Korolev Nikolay, Lyubartsev Alexander P, Nordenskiöld Lars
Division of Physical Chemistry, Arrhenius Laboratory, Stockholm University, S-106 91 Stockholm, Sweden.
Biophys Chem. 2003 May 1;104(1):55-66. doi: 10.1016/s0301-4622(02)00338-1.
The Poisson Boltzmann (PB) cell model of polyelectrolyte solution has been used for calculation of the electrostatic free energy difference, Delta G(el), between double- and single-stranded DNA. The calculations have been performed for conditions relevant to describe the DNA helix-coil transition in NaCl solution in the presence of the natural polyamines putrescine(2+), spermidine(3+), spermine(4+) and their synthetic homologs with different spacing between the charged amino groups, for which experimental values of the DNA 'melting' transition temperature (T(m)) are available. Using the PB theory and the polyamine ion radius as an adjusting parameter provides quantitative agreement between experimental and theoretical T(m)--salt concentration dependencies only by using physically unreasonable radii for the polyamine. Thus, modeling the linear and flexible polyamines as charged spheres within the PB cell model is an implausible oversimplification. We propose another explanation for the experimental observations, still within the frame of the 'primitive' PB polyelectrolyte theory. This explanation is based on an analysis of the Delta G(el) dependence on the stoichiometry of polyamine-polyanion binding to double- and single-stranded DNA.
聚电解质溶液的泊松-玻尔兹曼（PB）细胞模型已用于计算双链和单链DNA之间的静电自由能差ΔG(el)。计算是在与描述NaCl溶液中DNA螺旋-线圈转变相关的条件下进行的，该溶液中存在天然多胺腐胺（2+）、亚精胺（3+）、精胺（4+）及其带电氨基之间具有不同间距的合成同系物，对于这些多胺，DNA“熔解”转变温度（T(m)）的实验值是可用的。使用PB理论并将多胺离子半径作为调整参数，仅通过使用物理上不合理的多胺半径，才能使实验和理论T(m) - 盐浓度依赖性之间达成定量一致。因此，在PB细胞模型中将线性和柔性多胺建模为带电球体是一种不合理的过度简化。我们提出了对实验观察结果的另一种解释，该解释仍在“原始”PB聚电解质理论的框架内。这种解释基于对ΔG(el)对多胺 - 多阴离子与双链和单链DNA结合化学计量的依赖性的分析。
