Molecular Dynamics Study of 2-Nitrophenyl Octyl Ether and Nitrobenzene

Abstract

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.

Molecular Dynamics Study of the Interface between Water and 2-Nitrophenyl Octyl Ether

“…The first major difference is the higher density reached in the bulk phase by NB. The bulk density values of both organic liquids agree well with independent calculations from pure-component simulations 7 . The other main difference is that the density oscillations persist for longer distances in the case of NPOE, relative to NB.…”

“…We have concentrated on the orientation of the nitro group because this group is the one involved in hydrogen bonds with water 8 . Furthermore, even though the full nitrobenzene orientation cannot strictly be defined by only two angles, the orientation of the nitro group provides a good estimate of the orientation of the entire NB molecule, since it is preferentially aligned with the aromatic plane 7 . Unfortunately, this is not the case for NPOE, since the orientation of this molecule possesses many more degrees of freedom.…”

“…NPOE molecules in the bulk region experience significant entanglement of the alkyl chains, manifested by close contacts present in RDFs between NPOE chain atoms 7 . This entanglement is the main cause for the observed strong reduction of the pure-component diffusion coefficient (and concomitant increase in viscosity) of NPOE relative to NB 7 . As we approach the interface, contact with smaller and more mobile water molecules reduces this entanglement, increasing the diffusion coefficient.…”

Voltammetric Insights in the Transfer of Ionizable Drugs Across Biomimetic Membranes - Recent Achievements

“…Shao and Pereira et al [78] reported, for first time, the polarization of a nano-interface between water and n-octanol by using a modified version of the classical four electrode voltammetry at ITIES. Additionaly, nitrophenyloctyl ether (NPOE) emerged as a viable non-toxic organic solvent in experiments at the polarized liquid-liquid interface [5,9,37,44,46,[79][80][81][82]. NPOE has a moderate dielectric constant and a high viscosity that makes it a good ionic solvent suitable for kinetic studies.…”

Molecular dynamics study of nitrobenzene and 2-nitrophenyloctyl ether saturated with water

“…Due to the importance of these solvents in chemistry, there is no question that computer simulations of these systems will be of great help for a proper understanding of their solvation features. We have recently presented a comprehensive molecular dynamics study of pure NB and NPOE, including the calculation of thermodynamic, structural and dynamic properties of the bulk liquids, as well as the solvation of potassium and chloride ions [16]. However, a crucial aspect that is missing is a detailed study of the interactions of these solvents with water.…”