A Comparison of the Solvation Properties of 2-Nitrophenyloctyl Ether, Nitrobenzene, and n-Octanol as Assessed by Ion Transfer Experiments
Abstract: 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,
Summary (2 min read)
- The processes of ion transfer across the interface of two adjacent immiscible liquids attract significant attention due to their wide applicability in different fields such as ion-selective electrodes, phase-transfer catalysis, biomimetic studies of membrane function, drug uptake, and so forth.
- ∆Gi,R Qâ is directly related to the standard potential of ion transfer (∆φi,R Qâ) and standard partition coefficient (Pi) (see eqs 6 and 7, respectively).
- 1,2 Moreover, logP has been used for predicting various biological properties such as toxicity,2 transfer through biological membranes, and affinity between receptors and enzymes.
- 5,6 The introduction of fourelectrode voltammetry at the interface of two immiscible electrolyte solutions led to significant progress in the lipophilicity determinations of different organic and inorganic ions,7-13 providing access to the standard values of partition coefficients of ions, which are independent of experimental conditions.
- The nonpolarizability of some important organic solvent-water interfaces such as n-octanol-water is one of the weaknesses of this technique.
2. Experimental Section
- All the studied compounds were purchased from Fluka (Buch, Switzerland), except sulfinpyrazone (kindly donated by Novartis Pharma, Basel, Switzerland).
- NPOE and n-octanol were purchased form Acros Organics (Geel, Belgium).
- All chemicals were of analytical grade and supplied by Fluka.
- An Ag/AgCl (saturated NaCl solution) reference electrode was used, while a platinum wire served as an auxiliary electrode.
- All experiments were performed at room temperature.
3. Principles of the Three-Phase Electrode Approach
- The determination of the lipophilicity of ions by using the three-phase electrode approach is based on the concept of preserving the electroneutrality of both phases.
- This latter, with the attached droplet, is then immersed into the aqueous electrolyte solution.
- Chemical structures of the compounds that have been studied in their anionic form.
- Since no electrolyte is deliberately added to the organic phase, the applied potential can start the electrochemical reaction only at the three-phase junction where all three phases are in intimate contact.
4. Results and Discussion
- With the three-phase electrode approach, a pre-requirement in the determination of the standard partition coefficient of anions by using eq 5 is the estimation of the standard redox potential of dmfc in the organic solvent used for the droplet (Edmfc+(o)|dmfc(o) Q ).
- An alternative method was previously used for the evaluation of the redox potentials of dmfc in NB34 and n-octanol,29 consisting in applying the three-phase electrode approach to measure the formal potential of dmfc in the presence of various transferring anions with standard transfer potentials known from literature.
- A good correlation was obtained between logPA-,aq QNPOE and log PA-,aq QNB (eq 8), with a slope close to unity and ay-intercept of -0.47.
- The cavity formation energy term is proportional to the dimensions of the solute molecules.
- In this paper the authors have determined the lipophilicity data of a number of anions of drugs and model compounds at the waternitrophenyloctyl ether (NPOE) and water-nitrobenzene (NB) interfaces by using the three-phase electrode approach.
- It has been also shown how the lipophilicities determined in all solvents depend on ionic radii, charge delocalization effects, and the molecular size of the investigated compounds.
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Q1. What contributions have the authors mentioned in the paper "A comparison of the solvation properties of 2-nitrophenyloctyl ether, nitrobenzene, and n-octanol as assessed by ion transfer experiments" ?
In this paper, the authors proposed a three-phase electrode technique to measure the lipophilicity of compounds, which is one of the major parameters included in quantitative structure properties and quantitative structure activity ( QSAR ) relationships.