title: Molecular dynamics of electrosprayed water nanodroplets containing sodium bis(2-ethylhexyl)sulfosuccinate.
abstract: The behavior of aqueous solutions of sodium bis(2-ethylhexyl)sulfosuccinate (AOTNa) subject to electrospray ionization (ESI) has been investigated by molecular dynamics (MD) simulations at three temperatures (350, 500 and 800 K). We consider several types of water nanodroplets containing AOTNa molecules and composed of a fixed number of water molecules (1000), N(AOT)(0) AOT(-) anions (N(AOT)(0) =  0, 5, 10) and N(Na)(0) sodium ions (N(Na)(0) =  0, 5, 10, 15, 20): in a short time scale (less than 1 ns), the AOTNa molecules, initially forming direct micelles in the interior of the water nanodroplets, are observed in all cases to diffuse nearby the nanodroplet surface, so that the hydrophilic heads and sodium ions become surrounded by water molecules, whereas the alkyl chains lay at the droplet surface. Meanwhile, evaporation of water molecules and of solvated sodium ions occurs, leading to a decrease of the droplet size and charge. At 350 K, no ejection of neutral or charged surfactant molecules is observed, whereas at 500 K, some fragmentation occurs, and at 800 K, this event becomes more frequent. The interplay of all these processes, which depend on the values of temperature, N(AOT)(0) and N(Na)(0) eventually leads to anhydrous charged surfactant aggregates with prevalence of monocharged ones, in agreement with experimental results of ESI mass spectrometry. The quantitative analysis of the MD trajectories allows to evidence molecular details potentially useful in designing future ESI experimental conditions.
authors.affiliation: Dipartimento di Scienze Biomediche e Biotecnologie, Università di Brescia, Viale Europa 11, 25123, Brescia, Italy.
authors.forename: Giovanna
authors.initials: G
authors.lastname: Longhi
authors.forename: Alberto
authors.initials: A
authors.lastname: Ceselli
authors.forename: Sandro L
authors.initials: SL
authors.lastname: Fornili
authors.forename: Sergio
authors.initials: S
authors.lastname: Abbate
authors.forename: Leopoldo
authors.initials: L
authors.lastname: Ceraulo
authors.forename: Vincenzo Turco
authors.initials: VT
authors.lastname: Liveri
mesh_terms: D004143:Dioctyl Sulfosuccinic Acid / Q000737:chemistry*; D008823:Micelles; D056004:Molecular Dynamics Simulation; D053758:Nanoparticles / Q000737:chemistry*; D010316:Particle Size; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D014867:Water
chemical_list: D008823:Micelles; D014867:Water; D004143:Dioctyl Sulfosuccinic Acid