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 interfacial 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 intrinsi...

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Intrinsic structure and dynamics of the water/nitrobenzene interface

Ions can be transferred between immiscible liquid phases across a common interface, with the help of a three-electrode potentiostat, when one phase is an organic droplet attached to a solid electrode and containing a redox probe. This novel approach has been used in studies to determine the Gibbs energy of anion and cation transfer, ranging from simple inorganic and organic ions to the ionic forms of drugs and small peptides. This method of studying ion transfer has the following advantages: (1) no base electrolytes are necessary in the organic phase; (2) the aqueous phase contains only the salt to be studied; (3) a three-electrode potentiostat is used; (4) organic solvents such as n-octanol and chiral liquids such as D- and L-2-octanol can be used; (5) the range of accessible Gibbs energies of transfer is wider than in the classic 4-electrode experiments; (6) the volume of the organic phase can be very small, for example, 1 microL or less; (7) the experiments can be performed routinely and fast. Herein, the basic 5 principle is outlined, as well as a summary of the results obtained to date, and a discussion on the theoretical treatments concerning the kinetic regime of the three-phase electrodes with immobilized droplets.

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Determining the Gibbs energy of ion transfer across water-organic liquid interfaces with three-phase electrodes.

Electroactive ceramic carbon electrode modified with ionic liquid

Partition coefficients for transfer from water to wet octanol have been set out for permanent ions, and for ionic species derived from neutral molecules by loss or acceptance of a proton. A previous equation for the partition of neutral compounds from water to wet octanol has been extended to include the partition of permanent ions, and ionic species; the only additional descriptors required are J+ for cations and J− for anions. Fourteen cations and twelve anions are included in the equation. It is shown that differences in partition coefficients between neutral species and the corresponding ionic species, as log P(oct), are not at all constant. For carboxylic acids and the corresponding anion, differences are about 5.0 log units, for phenols and the corresponding anion differences range from 2.2 to 4.9 log units, and for amines and the corresponding protonated cations there is an enormous range of differences from 0.6 to 7.1 log units.

The transfer of neutral molecules, ions and ionic species from water to wet octanol

https://repositorio-aberto.up.pt/bitstream/10216/49750/2/60361.pdf

Evaluation of the lipophilic properties of opioids, amphetamine-like drugs, and metabolites through electrochemical studies at the interface between two immiscible solutions.

The lipophilicity of the anionic forms of drugs and model compounds was assessed by their transfer across (i) the water-2-nitrophenyloctyl ether (NPOE), (ii) the water-nitrobenzene (NB), and (iii) the water-noctanol interfaces by using the three-phase electrode technique. The lipophilicities, expressed in terms of logarithm of partition coefficients, range for the studied anions from -3.46 to 0.68 (log P A-,aq QNPOE ) for NPOE,

/pdf/a-comparison-of-the-solvation-properties-of-2-4i7wolfi7n.pdf

Ansgar Kretschmer

Papers

A Comparison of the Solvation Properties of 2-Nitrophenyloctyl Ether, Nitrobenzene, and n-Octanol as Assessed by Ion Transfer Experiments