Interfacial pH and polarity detection of amphiphilic self-assemblies using a single Schiff-base molecule

Abstract

The interfacial pH and polarity for different amphiphilic self-assemblies are estimated at a similar interfacial depth utilizing a unique Schiff-base molecule containing two identical phenol-conjugated-imine moieties.

Detection of Curvature-Radius-Dependent Interfacial pH/Polarity for Amphiphilic Self-Assemblies: Positive versus Negative Curvature

“… , Presumably, the interfacial negative charge for an anionic self-assembly attracts H 3 O + /H + ions and at the same time repels OH – ions electrostatically, causing a higher interfacial H 3 O + /H + ion concentration to result in a more acidic pH­(i) than the bulk value pH­(b) (Scheme ). The pH­(i) may be different by the same amount with the varying extent of the bulk pH (Δ / pH) induced by the self-assembled systems to obtain an identical amount of so-RHG between the interface and bulk. , The Δ / pH may be expressed by the self-assembled system induced difference in p K a (Δp K a ) owing to unchanged Δ / pH under different bulk pH values (Figure C, Table S2). However, for the precise measurement of pH­(i)/ΔpH, a polarity correction factor (ξ) equal to the p K a difference between the aqueous medium and mixed solvents (ethanol/buffer) of identical κ to that of the respective interface needs to be subtracted from the Δ / pH: or About a 0.50–0.60 unit decrease in p K a was detected due to a decrease in the solvent κ from 78.5 (pure aqueous medium) to a value similar to the κ­(i) of SDS micelles (∼44.0) or DMPG/DMPC (2:1) LUV (∼50.0) or TX-100/SDS (4:1) micelle (∼53.0) (Table , Figure C) .…”

“…The pH(i) may be different by the same amount with the varying extent of the bulk pH (Δ / pH) induced by the self-assembled systems to obtain an identical amount of so-RHG between the interface and bulk. 45,47 The Δ / pH may be expressed by the self-assembled system induced difference in pK a (ΔpK a ) owing to unchanged Δ / pH under different bulk pH values (Figure 1C, Table S2). However, for the precise measurement of pH(i)/ΔpH, a polarity correction factor (ξ) equal to the pK a difference between the aqueous medium and mixed solvents (ethanol/buffer) of identical κ to that of the respective interface needs to be subtracted from the Δ / pH: 45…”

“…Tahara and co-workers have established a heterodyne-detected electronic sum frequency generation (HD-ESFG) spectroscopic method to estimate the self-assembled system-induced acid/base p K a shift and have monitored the interfacial pH values. , It has been identified that the interfacial pH is substantially altered from the bulk pH. Recently, we have introduced a new interfacial pH/polarity monitoring method for biologically important micelles and vesicles by utilizing interface-interacting pH/polarity-detecting probes. − The estimated values of the pH/polarity differences between the bulk phase and the interface are observed to be similar to that obtained from the HD-ESFG method. Most importantly, the inherent simplicity of our detection technique can be highly effective for monitoring the shape- and structure-dependent manipulation of the pH/polarity at the complex biological membrane interfaces.…”

Structure Dependence of Pyridine and Benzene Derivatives on Interactions with Model Membranes

“…The pH value within the RM water pool is much more complicated. Depending on the charge of the headgroup surfactant used to form the RM microemulsion, a proton gradient can form. , The AOT RMs used in this study have a negative charge and therefore can cause an increase in proton concentration at the interface. , The p K a values of molecules have also been known to change within varying environments, such as the difference in p K a values of a specific amino acid depends on whether or not it is in the center or on the surface of a protein; therefore, the RM may affect the small aromatic molecules’ p K a values…”

Determination of proton concentration at cardiolipin-containing membrane interfaces and its relation with the peroxidase activity of cytochromec

“…Various anionic amphiphilic self-assemblies, including inner and outer mitochondrial membranes, interact electrostatically with cationic rhodamine derivatives 15. Recently, we have introduced an interface pH′ detection method for various amphiphilic self-assemblies by exploiting the acid/base equilibrium of a H + concentration probe (RHG), which is a glucose derivative of a spiro-rhodamine molecule 16…”