Phenylarsonic Acid Research Articles

Synthesis and Antitumour Activity of Hybrid Compounds Based on 4-Aminophenylarsonic Acid and Spatially Hindered Phenols.

One of the main modern approaches to the creation of effective drugs is the design of new biologically active substances containing two or more pharmacophore groups in their structure. In recent years, there have been many publications on the synthesis and study of biological activity, including antitumour activity, of new organo-arsenic compounds. It is known that spatially hindered phenols can also have antitumor activity, so the synthesis and study of hybrid compounds based on organo-arsenic compounds and spatially hindered phenols is a relevant area of research. In this work, the modification of 4-aminophenylarsonic acid with 3,5-di-tert-butyl-4-hydroxybenzylacetate was carried out. In contrast to a similar transformation of 2-aminophenylarsonic acid, in this case it was possible to obtain both mono- and di-benzyl derivatives of the acid. Using the Zandmeyer method, the oxime isatin containing an arsonic acid fragment in the fifth position of the heterocycle was synthesised. Azo derivatives containing fragments of para-aminophenylarsonic acid and sterically hindered phenols were obtained. 4-((3,5-Di-tert-butyl-2-hydroxyphenyl)diazenyl)phenylarsonic acid was isolated in pure form. At the same time, it was found that the reaction of the diazonium azo salt of 4-aminophenylarsonic acid with 2-hydroxymethyl-4-tert-butylphenol proceeds in two directions. In addition to the classical diazotisation reaction at the 6-position of 2-hydroxymethyl-4-tert-butylphenol, a diazotisation accompanied by a dehydroxymethylation process occurs. The obtained compounds showed cytotoxic activity against human tumor cell lines M-HeLa (cervical epithelioid carcinoma) and HuTu 80 (duodenal adenocarcinoma cells). The most promising is the sodium salt of 4-((3,5-di-tert-butyl-2-hydroxyphenyl)diazenyl)phenylarsonic acid, which is superior to Tamoxifen and 5-fluorouracil in terms of selectivity index towards M-HeLa and HuTu 80 cells.

Self-assembly of organoarsonic acid functionalized polyoxovanadate cage from cap-like building block

The cap-like {AsV4As4} is a commonly appearing building block in the assembly of organoarsonic acid functionalized polyoxovanadate cages, but to the best of our knowledge, the isolated {AsV4As4} has not been obtained until now. Herein, we have successfully synthesized the cap-like [(CH3)2NH2]2[DMF⊂V4O5(C6H5AsO3)3(C6H5AsO3H)2] ({AsV4As4}) for the first time. A cage-like [(CH3)2NH2]H3[CH3OH⊂V12O14(OH)4(C6H5AsO3)10]·7H2O ({(V2)2(AsV4As4)2}) composed of two {AsV4As4} caps and two {V2} units was obtained by reacting {AsV4As4} with an additional V source. In addition, a similar cage-like H6[CH3OH, H2O⊂V12O14(OH)4(O3AsC6H4-2-NH2)10]SO4·DMF ({(V2)2(AsV4As4-NH2)2}) was obtained by using 2-aminophenylarsonic acid instead of phenylarsonic acid. The three organoarsonic acid functionalized polyoxovanadates have been characterized by single crystal X-ray diffraction, elemental analysis, powder X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy. In addition, magnetic property studies indicate that there is antiferromagnetic coupling interaction between V centers of the three compounds.

Progress of photocatalytic oxidation-adsorption synergistic removal of organic arsenic in water.

Photocatalytic oxidation-adsorption synergistic treatment of organic arsenic pollutants is a promising wastewater treatment technology, which not only degrades organic arsenic pollutants by photocatalytic degradation but also removes the generated inorganic arsenic by adsorption. This paper compares the results of photocatalytic oxidation-adsorption co-treatment of organic arsenic pollutants such as monomethylarsonic acid, dimethylarsinic acid, phenylarsonic acid, p-arsanilic acid, and 3-nitro-4-hydroxyphenylarsonic acid on titanium dioxide, goethite, zinc oxide, and copper oxide. It examines the influence of the morphology of organic arsenic molecules, pH, coexisting ions, and the role of natural organic matter. The photocatalytic oxidation-adsorption co-treatment mechanism is investigated, comparing the hydroxyl radical oxidation mechanism, the hydroxyl radical and superoxide anion radical cooxidation mechanism, and the hydroxyl radical and hole cooxidation mechanism. Finally, the future prospects of metal oxide photocatalytic materials and the development of robust and efficient technologies for removing organic arsenic are envisioned.

Element recycling in arsoles

Abstract The incorporation of heteroatoms serves as a potent tool for the development of advanced materials, and arsenic (As) has recently become increasingly popular in the field of conjugated molecules. However, the potential toxicity of As-containing materials upon disposal remains a concern. In this study, we propose a chemical recycling approach for the As in arsoles. The oxidative ring-opening reaction of arsoles proceeds efficiently under ultraviolet irradiation, leading to the production of phenylarsonic acid, a precursor of arsoles.

Degradation of phenylarsonic acid in phenylarsenic chemical warfare agents by Fe-modified CNT electroactive filter activating peroxymonosulfate: Performance and mechanism

Phenylarsonic acid (PAA) is a major organic arsenic contaminant in abandoned arsenic-based chemical weapons areas, and poses threats to the water environment due to potential arsenic pollution; However, relevant remediation methods are lacking. In this study, a Fe-modified carbon nanotube (CNT) electroactive filter was developed for peroxymonosulfate (PMS) activation towards PAA decontamination. The developed system can realise synchronous adsorption and oxidation of PAA (85.6 %) with PMS (1.5 mM) under electric field assistance (-1 V). Radicals (SO4•– and HO•) and non-radicals (1O2) contributed to PAA degradation and the formation of As (V). The preferable PAA degradation efficiency stemmed from facilitated Fe (II)/Fe (III) redox cycles with applied electric field assistance. Secondary inorganic arsenic could also be immobilised as FeOAs bonds on the Fe-modified CNT filter. Additionally, PAA degradation pathways were proposed based on density functional theory (DFT) and intermediate identification. The system efficacy was also evaluated by regulating the critical operational parameters (applied voltage, flow rate, PMS concentration, pH and co-existing anions) and using complicated matrices (tap water and lake water). Our findings provide a new solution for PAA remediation and simultaneous immobilisation of secondary inorganic arsenic by combining membrane, PMS activation and electrochemical methods.

In situ interface oxidation-adsorption by ferrate (VI)/PMS self-excitation: Unique dual-reaction platform for phenylarsonic acid degradation and immobilization

In this study, we dexterously constructed a unique in situ interface oxidation–adsorption dual-reaction platform through the self-excitation of ferrate (Fe(VI))/peroxymonosulfate (PMS) for phenylarsonic acid (PAA) and inorganic As(V) removal. When the molar ratio of Fe(VI)/PMS was 1:2, 80% degradation of PAA could be achieved within 180 min and the apparent constant value of the reaction rate (kobs) would reach up to 0.185 min−1. 1O2 and Fe(IV) were the main active species for degradation of PAA in Fe(VI)/PMS reaction system. In addition, we explored the possible degradation intermediates and pathway of PAA. In situ Fe(III) oxides generated from Fe(VI) decomposition could adsorb arsenic pollutants through ligand exchange with inorganic As(V) through surface hydroxyl groups to form Fe-O-As bonds. The effect of coexisting anions on the removal performance of the system was investigated, and the results showed that the presence of PO43− and CO32− promoted the oxidative degradation of PAA owing to the activation of PMS by PO43− and CO32−, but Cl− can inhibit the PAA degradation through a free radical scavenging mechanism. PO43− and SiO32− affected the adsorption and removal of the released inorganic As(V) due to their competitive adsorption of in situ Fe(III) oxides. Density functional theory (DFT) calculations indicated an obvious electron transfer (1.83 e) between the in situ Fe(III) oxides and inorganic As(V) with a high adsorption energy of −10.30 eV. These results indicate that the combination of Fe(VI) and PMS can effectively control the total arsenic (total-As) in water bodies.

Simple Co-Precipitation of Iron Minerals for the Removal of Phenylarsonic Acid: Insights into the Adsorption Performance and Mechanism.

In this study, three kinds of iron minerals, ferrihydrite, hematite, and goethite, were prepared by a simple coprecipitation method for the adsorption and removal of phenylarsonic acid (PAA). The adsorption of PAA was explored, and the influences of ambient temperature, pH, and co-existing anions on adsorption were evaluated. The experimental results show that rapid adsorption of PAA occurs within 180 min in the presence of iron minerals, and the adsorption process conforms to a pseudo-second-order kinetic model. The isothermal adsorption of PAA by ferrihydrite, goethite, and hematite agrees with the Redlich-Peterson model. The maximum adsorption capacities of PAA are 63.44 mg/g, 19.03 mg/g, and 26.27 mg/g for ferrihydrite, goethite, and hematite, respectively. Environmental factor experiments illustrated that an alkaline environment will significantly inhibit the adsorption of PAA by iron minerals. CO32-, SiO32-, and PO43- in the environment will also significantly reduce the adsorption performance of the three iron minerals. The adsorption mechanism was analyzed by FTIR and XPS, which indicated that ligand exchange between the surface hydroxyl group and the arsine group leads to the formation of an Fe-O-As bond, and electrostatic attraction between the iron minerals and PAA played an important role in the adsorption.

Autocatalytic effect of in situ formed (hydro)quinone intermediates in Fenton and photo-Fenton degradation of non-phenolic aromatic pollutants and chemical kinetic modeling

While the electron-shuttling properties of (hydro)quinones can facilitate the redox cycling of iron species (Fe2+ and Fe3+), the impact of in situ formed (hydro)quinones from degradation of non-phenolic aromatic pollutants in Fenton-type processes has not been reported. This study investigated the catalytic effect of (hydro)quinone intermediates produced from degradation of p-arsanilic acid (p-ASA) and roxarsone (ROX) in Fenton and photo-Fenton processes, and its chemical kinetic modeling. The bimolecular rate constants of the reactions of OH with p-ASA and ROX were determined to be (2.79 ± 0.29) × 109 and (2.03 ± 0.07) × 109 M−1·s−1, respectively. However, ROX degraded faster than p-ASA in Fenton process under the same conditions, which was attributed to the greater catalytic effect of the in situ formed (hydro)quinone intermediates. p-Hydroquinone, p-benzoquinone, and 1,2,4-benzenetriol were identified among the oxidation intermediates of p-ASA, while 2-nitrohydroquinone, 2-nitrobenzoquinone, 1,2,4-benzenetriol, and 2-hydroxy-benzoquinone were found for ROX oxidation. The autocatalytic degradation of p-ASA and ROX in Fenton and photo-Fenton processes could be well described by a chemical kinetic model after accounting for the reactions of the (hydro)quinone intermediates. Both experimental and modeling results consistently showed that the redox cycling of iron promoted by the in situ formed (hydro)quinone intermediates was critical for the oxidation of p-ASA and ROX in Fenton process. Chemical kinetic modeling revealed that (hydro)quinone-related reactions and photo-reduction of Fe3+-complexes were responsible for producing the vast majority of OH that sustained the continuous degradation of p-ASA and ROX in photo-Fenton process with the presence of limited amount of Fe2+. The autocatalytic effect observed for phenylarsonic acid compounds and the chemical kinetic model developed in this study could guide the development of Fenton and solar photo-Fenton treatment for other non-phenolic aromatic pollutants.

Removal of phenylarsonic acid compounds by porous nitrogen doped carbon: Experimental and DFT study

Phenylarsonic acids are deemed as emerging contaminants, and their removal by carbonaceous materials has aroused wide attentions. However, the adsorption behaviors and mechanisms on nitrogen doped carbon still remain unclear. Herein, nitrogen doped porous carbons (NC-x) for adsorbing p-arsanilic acid and roxarsone were fabricated by hydrothermal and following activation treatment of peanut shell. The results revealed that NC-750 which was activated at 750 °C exhibited high BET surface area of 1331.11 m2/g, total pore volume of 0.97 cm3/g and average pore size of 2.91 nm, and its maximum equilibrium capacities based on Sips model for p-arsanilic acid and roxarsone were 287.3 mg/g and 462.6 mg/g, respectively. The sufficient adsorption space, rich defect structure and high affinity of nitrogen-containing groups endow NC-750 with high adsorption capacities, and the adsorption mechanisms involve with pore-filling, hydrogen bonding and π-π interactions. Density functional theory (DFT) calculation demonstrated that p-arsanilic acid was electron donor while roxarsone was electron acceptor, and graphitic nitrogen was conducive to the π-π interactions while pyrrolic nitrogen and pyridinic nitrogen were preferential for hydrogen bonding interactions. This work can provide reference for understanding the adsorption behaviors and interfacial mechanisms between phenylarsonic acid and nitrogen doped carbonaceous materials.

Application of iron oxyhydroxide to stabilize As(V) and phenylarsonic acid in contaminated soil: adsorption and the relevance to bioavailability.

The leaked arsenic-containing chemical warfare agent has caused severe contamination to the surrounding soil and water. In this study, iron oxyhydroxide (FeOOH) with different crystalline phases was used to stabilize arsenic. The results revealed that α/β- mixed crystalline iron oxyhydroxide (MIX-FeOOH) had better adsorption performance for As(V) and phenylarsonic acid (PAA) in water, with the adsorption capacity 71.4 and 54.7mgg-1 at 50mg L-1 equilibrium concentration, respectively. The adsorption mechanism was proved to be inner-sphere complexation, electrostatic interaction, and hydrogen bonding. Meanwhile, the oxygen vacancies on FeOOH could increase the isoelectric point and further promote the adsorption capacity through inner-sphere complexation. In arsenic contaminated soil, when the addition amount of MIX-FeOOH was 5%, the bioavailability of arsenic in As(V) and PAA contaminated soil was significantly reduced after 28days, and the stabilization rate reached 77.2% and 76.5%, respectively. After 7days of remediation, 17.1% and 11.9% of the most mobile portions of As(V) and PAA could be converted into poorly mobile portions, respectively. The stabilization mechanism includes inner-sphere complexation, mineral adsorption, and coprecipitation. In summary, this study can provide technical support for the remediation practice of arsenic-containing warfare agent contaminated sites.

Ultrasensitive detection of four organic arsenic compounds at the same time using a five-link cardboard-based assay

In order to effectively control the excessive use of organic arsenic reagents in livestock and poultry products, there is an urgent need to develop a method for rapid detection of multiple organic arsenic reagents. In this study, two haptens were designed and derivatized around the structural formula of roxarsone, and a highly-sensitive group-selective mAb 3F2 was prepared, which can simultaneously detect roxarsone, 4-aminophenylarsonic acid, 2-aminophenylarsonic acid and phenylarsonic acid. We further developed a colloidal gold immunochromatographic test strip (ICS) and prepared a five-link card that can simultaneously detect four organic arsenics in chicken and pork samples. Its quantitative detection limits (LOQ) for the four compounds in chicken and pork samples were 0.06 and 0.32 ng/mL, 0.11 and 0.29 ng/mL, 0.34 and 0.99 ng/mL, and 0.88 and 1.5 ng/mL, respectively. This multi-ICS detection provides a powerful tool for the on-site detection and rapid screening of organic arsenic reagents in actual samples.

The ArsH Protein Product of the Paracoccus denitrificans ars Operon Has an Activity of Organoarsenic Reductase and Is Regulated by a Redox-Responsive Repressor.

Paracoccus denitrificans ArsH is encoded by two identical genes located in two distinct putative arsenic resistance (ars) operons. Escherichia coli-produced recombinant N-His6-ArsH was characterized both structurally and kinetically. The X-ray structure of ArsH revealed a flavodoxin-like domain and motifs for the binding of flavin mononucleotide (FMN) and reduced nicotinamide adenine dinucleotide phosphate (NADPH). The protein catalyzed FMN reduction by NADPH via ternary complex mechanism. At a fixed saturating FMN concentration, it acted as an NADPH-dependent organoarsenic reductase displaying ping-pong kinetics. A 1:1 enzymatic reaction of phenylarsonic acid with the reduced form of FMN (FMNH2) and formation of phenylarsonous acid were observed. Growth experiments with P. denitrificans and E. coli revealed increased toxicity of phenylarsonic acid to cells expressing arsH, which may be related to in vivo conversion of pentavalent As to more toxic trivalent form. ArsH expression was upregulated not only by arsenite, but also by redox-active agents paraquat, tert-butyl hydroperoxide and diamide. A crucial role is played by the homodimeric transcriptional repressor ArsR, which was shown in in vitro experiments to monomerize and release from the DNA-target site. Collectively, our results establish ArsH as responsible for enhancement of organo-As(V) toxicity and demonstrate redox control of ars operon.

Phenylarsonic acid–DMPS redox reaction and conjugation investigated by NMR spectroscopy and X-ray diffraction

The reaction between 2,3-dimercaptopropane-1-sulfonate (DMPS, unithiol) and four phenylarsonic(V) acids, i.e. phenylarsonic acid (PAA), 4-hydroxy-3-nitrophenylarsonic acid (HNPAA), 2-aminophenylarsonic acid (o-APAA) and 4-aminophenylarsonic acid (p-APAA), is investigated in aqueous solution. The pentavalent arsenic compounds are reduced by DMPS to their trivalent analogs and instantly chelated by the vicinal dithiol, forming covalent As–S bonds within a five-membered chelate ring. The different types and positions of polar substituents at the aromatic ring of the arsonic acids influence the reaction rates in the same way as observed for reaction with glutathione (GSH), as well as the syn/anti molar ratio of the diastereomeric products, which was analyzed using time- and temperature-dependent nuclear magnetic resonance (NMR) spectroscopy. Addition of DMPS to the conjugate formed by a phenylarsonic(V) acid and the biologically relevant tripeptide GSH showed the immediate replacement of GSH by chelating DMPS, underlining the importance of dithiols as detoxifying agent.

Removal of Phenylarsonic Acid Compounds by Porous Nitrogen Doped Carbon: Experimental and Dft Study

Removal of Phenylarsonic Acid Compounds by Porous Nitrogen Doped Carbon: Experimental and Dft Study

CTAB-functionalized δ-FeOOH for the simultaneous removal of arsenate and phenylarsonic acid in phenylarsenic chemical warfare

This study prepared a cetyltrimethylammonium bromide (CTAB) functionalized δ-FeOOH using the coprecipitation method to remove arsenate and phenylarsonic acid in water polluted by phenylarsonic chemical warfare agents. Under neutral conditions, the adsorption capacity for arsenate and phenylarsonic acid was 45.7 and 85.3 mg g−1, respectively. The adsorption process conformed to the pseudo-second-order kinetics and Freundlich isothermal adsorption model, and the adsorption was spontaneous and endothermic. The CTAB-functionalized δ-FeOOH could effectively resist the interference of coexisting anions except for CO32−, SiO32− and PO43−. Furthermore, the adsorption mechanism was proposed by combining the adsorption experimental results, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and density functional theory analyses. The results showed that the adsorption of arsenate by the CTAB-functionalized δ-FeOOH was mainly through the formation of bidentate-dinuclear inner-sphere complexes and electrostatic interactions. While for phenylarsonic acid, the formation of monodentate-mononuclear inner-sphere complexes on (100) and (110) crystal facets, and the formation of bidentate-dinuclear inner-sphere complexes on the (002) crystal facet, as well as hydrogen bonding, electrostatic interaction, and π-hydrophobic interaction between organic compounds were the primary mechanism. Moreover, the CTAB-functionalized δ-FeOOH could maintain about 60% of the adsorption capacity for the two pollutants after five cycles. Overall, CTAB-functionalized δ-FeOOH has good potential for the remediation of inorganic and organic arsenic-contaminated water bodies.

Removal of p-arsanilic acid and phenylarsonic acid from water by Fenton coagulation process: influence of substituted amino group

Phenylarsonic acid compounds, which were widely used in poultry and swine production, are often introduced to agricultural soils with animal wastes. Fenton coagulation process is thought as an efficient method to remove them. However, the substituted amino group could apparently influence the removal efficiency in Fenton coagulation process. Herein, we investigated the optimal conditions to treat typical organoarsenic contaminants (p-arsanilic acid (p-ASA) and phenylarsonic acid (PAA)) in aqueous solution based on Fenton coagulation process for oxidizing them and capturing the released inorganic arsenic, and elucidated the influence mechanism of substituted amino group on removal. Results showed that the pH value and the dosage of H2O2 and Fe2+ significantly influenced the performance of the oxidation and coagulation processes. The optimal conditions for removing 20 mg L-1-As in this research were 40mg L-1 Fe2+ and 60mg L-1 H2O2 (the mass ratio of Fe2+/H2O2 = 1.5), initial solution pH of 3.0, and final solution pH of 5.0 adjusting after 30-min Fenton oxidation reaction. Meanwhile, the substituted amino group made p-ASA much more easily be attacked by ·OH than PAA and supply one more binding sites for forming complexes with Fe3+ hydrolysates, resulting in 36% higher oxidation rate and 7% better coagulation performance at the optimal conditions.

Anion inhibition studies of the Zn(II)-bound ι-carbonic anhydrase from the Gram-negative bacterium Burkholderia territorii

Burkholderia territorii, a Gram-negative bacterium, encodes for the ι-class carbonic anhydrase (CA, EC 4.2.1.1) BteCAι, which was recently characterised. It acts as a good catalyst for the hydration of CO2 to bicarbonate and protons, with a kcat value of 3.0 × 105 s−1 and kcat/KM value of 3.9 × 107 M−1 s−1. No inhibition data on this new class of enzymes are available to date. We report here an anion and small molecules inhibition study of BteCAι, which we prove to be a zinc(II)- and not manganese(II)-containing enzyme, as reported for diatom ι-CAs. The best inhibitors were sulphamic acid, stannate, phenylarsonic acid, phenylboronic acid and sulfamide (KI values of 6.2–94 µM), whereas diethyldithiocarbamate, tellurate, selenate, bicarbonate and cyanate were submillimolar inhibitors (KI values of 0.71–0.94 mM). The halides (except iodide), thiocyanate, nitrite, nitrate, carbonate, bisulphite, sulphate, hydrogensulfide, peroxydisulfate, selenocyanate, fluorosulfonate and trithiocarbonate showed KI values in the range of 3.1–9.3 mM.

Anion inhibition studies of the α-carbonic anhydrases from Neisseria gonorrhoeae

The bacterial pathogen Neisseria gonorrhoeae encodes for an α-class carbonic anhydrase (CA, EC 4.2.1.1), NgCA, which was investigated for its inhibition with a series of inorganic and organic anions. Perchlorate and hexafluorophosphate did not significantly inhibit NgCA CO2 hydrase activity, whereas the halides, azide, bicarbonate, carbonate, stannate, perosmate, diphosphate, divanadate, perruthenate, and trifluoromethanesulfonate showed inhibition constants in the range of 1.3–9.6 mM. Anions/small molecules such as cyanate, thiocyanate, nitrite, nitrate, bisulphite, sulphate, hydrogensulfide, phenylboronic acid, phenylarsonic acid, selenate, tellurate, tetraborate, perrhenate, peroxydisulfate, selenocyanate, iminodisulfonate, and fluorosulfonate showed KIs in the range of 0.15–1.0 mM. The most effective inhibitors detected in this study were sulfamide, sulfamate, trithiocarbonate and N,N-diethyldithiocarbamate, which had KIs in the range of 5.1–88 µM. These last compounds incorporating the CS2 - zinc-binding group may be used as leads for developing even more effective NgCA inhibitors in addition to the aromatic/heterocyclic sulphonamides, as this enzyme was recently validated as an antibacterial drug target for obtaining novel antigonococcal agents

Adsorption and desorption of phenylarsonic acid compounds on metal oxide and hydroxide, and clay minerals

Adsorption and desorption of p-arsanilic acid (p-ASA) and roxarsone (ROX) on six soil minerals, including hematite (α-Fe2O3), goethite (α-FeOOH), ferrihydrite (Fe(OH)3), aluminum oxide (α-Al2O3), manganese oxide (γ-MnO2), and kaolinite, were studied, and the impact of solution matrices on their adsorption was systematically evaluated. Adsorption of p-ASA/ROX on the metal (hydro)oxide and clay minerals occurred quickly (mostly within 2 h), and could be well described by the pseudo second-order kinetic model. The apparent maximum adsorption capacities of α-Fe2O3, α-FeOOH, Fe(OH)3, α-Al2O3, γ-MnO2, and kaolinite (at an initial pH of 7.0) for p-ASA were 1.7, 0.9, 2.5, 0.08, 1.1, and 0.02 μmol/m2, while those for ROX were 1.6, 0.7, 2.4, 0.1, 0.5, and 0.05 μmol/m2, respectively. Besides adsorbing p-ASA/ROX, γ-MnO2 also caused their oxidation. Experimental results suggest that formation of inner-sphere complexes through the arsonic acid group is the primary mechanism for adsorption of p-ASA/ROX on iron (hydro)oxides and γ-MnO2, while outer-sphere complexation plays a critical role in their adsorption on α-Al2O3 and kaolinite. Adsorption of p-ASA/ROX on the metal (hydro)oxide and clay minerals was affected by solution pH, co-existing metal ions (Ca2+, Mg2+, Al3+, Cu2+, Fe3+, and Zn2+), oxyanions (H2PO4−, HCO3−, and SO42−), and humic acid. The solid-to-liquid partition coefficients of p-ASA during the desorption from α-Fe2O3, α-FeOOH, Fe(OH)3, α-Al2O3, γ-MnO2, and kaolinite were 0.47, 2.69, 4.38, 0.03, 30.4, and 0.1 L/g, while those of ROX were 0.28, 1.68, 3.48, 0.02, 4.0, and 0.02 L/g, respectively. Agricultural soils with lower contents of organic carbon exhibited higher adsorption capacities towards p-ASA/ROX, which indicates that soil minerals play a key role in the adsorption of phenylarsonic acid compounds while organic matter could have strong inhibitory effect. These findings could help better understand and predict the transport and fate of p-ASA/ROX in surface soils with low contents of organic matter.

Effective separation of chromium species in technological solutions using amino-immobilized silica prior to their determination

Amino-immobilized (poly(4,9-dioxadodecane-1,12-guanidine, polydiallyldimethylammonium, hexadimethrin bromide, polyhexamethylene guanidine) silicas were proposed for chromium speciation for the first time. Adsorbents surface was characterized by TGA-DSC, FT-IR, CHN, XRD and SEM analysis. Polyamines were strongly fixed on the silica surface and were not washed off with solutions of 3М HNO3 and 20 g L−1 NaCl. Аmino-immobilized silica quantitatively removed (R ≥ 99%) Cr(VI) from solutions at pH 4–7. Cr(III) was not recovered in this pH range, which makes it possible to separate Cr(VI) from Cr(III). The separation factor (КCr(VI)/Cr(III)) was ≥ 1∙104. Silica-based adsorbents layer-by-layer immobilized with polyamines and 2-(1,8-dihydroxy-3,6-disulfo-2-naphthylazo)benzenearsonic acid were proposed for quantitative removal of Cr(III) from aqueous solutions with pH 4–6 at 90 °C. A system of sequentially connected columns filled with selective adsorbents was used to separate the chromium species in stream at рН= 5 and a flow rate of 1 mL min−1. Chromium was determined after its elution with 5 mL of 2 M HNO3 at a flow rate of 1 mL min−1 using ICP-OES or ICP-MS. The pre-concentration factors for Cr(VI) and Cr(III) was 60. A two-column system was used for chromium speciation in technological solutions. The efficiency of chromium speciation was confirmed by state standard procedure.