Molecular hologram derived quantitative structure-property relationships to predict physico-chemical properties of polychlorinated biphenyls

Complementary Quantitative Structure⁻Activity Relationship Models for the Antitrypanosomal Activity of Sesquiterpene Lactones

Three complementary quantitative structure–activity relationship (QSAR) methodologies, namely, regression modeling based on (i) “classical” molecular descriptors, (ii) 3D pharmacophore features, and (iii) 2D molecular holograms (HQSAR) were employed on the antitrypanosomal activity of sesquiterpene lactones (STLs) toward Trypanosoma brucei rhodesiense (Tbr), the causative agent of the East African form of human African trypanosomiasis. In this study, an extension of a previous QSAR study on 69 STLs, models for a much larger and more diverse set of such natural products, now comprising 130 STLs of various structural subclasses, were established. The extended data set comprises a variety of STLs isolated and tested for antitrypanosomal activity within our group and is furthermore enhanced by 12 compounds obtained from literature, which have been tested in the same laboratory under identical conditions. Detailed QSAR analyses yielded models with comparable and good internal and external predictive ability. For a set of compounds as chemically diverse as the one under study, the models exhibited good coefficients of determination (R²) ranging from 0.71 to 0.85, as well as internal (leave-one-out Q² values ranging from 0.62 to 0.72) and external validation coefficients (P² values ranging from 0.54 to 0.73). The contributions of the various tested descriptors to the generated models are in good agreement with the results of previous QSAR studies and corroborate the fact that the antitrypanosomal activity of STLs is very much dependent on the presence and relative position of reactive enone groups within the molecular structure but is influenced by their hydrophilic/hydrophobic properties and molecular shape.

QSPR models for predicting generator-column-derived octanol/water and octanol/air partition coefficients of polychlorinated biphenyls

Octanol/water (K(OW)) and octanol/air (K(OA)) partition coefficients are two important physicochemical properties of organic substances. In current practice, K(OW) and K(OA) values of some polychlorinated biphenyls (PCBs) are measured using generator column method. Quantitative structure-property relationship (QSPR) models can serve as a valuable alternative method of replacing or reducing experimental steps in the determination of K(OW) and K(OA). In this paper, two different methods, i.e., multiple linear regression based on dragon descriptors and hologram quantitative structure-activity relationship, were used to predict generator-column-derived log K(OW) and log K(OA) values of PCBs. The predictive ability of the developed models was validated using a test set, and the performances of all generated models were compared with those of three previously reported models. All results indicated that the proposed models were robust and satisfactory and can thus be used as alternative models for the rapid assessment of the K(OW) and K(OA) of PCBs.

Fabrication of metal-organic framework MIL-88B films on stainless steel fibers for solid-phase microextraction of polychlorinated biphenyls

Metal-organic frameworks (MOFs) have received considerable attention as novel sorbents for sample preparation due to their fascinating structures and functionalities such as large surface area, good thermal stability, and uniform structured nanoscale cavities. Here, we report the application of a thermal and solvent stable MOF MIL-88B with nanosized bipyramidal cages and large surface area for solid-phase microextraction (SPME) of polychlorinated biphenyls (PCBs). Novel MIL-88B coated fiber was fabricated via an in situ hydrothermal growth of MIL-88B film on etched stainless steel fiber. The MIL-88B coated fiber gave large enhancement factors (757-2243), low detection limits (0.45-1.32ngL(-1)), and good linearity (5-200ngL(-1)) for PCBs. The relative standard deviation (RSD) for six replicate extractions of PCBs at 100ngL(-1) on MIL-88B coated fiber ranged from 4.2% to 8.7%. The recoveries for spiked PCBs (10ngL(-1)) in water and soil samples were in the range of 79.7-103.2%. Besides, the MIL-88B coated fiber was stable enough for 150 extraction cycles without significant loss of extraction efficiency. The developed method was successfully applied to the determination of PCBs in water samples and soil samples.

Mutagenicity test using Vibrio harveyi in the assessment of water quality from mussel farms

This work analyses the mutagenicity of seawater from mussel farms using the Vibrio harveyi mutagenicity test and its relationship with the accumulated pollutants and the development of gonadal neoplasia in mussels. Histological disorders identified as germinoma were observed in the gonad of Mytilus galloprovincialis during the period of study. The prevalence of this pathology is significantly correlated with certain levels of pollutants accumulated in mussels, mainly of PAHs and PCBs, whose toxic equivalents were calculated as EROD induction equivalency. The mutagenicity and toxicity of the water surrounding mussel's farms is clearly correlated with the pollutants accumulated and with the neoplasia prevalence in mussels. Such correlations are corroborated by a multivariate analysis. Our results conclude with the utility of V. harveyi test as an optimal and rapid method in the monitoring of the quality of the water from mussel farms and as a tool to control the risks of pollution on mussel production and its safety for human food.

Organochlorine compounds in mussels cultured in the Ría of Vigo: accumulation and origin

This paper analyzes the influence of mussel physiological conditions on bioaccumulation of organochlorine pollutants. A direct relationship between reproductive stage, lipid content and accumulation of PCBs, DDTs and HCHs was observed. The organochlorine compounds accumulated by mussels cultured in the Ría of Vigo show levels below the limits set by the European legislation for human consumption, ranging between 12.50-58, 2.21-10.80 and 0.50-2.69 μg kg(-1) dry weight for PCBs, DDTs and HCHs, respectively. Other organochlorine pesticides normally present in estuarine areas, such as hexachlorobenzene (HCB), aldrin, chlordane and nonachlor were not detected. The proportion of PCBs, between 2 and 7 times higher than OCPs, indicates a pollution of predominantly industrial origin in the sampling area. Several molecular indices were used to identify the source of accumulated OCPs by Mytilus, showing recent inputs of technical DDT, mainly in summer-autumn, and continued discharges of lindane. On the other hand, other pesticides containing DDT impurities, such as dicofol, can contribute to DDT pollution in the Ría of Vigo. Multivariate analysis suggests the usefulness of including physiological parameters such as the gonad condition index and lipid content of sentinel organisms in environmental biomonitoring of lipophilic pollutants, as well as in the determination of their origin.

Compound-class specific estimation of solid organic compound vapour pressure and aqueous solubility from simple molecular structure descriptors and the temperature of melting

For many solid organic compounds, experimental data for their aqueous solubility and vapour pressure are lacking. Therefore, estimation procedures for these compound properties are needed. On theoretical grounds, this study derives a general compound-class specific estimation procedure for solid organic compound aqueous solubility and vapour pressure. The estimation procedure uses a linear combination of simple molecular descriptors for the molecular structure variation within the compound class and a polynomial for the temperature of melting. This procedure is applied to the vapour pressure of polycyclic aromatic hydrocarbons (PAHs), alkylated PAHs, polychlorinated dibenzo-p-dioxins and biphenyls and to the aqueous solubility of PAHs, methylated PAHs, chlorinated benzenes, polychlorinated and polybrominated biphenyls, chlorinated phenols, cresols, and chlorinated 2-methoxyphenols. The standard error of the solid vapour pressure or aqueous solubility estimates from the various compound-class specific regression equations was about 0.2 log units. For PAHs, chlorobenzenes, and PCBs used in the present study, aqueous solubility estimated from the regression equations taking the temperature of melting equal to 298 K, i.e. assuming that the compounds are in a hypothetical liquid state, was equal, within 0.1-0.3 log units to the subcooled liquid solubility estimated from literature regression equations.

A new approach on estimation of solubility and n-octanol/water partition coefficient for organohalogen compounds

The aqueous solubility (logW) and n-octanol/water partition coefficient (logP_OW) are important properties for pharmacology, toxicology and medicinal chemistry. Based on an understanding of the dissolution process, the frontier orbital interaction model was suggested in the present paper to describe the solvent-solute interactions of organohalogen compounds and a general three-parameter model was proposed to predict the aqueous solubility and n-octanol/water partition coefficient for the organohalogen compounds containing nonhydrogen-binding interactions. The model has satisfactory prediction accuracy. Furthermore, every item in the model has a very explicit meaning, which should be helpful to understand the structure-solubility relationship and may be provide a new view on estimation of solubility.

Quantum mechanical predictions of the Henry's law constants and their temperature dependence for the 209 polychlorinated biphenyl congeners

The Henry's law constants (HLCs) for all 209 polychlorinated biphenyl (PCB) congeners were predicted at 25 degrees C using the quantum mechanical (QM) continuum solvation models COSMO-SAC and SM6, and trends were examined. COSMO-SAC HLCs were also predicted for all congeners at 4, 11, 18, and 31 degrees C. The temperature dependences of the HLCs were used to calculate enthalpy of solvation (deltaHs) values. At 25 degrees C, COSMO-SAC and SM6 predicted similar values of the HLC, which are consistent with all but one of the available sets of measurements, and have smaller root-mean-square prediction errors than other models tested. This supports the validity of the QM values, and the recommendation of their use in environmental transport and fate models. Intercongener trends in the HLCs appear to be dominated by the strength of PCB-water polar interactions. The COSMO-SAC predictions between 4 and 31 degrees C indicate that the temperature dependence of the HLC is similar for all congeners. At low temperatures, the HLC predictions for several heavy congeners are substantially higher than recently reported measurements, supporting claims in the literature that these low-temperature data are inaccurate.

QSPR/QSAR models for prediction of the physicochemical properties and biological activity of polybrominated diphenyl ethers

Polybrominated diphenyl ethers (PBDEs) are a group of important persistent organic pollutants. In the present study, geometrical optimization and electrostatic potential calculations have been performed for all 209 PBDE congeners at the HF/6-31G level of theory. A number of statistically-based parameters have been obtained. Linear relationships between gas-chromatographic relative retention time (RRT), n-octanol/air partition coefficient (lgK(OA)), 298 K supercooled liquid vapour pressures (lgp(L)), Henry's law constant (lgH) and Ah receptor binding affinity (-lgRBA) of PBDEs and the structural descriptors have been established by multiple regression method. The result shows that the quantities derived from electrostatic potential V(s,max),V(s,min),Pi, Sigma V+(S), V-(S) , nu, sigma 2(tot), and N-(v), together with the molecular volume (Vmc) can be well used to express the quantitative structure-property relationships of PBDEs, which proves the general applicability of this parameter set to a great extent. Good predictive capabilities have also been demonstrated. Based on these equations, the predicted values have been presented for those PBDE congeners whose experimentally determined physicochemical properties are unavailable. The QSAR model for the Ah receptor binding affinity is relatively poor, which can be ascribed to the complexity of factors which affect biological activity and the limitations of the present parameter set in describing steric characters of the molecule.

Prediction of environmental partition coefficients and the Henry's law constants for 135 congeners of chlorodibenzothiophene

Polychlorinated dibenzothiophenes (PCDTs) could be classified as persistent organic pollutants (POPs) in the environment and are particularly interesting due to their structural resemblance to highly toxic dioxins. We show here some basic environmental properties such as n-octanol water (K(OW)), n-octanol/air (K(OA)) and air/water (K(AW)) partition coefficients as well as Henry's law constants (K(H)) for all 135 congeners of chlorodibenzothiophene. Predictions were made by regression of principal components (PCR) and with aid of a set of standard chemicals, for which physical-chemical properties are well featured. Computed K(OW), K(OA), K(AW) and K(H) values for mono-CDTs ranged, respectively, between 4.66 and 4.71, 7.48 and 7.55, -2.84 and -2.82, 3.56 and 3.74; for di-CDTs between 5.02 and 5.28, 8.03 and 8.29, -3.01 and -2.95, 2.42 and 2.75; for tri-CDTs between 5.53 and 5.70, 8.65 and 8.87, -3.2 and -3.11, 1.58 and 1.92; for tetra-CDTs between 5.95 and 6.13, 9.27 and 9.50, -3.39 and -3.27, 1.02 and 1.33; for penta-CDTs between 6.38 and 6.51, 9.88 and 10.05, -3.54 and -3.45, 0.72 and 0.88; for hexa-CDTs between 6.83 and 6.97, 10.54 and 10.66, -3.72 and -3.64, 0.47 and 0.56; for hepta-CDTs between 7.28 and 7.35, 11.12 and 11.20, -3.81 and -3.87, 0.33 and 0.38; for octa-CDT 7.74, 11.78, -4.04 and 0.23. An estimated value of the three types of partition coefficient and Henry's law constants suggest that polychlorinated dibenzothiophenes are lipophilic and semi-volatile persistent organic pollutants. Their mobility in the environment seems to be very similar to that of some well-known POPs such as polychlorinated dibenzofurans, -dibenzo-p-dioxins, and -biphenyls or organochlorine pesticides.

Water solubility enhancement effects of some polychlorinated organic pollutants by dissolved organic carbon from a soil with a higher organic carbon content

To elucidate the role of a soil humic acid (HA) in the transport of polychlorinated organic pollutants (PCOPs), such as polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans and coplanar-polychlorinated biphenyls, their partition coefficients (Kdoc) into an HA were compared with their adsorption coefficients (KOC) for a soil with a higher organic carbon (OC) content. The soil sample (ando soil) used in the present study was collected in the same location as the HA. The log Kdoc values were positively correlated with logarithm of octanol-water partition coefficients (log KOW) of the PCOPs, indicating that the partitioning of PCOPs into the HA was mainly due to hydrophobic interactions. However, the correlation between log Kdoc and log KOC was negative. This can be attributed to the enhanced water solubility of the PCOPs as the result of the dissolved organic matter from the soil. That is, when the more hydrophobic PCOPs with higher log KOW values are partitioned into the HA, then the larger quantities of PCOPs that are partitioned into the HA are able to dissolve in the aqueous phase. These results suggest that, in a soil with a higher OC content, the HA can serve as more effective carrier of PCOPs from the soil to an aquatic environment.

Henry's law constant of hydrocarbons in air-water system: the cavity ovality effect on the non-electrostatic contribution term of solvation free energy

In this study, a quantitative structure-property relationship (QSPR) model for the prediction of Henry's law constants of aliphatic hydrocarbons in air-water system has been developed, based on a data-set of 189 compounds. The well-known linear thermodynamic relation between the logarithm of Henry's law constant and solvation free energy has been used for developing the model. It is emphasised that the solvent-accessible surface area (SASA) descriptor is not adequate for predicting the solvation free energy of a wide range of aliphatic hydrocarbons; there are many compounds that have the same solvent-accessible surface area with different solvation free energy. Therefore, we have introduced cavity ovality as a good descriptor of molecular cavity shape factor. The root mean square error (RMSE) of the QSPR regression model based on SASA improves from 0.40 to 0.22 by introducing the cavity ovality descriptor. The QSPR linear ovality model has good statistical parameters (r(2) = 0.90). To emphasise the significant effect of the new descriptor, a non-linear neural network model with only two nodes in the hidden layer was developed, and also yielded a RMSE of 0.22.

High-resolution gas chromatography retention data as a basis for estimation of the octanol–water distribution coefficients (Kow) of PCB: the effect of experimental conditions

The semi-experimental approach to approximating physicochemical data relevant to environmental distribution (vapor pressure and gas-octanol distribution) by correlation with gas chromatography (GC) retention data has been extended to the determination of Kow values. We estimated Kow values >10(4) for polychlorinated biphenyls (PCB), which are often derived by liquid chromatography, by correlation with gas chromatographic retention data. Selecting a set of reference compounds with known Kow values for relative retention time (RRT) correlation enables easy and accurate semi-empirical calculation of further Kow values for a given group of congeners. The RRT/log Kow correlation is validated in this paper with regard to the following gas chromatographic conditions: (1) isothermal versus temperature-programmed elution, (2) the possible effect of the polarity of the stationary phase, and (3) the effect of the format of the standardized GC retention data. The advantages of our Kow(GC) method can be summarized as follows: complex mixtures can be analyzed, only amounts in the nanogram-range or less are required, Kow values of isomers can be determined and the exact structure of compounds need not be known. Normalized GC retention data of persistent organic pollutants are readily available. The quality of the Kow values obtained by the GC method compares well with that for other Kow estimation methods. It depends mainly on the accuracy of the Kow data of the structurally correlated compounds used as standards for the correlation cohort. The Kow(GC) data for all 209 PCB congeners are given.

Solvation parameters for the 209 PCBs: calculation of physicochemical properties

Descriptors in the Abraham equations for all the 209 PCBs have been obtained from literature chromatographic data. The six descriptors suffice for the prediction of water to octanol partitions, and for the prediction of various water to solvent and gas to solvent partitions, solubility in water, and water to micelle partition. For water to octanol, gas to dry octanol, gas to wet octanol, solubility of the solid PCBs in water, and gas to water processes, our predictive values agree excellently with the adjusted experimental values of Li et al. for sixteen particular PCBs, and with other experimental observations. We use our predictions to shed light on Henry's law constants of PCBs in water, which are the inverse of gas to water partitions.