Quantitative Determination of Relative Permittivity Based on the Fluorescence Property of Pyrene Derivatives: An Interpretation of Hydrophobicity in Self-Assembled Aggregates of Nonionic Amphiphiles

Abstract

Aggregates in aqueous solutions can embed hydrophobic molecules, and their interactions depend on the properties of the aggregates. The electric surface potential, molecular mobility, and gradual hydrophobicity are the properties that regulate the interactions, and it is essential to understand these to quantify the properties. Electric surface potential and molecular mobility are quantified using the zeta potential and NMR measurements. In this study, the quantification of gradual hydrophobicity within the aggregate based on the relative permittivity, also called the dielectric constant, has been estimated from fluorescence spectra of pyrene−dicarboxylic acid conjugates. The localization of the pyrene moiety was modified by conjugation with succinic acid, suberic acid, or dodecanedioic acid, and the conjugates were evaluated in the shallow, middle, and deep regions of the aggregates. Span and Tween surfactants have been employed to prepare these aggregates, because they form various kinds of aggregates such as micelles and vesicles. It was realized that the hydrophobicity gradually increased from the interface to the hydrophobic core. Alternatively, a comparison of hydrophobicity within the aggregates showed no remarkable difference. Moreover, the analyses suggested that there are a few water molecules in the deep region. These results support the idea of the localization of embedded molecules in aggregates.

Possible Role of Bent Structure of Methylated Lithocholic Acid on Artificial and Plasma Membranes

“…Pyrene was used to evaluate hydrophobicity based on values of I I / I III , which is the ratio of the intensities of peak I (377 ± 2 nm, I I ) and peak III (387 ± 2 nm, I III ) of the pyrene fluorescence spectrum. I I / I III values were used to estimate the relative permittivity, and Py-C 3 -COOH, Py-C 7 -COOH, and Py-C 11 -COOH were evaluated in the shallow, middle, and deep regions [ 27 ]. Figure 6 shows the estimated ε r of liposomes using Py-C 7 -COOH.…”

“…Pyrene is also an environmentally responsive fluorescent probe [ 24 , 25 ], and pyrene is used to evaluate the hydrophobicity of micelles [ 26 ]. Moreover, the conjugation of dicarboxylic acids (succinic acid, suberic acid, and dodecanedioic acid) can evaluate gradual hydrophobicity in the hydrophobic region ( Figure S7 ) [ 27 ]. The pyrene-succinic acid conjugate (Py-C 3 -COOH), pyrene-suberic acid conjugate (Py-C 7 -COOH), and pyrene-dodecanedioic acid conjugate (Py-C 11 -COOH) were dissolved in THF, and their concentrations were adjusted to 10 mM.…”

“…The ratio of I I to I III ( I I / I III ) is related to the relative permittivity of aliphatic monoalcohols. The correlation with the relative permittivity was fitted using the following equation: where α , β , and γ are constants, ε r corresponds to the relative permittivity, and each equation of Py-C3-COOH, Py-C7-COOH, and Py-C11-COOH has already been reported [ 27 ]. The relative permittivity of the liposomes was estimated from the I I / I III values based on the correlation equations.…”

Surface Properties and Liquid Crystal Properties of Alkyltetra(oxyethyl) β-d-Glucopyranoside

“…Moreover, the modified glucopyranosides had good surface activity, stronger hydrophilicity, and interesting thermotropic/lyotropic liquid crystal phase behavior. There are reasons to believe that they have potential applications in the commercial formulations of biotechnology, membrane protein separation, biomedicine, food, cosmetics, self-assembly, and so on. Despite promising advantages, further in-depth research should be needed to explore thoroughly specific and meaningful practical application solutions related to preparation, eco-environmental issue, , economic benefit, reconstruction, and technology progress due to their unique structure and multifaceted performance to the perspective of supervision and management.…”

Cholesterol as a Subsidiary Component of Sorbitan Surfactant-Based Aggregates: A Study of Formation, Hydrophobicity, and Estimation of Localization of Embedded Molecules

“…The ratio of fluorescence intensities at 377 ± 2 nm ( I I ) and 387 ± 2 nm ( I III ) is known to be related to the polarity of monoalcohols, meaning that similar to Laurdan, pyrene can also be used as a fluorescence probe for evaluating the hydrophobicity. Moreover, gradual evaluation of hydrophobicity in aggregates using pyrene–dicarboxylic acid (succinic acid, suberic acid, or dodecanedioic acid) conjugates (Py-C 3 -COOH, Py-C 7 -COOH, and Py-C 11 -COOH) has been reported . Conjugation with succinic acid, suberic acid, and dodecanedioic acid enables the regulation of the localization of the pyrene moiety, which enables the gradual evaluation of hydrophobicity from an interface to a hydrophobic core.…”