Monitoring Local pH of Membranous Aggregates via Ratiometric Color Changing Response

Abstract

A series of oxidized di(indolyl)arylmethanes (DIAM) with polyaromatic signaling moieties have been designed for monitoring local pH at the interfacial region of surfactant aggregates, such as micelles and vesicles. The oxidized DIAMs show changes in solution color from red to yellow when incorporated in cationic surfactants (at pH 7.4) and yellow to reddish pink when exposed to negatively-charged surfactants (at pH 5.0). The changes in surface charge can influence the interfacial pH (distinct from bulk pH of the medium) of the surfactant aggregates. The mechanistic studies indicate that the red-shifted absorption maxima observed in the presence of anionic amphiphiles (acidic local pH) originated from the protonated species. On the contrary, maxima in the blue region, triggered by positively charged amphiphiles (basic local pH), is attributed to the zwitterionic species. Such prototropic equilibrium affects charge transfer states of the molecules along with their self-assembly properties. Thus, it is evident that probes can predict as well as quantify the local pH change using the pseudophase ion exchange formalism. Also, the probes can detect the presence of anionic amphiphiles even when bound to phospholipid membranes.

Modulation of Analytical Performance of a Bifunctional Optical Probe at the Micelle‐Water Interface: Selective Sensing of Histidine in Biological Fluid

“…Interaction with heavy metal pollutants: Recently, we have demonstrated that oxidized bisindolyl based chromogenic probes could sense the local pH of the micellar interface. [12] In another report, we reported that compound 1 could bind with two different metal ions, Cu 2 + and Hg 2 + via two mutually independent metal ion binding units (Figure 4a). [13] The Cu 2 + ion binds to the carboxylate moieties of 1 and retards the charge transfer interaction, while Hg 2 + coordinates through bisindolyl nitrogen which facilitates the extent of charge transfer (Figure 4b).…”

“…Interaction with heavy metal pollutants : Recently, we have demonstrated that oxidized bisindolyl based chromogenic probes could sense the local pH of the micellar interface [12] . In another report, we reported that compound 1 could bind with two different metal ions, Cu 2+ and Hg 2+ via two mutually independent metal ion binding units (Figure 4a) [13] .…”

Surfactant-induced alterations in optoelectronic properties of perylene diimide dyes: modulating sensing responses in the aqueous environment

“…Such a distinct absorption profile indicated the formation of a mixed micelle system via co-assembly of dye molecules with the surfactant. 15 A similar titration study was also conducted in fluorescence mode (Fig. 3c).…”

Tuning Sensing Efficacy of Oligo(phenylenevinylene) Based Chromogenic Probes: Effect of Alkyl Substituents on Metal Ion Detection at Micelle‐Water Interface

“…It is worth noting that recent work by Bhattacharya et al demonstrated that compound 2 (bearing À C 16 H 33 long alkyl chains) in THF medium exhibited chromogenic responses to both Cu 2 + and Hg 2 + ions (Figure 4d), resembling what we observed in the Brij-58 micelle medium. [40,41] Consequently, it is evident that despite their very similar chemical structures, compound 1 and compound 2 displayed distinct metal ion-binding properties in both THF and Brij-58 micelle mediums.…”