Structure of Nanoparticles Derived from Designer Surfactant TPGS-750-M in Water, As Used in Organic Synthesis.

Abstract

Using density functional theory and the COSMO-RS implicit solvent model, we predict the structure and physical chemical properties of nanomicelles derived from the designer surfactant TPGS-750-M used in organic synthesis. We predict that the influence of chain length of the PEG region is low, while the termination of the PEG chain (-OH vs.-OCH3 ) plays a very large role. The interfacial tension is considerably lower between the micellar and water phases for the -OH than the -OCH3 terminated surfactant, and our calculations reproduce the large difference observed in average particle size as a function of PEG chain termination. We propose a structure for the nanoparticles formed by TPGS-750-M in water that is consistent with a ≈50 nm average diameter, which is significantly larger than a single micelle. According to the calculations, each nanoparticle would consist of 30-40 aggregated TPGS-750-M micelles forming a compartmentalized nanoparticle, with considerable amounts of water in the PEG region. The whole particle is stabilized by vitamin E succinate at the nanoparticle-water interface. In the presence of Zn dust or powder, the surfactant collides with the Zn surface, and by interactions with the hydrophobic inner cores, form organozinc species that are protected from the surrounding water. This explains why highly moisture-sensitive Negishi-like couplings take place in surfactant-water systems.