Molecular dynamics study of 2-nitrophenyl octyl ether and nitrobenzene

The pure organic liquids nitrobenzene (NB) and 2-nitrophenyl octyl ether (NPOE) have been studied by means of molecular dynamics simulations. Both solvents are extremely important in various interfacial processes, mainly connected with ion transfer taking place across the interface with water. Thermodynamic (mass density, enthalpy of vaporization, isothermal compressibility, dipole moment) and dynamic (viscosities and self-diffusion coefficients) properties of both liquids have been calculated and are in very good agreement with the experimental data. In the case of NB, several potentials have been tested and the obtained results compared and discussed. In most cases, the OPLS all-atom potential gives results that are in better agreement with available experimental values. Atomic radial distribution functions, dihedral and angle distributions, as well as dipole-orientation correlation functions are used to probe the structure and interactions of the bulk molecules of both organic solvents. These were seen to be very similar in terms of structure and thermodynamics, but quite distinct in terms of dynamic behavior, with NPOE showing a much slower dynamic response than NB. A simulation study of the simple Cl- and K+ ions dissolved in both solvents has been also undertaken, revealing details about the diffusion and solvation mechanisms of these ions. It was found that in both liquids the positive potassium ion is solvated by the negative end of the molecular dipole, whereas the negative chloride ion is solvated by the positive end of the dipole

Intrinsic structure and dynamics of the water/nitrobenzene interface

In this paper we present results of a detailed and systematic molecular dynamics study of the water/nitrobenzene interface. Using a simple procedure to eliminate fluctuations of the interface position, we are able to obtain true intrinsic profiles for several properties (density, hydrogen bonds, molecular orientation, etc.) in the direction perpendicular to the interfacial plane. Our results show that both water and organic inter-facial molecules form a tightly packed layer oriented parallel to the interface, with reduced mobility in the perpendicular direction. Beyond this layer, water quickly restores its bulk structure, while nitrobenzene exhibits structural anisotropies that extend further into the bulk region: Water molecules that protrude farthest into the organic phase point one hydrogen atom in the direction perpendicular to the interface, forming a hydrogen bond with a nitrobenzene oxygen. By fitting both the global and the intrinsic density profiles, we obtain estimates for the total and intrinsic interface widths, respectively. These are combined with capillary wave theory to produce a self-consistent method for the calculation of the inter-facial tension. Values calculated using this method are in very good agreement with direct calculations from the components of the pressure tensor

Partition of neutral molecules and ions from water to o-nitrophenyl octyl ether and of neutral molecules from the gas phase to o-nitrophenyl octyl ether

YesWe have set out an equation for partition of 87 neutral molecules from water to o-nitrophenyl octyl ether, NPOE, an equation for partition of the 87 neutral molecules and 21 ionic species from water to NPOE, and an equation for partition of 87 neutral molecules from the gas phase to NPOE. Comparison with equations for partition into other solvents shows that, as regards partition of neutral (nonelectrolyte) compounds, NPOE would be a good model for 1,2-dichloroethane and for nitrobenzene. In terms of partition of ions and ionic species, NPOE is quite similar to 1,2-dichloroethane and not far away from other aprotic solvents such as nitrobenzene