CEFITEC, Departamento de Física, Faculdade de Ciências e Tecnologia, UNL, Campus de Caparica, 2829-516, Caparica, Portugal.
Langmuir. 2013 Jan 8;29(1):448-55. doi: 10.1021/la304036h. Epub 2012 Dec 26.
Electrostatic and hydrophobic interactions govern most of the properties of supramolecular systems, which is the reason determining the degree of ionization of macromolecules has become crucial for many applications. In this paper, we show that high-resolution ultraviolet spectroscopy (VUV) can be used to determine the degree of ionization and its effect on the electronic excitation energies of layer-by-layer (LbL) films of poly(allylamine hydrochloride) (PAH) and poly[1-[4-(3-carboxy-4 hydroxyphenylazo)benzene sulfonamido]-1,2-ethanediyl, sodium salt] (PAZO). A full assignment of the VUV peaks of these polyelectrolytes in solution and in cast or LbL films could be made, with their pH dependence allowing us to determine the pK(a) using the Henderson-Hasselbach equation. The pK(a) for PAZO increased from ca. 6 in solution to ca. 7.3 in LbL films owing to the charge transfer from PAH. Significantly, even using solutions at a fixed pH for PAH, the amount adsorbed on the LbL films still varied with the pH of the PAZO solutions due to these molecular-level interactions. Therefore, the procedure based on a comparison of VUV spectra from solutions and films obtained under distinct conditions is useful to determine the degree of dissociation of macromolecules, in addition to permitting interrogation of interface effects in multilayer films.
静电和疏水性相互作用控制着超分子系统的大多数性质，这就是决定大分子的电离程度对许多应用变得至关重要的原因。在本文中，我们表明，高分辨率紫外光谱（VUV）可用于确定电离程度及其对聚（盐酸烯丙胺）（PAH）和聚[1-[4-（3-羧基-4-羟基苯基偶氮）苯磺酰胺基]-1,2-乙二基，钠盐]（PAZO）层层（LbL）薄膜的电子激发能的影响。可以对这些聚电解质在溶液中和浇铸或 LbL 薄膜中的 VUV 峰进行完全分配，其 pH 依赖性允许我们使用 Henderson-Hasselbach 方程来确定 pK(a)。由于来自 PAH 的电荷转移，PAZO 的 pK(a)从溶液中的约 6 增加到 LbL 薄膜中的约 7.3。值得注意的是，即使对于 PAH 使用固定 pH 的溶液，由于这些分子水平的相互作用，吸附在 LbL 薄膜上的量仍随 PAZO 溶液的 pH 而变化。因此，基于在不同条件下获得的溶液和薄膜的 VUV 光谱进行比较的程序不仅可用于确定大分子的离解程度，还可用于研究多层薄膜中的界面效应。
