0000000000073471
AUTHOR
Sandro L. Fornili
Structure and dynamics of dibutylphosphate/n-propylamine ionic liquid: A multi-scale theoretical study
Abstract Owing to the amphiphilic nature of their constituent molecules, binary mixtures of pure liquid surfactants are usually characterized by enhanced nano-segregation and thus can exhibit interesting transport properties and complex macroscopic behavior. In this ambit it was recently shown by Turco Liveri et al. (2018) that mixtures of short aliphatic chains compounds at room temperature, such as dibutyl phosphate (DBP) and n-propylamine (PA) liquids, display ionic liquid–like behavior ascribed to phosphate-to-amine proton transfer. To gain a detailed molecular picture of the system structure and dynamics and to understand the molecular mechanisms at the basis of the observed behavior, …
Structural organization of surfactant aggregates in vacuo: a molecular dynamics and well-tempered metadynamics study
Experimental investigations using mass spectrometry have established that surfactant molecules are able to form aggregates in the gas phase. However, there is no general consensus on the organization of these aggregates and how it depends on the aggregation number and surfactant molecular structure. In the present paper we investigate the structural organization of some surfactants in vacuo by molecular dynamics and well-tempered metadynamics simulations to widely explore the space of their possible conformations in vacuo. To study how the specific molecular features of such compounds affect their organization, we have considered as paradigmatic surfactants, the anionic single-chain sodium …
A molecular dynamics study of structure, stability and fragmentation patterns of sodium bis(2-ethylhexyl)sulfosuccinate positively charged aggregates in vacuo
Positively charged supramolecular aggregates formed in vacuo by n AOTNa (sodium bis(2-ethylhexyl)sulfosuccinate) molecules and n(c) additional sodium ions, i.e. [AOT(n)Na(n+n(c))](n(c)), have been investigated by molecular dynamics (MD) simulations for n = 1-20 and n(c) = 0-5. Statistical analysis of physical quantities like gyration radii, atomic B-factors and moment of inertia tensors provides detailed information on their structural and dynamical properties. Even for n(c) = 5, all stable aggregates show a reverse micelle-like structure with an internal solid-like core including sodium counterions and surfactant polar heads surrounded by an external layer consisting of the surfactant alky…
Molecular dynamics and metadynamics simulations of electrosprayed water nanodroplets including sodium bis(2-ethylhexyl)sulfosuccinate micelles.
The behavior of aqueous solutions of sodium bis(2-ethylhexyl)sulfosuccinate (AOTNa) under conditions of electrospray ionization (ESI) has been investigated by molecular dynamics (MD) and well-tempered metadynamics (WTM) simulations at 300 K and 400 K. We have examined water droplets with initial fixed numbers of water molecules (1000) and AOT− anions (100), and with sodium cations in the range of 70–130. At 300 K, all charged droplets show the water evaporation rate increasing with the absolute value of the initial droplet charge state (Z), accompanied by ejection of an increasing number of solvated sodium ions or by expulsion of AOT− anions depending on the sign of Z and by fragmentation i…
Sodium bis(2-ethylhexyl)sulfosuccinate self-aggregation in vacuo: molecular dynamics simulation.
Molecular dynamics (MD) simulations were conducted for systems in vacuo consisting of n AOT(-) anions (bis(2-ethylhexyl)sulfosuccinate ions) and n+/- 1 or n Na(+) ions up to n = 20. For n = 15, positively charged systems with Li(+), K(+), and Cs(+) cations were also considered. All systems were observed to form reverse micelle-like aggregates whose centre is occupied by cations and polar heads in a very compact solid-like way, while globally the aggregate has the form of an elongated and rather flat ellipsoid. Various types of statistical analyses were carried out on the systems to enlighten structural and dynamical properties including gyration radius, atomic pair correlation functions, at…
Hydration of agarose double helix: A monte carlo simulation
The structure of the water around agarose double helix is analyzed with ab initio quantum mechanical calculations and Monte Carlo simulations. The potential surface is sampled by computing the interaction energy between fragments of agarose and a water molecule placed at 221 different orientations and/or positions. These energy values are fitted to a simple analytical expression representing atom-atom pair potentials for a water molecule interacting with agarose. A preliminary understanding of the agarose-water interaction is obtained from isoenergy contour maps at planar cross sections, perpendicular to the long axis of the double helix, and for cylindrical surfaces enclosing the double he…
Structure, stability, and fragmentation of sodium bis(2-ethylhexyl)sulfosuccinate negatively charged aggregates in vacuo by MD simulations.
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 …
Molecular dynamics of electrosprayed water nanodroplets containing sodium bis(2-ethylhexyl)sulfosuccinate
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 …