Arsenic distribution and partitioning in multiple media in a typical catchment in the Qinghai-Tibetan plateau: A comparison between freshwater and saltwater lakes.

Arsenic (As) has been widely detected in surface media on the Qinghai-Tibetan Plateau (QTP); however, the differences in the As distribution and partitioning characteristics between freshwater and saltwater lakes remain poorly understood. To determine the distribution and partitioning characteristics of As, multimedia environmental samples were collected from a typical small watershed consisting of a river, wetland, and both freshwater and saltwater lakes on the QTP. Results showed that freshwater systems, represented by Hurleg Lake, were high in particulate arsenic (PAs) and low in dissolved arsenic (DAs), whereas the saltwater system represented by Tosen Lake, exhibited the reverse distribution. This discrepancy in As distribution was primarily attributed to evaporation enrichment, competitive adsorption of HCO3- and pH variations, as suggested by correlation analysis and stable isotopic composition of water. In the stratified Tosen Lake, an increasing trend of DAs in the water column was observed, potentially driven by the reductive dissolution of Fe (hydr)oxides and bacterial sulfate reduction in the anoxic bottom hypolimnion. Conversely, Hurleg Lake maintained oxic conditions with stable DAs concentrations. Notably, PAs was elevated in the bottom layer of both lakes, possibly due to uptake/adsorption by biogenic particles, as indicated by high levels of chl.α and suspended particulate matter. These findings offer insights into the potential future impact of climate change on As mobilization/redistribution in arid plateau lakes, with implications for management policies that regulate As pollution.

Impact of low molecular weight organic acids on heavy metal(loid) desorption in biochar-amended paddy soil.

Low molecular weight organic acids (LMWOAs) are important soil components and play a key role in regulating the geochemical behavior of heavy metal(loid)s. Biochar (BC) is a commonly used amendment that could change LMWOAs in soil. Here, four LMWOAs of oxalic acid (OA), tartaric acid (TA), malic acid (MA), and citric acid (CA) were evaluated for their roles in changing Cd and SB desorption behavior in contaminated soil with (S1-BC) or without BC (S1) produced from Paulownia biowaste. The results showed that OA, TA, MA, and CA reduced soil pH with rising concentrations, and biochar partially offset the pH reduction by LMWOAs. The LMWOAs reduced Cd desorption from the soil at low concentrations but increased Cd desorption at high concentrations, and CA was the most powerful in this regard. The LMWOAs had a similar effect on Sb desorption, and CA was the most effective species of LMWOAs. Adding BC to the soil affects Cd and Sb dynamics by reducing the Cd desorption but increasing Sb desorption from the soil and increasing the distribution coefficient (Kd) values of Cd but lowering the Kd values of Sb. This study helped understand the effects of LMWOAs on the geochemical behavior of Cd and Sb in the presence of biochar, as well as the potential risks of biochar amendment in enhancing Sb desorption from contaminated soil.

Characterization of piroctone olamine for topical delivery to the skin.

OBJECTIVE: Dandruff and its more severe related condition, seborrheic dermatitis affects a high proportion of the population at some point in their life. Piroctone olamine, also known as Octopirox® (OPX) is the monoethanolamine salt of piroctone and is an antifungal agent widely used for the management of dandruff. The aim of the present work was to characterize the physicochemical properties of piroctone olamine and to conduct pre-formulation studies for the development of novel topical formulations of this active. METHODS: An HPLC method was developed and validated for the analysis of OPX. The melting point was determined using the DSC Q2000 (TA Instruments, USA). The distribution coefficient (logD(O/PBS) ) and partition coefficient (log Po/w ) was determined in phosphate-buffered saline (PBS) AND deionized (DI) water using the shake flask method. All experiments were performed at room temperature. The solubility was determined experimentally by adding amount of active to a solvent. The samples were kept at 32° ± 1°C for 48 h in a water bath. The stability of the compound was determined in a range of solvents by preparing solutions of 1 mg mL-1 in the relevant solvents. These solutions were kept and stirred throughout the experiment at 32 ± 1°C, and aliquots were taken at 24, 48 and 96 h. RESULTS: The HPLC method was developed successfully; however, samples at the lower end of the calibration curve showed lower degrees of precision and accuracy. Based on experiments with DSC, the melting point was observed at an onset temperature of 132.4°C. The LogD was determined to be 1.84. The compound had the highest solubility in methanol (278.4 mg mL-1 ) and propylene glycol (PG), with a value of 248.8 mg mL-1 . The lowest solubility for OPX was in dimethyl isosorbide (9.9 mg mL-1 ), Labrafac™ (3.6 mg mL-1 ) and isostearyl isostearate (0.5 mg mL-1 ). Over the 4 days, OPX showed stability in ethanol and PG, while a notable decrease in OPX was observed in PBS and DI water at 32 ± 1°C. CONCLUSION: The physicochemical properties of OPX were characterized to find suitable excipients able to target the epidermis for topical delivery. Building on these findings, future work will focus on the development of novel topical formulation of OPX.

OBJECTIF: la production de pellicules et la maladie plus grave qui y est apparentée, la dermatite séborrhéique, touchent une grande partie des personnes à un moment donné de leur vie. La piroctone olamine, également connue sous le nom d'Octopirox® (OPX), est le sel de monoéthanolamine de la piroctone. Il s'agit d'un agent antifongique largement utilisé pour le traitement des pellicules. L'objectif de ce travail était de caractériser les propriétés physicochimiques de la piroctone olamine et de mener des études de préformulation pour le développement de nouvelles formulations topiques de ce principe actif. MÉTHODES: une méthode de chromatographie liquide à haute performance (CLHP) a été développée et validée pour l'analyse de l'OPX. Le point de fusion a été déterminé à l'aide du calorimètre à balayage différentiel (Differential Scanning Calorimetry, DSC) Q2000 (TA Instruments, États-Unis). Le coefficient de distribution (logD(Octanol/PBS) ) et le coefficient de partage (log Poctanol/eau , ou log Poe ) ont été déterminés dans le tampon phosphate salin (phosphate buffered saline, PBS) et dans l'eau désionisée (deionised, DI) à l'aide de la méthode par agitation en flacon. Toutes les expériences ont été réalisées à température ambiante. La solubilité a été déterminée de manière expérimentale. Une certaine quantité du principe actif a été ajoutée au solvant. Les échantillons ont été conservés à une température de 32 °C ± 1 °C pendant 48 h dans un bain-marie. La stabilité du composé a été déterminée à l'aide d'une gamme de solvants. Des solutions de 1 mg mL−1 ont été préparées dans les solvants correspondants. Les solutions ont été conservées et agitées tout au long de l'expérience à une température de 32°C ± 1°C. Des aliquotes ont été prélevées après 24, 48 et 96 h. RÉSULTATS: la méthode CLHP a été développée avec succès. Toutefois, les échantillons situés dans la partie inférieure de la courbe d'étalonnage ont montré des degrés inférieurs de précision et d'exactitude. Sur la base des expériences avec le DSC, le point de fusion a été observé à une température initiale de 132,4°C. Le LogD a été déterminé à 1,84. Le composé présentait la solubilité la plus élevée dans le méthanol (278,4 mg mL−1 ) et le propylène glycol (PG), avec une valeur de 248,8 mg mL−1 . L'OPX présentait la solubilité la plus faible dans l'isosorbide de diméthyle (9,9 mg.mL−1 ), le LabrafacTM (3,6 mg mL−1 ) et l'isostéarate d'isostéaryle (0,5 mg mL−1 ). Sur les 4 jours, l'OPX a montré une stabilité dans l'éthanol et le PG, tandis qu'il a diminué de manière notable dans le PBS et l'eau désionisée à une température de 32°C ± 1°C. CONCLUSION: les propriétés physicochimiques de l'OPX ont été caractérisées afin de trouver des excipients appropriés capables de cibler l'épiderme dans le cadre d'une administration topique. En s'appuyant sur ces résultats, les travaux futurs se concentreront sur le développement d'une nouvelle formulation topique de l'OPX.

Predicting octanol/water partition coefficients and pKa for the SAMPL7 challenge using the SM12, SM8 and SMD solvation models.

Blind predictions of octanol/water partition coefficients and pKa at 298.15 K for 22 drug-like compounds were made for the SAMPL7 challenge. Octanol/water partition coefficients were predicted from solvation free energies computed using electronic structure calculations with the SM12, SM8 and SMD solvation models. Within these calculations we compared the use of gas- and solution-phase optimized geometries of the solute. Based on these calculations we found that in general the use of solution phase-optimized geometries increases the affinity of the solutes for water as compared to octanol, with the use of gas-phase optimized geometries resulting in the better agreement with experiment. The pKa is computed using the direct approach, scaled solvent-accessible surface model, and the inclusion of an explicit water molecule, where the latter two methods have previously been shown to offer improved predictions as compared to the direct approach. We find that the use of an explicit water molecule provides superior predictions, and that the predicted macroscopic pKa is sensitive to the employed microstates.

Comparison of logP and logD correction models trained with public and proprietary data sets.

In drug discovery, partition and distribution coefficients, logP and logD for octanol/water, are widely used as metrics of the lipophilicity of molecules, which in turn have a strong influence on the bioactivity and bioavailability of potential drugs. There are a variety of established methods, mostly fragment or atom-based, to calculate logP while logD prediction generally relies on calculated logP and pKa for the estimation of neutral and ionized populations at a given pH. Algorithms such as ClogP have limitations generally leading to systematic errors for chemically related molecules while pKa estimation is generally more difficult due to the interplay of electronic, inductive and conjugation effects for ionizable moieties. We propose an integrated machine learning QSAR modeling approach to predict logD by training the model with experimental data while using ClogP and pKa predicted by commercial software as model descriptors. By optimizing the loss function for the ClogD calculated by the software, we build a correction model that incorporates both descriptors from the software and available experimental logD data. Additionally, we calculate logP from the logD model using the software predicted pKa's. Here, we have trained models using publicly or commercial available logD data to show that this approach can improve on commercial software predictions of lipophilicity. When applied to other logD data sets, this approach extends the domain of applicability of logD and logP predictions over commercial software. Performance of these models favorably compare with models built with a larger set of proprietary logD data.

Comment on the calculation of equilibrium constant and thermodynamic parameters by the distribution coefficient in Environmental Research 203 (2022) 111814.

This comment discussed the calculation of equilibrium constant and thermodynamic parameters in the paper of Kayalvizhi et al. (2022). This paper is of high academic value, however, there are some calculation and quotation errrors. The equilibrium constant K evolved from the distribution coefficient has a dimension of L/g, which is not the standard equilibrium constant, therefore, it cannot be used to calculate the thermodynamic parameters. This comment firstly analyzed the calculation errors made by Kayalvizhi et al. (2022), then established the relationship between distribution coefficient and standard equilibirum constant, and recalculated the thermodynamic parameters by using the correct distribution coefficient equation. As a research paper, authors not only provide the originality and novelty, but also give its correct results. This comment can bring to the attention of readers, authors, editors and reviewers about the thermodynamic calculation. At the same time, it is helpful to avoid the misuse and propagation of the incorrect equation in the area of adsorption thermodynamics.

Improved Adaptive Kalman-Median Filter for Line-Scan X-ray Transmission Image.

With their wide application in industrial fields, the denoising and/or filtering of line-scan images is becoming more important, which also affects the quality of their subsequent recognition or classification. Based on the application of single source dual-energy X-ray transmission (DE-XRT) line-scan in-line material sorting and the different horizontal and vertical characteristics of line-scan images, an improved adaptive Kalman-median filter (IAKMF) was proposed for several kinds of noises of an energy integral detector. The filter was realized through the determination of the off-line noise total covariance, the covariance distribution coefficient between the process noise and measurement noise, the adaptive covariance scale coefficient, calculation scanning mode and single line median filter. The experimental results show that the proposed filter has the advantages of simple code, good real-time control, high precision, small artifacts, convenience and practicality. It can take into account the filtering of high-frequency random noise, the retention of low-frequency real signal fluctuation and the preservation of shape features. The filter also has a good practical application value and can be improved and extended to other line-scan image filtering scenarios.

Soil heterogeneity influence on the distribution of heavy metals in soil during acid rain infiltration: Experimental and numerical modeling.

Acid rain is a global environmental problem that mobilizes heavy metals in soils, while the distribution and geochemical fraction of heavy metals during acid rain infiltration in heterogeneous soils are still unclear. In this study, we performed column experiments to investigate the distribution and geochemical fraction of Cu, Pb, Ni and Cd in heterogeneously layered soils during continuous acid rain infiltration. Chloride ion used as a conservative tracer was found to be uniformly distributed during acid rain infiltration, showing insignificant preferential flow effects in the column. In contrast, however, the distribution of heavy metals was highly non-uniform, especially in the silty soil at the lower part of the column, indicating a heterogeneous distribution of adsorption capacity. In addition, in the control experiments with neutral rain infiltration, uniform distribution of heavy metals was observed, indicating that the heterogeneous distribution of adsorption coefficient during acid rain infiltration was mainly caused by different pH buffering capacities. A numerical model considering water flow and solute transport was developed, where the average water-solid distribution coefficient (Kd) in Layer 2 was only 1.5-12.5% of that in Layer 1 during acid rain infiltration. The model could predict the variation of heavy metal concentrations in soil with the majority of error less than 35%, confirming that different Kd induced the heterogeneous distribution of heavy metals. In addition, the geochemical fraction of heavy metals in the upper coarse sand layer remained stable, while the acid-extractable fractions in the lower loam and silt loam layer gradually increased. Our findings suggest that soil heterogeneity, especially chemical heterogeneity affected by rainfall acidity, has an important influence on the infiltration, migration and geochemical fraction of heavy metals in soils. This study could help guide the risk assessment of heavy metal-contaminated sites that were polluted by acid rain or landfill leachate.

Influence of Organic Matter on the Sorption of Cefdinir, Memantine and Praziquantel on Different Soil and Sediment Samples.

Pharmaceuticals are known for their great effects and applications in the treatment and suppression of various diseases in human and veterinary medicine. The development and modernization of science and technologies have led to a constant increase in the production and consumption of various classes of pharmaceuticals, so they pose a threat to the environment, which can be subjected to the sorption process on the solid phase. The efficiency of sorption is determined by various parameters, of which the physicochemical properties of the compound and the sorbent are very important. One of these parameters that determine pharmaceutical mobility in soil or sediment is the soil−water partition coefficient normalized to organic carbon (Koc), whose determination was the purpose of this study. The influence of organic matter, suspended in an aqueous solution of pharmaceutical (more precisely: cefdinir, memantine, and praziquantel), was studied for five different types of soil and sediment samples from Croatia. The linear, Freundlich, and Dubinin−Raduskevich sorption isotherms were used to determine specific constants such as the partition coefficient Kd, which directly describes the strength of sorbate and sorbent binding. The linear model proved to be the best with the highest correlation coefficients, R2 > 0.99. For all three pharmaceuticals, a positive correlation between sorption affinity described by Kd and Koc and the amount of organic matter was demonstrated.

The use of the IAEA MARIS database in determining the variability of sediment distribution coefficients in the marine environment and potential implications for marine dispersion modelling.

A prototype tool has been developed for deriving sediment distribution coefficients,Kd, in the marine environment by harvesting simultaneous measurements of activity concentrations of radionuclides in seawater and sediments based on the International Atomic Energy Agency's Marine Radioactivity Information System (MARIS). As a case study, theKdvariability in the Baltic Sea was investigated as this region has been extensively monitored by HELCOM since 1984 resulting in a comprehensive dataset with good spatial and temporal coverage and required ancillary parameters. The prototype tool was used to derive a dataset ofin-situapparentKd(a)values derived from measurements of seawater and sediment in quasi-equilibrium conditions from the Baltic Sea over a period of approximately 35 years. For Cs, a comprehensive analysis of the Baltic SeaKd(a)dataset was undertaken, focusing on the temporal trend ofKd(a)and comparing the results toKdvalues derived elsewhere. For Sr and Pu, for which there were fewer data records available a more rudimentary analysis was carried out. The CsKd(a)median values derived from137Cs data in this study were estimated to be 2154 l kg-1for seabed sediment and 10 000 l kg-1for suspended sediment. The value derived for seabed sediment is in good agreement with the previously recommended ocean margin CsKdvalue of 4000 l kg-1. The analysis demonstrated the important distinction in the Baltic Sea betweenKdvalues for seabed sediment and suspended sediments, which differed by an order of magnitude. The analysis also highlighted the dependence ofKdvalues on the variation in both the salinity of seawater and the type of seabed sediment. Such variability can significantly influence outcomes when modelling the behaviour of radionuclides in marine dispersion modelling.

SAMPL7 physical property prediction from EC-RISM theory.

Inspired by the successful application of the embedded cluster reference interaction site model (EC-RISM), a combination of quantum-mechanical calculations with three-dimensional RISM theory to predict Gibbs energies of species in solution within the SAMPL6.1 (acidity constants, pKa) and SAMPL6.2 (octanol-water partition coefficients, log P) the methodology was applied to the recent SAMPL7 physical property challenge on aqueous pKa and octanol-water log P values. Not part of the challenge but provided by the organizers, we also computed distribution coefficients log D7.4 from predicted pKa and log P data. While macroscopic pKa predictions compared very favorably with experimental data (root mean square error, RMSE 0.72 pK units), the performance of the log P model (RMSE 1.84) fell behind expectations from the SAMPL6.2 challenge, leading to reasonable log D7.4 predictions (RMSE 1.69) from combining the independent calculations. In the post-submission phase, conformations generated by different methodology yielded results that did not significantly improve the original predictions. While overall satisfactory compared to previous log D challenges, the predicted data suggest that further effort is needed for optimizing the robustness of the partition coefficient model within EC-RISM calculations and for shaping the agreement between experimental conditions and the corresponding model description.

Potentially toxic elements leachates from cigarette butts into different types of water: A threat for aquatic environments and ecosystems?

Trillions of cigarette butts (CBs) are released into the environment and the leached potentially toxic elements (PTEs) from CBs may contaminate the environments. In this study, the leaching of PTEs including both heavy metals and metalloids (metal(loid)s) from CBs into deionized water (DW), tap water (TW), and seawater (SW) was checked during the different contact times (from 60 min to 60 days). According to the results, PTEs were leached from CBs into different water samples. However, there were no significant differences between leachates in DW and TW samples (p > 0.05). The results of the distribution coefficient indicated the high tendency of most PTEs to enter the liquid phase. The levels of leached PTEs into DW and TW exceeded the standards of surface freshwater to maintain aquatic life. Although the maximum level of leached metal(loid)s into DW, TW, and SW occurred at different times, for each type of water sample no significant differences were found among the levels of most PTEs at various contact times. Based on the results, the levels of leached metal(loid)s from CBs in seawater peak soon after being released into the water, while for the freshwater, they occur after some days. This phenomenon could possibly have short-term and long-term effects on marine and freshwater organisms, respectively. Due to the ability of the dissolved PTEs to integrate into the aquatic/terrestrial food web and threaten human health, some control measures regarding the disposal of CBs are necessary.

Preformulation studies of thymopentin: analytical method development, physicochemical properties, kinetic degradation investigations and formulation perspective.

Thymopentin (TP5) is a synthetic pentapeptide with immunomodulatory properties. Given the previously described poor absorption of TP5, preformulation data is required to support effective formulation development. In this manuscript, an analytical method of TP5 was developed and validated to determine the aqueous solubility, stability, and Log P of TP5. Thermal properties were investigated, and chemical, physical and enzymatic degradation were evaluated. TP5 was informed to load in a microemulsion (ME) system according to the preformulation parameters and characterized for rheological behavior, droplet size, morphology and in vitro drug release. TP5 displayed high aqueous solubility (294.3 mg/mL), low Log P (-4.2) and 2% water content with a melting temperature of 193 °C. TP5 degraded rapidly in alkaline conditions, at elevated temperature, in oxidizing agents, and with UV exposure, however TP5 had a longer half-life in acidic conditions. The fastest enzymatic degradation was with Trypsin (half-life 6.3 h) compared with other digestive enzymes. The different degradation pathways followed first-order kinetics, and half-lives were obtained from the kinetic studies. The TP5 loaded ME exhibited a droplet size of 143 ± 35 nm with a Higuchi-model fitted sustained release profile for 24 h. These data justify and support the design of formulations to stabilize and enhance the absorption of TP5, with a ME formulation demonstrated.

Band-selective excitation NMR spectroscopy and quantitative time-domain analysis using Complete Reduction to Amplitude-Frequency Table (CRAFT) to determine distribution coefficients during drug development.

A sensitive quantitative 1 H NMR method for determining distribution or partition coefficients has been developed that is applicable to early drug discovery. After partitioning and equilibration, aliquots from each layer are analyzed using band-selective excitation 1 H NMR spectroscopy in regions that are free of 1-octanol and water solvent signals. Signals are quantitated directly using CRAFT software, and their amplitudes are adjusted to correct for nonuniformity within the excitation band. Using this approach, the distribution coefficients for 20 drugs present at low concentrations were determined giving values that were in excellent agreement with literature values.

Phosphorus availability and dynamics in soil affected by long-term ruzigrass cover crop.

The use of grasses as cover crops in the off-season of cash crops under no-till has been largely adopted. However, soil phosphorus (P) uptake was previously shown to be reduced when ruzigrass is introduced in the rotation, affecting the viability and sustainability of this cropping system. The objective of this study was to assess the effect of ruzigrass on soil P availability and desorption kinetics under different P fertilizer application rates. A long-term field experiment where soybean (Glycine max) has been grown in rotation with ruzigrass (Urochloa ruziziensis) or fallow for 10 years, with the application of 0, 13, and 26 kg ha-1 of P, was evaluated for two consecutive years. Soil P desorption kinetics was assessed using diffusive equilibrium (DET) and gradient in thin films (DGT) techniques, as well as the DGT-induced fluxes in soils model (DIFS). Microbial biomass P (MBP) was assessed to verify if soil solution P (PDET) was reduced due to immobilization by microorganisms. Ruzigrass reduced MBP and PDET especially when P fertilizer was applied. The concentration of labile P (PDGT) was also lower after ruzigrass than in fallow. The soil ability to resupply P to soil solution was lower after ruzigrass regardless of P rates due to a slower desorption in response to the perturbation imposed by DGT. Growing ruzigrass as cover crop in the soybean off-season decreases soil P availability regardless of P fertilizer application rates by fundamentally reducing P mobility and P resupply from soil solid phase into soil solution.

Effect on herbicide adsorption of organic forestry waste products used for soil remediation.

Organic soil amendments can be useful for improving degraded soil, but this increase in organic matter (OM) may influence adsorption of herbicides subsequently applied to the treated soil, even though the particle size of amendments and their nature differ from typical soil OM. In this study, a batch equilibrium method was used to measure adsorption of five herbicides following application to two organic media, wood pulp and sawdust, comparing these with two cropping soils. Herbicide adsorption, quantified by distribution coefficients (kd), was much higher in the two organic media than in the cropping soils. The increases in adsorption were strongly correlated to the percentage of organic carbon. When the kd was normalized to adsorption coefficients corrected for OM content (koc), variation in results between the media was greatly reduced, indicating that OM is an important factor influencing adsorption in these media. The results of this study suggest that herbicides will be less effective when applied to soils in which sawdust and wood pulp have been added. Using organic amendments to remediate soil will increase adsorption of pesticides, reducing their bio-availability and efficacy, but also reducing their tendency to leach into root zones of deep-rooted crops and into groundwater.

Prediction of partition and distribution coefficients in various solvent pairs with COSMO-RS.

Performance of COSMO-RS method as a tool for partition and distribution modeling in 20 solvent pairs-composed of neutral or acidic aqueous solution and organic solvents of different polarity, ranging from alcohols to toluene and hexane-was evaluated. Experimental partition/distribution data of lignin-related and drug-like compounds (neutral, acidic, moderately basic) were used as reference. Several aspects of partition modeling were addressed: accounting for mutual saturation of aqueous and organic phases, variability of systematic prediction errors across solvent pairs, taking solute ionization into account. COSMO-RS was found to predict extraction outcome for both ligneous and drug-like compounds in various solvent pairs fairly well without any additional empirical input. The solvent-specific systematic errors were found to be moderate, despite being statistically significant, and related to the solvent hydrophobicity. Accounting for mutual solubilities of the two liquids was proven crucial in cases where water was considerably soluble in the organic solvent. The root mean square error of a priori logP prediction varied, depending mainly on the solvent pair, from 0.2 to 0.7, overall value being 0.6 log units. The accuracy was higher in case of hydrophilic than hydrophobic solvents. The logD predictions were less accurate, due to pKa prediction being an additional source of error, and also because of the complexity of modeling the behaviour of ionic species in the two-phase system. A simple correction for partitioning of free ions was found to notably improve logD prediction accuracy in case of the most hydrophilic organic phase (butanol/water).

A metal organic framework prepared from benzene-1,3,5-tricarboxylic acid and copper(II), and functionalized with various polysulfides as a sorbent for selective sorption of trace amounts of heavy metal ions.

Novel composites were obtained via direct assembly of polysulfides (Sx2-, X = 3, 4, 6) on the surface of a metal organic framework (MOF; type benzene-1,3,5-tricarboxylic/Cu(II). They are referred to as Sx-MOFs and were used for highly selective and efficient extraction of ultra-trace amounts of heavy metal ions from aqueous solutions. The structure of the Sx-MOFs was characterized by Raman spectroscopy, FT-IR, X-ray diffraction, and scanning electron microscopy. The Raman spectra of Sx-MOF is similar to the bare MOF and shows the MOFs structure to be well retained after Sx functionalization. The selective interaction of Sx with soft metal ions and the high surface area of MOFs resulted in excellent affinity and selectivity for ions such as Hg(II). The Sx-MOFs of type S4-MOF had the highest distribution coefficient Kd value (~107) and best extraction recovery (~100%) for Hg(II). The S4-MOF also has high selectivity in the following order: Hg(II) > > Pb(II) > Zn(II) > Ni(II) > Co(II). The binding process of the metals occurs via M-S bonding. The ions were quantified by inductively coupled plasma optical emission spectrometry (ICP-OES). The detection limit for Hg(II) is 0.13 µg L-1. The S4-MOF was applied to the extraction of trace metal ions from natural and contaminated waters and data were compared with other sorbets. The results revealed that S4-MOF is an excellent adsorbent for sorption of heavy metal ions even in the presence of the relatively high concentration of other ions. Graphical abstract A composite was synthesized via direct assembly of polysulfides (Sx2-, X = 3, 4, 6) on surface of the metal organic framework (Sx-MOF) and was used for selective and efficient extraction of ultra-trace amounts of heavy metal ions from aqueous solutions.

Dioxin leaching risk assessment through selected soils by estimating distribution coefficient and breakthrough curves.

From health and environmental point of views, dioxins are important due to their toxicity and persistence. Dioxins have the potential to reside in the environment for longer time if sorbed onto the clay and organic content of the soil matrix. Their transport or leaching under certain environmental conditions such as preferential flow can increase the risk of groundwater contamination. In the current study, breakthrough curves (BTCs) against time were plotted for selected dioxin transport prediction; based on measured distribution coefficient (Kd), dispersion coefficient (D), and retardation factor (R). Three representative soil series named Burhan, Warsak, and Kunda were selected. For dibenzo-p-dioxin (DD), Kd values followed the order as: Burhan> Warsak > Kunda, while for 2-chloro dibenzo-p-dioxin (2 Cl-DD), Kd values followed an order as: Kunda > Burhan > Warsak. Dioxin transport was measured at two different linear velocities (20 and 50 cm day-1). Attainment of equilibrium was verified to be dependent upon the Kd, R, D, and chlorination on dioxin. Kunda series with low OM (0.6%), clay (0.2%), and R (377) was found to have relatively high DD transport potential under normal velocity, due to high dispersion values for its sandy nature. Under the steady or preferential flow conditions, all the plots obtained were identical irrespective of soil type and dioxin nature.

Prostaglandin H synthase kinetics in the two-phase aqueous-micellar system.

Reaction mixture for PGHS (prostaglandin-H-synthase) is a two-phase system including micellar hydrophobic phase and hydrophilic aqueous phase. Reagents added to the mixture are distributed between phases, thus concentrations of reagents dissolved in phases can differ significantly from their overall contents. Using dynamic light scattering we found that the hydrophobic phase produced by tween-20 consists of micelles, which radius (4-5nm) does not depend on either tween-20 overall content (0.1%-1% v/v) or arachidonic acid (AA) addition (10-1000µM) or PGHS addition (1µM). Tween-20 overall content changing from 0.1% to 2% v/v dramatically affected COX kinetic, but accounting AA distribution between phases allowed us to estimate "true" parameters, independent of the tween-20 overall content and the concentration of another substrate: KM(Ox) equals 9.8µM O2 in the aqueous phase or 0.0074bar in the gaseous phase, KM(AA) equals 5400µM AA in the phase of tween-20 micelles and 5400/PµM AA in the aqueous phase (P is the distribution ratio for the AA between the aqueous phase and the hydrophobic phase (P≫1000)). This approach allowed to evaluate PS, the distribution ratio for the AA between the hydrophobic phase and the PGHS active center (PS ~310). This coefficient indicates the AA selectivity toward the cyclooxygenase active center.