Molecular Dynamics Simulation of SDS and CTAB Micellization and Prediction of Partition Equilibria with COSMOmic

Abstract

Molecular dynamics (MD) simulations of the self-assembly of different ionic surfactants have been performed in order to obtain representative micellar structures. Subsequently, these structures were used to predict the partition behavior of various solutes in these micelles with COSMOmic, an extension of COSMO-RS. This paper includes multiple self-assembled micelles of SDS (sodium dodecyl sulfate, anionic surfactant) and CTAB (cetyltrimethylammoniumbromide, cationic surfactant) at different concentrations. Micellar size, density profiles, and shape (eccentricity) have been investigated. However, the size strongly depends on the functional definition of a micelle. For this reason, we present a method based on the free monomer concentration in aqueous solution as an optimization criterion for the micelle definition. The combination of MD with COSMOmic has the benefit of combining detailed atomistic information from MD with fast calculations of COSMOmic. For the first time the influence of micelle structure on pratition equilibria, predicted with COSMOmic, were investigated. In case of SDS more than 4600 and for CTAB more than 800 single micelles have been studied. The predictions of the partition coefficients with COSMOmic are in good agreement with experimental data. Additionally, the most favorable locations of selected molecules in the micelles as well as probable energy barriers are determined even for complex solutes such as toluene, propanolol, ephedrine, acetone, phenol, lidocaine, syringic acid, coumarin, isovanillin, ferulic acid, and vanillic acid. This method can therefore be applied as a potential screening tool for solutes (e.g., drugs) to find the optimal solute-surfactant combination.

Shedding light on the puzzle of drug-membrane interactions: Experimental techniques and molecular dynamics simulations

“…COSMOmic was recently optimized for charged solutes, with regards to the membrane dipole potential [181]. COSMOmic has proved its usefulness for the determination of membrane/water partition coefficients for different solutes [77,126,[179][180][181][182][183][184][185][186][187] and for micelle/water partition coefficients [183,[188][189][190][191]. It was also shown that the results of COSMOmic and MD simulations are comparable [126,182].…”

Molecular dynamics simulation study of sodium dodecyl sulfate micelle: Water penetration and sodium dodecyl sulfate dissociation

“…Please note that SDS micelle has been selected as a model system because it is the most intensively-characterized micelle through experimental analysis [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] and simulation methods [34][35][36][37][38][39][40][41][42][43][44][45]. In experimental approaches, various techniques such as light scattering [18][19][20][21], fluorescence [24,25], SAXS [17,31] and SANS [23,26,27] have been used to characterize the size, shape, aggregation and charge of the SDS micelle at various conditions for concentration and temperature.…”

“…In this context, the molecular dynamics (MD) simulation methods have been extensively used to provide such detailed structural information on the micelle in general as well as the SDS micelle [34][35][36][37][38][39][40][41][42][43][44][45]. In 1990, Shelley and coworkers [34] reported the first large scale 182-picosecond MD simulation study on 42 monomer SDS micelle, in which they found that ∼12% of the sodium ions form contact ion pairs with the micelle.…”

Atomistic Description of the Solubilisation of Testosterone Propionate in a Sodium Dodecyl Sulfate Micelle

“…More recently, groups have been utilizing the structure of surfactant (including SDS) micelles in combination with COSMOmic to determine the partitioning and free energy of adsorption of drug molecules within the micelles, which allows for a relatively fast way of determining the most probable location of a drug molecule but does not provide any direct information regarding the interactions which govern the encapsulation of the drugs within the micelle. 23,24 In this study, we present results from large scale all-atom MD simulations of SDS micelles with and without testosterone propionate (TSTP). TSTP is a steroid which is used in hormone replacement therapy for individuals who have abnormally low testosterone levels.…”