THERMODYNAMICS AND EQUILIBRIUM SEDIMENTATION ANALYSIS OF THE CLOSE APPROACH OF DNA-MOLECULES AND A MOLECULAR ORDERING TRANSITION
THERMODYNAMICS AND EQUILIBRIUM SEDIMENTATION ANALYSIS OF THE CLOSE APPROACH OF DNA-MOLECULES AND A MOLECULAR ORDERING TRANSITION
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DOI：
10.1002/bip.1981.360200615
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发表时间：
1981-01-01
期刊：
影响因子：
2.9
通讯作者：
LERMAN, LS
中科院分区：
文献类型：
--
作者：
BRIAN, AA;FRISCH, HL;LERMAN, LS
对超浓凝胶中高浓度DNA持久长度片段平衡分布的测量表明，约化渗透压的上升比线性上升快得多。从Zimm簇积分的数据分析，螺旋之间的净相互作用显然是纯粹的排斥在所有的距离。在盐浓度不太低的情况下，由标度粒子理论导出的具有1个可调参数的理论状态方程与实验数据符合得很好。该参数表示螺旋之间静电排斥的势函数的简化近似中的硬核半径。它的值取决于盐的浓度，它在高盐收缩到与直接结构估计密切一致的半径。在仅轻微盐依赖的渗透压的特定值下，溶液经历可逆转变为更致密、浑浊、光学各向异性相。DNA的体积分数（包括静电半径）之间的关系在过渡点，和有效的不对称性的分子作为盐的函数，是近似对应于各种理论处理。实验函数外推到球形粒子的正确极限。估计了使DNA达到高浓度所需的工作。相变明显为一阶相变。
Measurement of the equilibrium distribution of persistence length fragments of DNA in high concentration in the ultracentrifuge shows that the reduced osmotic pressure rises much faster than linearly. From analysis of the data in terms of the Zimm cluster integral, the net interactions between helices are apparently purely repulsive at all distances. A theoretical equation of state derived from scaled particle theory with 1 adjustable parameter is in excellent agreement with the experimental data if the salt concentration is not excessively low. The parameter represents the hard-core radius in a simplified approximation to the potential function for the electrostatic repulsion between helices. It value depends on the salt concentration, and it shrinks at high salt to a radius in close agreement with direct structural estimates. At a particular value of the osmotic pressure that is only slightly salt dependent, the solution undergoes a reversible transition to a denser, turbid, optically anisotropic phase. The relation between DNA volume fraction (including the electrostatic radius) at the transition point, and the effective asymmetry of the molecules as a function of salt, is in approximate correspondence with various theoretical treatments. The experimental function extrapolates to the correct limit for spherical particles. The work needed to bring DNA to a high concentration is estimated. The phase transition is evidently 1st order.