Abstract
A computational methodology using Density-Functional Theory (DFT) calculations was developed to determine the partition coefficient of a compound in a solution of Sodium Dodecyl Sulfate (SDS) micelles. Different sets of DFT calculations were used to predict the free energy of a set of 63 molecules in 15 different solvents with the purpose of identifying the solvents with similar physicochemical characteristics to the studied micelles. Experimental partition coefficients were obtained from Micellar Electrokinetic Chromatography (MEKC) measurements. The experimental partition coefficient of these molecules was compared with the predicted partition coefficient in heptane/water, cyclohexane/water, N-dodecane/water, pyridine/water, acetic acid/water, decan-1-ol/water, octanol/water, propan-2-ol/water, acetone/water, propan-1-ol/water, methanol/water, 1,2-ethane diol/water, dimethyl sulfoxide/water, formic acid/water, and diethyl sulphide/water systems. It is observed that the combination of pronan-1-ol/water solvent was the most appropriated to estimate the partition coefficient for SDS micelles. This approach allowed us to estimate the partition coefficient orders of magnitude faster than the classical molecular dynamics simulations. The DFT calculations were carried out with the well-known exchange correlation functional B3LYP and with the global hybrid functional M06-2X from the Minnesota functionals with 6-31++G ** basis set. The effect of solvation was considered by the continuum model based on density (SMD). The proposed workflow for the prediction rate of the participation coefficient unveiled the symmetric balance between the experimental data and the computational methods.
Highlights
Apparatus and ConditionsSystem 5500 capillary electrophoresis equipped with a UV diode array detector. A fused silica capillary with a total length of 47 cm (40 cm of effective length) and 50 ÎŒm of internal diameter was used
Introduction published maps and institutional affilA compoundâs solventâwater partition coefficient measures the equilibrium ratio of the compoundâs concentrations in a two-phase system, as for example, two immiscible solvents or a system of micelles in an aqueous solution [1]
The experimental partition coefficients in Sodium Dodecyl Sulfate (SDS) micelle of those molecules were correlated with respect to the predicted partition coefficients in all 15 solvents with respect to water
Summary
System 5500 capillary electrophoresis equipped with a UV diode array detector. A fused silica capillary with a total length of 47 cm (40 cm of effective length) and 50 ÎŒm of internal diameter was used. Measurements were made at 25 ⊠C and +15 kV. The test compounds were injected into the capillary by pressure, applying 0.5 p.s.i. The capillary was conditioned with the following sequence: 5 min of water, 20 min of 1 M sodium hydroxide solution, 10 min of water, 10 min of 0.1 M sodium hydroxide solution and 20 min of separation buffer. Prior to each injection the capillary was flushed with 5 min of separation buffer. The 40 mM SDS separation buffer was prepared by solving the corresponding amount of surfactant in a 20 mM sodium phosphate buffer at pH 7.0. Test compounds were solved in a methanol solution (used as electroosmotic flow marker), which already contained. Concentration of the test compounds was 2 mg mLâ1.
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