Molecular Dynamics Simulations of Specific Anion Adsorption on Sulfobetaine (SB3-14) Micelles

Abstract

Structures of zwitterionic micelles of 61 sulfobetaine SB3-14, CH3(CH2)13[N(+)(CH3)2](CH2)3SO3(-), molecules in water and in 0.15 and 0.015 mol L(-1) NaX (X = F(-), Cl(-), Br(-), I(-), and ClO4(-)) aqueous solutions were investigated by atomistic molecular dynamics simulations. The micelle presents a near-spherical shape and an average angle of 110° between the zwitterionic headgroup and the alkyl tail that provides an L-type shape for the surfactants and exposes the positive charged ammonium groups to the solution. This allows anions to adsorb at the surface of the micelle and the amount of adsorbed anions follows the Hofmeister series F(-) < Cl(-) < Br(-) < I(-) < ClO4(-), which directly correlates to the measured values of the zeta-potential. The size and shape of the micelle are not affected by the salt, except the solvent accessible surface area that decreases for strongly adsorbing anions such as ClO4(-) due to the approximation of the headgroups between adjacent surfactants. Indeed, the ion distribution shows the formation of ion-pair-type species between ammonium and perchlorate, which indicates that the adsorption is directly related to the easiness of the anion to partially lose its hydration shell.

Nanoparticle induced formation of self-assembled zwitterionic surfactant microdomains which mimic microemulsions for the in situ fabrication and dispersion of silver nanoparticles

“…These values are in the range of reported values for other zwitterionic surfactant systems which can range from slightly positive to À70 mV depending upon the type and concentration of added salts and pH. [20][21][22][23] The bipolar ionic moiety of the zwitterionic surfactants can interact with the uncapped or citrate capped Ag-NPs and the values become more negative, i.e., À89 AE 12 mV for C 10 -APSO 4 at pH 11. A similar phenomenon was reported for the potential of a NP-surfactant bilayer composite, in which the potential was gradually decreased by the surfactant-coating on metallic NPs from 0 mv to À57.9 mV.…”

“…19,20 For instance, the surfactant SB3-10 (same formula as C 10 -APSO 4 except the terminal anionic group is sulfonate, -SO 3 , rather than sulfate) has a diameter of only 2-4 nm. 19,20 Although a C n -APSO 4 surfactant is neutral overall, the zetapotential of the solution including this surfactant at pH 3 (without Ag-NPs) was determined to be +23.2, +10.2 and À20.0 mV for C 8 -, C 9 -, and C 10 -APSO 4 respectively. These values are in the range of reported values for other zwitterionic surfactant systems which can range from slightly positive to À70 mV depending upon the type and concentration of added salts and pH.…”

Interaction-based ion selectivity exhibited by self-assembled, cross-linked zwitterionic copolymer membranes

“…This would provide a clear mechanism to achieve interactionbased selectivity, since interactions are known to simultaneously affect partitioning and diffusivity (19). Experimental (28-30) and simulation (31) studies indicate that SB groups preferentially bind with weakly hydrated anions (e.g., ClO 4…”

Computational Models of the Gastrointestinal Environment. 1. The Effect of Digestion on the Phase Behavior of Intestinal Fluids

“…MD simulation has wide application in the study of biomolecular systems, for example, in modeling ligand binding to G protein-coupled receptors , or in investigating the structures formed by nucleic acids . MD simulations are well suited to the modeling of bilayers, , micelles, − and mixtures of colloidal phases. The modeling of colloidal systems is increasingly being used to study the interactions among drugs, drug formulations, and their biological environments. − In this study, we use an extensive series of MD simulations to investigate the ternary systems of water, bile salt, and phospholipid in the micelle and vesicle regions of the phase diagram, and also investigate the changes that result from hydrolysis of the phospholipid into molecules of lysophosphatidylcholine and fatty acid.…”