title: Structure, stability, and fragmentation of sodium bis(2-ethylhexyl)sulfosuccinate negatively charged aggregates in vacuo by MD simulations.
abstract: Negatively charged supramolecular aggregates formed in vacuo by n bis(2-ethylhexyl)sulfosuccinate (AOT(-)) anions and n + n(c) sodium counterions (i.e., [AOT(n) Na(n+nc)](nc)) have been investigated by molecular dynamics (MD) simulations for n = 1 to 20 and n(c) = -1 to -5. By comparing the maximum excess charge values of negatively and positively charged AOTNa aggregates, it is found that the charge storage capability is higher for the latter systems, the difference decreasing as the aggregation number increases. Statistical analysis of physical properties like gyration radii and moment of inertia tensors of aggregates provides detailed information on their structural properties. Even for n(c) = -5, all stable aggregates show a reverse micelle-like structure with an internal core, including sodium counterions and surfactant polar heads, surrounded by an external layer consisting of the surfactant alkyl chains. Interestingly, the reverse micelle-like structure is retained also in proximity of fragmentation. Moreover, the aggregate shapes may be approximated by elongated ellipsoids whose longer axis increases with n and |n(c)|. The fragmentation patterns of a number of these aggregates have also been examined and have been found to markedly depend on the aggregate charge state. The simulated fragmentation patterns of a representative aggregate show good agreement with experimental data obtained using low collision voltages.
authors: Dipartimento di Medicina Molecolare e Traslazionale, Università di Brescia, 25123, Brescia, Italy, giovanna.longhi@unibs.it.
authors: Giovanna
authors: G
authors: Longhi
authors: Sergio
authors: S
authors: Abbate
authors: Alberto
authors: A
authors: Ceselli
authors: Leopoldo
authors: L
authors: Ceraulo
authors: Sandro L
authors: SL
authors: Fornili
authors: Vincenzo
authors: V
authors: Turco Liveri
mesh_terms: D004143:Dioctyl Sulfosuccinic Acid / Q000737:chemistry*; D007477:Ions / Q000737:chemistry; D008823:Micelles; D008968:Molecular Conformation; D056004:Molecular Dynamics Simulation; D013501:Surface-Active Agents / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D007477:Ions; D008823:Micelles; D013501:Surface-Active Agents; D004143:Dioctyl Sulfosuccinic Acid