Determination of Degree of Ionization of Poly(allylamine hydrochloride) (PAH) and Poly[1-[4-(3-carboxy-4 hydroxyphenylazo)benzene sulfonamido]-1,2-ethanediyl, sodium salt] (PAZO) in Layer-by-Layer Films using Vacuum Photoabsorption Spectroscopy

Abstract

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.

Nano-Molar Deltamethrin Sensor Based on Electrical Impedance of PAH/PAZO Layer-by-Layer Sensing Films

“…The presence of adsorbed DM on the sensing layer was also inferred by comparing the UV-Vis spectra of a (PAH/PAZO) 5 film before and after DM adsorption, see Figure 5b. The spectra show that although the baseline to be shifted due to the adsorption of the colorless DM molecules, the absorbance intensity of the azo chromophore absorbance peak at 360 nm [31] remains constant.…”

“…However, the LBL films structure is also influenced by the surface morphology of each layer. For the first five bilayers, it was seen that the surface roughness increases slightly with the number of bilayers [30], which indicates that all bilayers are essentially similar without increase of larger grains and consequently the bilayers are more or less planar with similar values of thickness [31] and roughness [30]. Since the film structure, namely, the thickness and roughness, is also relevant for the sensor response, and being the film composed by a set of bilayers, the resistance and capacitance values of the sensing film can be controlled by the number of bilayers.…”

Triclosan Detection in Aqueous Environmental Matrices by Thin-Films Sensors

“…The adsorption of TCS onto polyelectrolytes thin-films, is affected by the pH of TCS solution [15]. The pH affected both the degree of ionization of the last polyelectrolyte in the LbL thin-film and the dissociation of TCS [16]. DW, LW and EF pH: 8.00, 5.80, 8.26.…”

Mechanisms of L‐lysine extraction with sec‐octylphenoxy acetic acid in sulfonated kerosene

“…In this study, D2EHPA reacts with L‐Lys to form a medium strong acid–weak base salt D2EHPA‐O −+ H 2 N‐Lys, while CA‐12 reacts with L‐Lys to form a weak acid–weak base salt CA‐12‐COO −+ H 2 N‐Lys which has a much lower ionization degree than D2EHPA‐O −+ H 2 N‐Lys. As a result, the extraction efficiency of CA‐12 is higher than that of D2EHPA, because the stability of CA‐12‐COO −+ H 2 N‐Lys is significantly higher than that of D2EHPA‐O −+ H 2 N‐Lys …”

“…As a result, the extraction efficiency of CA-12 is higher than that of D2EHPA, because the stability of CA-12-COO −+ H 2 N-Lys is significantly higher than that of D2EHPA-O −+ H 2 N-Lys. 57 As mentioned above, CA-12 is an organic weak acid, whose carboxyl dissociation is influenced by acidity; while L-Lys is a basic amino acid, and the charge properties of its amino groups are also influenced by acidity. Accordingly, in this study, the electrostatic interaction between CA-12 and L-Lys is controlled by acidity, so is the extraction efficiency.…”