Localization of Hydrophobized Coumarin and Xanthene Acid–Base Indicators in Micelles

Farafonov, Vladimir; Lebed, Alexander V.; Mchedlov‐Petrossyan, Nikolay O.

doi:10.1007/s11237-022-09734-5

Cited by 3 publications

(10 citation statements)

References 27 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…We note that they are calculated using not the free energy MD runs (as in Tables and ) but the dedicated more extensive simulations. For TX-100, they are reported here in the Supporting Information, while for SDS and CTAB, they are published elsewhere …”

Section: Resultsmentioning

confidence: 99%

“… a Δχ(water) in SDS or CTAB = χ(water) there – χ(water) in TX-100. b For DDP ref . c For DDP ref , for the rest ref . …”

Section: Resultsmentioning

confidence: 99%

“…For TX-100, they are reported here in the Supporting Information, while for SDS and CTAB, they are published elsewhere. 27 Overall, the data predict a considerable mismatch between pK a i in SDS and TX-100, indicating that the corresponding Ψ calc and Ψ expt values are distorted. In contrast, for CTAB micelles, the mismatch is very small (with the exception of DF cations), meaning that the Ψ values reflect the effect of the electrostatic field rather well.…”

Section: ■ Computational Detailsmentioning

confidence: 91%

See 2 more Smart Citations

Estimation of Nanoparticle’s Surface Electrostatic Potential in Solution Using Acid–Base Molecular Probes II: Insight from Atomistic Simulations of Micelles

et al. 2023

View full text Add to dashboard Cite

Exploiting acid–base indicators as molecular probes is one of the most popular methods for determining the surface electrostatic potential Ψ in hydrophilic colloids like micellar surfactant solutions and related systems. Specifically, the indicator’s apparent acidity constant index is measured in the colloid solution of interest and, as a rule, in a nonionic surfactant solution; the difference between the two is proportional to Ψ. Despite the widespread use of this approach, a major problem remains unresolved, namely, the dissimilarity of Ψ values obtained with different indicators for the same system. The common point of view recognizes the effect of several factors (the choice of the nonionic surfactant, the probe’s localization, and the degree of hydration of micellar pseudophase) but does not allow to quantitatively assess their impact and decide which indicator reports the most correct Ψ value. Here, based on the ability to predict the reported Ψ values in silico, we examined the role of these factors using molecular dynamics simulations for five probes and two surfactants. The probe’s hydration in the Stern layer was found responsible for approximately half of the dissimilarity range. The probe’s localization is found important but hard to quantify because of the irregular structure of the Stern layer. The most accurate indicators among the examined set were identified. Supplementing experiments on measuring Ψ with molecular dynamics simulation is proposed as a way of improving the efficacy of the indicator method: the simulations can guide the choice of the most suitable probe and nonionic surfactant for the given nanoparticles.

show abstract

Section: Resultsmentioning

confidence: 99%

“… a Δχ(water) in SDS or CTAB = χ(water) there – χ(water) in TX-100. b For DDP ref . c For DDP ref , for the rest ref . …”

Section: Resultsmentioning

confidence: 99%

Section: ■ Computational Detailsmentioning

confidence: 91%

See 1 more Smart Citation

Estimation of Nanoparticle’s Surface Electrostatic Potential in Solution Using Acid–Base Molecular Probes II: Insight from Atomistic Simulations of Micelles

et al. 2023

View full text Add to dashboard Cite

show abstract

“…First of all, the simulations prove the expectation that the molecules of the indicators reside in the surface layer of the ionic micelles. Therefore, they should experience the influence of their electrostatic potential. , Regarding the nonionic micelles, the probes stay on the boundary between the hydrophilic shell and water.…”

Section: Resultsmentioning

confidence: 99%

“…As the probes, we chose four acid–base indicators, which were previously investigated both in vitro and in silico : 2,6-dinitro-4- n -dodecylphenol (DDP), 7- n -heptadecyl-4-hydroxycoumarin (HHC), n -decylfluorescein (DF), and N , N ′-di- n -octadecylrhodamin (DODR), Figure . On the one hand, numerous experiments have been done so far aimed at determining Ψ of various supramolecular aggregates. ,,,, On the other hand, the microscopic characteristics of these indicators in micelles of the chosen surfactants were comprehensively examined from a microscopic perspective using molecular dynamics simulations. , In general, all of them are weak acids or bases (DF dissociates by two stages) and have one or two long hydrocarbon radicals, ensuring complete binding by micelles.…”

Section: Simulation Setupmentioning

confidence: 99%

Estimation of Nanoparticle’s Surface Electrostatic Potential in Solution Using Acid–Base Molecular Probes I: In Silico Implementation for Surfactant Micelles

et al. 2023

View full text Add to dashboard Cite

Surface electrostatic potential Ψ is a key characteristic of colloid particles. Since the surface of the particles adsorbs various compounds and facilitates chemical reactions between them, Ψ largely affects the properties of adsorbed reactants and governs the flow of chemical reactions occurring between them. One of the most popular methods for estimating Ψ in hydrophilic colloids, such as micellar surfactant solutions and related systems, is the application of molecular probes, predominantly acid−base indicator dyes. The Ψ value is calculated from the difference of the probe's indices of the apparent acidity constant between the examined colloid solution and, usually, some other colloid solution with noncharged particles. Here, we show how to implement this method in silico using alchemical free energy calculations within the framework of molecular dynamics simulations. The proposed implementation is tested on surfactant micelles and is shown to predict experimental Ψ values with quantitative accuracy depending on the kind of surfactant. The sources of errors in the method are discussed, and recommendations for its application are given.

show abstract

Solvatochromic and Acid–Base Molecular Probes in Surfactant Micelles: Comparison of Molecular Dynamics Simulation with the Experiment

Mchedlov‐Petrossyan

Farafonov

Lebed

2023

Liquids

View full text Add to dashboard Cite

This article summarizes a series of seventeen publications by the authors devoted to molecular dynamics modeling of various indicator dyes (molecular probes) enclosed in surfactant micelles. These dyes serve as generally recognized tools for studying various types of organized solutions, among which surfactant micelles in water are the simplest and most explored. The modeling procedure involves altogether 50 to 95 surfactant molecules, 16 to 28 thousand water molecules, and a single dye molecule. The presentation of the simulation results was preceded by a brief review of the state of experimental studies. This article consists of three parts. First, despite numerous literature data devoted to modeling the micelles itself, we decided to revisit this issue. The structure and hydration of the surface of micelles of surfactants, first of all of sodium n-dodecylsulfate, SDS, and cetyltrimethylammonium bromide, CTAB, were studied. The values of the electrical potential, Ψ, were estimated as functions of the ionic strength and distance from the surface. The decrease in the Ψ value with distance is gradual. Attempts to consider both DS− and CTA+ micelles in water without counterions result in a decay into two smaller aggregates. Obviously, the hydrophobic interaction (association) of the hydrocarbon tails balances the repulsion of the charged headgroups of these small “bare” micelles. The second part is devoted to the study of seven pyridinium N-phenolates, known as Reichardt’s dyes, in ionic micelles. These most powerful solvatochromic indicators are now used for examining various colloidal systems. The localization and orientation of both zwitterionic and (colorless) cationic forms are generally consistent with intuitive ideas about the hydrophobicity of substituents. Hydration has been quantitatively described for both the dye molecule as a whole and the oxygen atom. A number of markers, including the visible absorption spectra of Reichardt’s dyes, enable assuming a better hydration of the micellar surface of SDS than that of CTAB. However, our data show that it is more correct to speak about the more pronounced hydrogen-bonding ability of water molecules in anionic micelles than about better hydration of the SDS micelles as compared to CTAB ones. Finally, a set of acid–base indicators firmly fixed in the micellar pseudophase were studied by molecular dynamics. They are instruments for estimating electrostatic potentials of micelles and related aggregates as Ψ= 2.303RTF−1 (pKai − pKaapp), where pKai and pKaapp are indices of so-called intrinsic and apparent dissociation constants. In this case, in addition to the location, orientation, and hydration, the differences between values of pKaapp and indices of the dissociation constants in water were estimated. Only a semi-quantitative agreement with the experimental data was obtained. However, the differences between pKaapp of a given indicator in two micellar solutions do much better agree with the experimental data. Accordingly, the experimental Ψ values of ionic micelles, as determined using the pKaapp in nonionic micelles as pKai, are reproduced with reasonable accuracy for the corresponding indicator. However, following the experimental data, a scatter of the Ψ values obtained with different indicators for given micelles is observed. This problem may be the subject of further research.

show abstract

Localization of Hydrophobized Coumarin and Xanthene Acid–Base Indicators in Micelles

Cited by 3 publications

References 27 publications

Estimation of Nanoparticle’s Surface Electrostatic Potential in Solution Using Acid–Base Molecular Probes II: Insight from Atomistic Simulations of Micelles

Estimation of Nanoparticle’s Surface Electrostatic Potential in Solution Using Acid–Base Molecular Probes II: Insight from Atomistic Simulations of Micelles

Estimation of Nanoparticle’s Surface Electrostatic Potential in Solution Using Acid–Base Molecular Probes I: In Silico Implementation for Surfactant Micelles

Solvatochromic and Acid–Base Molecular Probes in Surfactant Micelles: Comparison of Molecular Dynamics Simulation with the Experiment

Contact Info

Product

Resources

About