer of counterions and the overall electrostatic free energy depend on the helical parameters. At higher salt, the free energies of both single and double helix are negative, indicating electrostatic stabilization of the helical charge lattices due to the mixing entropy of the condensed counterions. Except at very low salt, the free energy of a single helix is higher than the free energy of a double helix with twice the charge density. With B-DNA parameters and single strands modeled as single helices, the predicted salt dependence of the free energy of transition from double helix to separated single strands has a maximum at approximately 0.2 M salt, close to the location in the laboratory of this well-known feature of the DNA strand separation transition. We also calculate the electrostatic free energy for the transition of the DNA double helix from the B to the A conformation. The B form is electrostatically stable over most of the salt range, but there is a spontaneous electrostatic transition to A near I M salt. The electrostatic free energy values are close to the experimental values of the overall (electrostatic plus non-electrostatic) transition free energies for A-philic base pair sequences. We are led to suggest that the experimentally observed B-to-A transition for A-philic sequences near I M salt in water is governed by the polyelectrolyte properties of these two conformations of the DNA double helix. The effect of ethanol, however, cannot be attributed to lowering of the bulk dielectric constant. (C) 2002 Elsevier Science B.V. All rights reserved. [References: 17]
机译：基于抗衡离子缩合的聚电解质理论已从标准线电荷模型扩展到螺旋和双螺旋电荷阵列。事实证明，稠合抗衡离子的数量与电荷密度等于螺旋的轴向电荷密度的线电荷相同。而且，静电自由能的对数盐依赖性在较低盐浓度的范围内是相同的，因此限制律保持不变。但是，抗衡离子凝结层的内部自由能和总静电自由能取决于螺旋参数。在较高的盐浓度下，单螺旋和双螺旋的自由能均为负，表明由于缩合抗衡离子的混合熵，螺旋电荷晶格的静电稳定。除了在非常低的盐浓度下，单螺旋的自由能比电荷密度翻倍的双螺旋的自由能高。使用B-DNA参数并将单链建模为单螺旋，从双螺旋到分离的单链的过渡自由能的预计盐依赖性在约0.2 M盐处具有最大值，接近该井的实验室位置。 DNA链分离过渡的已知特征。我们还计算了从B到A构象的DNA双螺旋过渡的静电自由能。 B形式在大部分盐范围内都是静电稳定的，但在I M盐附近会自发发生静电转变为A。静电自由能值接近于亲A碱基对序列的整体（静电加非静电）跃迁自由能的实验值。我们被认为是在水中观察到的I盐附近的A亲子序列从实验观察到的B到A过渡是由DNA双螺旋的这两个构象的聚电解质性质决定的。然而，乙醇的作用不能归因于整体介电常数的降低。 （C）2002 Elsevier Science B.V.保留所有权利。 [参考：17]

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