Electrostatic compaction of double stranded DNA induced by a positively charged poly(amidoamine) (PAMAM) dendrimer of generation four (G4) was found to produce two unique types of DNA mesophases, in which the DNA bent into superhelices packed in a tetragonal or hexagonal lattice. The structure formed at a lower dendrimer charge density was three-dimensionally (3D) ordered, as characterized by the P4₁2₁2 space group with a 4₁ screw axis in a tetragonal arrangement, showing that the weakly bent DNA superhelices with a pitch length of ca. 5.0 nm possessed both identical handedness and phase conservation. The 3D ordered structure transformed into a 2D mesophase at a higher dendrimer charge density, wherein the strongly bent superhelices with a pitch length of ca. 4.0 nm organized in a hexagonal lattice without lateral coherence of helical trajectory. The counterion valency of the protonic acid that is used to charge the dendrimer was found to influence the phase diagram. Under a given dendrimer charge density, the complex with a multivalent acid-protonated dendrimer tended to form structures with less curved DNA, attesting that the driving force of charge matching was reduced by increasing the counterion valency of the dendrimer.

中文翻译：

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来自树枝状聚合物诱导的 DNA 压实的超螺旋 DNA 液晶

发现由第四代 (G4) 带正电荷的聚（酰氨基胺）（PAMAM）树枝状大分子诱导的双链 DNA 的静电压实产生两种独特类型的 DNA 中间相，其中 DNA 弯曲成超螺旋，堆积在四方或六方晶格中. 在较低的树枝状聚合物电荷密度下形成的结构是三维（3D）有序的，其特征在于P 4 ₁ 2 ₁ 2 空间群具有四方排列的 4 ₁螺旋轴，表明弱弯曲的 DNA 超螺旋具有节距长度约。5.0 nm 具有相同的旋向性和相位守恒。3D 有序结构以更高的树枝状大分子电荷密度转变为 2D 中间相，其中强烈弯曲的超螺旋的节距长度约为 4.0 nm 组织在六边形晶格中，没有螺旋轨迹的横向相干性。发现用于使树枝状聚合物带电的质子酸的反离子化合价会影响相图。在给定的树枝状聚合物电荷密度下，与多价酸质子化树枝状聚合物形成的复合物倾向于形成具有较少弯曲 DNA 的结构，证明电荷匹配的驱动力通过增加树枝状聚合物的反离子价而降低。