Interaction between sodium dodecylsulfate (SDS) and pluronic L61 in aqueous medium: assessment of the nature and morphology of the formed mixed aggregates by NMR, EPR, SANS and FF-TEM measurements

Molecular Insights on Morphology, Composition, and Stability of Mixed Micelles Formed by Ionic Surfactant and Nonionic Block Copolymer in Water Using Coarse-Grained Molecular Dynamics Simulations

The nanoscale association domains are the ultimate determinants of the macroscopic properties of complex fluids involving amphiphilic polymers and surfactants, and hence, it is foremost important to understand the role of polymer/surfactant concentration on these domains. We have used coarse-grained molecular dynamics simulations to investigate the effect of polymer/surfactant concentration on the morphology of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO, i.e., pluronics or poloxamers) block copolymer, and ionic surfactants sodium dodecyl sulfate (SDS), mixed micelles in aqueous solution. The proclivity of the surfactant to form the mixed micelles is also probed using umbrella sampling simulations. In this study, we observed that the core of the pluronic + SDS formed mixed micelles consists of PPO, the alkyl tail of SDS, and some water molecules, whereas the PEO, water, and sulfate headgroups of SDS form a shell, consistent with experimental observations. The micelles are spherical at high-pluronic/low-SDS compositions, ellipsoidal at high-SDS/low-pluronic compositions, and wormlike-cylindrical at high-pluronic/high-SDS compositions. The transitions in micelle morphology are governed by the solvent accessible surface area of mixed aggregates, electrostatic repulsion between SDS-headgroups, and dehydration of PEO and PPO segments. The free energy barrier for SDS escape is much higher in mixed micelles than in pure SDS micelles, indicating a stronger tendency for SDS to form pluronic-SDS mixed micelles.

NMR Studies on the Interaction of Anticancer Drug Doxorubicin with Membrane Mimetic SDS

In the formulation of efficient drug delivery systems, it is essential to unravel the structural and dynamical aspects of the drug's interaction with biological membranes. This has been done for the anticancer drug-membrane system comprising doxorubicin hydrochloride (DOX), a water-soluble anticancer drug, and the micellar sodium dodecyl sulfate (SDS), the latter serving as a useful mimic for membrane proteins. Using a multimodal NMR approach involving ¹H, ²H, and ¹³C as probe nuclei and through the determination of chemical shifts, spin-relaxation, nuclear Overhauser enhancements (NOE), and translational self-diffusion (SD), the binding characteristics of the DOX with SDS have been determined. The perturbation to ¹³C chemical shifts of SDS indicate the penetration of DOX into the SDS micelle, which is further revealed by ¹H-¹H NOESY and SD measurements. ²H spin-relaxation measurements and their analysis using a two-step model show DOX induced SDS micellar volume changes, which determine the correlation times involved in the DOX-SDS mobility.