Department of Chemistry, Coimbra University, Rua Larga, 3004-535 Coimbra, Portugal.
Biomacromolecules. 2010 Sep 13;11(9):2399-406. doi: 10.1021/bm100565r.
This work addresses the impact of pH variation on DNA-polyethylenimine (PEI) complex formation, in aqueous solution and at constant ionic strength. An initial potentiometric characterization of the acid-base behavior of PEI is carried out to measure the concentration of ionized species in the relevant systems. The characterization of the DNA-PEI complexes is performed by precipitation assays, agarose gel electrophoresis, photon correlation spectroscopy, and zeta potential analysis. It is observed that the variations on the electrophoretic mobility, size, and electrical properties of complexes display nonmonotonic, nontrivial trends with pH, if the same polycation/polyanion charge ratios are used for different values of pH. It is seen that both linear charge density and the relative number of chains of the condensing agent are important factors governing the condensation behavior. Complexes prepared at pH 4, for example, indicate strong binding and a large mean size, while those prepared at pH 8 are smaller, in a more uniform population. Finally, charge inversion was observed for all studied pH values (even below charge neutralization).
这项工作研究了在恒定离子强度下，pH 值变化对 DNA-聚乙二烯亚胺（PEI）复合物形成的影响。首先对 PEI 的酸碱行为进行了电位滴定表征，以测量相关体系中离子化物种的浓度。通过沉淀分析、琼脂糖凝胶电泳、光子相关光谱和zeta 电位分析对 DNA-PEI 复合物进行了表征。结果表明，如果使用不同 pH 值下相同的聚阳离子/聚阴离子电荷比，则复合物的电泳迁移率、大小和电性质的变化呈现出非单调的、非平凡的趋势。结果表明，线性电荷密度和缩合剂的相对链数都是影响缩合行为的重要因素。例如，在 pH 值为 4 时制备的复合物表明具有强结合和较大的平均尺寸，而在 pH 值为 8 时制备的复合物则较小，且分布更为均匀。最后，在所有研究的 pH 值下（甚至低于电荷中和）都观察到了电荷反转。
