Hydrophobicity Parameter (log Kow) Estimation for Some Phenolic Compounds of Pharmaceutical Interest from Retention Studies with Mobile Phase Composition in Reversed‐Phase Liquid Chromatography

Abstract:

Chromatographic retention of some phenolic compounds (impurities of related pharmaceutical active substances) was studied for different organic modifier contents in mobile phase. Their capacity factors k′ versus organic modifier content (acetonitrile, or methanol) in mobile phase were measured and the corresponding dependences were studied by linear and polynomial regressions and then they were extrapolated to a mobile phase with no content in organic modifier in order to estimate their octanol/water partition coefficient (log K_ow). The values of log K_ow from retention data were compared to known shake‐flask experimental values and theoretical values predicted by fragment methodology. Linear dependences for methanol and second‐degree polynomial dependences for acetonitrile between organic modifier volume percentage and log k′ provided good estimation of log K_ow. The chromatographic method can be considered as a method of choice for estimating hydrophobicity parameter for different solutes. The linear dependence between extrapolated values of log k′ for 0% organic modifier and log K_ow estimated by means of fragment methodology for the model compounds can be used to predict chromatographic retention of other similar compounds.     

Sorption of organic compounds of varying hydrophobicities from water and industrial wastewater by long- and short-chain organoclays

It is generally assumed that short-chain organoclays are better sorbents for non-ionic organic compounds than are the long-chain organoclays. We believe that the above statement is correct only for relatively hydrophilic or slightly hydrophobic compounds and that the opposite should be true for highly hydrophobic compounds, namely, that long-chain organoclays are expected to be superior to the short-chain analogs for sorption of highly hydrophobic materials.To verify our hypothesis, the sorption of six compounds with a range of log K_ow values from 2.5 to 6 was studied on tetramethyltriammonium-(TMA) and octadecyltrimethylammonium-(ODTMA) bentonite, representing short- and long-chain organoclays, respectively. Compounds with low or medium hydrophobicities (log K_ow 2.5–3.8) were more strongly sorbed on the short-chain organoclay, whereas the more hydrophobic compounds (log K_ow 5.2–6.1) were better sorbed on the long-chain organoclay, in agreement with our hypothesis.The efficacy of organoclays in removing organic pollutants from the effluent of a pesticide producing plant was evaluated. Pesticide sorption from the wastewater was studied on both types of organoclays. It was found that both organoclays were able to remove organic pollutants from industrial wastewater, but solute uptake by short-chain organoclays was strongly depressed by competition, while long-chain organoclays were only slightly affected, if at all, by the presence of competing solutes in the industrial wastewater.     

Partitioning and Localization of Fragrances in Surfactant Mixed Micelles

The localization and dynamics of fragrance compounds in surfactant micelles are studied systematically in dependence on the hydrophobicity and chemical structure of the molecules. A broad range of fragrance molecules varying in octanol/water partition coefficients P _ow is employed as probe molecules in an aqueous micellar solution, containing anionic and nonionic surfactants. Diffusion coefficients of surfactants and fragrances obtained by Pulsed Field Gradient (PFG)-NMR yield the micelle/water distribution equilibrium. Three distinct regions along the log(P _ow) axis are identified: hydrophilic fragrances (log(P _ow) < 2) distribute almost equally between micellar and aqueous phases whereas hydrophobic fragrances (log(P _ow) > 3.5) are fully solubilized in the micelles. A steep increase of the incorporated fraction occurs in the intermediate log(P _ow) region. Here, distinct micelle swelling is found, while the incorporation of very hydrophobic fragrances does not lead to swelling. The chemical structure of the probe molecules, in addition to hydrophobicity, influences fragrance partitioning and micelle swelling. Structural criteria causing a decrease of the aggregate curvature (flattening) are identified. ²H-NMR spin relaxation experiments of selectively deuterated fragrances are performed monitoring local mobility of fragrance and leading to conclusions about their incorporation into either micellar interface or micelle core. The tendencies of different fragrance molecules (i) to cause interfacial incorporation, (ii) to lead to a flattening of the micellar curvature and (iii) to incorporate into micelles are shown to be correlated.     

Examination of data relating to the thermodynamic and kinetic interactions between nonvolatile aqueous solutes and three ethylene–vinyl acetate copolymers

Distribution coefficient (K_s) and diffusivity [diffusion coefficient (D)] values for 19 nonvolatile solutes were previously reported for three ethylene–vinyl acetate (EVA) copolymers. In this article, the interaction properties of these solutes are compared with their octanol/water partition coefficient (P_o/w) values. Adequate linear log/log correlations between K_s and P_o/w are obtained for all three copolymers, once the effect of the solution pH on solute speciation is taken into account. The resultant correlations are similar for all three copolymers, suggesting that they share a common interaction mechanism. Inverse correlations between log D and log P_o/w are established for all three materials. Although the relationship between log D and log P_o/w is linear for the EVA polymers, the scatter in the poly(vinyl acetate) data is sufficiently large that a linear relationship cannot be unilaterally established. The utility of such a model in terms of assessing the potential interaction between a plastic container and its contained contents is demonstrated. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 253–259, 2006     

Determination of K ow of Substituted Polycyclic Aromatic Compounds

Octanol-water partition coefficients (K _ow s) of substituted polycyclic aromatic compounds (PACs), anthracene-, pyrene- and quinoline-derivatives, have been determined using HPLC. The determined K _ow s have been compared with results from theoretical fragment methods, developed by Rekker and Mannhold [1] and by Hansch and Leo [2]. The results showed that if these theoretical methods are to be useful with simple substituted PAHs they must be applied differently than normally supposed, due to intramolecular steric conditions. Comparison of the determined K _ow s with measured K _oc values showed that the relationship between K _oc and K _ow is not straightforward, and that prediction of K _oc from K _ow alone will not give results applicable for substituted polycyclic aromatic compounds.     

Determination and prediction of Kow and dimensionless Henry's constant (H) for 6 ether compounds at several temperatures

The octanol–water partition coefficient (K_ow) and air–water partition coefficient (K_aw) as well as the dimensionless Henry's constant (H) are used to calculate the transport and fate of chemicals in the environment or eco-system. In this work, the K_ow and the H were measured for 6 ether compounds; di-n-butyl ether (DBE), di-isopropyl ether (DIPE), tert-butyl ethyl ether (ETBE), tert-butyl methyl ether (MTBE), propyl vinyl ether (PVE) and tert-amyl methyl ether (TAME) at 4 different temperatures. The K_ow was directly measured by using a conventional slow stirring (SS) method, while the H was measured using headspace gas chromatography (HSGC). Additionally, the measured K_ow and H values were compared with the predicted values by the fragment constant method or HENRYWIN program approaches.     

Effect of Electrolyte and Temperature on Volatile Organic Compounds Removal from Wastewater Using Aqueous Surfactant Two-Phase System of Cationic and Anionic Surfactant Mixtures

Abstract

Benzene, toluene, ethylbenzene, and xylene are frequently observed contaminants in industrial wastewaters causing concerns about environmental and health effects. An aqueous surfactant two-phase (ASTP) extraction system using mixtures of cationic and anionic surfactants have been shown to be a promising surfactant-based separation technique to concentrate solutes such as proteins and dyes from aqueous solution. A phase separation of a surfactant solution occurs at certain surfactant compositions and concentrations, forming two isotropic phases. One is rich in surfactant aggregates (surfactant-rich phase) and the other is lean in surfactant aggregates (surfactant-dilute phase). Most of the organic contaminants tend to solubilize and concentrate in the surfactant-rich phase, leaving the surfactant-dilute phase containing only small amounts of contaminants as remediated water. The effect of NaCl addition on the critical micelle concentration (CMC) and the extraction ability of ASTP formed by mixtures of cationic surfactant (dodecyltrimethylammonium bromide; DTAB) and anionic surfactant (alkyl diphenyloxide disulfonate; DPDS) at 50 mM total surfactant concentration with a 2:1 molar ratio of DTAB:DPDS was investigated; the CMC of the mixture slightly decreases with increasing NaCl concentration. The extraction and preconcentration of benzene are greatly enhanced by added NaCl. The higher the degree of hydrophobicity of contaminants, the greater the extraction into the surfactant-rich phases. At 1.0 M NaCl addition, about 95% of xylene, 92% of ethylbenzene, 90% of toluene, and 79% of benzene are extracted into the surfactant-rich phase within a single stage extraction and the contaminant partition ratios can be as high as 395 for xylene, 273 for ethylbenzene, 206 for toluene, and 84 for benzene, which are greater than those obtained from the conventional ASTP extraction system using nonionic surfactants.     

Adsorption of Ibuprofen and Atenolol at Trace Concentration on Activated Carbon

Abstract

Adsorption isotherms of atenolol and ibuprofen onto activated carbon (AC) at trace concentration in water (initial concentration, 80 μg/L – equilibrium concentration as low as 0.13 μg/L) are presented in this paper. Their adsorption was studied considering two ACs (F400 and Picabiol) showing different textural and chemical characteristics. Experiments were performed in buffered ultrapure water with and without humic acids to evaluate their influence on adsorption. It was found that adsorption was not in agreement with expectations based either on the log K_ow or log D values of the target compounds. Adsorption mechanisms were discussed and the experimental isotherms were modelled.     

Comparison of Partition Chromatographic Parameters of Lipophilic Organic Electrolytes for Solvents of Various Donor-Acceptor Properties. V. Phenols in Systems of the Type Organic Solvent/Formamide

Abstract

R_M values of a number of phenols (cresols, xylenols, chlorophenols, hydroxynaphthalenes) have been determined for numerous solvent systems of the type, weakly polar solvent/formamide. To determine a quantitative scale of extraction strengths, R_M -solvent spectra have been plotted using a modified method of Rohrschneider and Littlewood. 2-Methylquinoline, used in previous investigations as a reference solute for nitrogen bases, has been found unsuitable for phenols, and much more regular spectra have been obtained with 1-naphthol as the reference compound. The experimental results indicate that the extraction strengths of solvents cannot be characterized by a single series. Much more satisfactory results are obtained when two series are determined, based on the partition chromatographic parameters of two solutes of opposite H-bonding properties, e.g., 2-methylquinoline and 1-naphthol. For many of the phenols, linear R_M -solvent spectra are obtained when the solvents on the abscissa are arranged to give a linear spectrum for 1-naphthol, so that the spectra can be used to predict chromatographic parameters of related solutes.     

Efficiency of different clay minerals modified with a cationic surfactant in the adsorption of pesticides: Influence of clay type and pesticide hydrophobicity

In the present work we studied the efficiency of a series of clay minerals (montmorillonite, illite, muscovite, sepiolite and palygorskite) modified with the cationic surfactant octadecyltrimetylammonium bromide (ODTMA) in the adsorption of the pesticides penconazole, linuron, alachlor, atrazine and metalaxyl. A study was also carried out on the effect of the structure (expansible and non-expansible layered, and non-layered), the surface area and charge density of the clay minerals, and the hydrophobicity of the pesticides (K_ow) on the adsorption process. Adsorption–desorption isotherms of the pesticides by clay minerals were obtained and the constants of the Freundlich model (K_f and K_fd) (natural clays) and of the linear model (K and K_des) (ODTMA-clays) were determined. Correlation coefficient values (r²) found between K and K_des, and organic matter (OM) content of ODTMA-clays indicate a more effective partitioning of the pesticides in the organic phase of ODTMA after desorption. Furthermore the positive significant correlation found between the K_desom values and the charge density of different ODTMA-clays indicates that a higher density of ODTMA in the clay gives rise to the formation of an organic phase more effective for the partition of the pesticides. This correlation explained that the highest K_desom value obtained was for kaolinite and the lowest K_desom value was for montmorillonite in the adsorption of all pesticides by the different organo clays. Simple correlations between adsorption constants and K_ow values, and multiple correlations between these constants and clay OM contents and K_ow values were also calculated. The results obtained indicate the interest of ODTMA-clays in the adsorption of hydrophobic pesticides. Non-expandible layered and fibrous clay minerals may also be of interest as adsorbents derived from their density charge, and these minerals, when modified with ODTMA, and used in appropriate amounts, higher than that of montmorillonite, or when present in soils with high clay contents, even in the absence of montmorillonite, may be good adsorbents for hydrophobic pesticides. According to the results of the study, ODTMA-clays and ODTMA-soils could be used as barriers to prevent the mobility of certain hydrophobic pesticides from a point source of pollution.     

Synergistic Extraction of Th(IV) by Mixtures of HTTA and TBP in Benzene

Abstract

Extraction of Th(IV) from dilute perchloric acid medium by mixtures of HTTA and TBP in benzene medium was studied. The species Th(TTA)₄ TBP was found responsible for the observed synergism. Equilibrium constants for the extraction equilibria involved are log K_A = 2.25, log K_AB = 6.88, and log β_AB = 4.63.     

Study on partition and release of molecules in superabsorbent thermosensitive nanocomposites

Nanocomposites are synthesized by in-situ polymerization of conducting polymers: polyaniline (PANI) or poly(N-methylaniline) (PNMANI) inside thermosensitive hydrogels based on poly(N-isopropylacrylamide) (PNIPAM) homopolymer and copolymers with 2-acrylamido-2-methyl propane sulfonic acid (AMPS). Large swelling capacities (up to 25,000%) are measured for a nanocomposite based on a hydrogel containing only 2% of anionic monomer units. Dynamic swelling experiences show that water intake follows a non-Fickian mechanism. Drug release kinetics and partition coefficients (K) of model compounds (Methyl Orange, Ruthenium-tris(2,2′-bipyridyl) ion, Dansyl Chloride) and pharmaceuticals (Tryptophan, Propranolol Chloride, Riboflavin) were measured. Log K values were determined by UV–visible or fluorescence spectroscopy, below and above the phase transition temperature of the materials. Large values of log K (>3) were measured for tryptophan while the same material shows small log K (1.5) for riboflavin. Depending on the nanocomposite/solute interactions, the partition increases or decreases upon phase transition. Several nanocomposites studied show potential for application in the separation of solutes or water purification. Additionally, it is possible to synthesize nanocomposites which show different partition coefficients for the same molecule. In that way, a specific pattern could be measured for each molecule allowing its identification.     

Cloud point and solvent extraction study of uranium(VI) by 8‐hydroxyquinoline

BACKGROUND: Cloud point extraction (CPE) is an attractive alternative to solvent extraction. However, comparisons between both techniques are lacking. In this paper, the extraction of uranium(VI) using 8‐hydroxyquinoline (HQ) as chelating agent was studied by CPE using Triton X‐114 as non‐ionic surfactant and by solvent extraction using CHCl₃ as diluent. RESULTS: Using CPE, a quantitative extraction was observed for pH higher than 4.5 with a HQ/U ratio of 10. Using solvent extraction an increase in the HQ/U ratio up to 50 is necessary to obtain a near quantitative extraction. Both extraction systems were then compared with respect to the nature of extracted species, and the extraction constants determined using log‐log analysis of the extraction data. In the solvent extraction system, the extracted species were identified as UO₂Q₂ and the corresponding extraction constant was found to be log k_ex = ? 3.6 ± 0.2 on the molar scale. Considering that UO₂Q₂ is also the extracted species in CPE, a slightly higher extraction constant, i.e. log k_ex = ? 2.5 ± 0.3, was found. CONCLUSION: Such a small difference in favour of the CPE system may arise from the combination of various phenomena, including effects of temperature and effects of ‘extractant environment’. However, a change in the nature of the extracted species, namely from UO₂Q₂ in the solvent extraction system to the formation of adducts, i.e. UO₂Q₂(HQ) and UO₂Q₂(HQ)₂ in the CPE system, due to higher HQ concentration in the surfactant‐rich phase compared with chloroform, cannot be precluded, but requires confirmation. Copyright © 2012 Society of Chemical Industry     

SOLVENT EXTRACTION OF PHOSPHORIC ACID WITH LONG CHAIN TERTIARY AMINES

Solvent extraction of phosphoric acid with Alamine 336 and tri-n-octylamine in toluene has been investigated. The activity of phosphoric acid is expressed as a polynomial of ionic strength and Bromley's model for electrolyte solutions is employed for calculation of ionic activity coefficients. Three species R₃N (H₃P0₄) _n with n = 1, 2 and 3 in the organic phase are taken into account for explanation of the distribution equilibria. The extraction constants have been determined as log K₁₁ = 2.05, log K₁₂ = 3.61 and log K₁₃ = 3.84 respectively. Aggregation and other non-ideal behaviour in the organic phase are described by letting the corresponding activity coefficient quotients be a function of the total concentration of acid in the organic phase.     

Adsorption properties of cyclic compounds on cellulose acetate

The interaction between solutes and semipermeable membranes is an important factor for the membrane‐separation process. As an extension to previous works, we studied the adsorption properties of cyclic compounds on cellulose acetate, a material commonly used for semipermeable membranes, in aqueous solution systems by high‐performance liquid chromatography (HPLC). Cycloalcohols, cycloethers, amino acids, heterocyclic aromatic compounds, and nucleosides were used in this study. The logarithm of the capacity factor (log k′) for these compounds was linearly correlated with the logarithm of 1‐octanol/water partition coefficients (log K_o/w) as well as noncyclic compounds. Cyclic compounds were relatively retained more than were noncyclic compounds in spite of their hydrophilic properties, which indicates the structural effects of the solute molecule on the adsorption. Although noncyclic compounds were retained mainly by hydrophobic interaction, the retention of cyclic compounds was suggested to be controlled by their inclusion within the micropore in cellulose acetate. The adsorption of heterocyclic aromatic compounds was not influenced only by ionic dissociation but also by tautomerism. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1657–1663, 1999     

Sorption and desorption kinetics of chlorophenols in hexadecyltrimethyl ammonium-montmorillonites and their model analysis

Sorption and desorption kinetics of chlorophenols, 2-chlorophenol (2-ChP), 2,4-dichlorophenol (2,4-DChP) and 2,4,5-trichlorophenol (2,4,5-TChP), in montmorillonite modified with hexadecyltrimethyl ammonium cations (HDTMA-mont) were investigated by using laboratory batch adsorbers. To investigate the effect of chemical concentration and sorbent weight on the sorption or desorption rate constants, the initial chemical concentration and sorbent weight were varied from 50 to 150 mg/L and from 0.2 to 1.0 g, respectively. A one-site mass transfer model (OSMTM) and two compartment first-order kinetic model (TCFOKM) were used to analyze kinetics. The OSMTM applicable to desorption rate analysis was newly derived. As expected from the number of model parameters involved, the three-parameter TCFOKM was better than the two-parameter OSMTM in describing sorption and desorption kinetics of chlorophenols in HDTMA-mont. The mass transfer coefficient for sorption (k_s) in OSMTM generally increased as K _ow value increases, except for 2,4,5-TChP, while the mass transfer coefficient for desorption (k _d ) consistently increases as K _ow value decreases, due to the weaker hydrophobic interaction between the solute and the organoclay. Since most sorption and desorption complete in an hour and half an hour, respectively, k _d values were found to be greater than k _s values for all three solutes studied. The fraction of the fast sorption (or desorption) and the first-order sorption (or desorption) rate constants for the fast and slow compartments in TCFOKM were determined by fitting experimental data to the TCFOKM. The results of kinetics reveal that the fraction of the fast sorption or desorption and the sorption rate constants in the fast and slow compartments were in the order 2,4,5-TChP>2,4-DChP>2-ChP, which agrees with the magnitude of the octanol-water partition coefficient, K _ow . The first-order sorption rate constants in the fast and slow compartments were found to vary 10¹–10² hr⁻¹ and 10⁻³–10⁻² hr⁻¹, respectively. However, the desorption rate constants in the fast and slow compartments were not correlated well withK _ow . The first-order desorption rate constants in the fast compartment (10¹−10² hr⁻¹) were found to be much larger than those in the slow compartment (10⁻³–10⁻⁴ hr⁻¹). Sorption affinity and desorption resistance of each chlorophenol in 50% HDTMA-mont were found to show the same tendency: the weakly-sorbed chlorophenol (i.e., 2-ChP) was easily desorbed, while the strongly-sorbed chlorophenol (i.e., 2,4,5-TChP) was rather resistant to desorption.     

PARTITIONING OF AROMATIC MOLECULES IN AQUEOUS BIPHASIC SYSTEMS

ABSTRACT

Aqueous biphasic systems (ABS) may be suitable for the separation of aromatic molecules in industrial and environmental settings; hence it is invaluable to have predictive models of partitioning behavior in these systems for design and evaluation purposes. In a continuing study of the partition of small aromatic organic molecules, the distribution of several relatively hydrophilic substituted benzene species is reported. The partitioning behavior of five charged substituted benzene species (phthalic acid, 4-hydroxybenzoic acid, benzoic acid, salicylic acid, and p-toluic acid) and one uncharged species (1,3-dinitrobenzene) has been studied in ABS prepared from stock solutions of 40% (w/w) PEG-2000 and increasing concentrations of four water-structuring salts [K₃PO₄, K₂CO₃, (NH₄)₂SO₄, and NaOH]. Comparison has been made with published data on the partitioning of these solutes in 1-octanol/water biphasic systems. In general, the partition of these species may be understood in terms of the free energy of hydration of the salt forming the ABS and the dissociation of the charged groups of the distributed solutes.     

Dependence of extraction equilibrium of monocarboxylic acid from aqueous solutions on the relative basicity of extractant

This paper describes monocarboxylic acid extraction from aqueous solution experiments, using five types of mixed solvents and 12 monocarboxylic acids. From the results of these experiments, a new mathematical model, including a new definition of extractant's basicity (pK_a,BS), was developed and validated. Trioctylamine (TOA)/1-octanol, TOA/methyl iso-butyl ketone (MIBK), TOA/tetrachloromethane (CCl₄), trialkylphosphine oxide (TRPO) /1-octanol and TRPO/ kerosene, were used as the extractant, and formic, acetic, propionic, butyric, valeric, caproic, monochloroacetic, dichloroacetic, trichloroacetic, glycolic, glyoxylic, and lactic acids, were used as the solutes extracted. The relative basicity of the extractant to the solute extracted (pK_a,BS) was measured in different extractant concentrations. The experimental result confirms the mathematic model to predict the extraction equilibrium more accurately. pK_a,BS can represent the complicated solvating power of the dilute to the association compound, and depends on the extractant concentration and the type of extractant, diluent and solute.     

Solubilization of selected polycyclic aromatic compounds by nonionic surfactants

Solubilization of selected polycyclic aromatic compounds (PAC) by biodegradable nonionic surfactants, Tergitol 15-S-X (X=7 or 9) and Neodol 25–7, was investigated and correlated with micellar properties of these surfactants. These PAC include dibenzofuran, phenanthrene, acenaphthene, fluoranthene, and 9-chloroanthracene. Tergitol surfactants are mixtures of secondary ethoxylated alcohols, and Neodol 25–7 is a mixture of similar species but has the alcohol group in the primary position. These surfactants have the same chain length of hydrophobic tails and similar numbers of ethylene oxides. The results show that the Neodol surfactant yields micelles having larger hydrophobic core volume and renders a higher solubilization capacity for the PAC solubilizates in comparison with Tergitol surfactants. In general, aggregation numbers and micellar sizes both increase at elevated temperatures still below the cloud point. The micellewater partition coefficients of these PAC by the nonionic surfactants were well correlated to their octanol-water partition coefficients. Moreover, an estimated log K _ow value of 9-chloanthracene is 4.78.     

KINETICS MODEL FOR INTERFACIAL REACTION OF COPPER EXTRACTION WITH 1-(2'-HYDROXY-5'-NONYLPHENYL)-l-ETHANONE (E)-OXIME AND 1-(2'-HYDROXY-5'-METHYLPHENYL)-1-DECANONE (E)-OXIME

Abstract

A kinetic model for the interfacial reaction of copper extraction with Individual 1-(2'-hydroxy-5'-nonylphenyl)-1-ethanone (E)-oxime and 1-(2'-hydroxy-5'-methylphenyl)-1-decanone (E)-oxime having the same hydrophobicity was used to interpret the effect of hydroxyoxime partition and interfacial activity upon the rate of copper extraction from acidic sulfate solutions. Due to similar hydrophobicity of studied extractants the proposed model, which is very sensitive to the errors of the partition coefficient determination, cannot support any version of extraction mechanism.