Interfacial Behavior of Fluorescent Species Associated with Dendritic Polymers at Polarized Liquid|Liquid Interfaces

Abstract

Charge transfer and adsorption reactions at interfaces between two immiscible electrolyte solutions (ITIES) have been investigated as a model of mass-transport and enzymatic reactions on biomembrane systems. In particular, the ion-partitioning property of bio-related materials in the liquid|liquid biphasic system is significantly important to evaluate their pharmacokinetics in vivo. Dendritic polymers such as dendrimer and hyperbranched polymer have unique properties as compared with conventional polymers. For instance, various organic molecules and metal ions have been reported to be accommodated into the internal cavity and captured on the peripheral region of dendrimers by hydrophobic or electrostatic interactions. The dendritic polymers have therefore the potential ability as the molecular capsule and/or carrier for the drug delivery systems (DDS), separation and detection regents. Recently, we have been reported that the interfacial association between the polyamidoamine (PAMAM) dendrimer and ionic species is strongly dependent on pH, the Galvani potential difference (Δw o φ) and generation of the dendrimer [1, 2]. In the present study, we investigated the interfacial behavior of flavin derivatives, i.e. riboflavin (RF) and flavin mononucleotide (FMN), in the presence of the generation 4 (G4) PAMAM dendrimer or hyperbranched bis-MPA polyster-64-hydroxyl (HBP) at the water|1,2-dichloroethane (DCE) interface. The interfacial mechanism was analyzed through the potential modulated fluorescence (PMF) spectroscopy [3]. In PMF measurements, the ion transfer and adsorption processes at ITIES are distinguishable through the complex analysis of ac fluorescence signals as a function of ac-potential modulation. The PMF responses obtained for RF were decreased by the addition of the PAMAM dendrimer. The real and imaginary components of PMF were obtained as positive and negative signs at Δw o φ = 0.33 V and vice versa at 0.36 V in the presence of the dendrimer. These PMF responses were associated with the ion transfer and adsorption of the dendrimer incorporating RF at the interface. In addition, the PMF responses arisen from the flavin derivatives were drastically weakened in the presence of HBP. These PMF results indicated that the PAMAM dendrimers effectively incorporate the flavin derivatives into the internal cavity. On the other hand, HBP strongly adsorbed at the interface inhibited the adsorption process of the flavin derivatives. The encapsulation behavior of anionic species in a cationic dendrigraft poly-L-lysine (DGL) was also investigated by using an anionic lipophilic probe, 8-anilino-1-naphthalenesulonic acid (ANS). The absorption and fluorescence spectra of ANS measured in aqueous solution were significantly affected by the addition of DGL, where the fluorescence intensity of ANS was increased in the presence of higher generation DGLs at 2 < pH < 10. In the PMF analysis, the real and imaginary components of PMF were obtained as negative and positive signs at the ion transfer potential of ANS−(Fig. 1). The PMF responses were negatively shifted by the third generation DGL (DGL-G3). These results indicated that ANS was effectively encapsulated in DGL even at the interface. H. Sakae, H. Nagatani, K. Morita, H. Imura, Langmuir, 30, 937 (2014).H. Sakae, H. Nagatani, H. Imura, Electrochim. Acta, 191, 631 (2016).H. Nagatani, T. Sagara, Anal. Sci., 23, 1041 (2007). Figure 1