Rapid Estimation of Octanol–Water Partition Coefficient for Triazole Fungicides by MEKC with Sodium Deoxycholate as Surfactant

A rapid estimation of octanol–water partition coefficient (log P _ow) was developed for triazole fungicides by micellar electrokinetic chromatography (MEKC). Five standard compounds with known log P _ow values from 2.9 to 4.3 (cyproconazole, bromuconazole, epoxiconazole, bitertanol and difenoconazole) were used for constructing the calibration curve of the log P _ow against the MEKC retention factor, log k. A linear relationship was achieved between log P _ow and log k, in the MEKC system containing 40 mM sodium deoxycholate (SDC) and 4 mM borate buffer at pH 9.3, with a correlation of determination, r ² = 0.9905. The log P _ow values of four test compounds of triazole fungicides (triadimenol, myclobutanil, propiconazole and penconazole) were calculated based on the log k values measured by MEKC and the slope and intercept of the calibration curve. This MEKC method can give good estimation of the log P _ow of the four test compounds of triazole fungicides with the differences between the literature log P _ow values and estimated log P _ow from the MEKC method were from 0.15 to 0.23 log units.     

Cyclodextrins for remediation of soils contaminated with chlorinated organics

The effect of random methylated ??CD (RAMEB) on the efficiency of various remediation technologies was studied in lab-scale model-experiments applying soil and groundwater originating from a site contaminated with trichloroethylene (TCE). The solubility of TCE was enhanced to tenfold in 10% solution of RAMEB compared to that in water. This solubilizing effect was utilized for remediation of the TCE contaminated soil using enhanced groundwater extraction and in situ TCE oxidation by ISCO (= in situ chemical oxidation). The effect of CD on TCE extraction from soil was studied using two technologies: ground-water extraction followed by air stripping or UV irradiation. The RAMEB-enhanced ISCO was applied directly to the water-saturated soil without water extraction or separation. The efficiency of air stripping of TCE (removal by bubbling air through the contaminated ground-water obtained by extraction) was decreased in the presence of RAMEB due to the volatility decreasing effect of complexation. The efficiency of the entire technology (extraction and air stripping together) was, however, enhanced as three times more TCE was dissolved, and more than twice as much could be removed when 5% RAMEB solution was applied instead of water. Similar results were obtained by UV irradiation. Although the complexation has a protective effect against degradation caused by irradiation, the efficiency of the technology (extraction and subsequent UV irradiation) is enhanced to approximately threefold, because more than 10 times higher TCE concentration was found in the extract using 20% RAMEB concentration. ISCO is based on Fe-catalyzed oxidation using hydrogen peroxide. The catalytic effect of RAMEB was observed only when it was applied together with Fe(II) salts. Without Fe(II) the effect of complex formation dominated. When hydrogen peroxide and FeSO₄ were applied with RAMEB, over five times enhancement in TCE removal was obtained compared to the technology based on the addition of hydrogen peroxide and Fe(II) salts without RAMEB. This effect shows that the solubilizing effect on iron catalyst is at least as much or even more important than the solubilizing effect on TCE. The ternary complex formation with ferrous/ferric ion and TCE seems to be responsible for the enhanced efficacy.     

The role of hydrophobicity in the Ames test. The correlation of the mutagenicity of nitropolycyclic hydrocarbons with partition coefficients and molecular orbital indices

A set of 20 nitropolycyclic aromatic hydrocarbons, whose mutagenicity has been determined in the Ames test, has been studied using octanol-water partition coefficients (P) as a measure of relative hydrophobicity and molecular orbital energies to account for variation in their electronic characteristics. A good structure-activity relationship was found using log P and ?_LUMO . The latter were taken from the results of ab initio calculations performed by Maynard, Pedersen, Posner, and McKinney [7] and were also calculated by the MNDO method. The dependence of mutagenicity on hydrophobicity was found to be similar to that observed for triazenes [2]. ?_LUMO values calculated by MNDO and STO -3G were found to be strongly correlated, and the role of hydrophobicity in correlating mutagenicity was not significantly affected by the molecular orbital model employed.     

Evaluation of Accuracy for the Measurement of Octanol–Water Partition Coefficient by MEEKC

Microemulsion electrokinetic chromatography (MEEKC) has been widely used as an indirect tool to measure octanol–water partition coefficients (logP _ow) of various kinds of compounds. In this paper, we present for the first time a mathematical model of the precision of logP _ow (ΔlogP _ow) as a function of the deviation of migration time (Δt _m) in MEEKC, and more importantly evaluated the accuracy of the MEEKC. Our model shows that for a given microemulsion system, there is an interval of migration times, where a high precision in the determination of logP _ow can be obtained. However, when the migration time approaches either the migration time of the electroosmotic flow or that of the microemulsion phase, the precision of logP _ow deteriorates rapidly. The model was experimentally verified by the microemulsion system with migration times of 6.50 and 32.00?min for the electroosmotic flow and microemulsion phase, respectively, and we found the useful logP _ow interval to be 0.50–5.50. The paper also demonstrates that the calibration constants between migration times t _m and predicted logP _ow values could be transferred with high accuracy from one MEEKC system to another as long as both systems are set up to use the same operational parameters.     

An open source multistep model to predict mutagenicity from statistical analysis and relevant structural alerts

Background

Mutagenicity is the capability of a substance to cause genetic mutations. This property is of high public concern because it has a close relationship with carcinogenicity and potentially with reproductive toxicity. Experimentally, mutagenicity can be assessed by the Ames test on Salmonella with an estimated experimental reproducibility of 85%; this intrinsic limitation of the in vitro test, along with the need for faster and cheaper alternatives, opens the road to other types of assessment methods, such as in silico structure-activity prediction models.A widely used method checks for the presence of known structural alerts for mutagenicity. However the presence of such alerts alone is not a definitive method to prove the mutagenicity of a compound towards Salmonella, since other parts of the molecule can influence and potentially change the classification. Hence statistically based methods will be proposed, with the final objective to obtain a cascade of modeling steps with custom-made properties, such as the reduction of false negatives.

Results

A cascade model has been developed and validated on a large public set of molecular structures and their associated Salmonella mutagenicity outcome. The first step consists in the derivation of a statistical model and mutagenicity prediction, followed by further checks for specific structural alerts in the "safe" subset of the prediction outcome space. In terms of accuracy (i.e., overall correct predictions of both negative and positives), the obtained model approached the 85% reproducibility of the experimental mutagenicity Ames test.

Conclusions

The model and the documentation for regulatory purposes are freely available on the CAESAR website. The input is simply a file of molecular structures and the output is the classification result.

     

Sorption and partitioning parameters of benzotriazole compounds

Benzotriazole compounds have major commercial applications as anticorrosive agents in automotive antifreeze and airplane deicer fluids. This study assesses the sorption of benzotriazole (BT), 5-methylbenzotriazole (MBT), and 5-chlorobenzotriazole (CBT) from aqueous solutions to four top soils. The concentration range of 10-500 mg l⁻¹ was used with soils differing in total organic carbon content from 0.27 to 1.72%. Batch systems facilitated the equilibrium sorption with analysis by HPLC. The sorption of these compounds was as much as 60% by mass to a soil with 0.33% Org. C. The log octanol-water partition coefficients (log K_ow) were determined to be 1.23 for BT, 1.89 for MBT, and 2.17 for CBT. The relationship between the log of the sorption partition coefficient, log K_oc and log K_ow differed from previous correlations because hydrophobicity was not the only factor affecting sorption. These compounds have substantial permanent dipole moments as well as being hydrophobic. At high pH where CBT molecules approach their pK_a, sorption was approximately 50% less (by mass) than that of relatively non-ionized CBT molecules.     

Water solubility and octanol/water-partitioning of hydrophobic chlorinated organic substances determined by using SPME/GC

The critical step in the determination of water solubilitiy (S _w) and octanol-water partition coefficient (K _ow) of hydrophobic organic chemicals by using the generator-column technique and the slow-stirring procedure, respectively, is the exact quantification of the low water-phase concentrations of the substances under investigation. We have tested the applicability of solid-phase microextraction (SPME) and gas chromatography with seven chlorinated organic compounds. The substances cover a S _w range from 500 mg/L to 7 ng/L and a log K _ow range from 3 to 8. The results show that SPME can be a valuable alternative to common preconcentration techniques in the quantification of hydrophobic organics in pure and octanol-saturated water. The apparent SPME distribution constants K _SPME (obtained with the 100 μm-PDMS fiber for analyte’s partitioning between fiber coating and aqueous sample) do not correlate directly with octanol/water partition coefficients and thus cannot be recommended as a surrogate parameter for K _ow.     

Use of a pentachlorophenol degrading bacterium to bioremediate highly contaminated soil

ASphingomonas species that mineralizes high concentrations of pentachlorophenol (PCP) was isolated from a PCP-contaminated EPA Superfund site. This bacterium, identified asSphingomonas sp. strain RA2, is able to degrade PCP at concentrations of up to 300 μg/mL in liquid culture. This organism was tested for its ability to degrade high concentrations of PCP in a soil that did not contain organisms capable of degrading high concentrations of PCP. When inoculated into contaminated soil,Sphingomonas sp. RA2 mineralized PCP at concentrations of 300, 600, 900, and 1200 μg PCP/g of soil, but was unable to mineralize 1500 μg PCP/g of soil. Only very minimal loss of PCP was seen in uninoculated soils. The results of this study demonstrate thatSphingomonas sp. RA2 may be a useful organism for remediation of sites contaminated with high concentrations of PCP.     

Zone fluidics for measurement of octanol–water partition coefficient of drugs

A novel zone fluidics (ZF) system for the determination of the octanol–water partition coefficient (P_ow) of drugs was developed. The ZF system consisted of a syringe pump with a selection valve, a holding column, a silica capillary flow-cell and an in-line spectrophotometer. Exact microliter volumes of solvents (octanol and phosphate buffer saline) and a solution of the drug, sandwiched between air segments, were sequentially loaded into the vertically aligned holding column. Distribution of the drug between the aqueous and octanol phases occurred by the oscillation movement of the syringe pump piston. Phase separation occurred due to the difference in densities. The liquid zones were then pushed into the detection flow cell. In this method, absorbance measurements in only one of the phase (octanol or aqueous) were employed, which together with the volumes of the solvents and pure drug sample, allowed the calculation of the P_ow. The developed system was applied to the determination of the P_ow of some common drugs. The log (P_ow) values agreed well with a batch method (R² = 0.999) and literature (R² = 0.997). Standard deviations for intra- and inter-day analyses were both less than 0.1log unit. This ZF system provides a robust and automated method for screening of P_ow values in the drug discovery process.     

Phase Ratio and Equilibrium Constant in RP-HPLC Obtained from Octanol/Water Partition Constant Through Solvophobic Theory

The experimentally known dependence in RP-HPLC of the retention factor k′ on octanol/water partition coefficient (K _ow) has been examined based on solvophobic theory. The result showed that the dependence provides a means for the evaluation of phase ratio (Φ) of RP-HPLC columns, and of the equilibrium constant for a given compound and mobile phase. Using this theory, the phase ratio was evaluated for a set of seven different C18 columns (five having fully porous particles and two core–shell particles), and the equilibrium constants were calculated for four homologous series of compounds in two mobile phase systems. One mobile phase was methanol/aqueous solution of 0.1% H₃PO₄, and the other was acetonitrile/aqueous solution of 0.1% H₃PO₄. Besides providing the values for Φ for the evaluated columns, the results of the study indicated that for a specific composition of the mobile phase and for a given compound displaying only hydrophobic interactions, the equilibrium constant K(X) for different C-18 columns is basically the same. The data were further used to provide guidance in the selection of a chromatographic column for a specific separation based on K _ow values and chemical structure of the analytes. The study indicated that the separation of compounds with identical polar groups (or no polar groups) and with very close values for the K _ow cannot be achieved based only on hydrophobic interactions that dominate the separation on RP-type columns. Only column that displays polar interactions may provide a solution to such separations. For hydrocarbons with close K _ow values, the separation cannot be achieved even on columns with some polarity. On the other hand, even compounds with equal K _ow values, but with different functionalities can be separated on RP-HPLC columns without involving polar interactions. The compounds with different K _ow values are expected to be easily separated on RP-HPLC columns.     

A novel evaluation method for extrapolated retention factor in determination of n-octanol/water partition coefficient of halogenated organic pollutants by reversed-phase high performance liquid chromatography

The retention factor corresponding to pure water in reversed-phase high performance liquid chromatography (RP-HPLC), k_w, was commonly obtained by extrapolation of retention factor (k) in a mixture of organic modifier and water as mobile phase in tedious experiments. In this paper, a relationship between log k_w and log k for directly determining k_w has been proposed for the first time. With a satisfactory validation, the approach was confirmed to enable easy and accurate evaluation of k_w for compounds in question with similar structure to model compounds. Eight PCB congeners with different degree of chlorination were selected as a training set for modeling the log k_w ? log k correlation on both silica-based C₈ and C₁₈ stationary phases to evaluate log k_w of sample compounds including seven PCB, six PBB and eight PBDE congeners. These eight model PCBs were subsequently combined with seven structure-similar benzene derivatives possessing reliable experimental K_ow values as a whole training set for log K_ow ? log k_w regressions on the two stationary phases. Consequently, the evaluated log k_w values of sample compounds were used to determine their log K_ow by the derived log K_ow ? log k_w models. The log K_ow values obtained by these evaluated log k_w were well comparable with those obtained by experimental-extrapolated log k_w, demonstrating that the proposed method for log k_w evaluation in this present study could be an effective means in lipophilicity study of environmental contaminants with numerous congeners. As a result, log K_ow data of many PCBs, PBBs and PBDEs could be offered. These contaminants are considered to widely exist in the environment, but there have been no reliable experimental K_ow data available yet.     

Validation of pH-Metric Technique for Measurement of pKa and log Pow of Ionizable Herbicides

Abstract

Knowing the values of pK_a and partition coefficients between 1-octanol and water (P_ow) of ionizable herbicides helps us to understand the movement of these compounds in plants and soil. However, shake-flask and high-pressure liquid chromatography (HPLC) techniques. though valuable for measurement of log P_ow of herbicide molecules that do not ionize in aqueous solution, are difficult to use for ionizable molecules; this is especially so for molecules that form ion pairs having appreciable log P_ow values, those with multiple ionizations and for bases with high pK_a values. Our aim in this study was to validate the use of the pH-metric technique (based on potentiometric titration) for measurements of pK_a and log P_ow of ionizable standard substances and herbicides. The values obtained show good correlation with results from other techniques, including shake-flask and HPLC. The OECD Guideline for Testing of Chemicals 117, adopted 30th March 1989, describes the use of HPLC for the measurement of log P_ow. It is hoped that these studies and further testing of this technique will permit it to be included in these OECD guidelines.     

Mutagenicity of flavonoids assayed by bacterial reverse mutation (Ames) test

The mutagenicity of ten flavonoids was assayed by the Ames test, in Salmonella typhimurium strains TA98, TA100 and TA102, with the aim of establishing hydroxylation pattern-mutagenicity relationship profiles. The compounds assessed were: quercetin, kaempferol, luteolin, fisetin, chrysin, galangin, flavone, 3-hydroxyflavone, 5-hydroxyflavone and 7-hydroxyflavone. In the Ames assay, quercetin acted directly and its mutagenicity increased with metabolic activation. In the presence of S9 mix, kaempferol and galangin were mutagenic in the TA98 strain and kaempferol showed signs of mutagenicity in the other strains. The absence of hydroxyl groups, as in flavone, only signs of mutagenicity were shown in strain TA102, after metabolization and, among monohydroxylated flavones (3-hydroxyflavone, 5-hydroxyflavone and 7-hydroxyflavone), the presence of hydroxyl groups only resulted in minor changes. Luteolin and fisetin also showed signs of mutagenicity in strain TA102. Finally, chrysin, which has only two hydroxy groups, at the 5-OH and 7-OH positions, also did not induce mutagenic activity in any of the bacterial strains used, under either activation condition. All the flavonoids were tested at concentrations varying from 2.6 to 30.7 nmol/plate for galangin and 12.1 to 225.0 nmol/plate for other flavonoids. In light of the above, it is necessary to clarify the conditions and the mechanisms that mediate the biological effects of flavonoids before treating them as therapeutical agents, since some compounds can be biotransformed into more genotoxic products; as is the case for galangin, kaempferol and quercetin.     

Capabilities and limitations of dispersive liquid–liquid microextraction with solidification of floating organic drop for the extraction of organic pollutants from water samples

Dispersive liquid–liquid microextraction with solidification of floating organic drop (DLLME-SFO) is one of the most interesting sample preparation techniques developed in recent years. Although several applications have been reported, the potentiality and limitations of this simple and rapid extraction technique have not been made sufficiently explicit. In this work, the extraction efficiency of DLLME-SFO for pollutants from different chemical families was determined. Studied compounds include: 10 polycyclic aromatic hydrocarbons, 5 pesticides (chlorophenoxy herbicides and DDT), 8 phenols and 6 sulfonamides, thus, covering a large range of polarity and hydrophobicity (Log K_ow 0–7, overall). After optimization of extraction conditions using 1-dodecanol as extractant, the procedure was applied for extraction of each family from 10-mL spiked water samples, only adjusting sample pH as required. Absolute recoveries for pollutants with Log K_ow 3–7 were >70% and recovery values within this group (18 compounds) were independent of structure or hydrophobicity; the precision of recovery was very acceptable (RSD < 12%) and linear behavior was observed in the studied concentration range (r² > 0.995). Extraction recoveries for pollutants with Log K_ow 1.46–2.8 were in the range 13–62%, directly depending on individual Log K_ow values; however, good linearity (r² > 0.993) and precision (RSD < 6.5%) were also demonstrated for these polar solutes, despite recovery level. DLLME-SFO with 1-dodecanol completely failed for extraction of compounds with Log K_ow ≤ 1 (sulfa drugs), other more polar extraction solvents (ionic liquids) should be explored for highly hydrophilic pollutants.     

Investigating the effect of randomly methylated β-cyclodextrin/block copolymer molar ratio on the template-directed preparation of mesoporous alumina with tailored porosity

Supramolecular assemblies formed between cyclodextrins and block copolymers can be efficiently used as templates for the preparation of mesoporous materials with controlled porosity. In this work, we use dynamic light scattering (DLS) and viscosity measurements to follow the variations occurring in the size and morphology of the triblock copolymer poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (P123) micelles in the presence of various amounts of randomly methylated β-cyclodextrin (RAMEB). The results obtained with a series of solution compositions reveal that the cyclodextrin-to-copolymer (RAMEB/P123) molar ratio plays a crucial role in the growth rate of the micelles. At low RAMEB/P123 molar ratios (below ~7.5), a swelling effect of the cyclodextrin in the P123 micelles is noticed together with a modification of the micellar curvature from spherical to ellipsoidal. At high molar ratios (~7.5 and above), an abrupt transition toward large supramolecular assemblies, which no longer resemble micelles, occurs. When the RAMEB-swollen P123 micelles are used as templates to direct the self-assembly of colloidal boehmite nanoparticles, mesoporous γ-Al₂O₃ materials with high surface areas (360–400 m²/g), tunable pore sizes (10–20 nm), large pore volumes (1.3–2.0 cm³/g) and fiberlike morphologies are obtained under mild conditions. The composition of the mixed micellar solution, in particular the cyclodextrin-to-copolymer molar ratio, appears to be a key factor in controlling the porosity of alumina.     

Static secondary ionization mass spectrometry detection of cyclohexylamine on soil surfaces exposed to laboratory air

Cyclohexylamine (CHA) is a common indoor air contaminant, which rapidly adsorbs to aluminosilicate soil samples. Static secondary ion mass spectrometry was used to study soil samples exposed to both CHA and CHA-d ₁₁, and the results showed (1) abundant [M+H]⁺ and fragment ions that originated from CHA, (2) an initial concentration of CHA equivalent to approximately 0.2 monolayer, and (3) a possible exchange reaction where excess CHA-d ₁₁ displaces CHA originally adsorbed to the surface. CHA was not removed from the surface by prolonged exposure to vacuum conditions (5×10^?7 torr), which indicates that CHA strongly adsorbs to aluminosilicate surfaces and should be expected as an endogenous surface contaminant where the chemical is used as a corrosion inhibitor.     

Assessing the effect of oxygen and microbial inhibitors to optimize ferricyanide-mediated BOD assay

Methods for short-term BOD analysis (BOD_st) based on ferricyanide mediator reduction have succeeded in overcoming some problems associated with the standard BOD test analysis (BOD₅) such as long-term incubations (5 days), the need to dilute samples and low reproducibility. Here we present a bioassay where a Klebsiella pneumoniae environmental strain successfully reduces ferricyanide without de-aeration of the samples with linear BOD₅ ranges between 30 and 500 mg L⁻¹ or 30 and 200 mg L⁻¹, using glucose-glutamic acid solution (GGA) or OECD standards respectively. We further propose a new assay termination solution that allows higher reproducibility and standardization of the cell-based assay, employing formaldehyde (22.7 g L⁻¹) or other compounds in order to stop ferricyanide reduction without affecting the amperometric detection and therefore replace the centrifugation step normally used to stop microbial-driven reactions in ferricyanide-mediated bioassays. These improvements led to an accurate determination of real municipal wastewater samples.     

Degradation of polychloroprene/natural rubber (PCP/NR) blends by photo-Fenton process

The effect of light and FeCl₃·6H₂O on polychloroprene (PCP)/natural rubber (NR) blends in toluene solution were investigated to demonstrate the influence of each polymer on the degradation process. The contributions of total polymer concentration (C_p), temperature (T) and polychromatic light exposure (L) on the degradation process were investigated through a 2³ factorial design approach. Degradation kinetics was examined by solution viscosity time data. FTIR spectroscopy and TGA were used to characterize the degradation. The exposure of the PCP/NR blend solution containing FeCl₃·6H₂O to light induces degradation in the polymers. A decrease of up to 70% in solution efflux time at constant temperature and without aggregation or phase separation was observed. PCP degradation by-products amplify the degradation of NR, as evidenced by the decrease in the PCP/NR 1:99 (w/w) solution efflux time, which was larger than that of the pure NR solution. The film cast from the solution exposed to light was thermally less stable than the one which was cast without FeCl₃·6H₂O.