Solvatochromic Reichardt’s Dye in Micelles of Sodium Cetyl Sulfate: Md Modeling of Location Character and Hydration

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

doi:10.26565/2220-637x-2017-28-01

Cited by 3 publications

(5 citation statements)

References 12 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The final point is an inspection of the local environment of the dye molecule or, in other words, its microenvironment. For this sake, the previously described approach was employed [9][10][11]. The atoms located in 0.4 nm vicinity of either whole dye molecule or its chosen atom were distributed into 3 categories, namely, micelle hydrocarbon core, surfactant headgroups, and water; the average number of atoms in each category was computed.…”

Section: Resultsmentioning

confidence: 99%

“…In a set of previous papers, we made an attempt to reveal probable location and, thus, the nature of the microenvironment of several dyes within the micelles of cationic and anionic surfactants via molecular dynamics (MD) modeling [9][10][11]. Some most widely used pyridinium N-phenolates were already involved in the research project, such as the standard betaine dye I, 4-(2,4,6triphenylpyridinium-1-yl)-2,6-diphenylphenolate (R 1 = R 2 = R 3 = C 6 H 5 ) and three other compounds with different hydrophilicity/hydrophobicity: II (R 1 = R 2 = C 6 H 5 ; R 3 = H), III (R 1 = R 2 = C 6 H 5 ; R 3 = Cl), and IV [R 1 = R 2 = C 6 H 5 ; R 3 = C(CH 3 ) 3 ] [9,10].…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

An MD simulation study of Reichardt’s betaines in surfactant micelles: Unlike orientation and solvation of cationic, zwitterionic, and anionic dye species within the pseudophase

2018

Chemical Series

View full text Add to dashboard Cite

Solvatochromic indicators of the pyridinium N-phenolate series, also known as Reichardt’s betaines, or Reichardt’s dyes, are often used for examining not only pure or mixed solvents, but also various colloidal aggregates, such as surfactant micelles, droplets of microemulsions etc. In order to disclose the locus of these molecular probes within the micellar pseudophase, we recently utilized the molecular dynamics (MD) simulations for the standard dye, i.e. 4-(2,4,6-triphenylpyridinium-1-yl)-2,6-diphenylphenolate, and three other dyes of this family of higher and lower hydrophobicity. Both zwitterionic (colored) and protonated (cationic, colorless) species were involved into the research, as these compounds are also used as acid-base indicators for micellar systems. In the present paper, we extended this investigation further. MD modeling was applied to another three dyes incorporated in sodium n-dodecyl sulfate and cetyltrimethylammonium bromide micelles. The following compounds were examined: (i) the most hydrophobic dye, bearing five tert-butyl groups, 4-[2,4,6-tri(4-tert-butylphenyl)pyridinium-1-yl]-2,6-di(4-tert-butylphenyl)phenolate, (ii) a dye with a hydrocarbon loop around the oxygen atom, 4-(2,4,6-triphenylpyridinium-1-yl)-n-(3,5-nonamethylene)phenolate, and (iii) the dye with additional carboxylate group attached to the phenyl group opposite to the phenol, 4-(4-carboxylatophenyl-2,6-diphenylpyridinium-1-yl)-2,6-diphenylphenol. The orientation and solvation of the cations, zwitterions (both colored and colorless), and the anion of the last-mentioned dye in micelles appeared to be dissimilar, depending on the molecular structure and ionization state. The results were compared with those obtained previously for the standard betaine dye. In some cases, the most probable orientation of the dyes in their colorless form was opposite to that of the standard Reichardt’s dye, i.e., their OH group is directed towards the center of the micelle.

show abstract

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

An MD simulation study of Reichardt’s betaines in surfactant micelles: Unlike orientation and solvation of cationic, zwitterionic, and anionic dye species within the pseudophase

2018

Chemical Series

View full text Add to dashboard Cite

show abstract

“…In total, seventeen molecular probes were examined mainly in SDS and CTAB micellar solutions. The results of our research group have been reported in seventeen articles from 2016 to the present [53][54][55][56][57][58][59][60][61][62][63][64][65][66][67][68][69]. We thought it is expedient to summarize the data obtained and the regularities found.…”

Section: Introductionmentioning

confidence: 80%

“…With regard to the microenvironment, in surfactant micelles with a longer hydrocarbon chain, the hydration of both the molecule as a whole and its O atom somewhat decreases, while the fraction of hydrocarbon around it increases [57].…”

Section: Influence Of Other Factors On the Aforementioned Characteris...mentioning

confidence: 99%

“…The effect of temperature on the microenvironment of the molecule is also insignificant, but in the microenvironment of the O atom the water content gradually decreases from 10.30 ± 0.04 at 298 K to 10.28 ± 0.14 and 9.97 ± 0.09 atoms at 310 K and 323 K, respectively. This can be caused by the thermal expansion of water, because the microenvironment of a constant volume accommodates fewer molecules [57].…”

Section: Influence Of Other Factors On the Aforementioned Characteris...mentioning

confidence: 99%

See 1 more Smart Citation

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

Nitroxyl spin probe in ionic micelles: A molecular dynamics study

Farafonov

Lebed

2020

Chemical Series

View full text Add to dashboard Cite

The compounds containing nitroxyl radical (NO˙) are actively used as spin probes to examine colloid systems, including lipid membranes and micelles. Their electron paramagnetic resonance spectrum provides information about the composition of the medium, in particular, the content of water there. Yet, the proper treatment of the measurement results demands understanding the microscopic characteristics of the molecular probe. In the present paper, we extend our previous studies on the microscopic state of acid-base and solvatochromic probes in surfactant micelles to the field of spin probes. We report the results of molecular dynamics simulation of a common spin probe, methyl-5-doxylstearate, in micelles of anionic (sodium n-dodecyl sulfate, SDS) and cationic (n-dodecyltrimethylammonium bromide, DTAB) surfactants. The localization of the molecule within the micelles, its shape, composition of the local environment, hydration were quantified and compared with the available relevant experimental data. No significant dissimilarity was found in the characteristics of the probe molecule in both kinds of micelles. However, the characteristics of the O˙ atom carrying the unpaired electron are pronouncedly different, namely, in DTAB micelles it is less hydrated and forms less hydrogen bonds with water. Similar situation was observed for the COO group. The main reason was found to be the interactions with cationic surfactant headgroups, which screen the O˙ atom and COO group from water. These findings allowed revisit the point of view that the surface layer of DTAB micelles as a whole is less hydrated in comparison to that of the SDS ones.

show abstract

Solvatochromic Reichardt’s Dye in Micelles of Sodium Cetyl Sulfate: Md Modeling of Location Character and Hydration

Cited by 3 publications

References 12 publications

An MD simulation study of Reichardt’s betaines in surfactant micelles: Unlike orientation and solvation of cationic, zwitterionic, and anionic dye species within the pseudophase

An MD simulation study of Reichardt’s betaines in surfactant micelles: Unlike orientation and solvation of cationic, zwitterionic, and anionic dye species within the pseudophase

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

Nitroxyl spin probe in ionic micelles: A molecular dynamics study

Contact Info

Product

Resources

About