碩士 ; 國立清華大學 ; 化學工程學系 ; GH029632542 ; 我們利用SAXS研究DNA和PAMAM G4 dendrimer之錯合物的自組裝結構，我們在固定N/P ratio=6的條件下分成兩部分來討論，第一部分為在純水中改變dendrimer的質子化程度(dp)解析錯合物之結構；第二部分為研究在不同NaCl濃度環境下，離子效應對於結構的影響。 在純水系統中我們發現，隨著dp的增加(即dendrimer表面的正電荷數目變多)，其與DNA之間的靜電吸引力增強，其結構為：由較低的質子化程度之四面推積結構(square columnar phase)(dp=0~0.2)；中間質子化程度的square-packed undulated DNA phase(dp=0.225~0.5)；高質子化程度(dp=0.6~0.9)的beads-on string結構。 在單價鹽類NaCl環境中，我們可以觀察到複雜的相轉化現象(如圖3-13)，這些相轉化似乎是鹽類對於DNA-dendrimer、DNA-DNA、dendrimer-dendrimer之靜電作用力的遮蔽效應間的互動與平衡所造成，這些互動性尚需要理論工作來釐清，本研究之成果應為此後續研究提供重要之基礎。 ; In this study, we investigate the nanostructures of the complexes of DNA with poly(amdoamine) (PAMAM) dendrimer of generation four (G4). The role of electrostatic interaction in the structure formation is examined by studying the effects of dendrimer charge density (prescribed by its degree of protonation, dp) and addition of monovalent salt NaCl. For the complex prepared in pure water, we show that increasing the charge density of dendrimer effectively compensates the DNA bending energy, thereby allowing DNA conformation to be templated by the surface curvature of the charged sphere. In this case, the DNA packaging state transforms from the square columnar phase to tetragonally-packed undulated DNA phase to beads-on-string structure with increasing dp. The addition of NaCl has a strong impact on the nanostructure of the complex. The structure transformation with increasing salt concentration tends to follow the trend of: square columnar phase? undulated phase ? hexagonal columnar phase or beads-on-string structure? undulated phase ? hexagonal columnar phase. The observed phase transition sequence implies that the screening of the electrostatic attraction between DNA and dendrimer is the most significant effect, while the screening of the intra-chain electrostatic repulsion of DNA is also operative to induce the transformation from square columnar phase to undulated phase.