Thioether Sulfur Research Articles

Mixed Thioether/Amine‐Functionalized Expanded Calixarenes, Related Macropolycycles, and Metal Complexes thereof

AbstractA series of tetraaza‐expanded calix[4]arene analogues (2–4), in which two of the four aryl groups are ethylene‐protected thiophenol components were prepared from tetraaldehyde 1. Two of these strapped macrocycles were characterized crystallographically, as well as the dipalladium complex of 4. The same tetraaldehyde had been previously used for the synthesis of a macrotricycle (5) and a macropentacycle (6), the coordination properties of which have been investigated. In particular, ligand 6 was shown to be able to encapsulate a Cu+ or a Ag+ ion in the tetrahedral coordination pocket offered by a bridgehead nitrogen atom and the three proximal thioether sulfur atoms.

Structural dependent degradation of histamine H2-receptor antagonists by UV/NH2Cl: Reactive species contribution and the role of carbonate ions on ·NO generation

Histamine H2-receptor antagonists (HRAs) are a group of widely used gastrointestinal drugs that have been frequently detected in natural environments. UV/chloramine (NH2Cl) is a widely used disinfection process in water treatment, while the performance of HRAs degradation by UV/NH2Cl is still unclear. In this work, the degradation kinetics, mechanism and disinfection byproducts formation of HRAs by UV/NH2Cl were studied. The degradation of HRAs, including ranitidine (RNTD), nizatidine (NZTD), roxatidine (RXTD), cimetidine (CMTD) and famotidine (FMTD) was fast in the UV/NH2Cl process, and ·OH, Cl· and ·NO contributed to their degradation. CMTD had the highest rate constants with ·OH, Cl· and ·NO. RXTD, NZTD and FMTD were more reactive with ·OH, while RNTD was more selective towards Cl·. The contribution of ·OH, Cl· and reactive nitrogen species to HRAs degradation in water matrices was further quantified by kinetic modeling. Interestingly, carbonate species were found to promote the yield of ·NO. Further investigation through sensitivity analysis of the modeling reactions concluded the sensitive reactions for ·NO promotion. The structure–activity assessment domenstrated that the reactivity of thioether sulfur, CMTD-C3 and RXTD-N48 and piperidine rings resulted in the difference of degradation rates. Hydroxylation, nitrosation, chlorine substitution and oxygen atom transfer were the primary pathways for HRAs degradation. The formation of NDMA might be a prevalent problem along HRAs’ degradation in the UV/NH2Cl process, and the formation potential of NDMA is dependent on the types of amine groups in HRAs. This work provides an effective strategy to eliminate HRAs, revealed the NDMA formation potential in HRAs, and emphasized the role of carbonate species in ·NO generation.

Selective oxidation of histamine H2-Receptor antagonists by peracetic Acid: Kinetics and mechanism

Peracetic acid (PAA) is an emerging substitutive oxidant to chlorine disinfectants owing to the low generation of harmful by-products. Herein, we report PAA-induced oxidation of histamine H2-receptor antagonists (HRAs) via non-radical participation for the first time. Results showed that PAA can selectively oxidize HRAs with high reactivity to ranitidine (RNTD), nizatidine (NZTD), cimetidine (CMTD), and famotidine (FMTD), but low reactivity to roxatidine (RXTD). PAA-induced HRAs oxidation followed the second-order kinetic reaction, the apparent second-order reaction rate constants (k2, app) of RNTD, FMTD, CMTD and NZTD were 18.78 ± (2.4), 37.22 ± (6.1), 36.53 ± (7.8), 30.04 ± (2.4) M−1•s−1, respectively. The value of k2, app decreased as pH increased. Scavenging experiments indicated that PAA-induced HRAs oxidation proceeded via a non-radical process. The theoretical calculation and product analysis further reveal that the reaction involves the double-electron transfer from thioether sulfur in HRAs to peroxide bond. HRAs oxidation by PAA was not affected by water matrices (Cl-, HCO3–, HA), which has good applicability in surface water (SW) and wastewater (WW). Toxicity assessment indicated ecotoxicity of oxidation products was much lower than that of HRAs. This work provided a facile and emerging technology to eliminate the HRAs and their toxicity in the wastewater.

Surface- and Structural-Dependent Reactivity of Titanium Oxide Nanostructures with 2-Chloroethyl Ethyl Sulfide under Ambient Conditions.

Robust materials capable of heterogeneous reactivity are valuable for addressing toxic chemical clean up. Synthetic manipulations for generating titanium oxide nanomaterials have been utilized to alter both photochemical (1000 nm > λ > 400 nm) and chemical heterogeneous reactivity with 2-chloroethyl ethyl sulfide (2-CEES). Synthesizing TiO2 nanomaterials in the presence of long-chain alkylphosphonic acids enhanced the visible light-driven oxidation of the thioether sulfur of 2-CEES. Photooxidation reaction rates of 99 and 168 μmol/g/h (quantum yields of 5.07 × 10-4 and 8.58 × 10-4 molecules/photon, respectively) were observed for samples made with two different alkylphosphonic acids (C14H29PO3H2 and C9H19PO3H2, respectively). These observations are correlated with (i) generation of new surface defects/states (i.e., oxygen vacancies) as a result of TiO2 grafting by alkylphosphonic acid that may serve as reaction active sites, (ii) better light absorption by assemblies of nanorods and nanowires in comparison to individual nanorods, (iii) surface area differences, and (iv) the exclusion of OH groups due to the surface functionalization with alkylphosphonic acids via Ti-O-P bonds on the TiO2. Alternatively, nanowire-form H2Ti2O5·H2O was produced and found to be capable of highly efficient hydrolysis of the carbon-chlorine (C-Cl) bond of 2-CEES in the dark with a reaction rate of 279.2 μmol/g/h due to the high surface area and chemical nature of the titanate structure.

Degradation of antibiotic Cephalosporin C in different water matrices by ionizing radiation: Degradation kinetics, pathways, and toxicity

Cephalosporin antibiotics are ubiquitous emerging pollutants in various aquatic environments due to their extensive production and application. Herein, the radiolytic degradation of antibiotic Cephalosporin C (CEP-C) in different water matrices was comprehensively investigated using gamma radiation at various experimental conditions. The results revealed that CEP-C oxidation obeyed pseudo first-order kinetics, and 100%, 94.9%, 67.0%, 44.6% and 34.5% removal of CEP-C with 10–200 mg/L was achieved at 0.4 kGy, respectively. The degradation was faster at higher absorbed dose and acidic conditions (pH = 3.5). The inorganic anions, including SO42−, NO3−, and HCO3−, had negative influence on the degradation of CEP-C, the corresponding rate constant decreased from 4.603 to 3.667, 1.677 and 2.509 kGy−1 respectively in the presence of SO42−, NO3−, and HCO3−. The analysis of intermediate products indicated that CEP-C was oxidized to generate about 10 intermediate products. Besides, it was inferred that the thioether sulfur oxidation, β-lactam ring opening, acetyl dissociation from dihydrothiazine ring and D-α-aminohexylamide group abscission were the major reaction mechanisms of CEP-C degradation by gamma radiation. Importantly, the antibacterial activity of CEP-C could be completely vanished by gamma radiation alone, while more toxic intermediate products might be formed. Addition of hydrogen peroxide and peroxymonosulfate could significantly improve the CEP-C degradation, and reduce the toxicity of intermediates of CEP-C degradation. Similar degradation behavior was observed in the groundwater and wastewater, implying that ionizing radiation can be used for degradation of Cephalosporin in water and wastewater.

Fundamental research on the influence of mercaptan and thioether structure on the solvent extraction of fluid catalytic cracking naphtha

The thioether and mercaptan components (over 50–100 mg/kg) of fluid catalytic cracking (FCC) naphtha must be removed to satisfy the rigorous sulfur content standard of the vehicle gasoline. Owing to the difference between the structures of thioether and mercaptan and that of thiophenic sulfur, the desulfurization process is usually divided. A serious loss of octane number (ON) occurs during typical desulfurization when the sulfur content is reduced to 10 mg/kg. With the oriented separation of FCC naphtha critical components process, the standard of sulfur content with losing 1 unit of ON can be satisfied. However, thioether and mercaptan require individual technologies for removal. Thioether, mercaptan, and thiophenic sulfur must be synchronously removed to improve the efficiency, simplify the technology, and reduce the energy consumption. In this study, quantum chemical calculation and ternary liquid–liquid equilibrium experiment were combined to investigate the effect of thioether and mercaptan structures on the sulfoxide solvent extraction performance. The results showed that the Van der Waals’ force was the main interaction between the thioether/mercaptan and the solvent because the peaks of solvent and sulfide by RDG analysis were located at −0.01 to 0.01 a.u. In addition, the dipole moment, steric hindrance, and displacement affected the solvent extraction performance. The selectivity coefficient θ¯ of C3 thioether and mercaptan was 5.80 and 6.48 by DMSO solvent, respectively, which were greater than those of C4 sulfides (4.48 and 5.56). The interaction energy Eint of DMSO-ethyl methyl sulfide and DMSO- propanethiol were −32.75 and −33.68 kJ/mol while DMSO-diethyl sulfide and DMSO- butanethiol were −24.72 and −29.20 kJ/mol. It also proves that the C3 thioether and mercaptan could better extract into the solvent. In this way, the extractive desulfurization rate of the real FCC naphtha by DMSO was 80%. Therefore, the use of sulfoxide composite solvent can simultaneously extract the thioether, mercaptan, and thiophenic sulfur. This analytical method could be used to predict the synchronous extraction performance for FCC naphtha sulfides by other typical solvents.

Visible light driven oxidation of harmful 2-Chloroethyl ethyl sulfide using SiO2-TiO2 composite particles and air

Materials for remediation of toxic chemicals released in the environment are necessary. The current study provides a demonstration of visible light driven aerobic oxidation of 2-chloroethyl ethyl sulfide (2-CEES, sulfur mustard (HD) simulant) using rationally designed hybrid nanostructures composed of 5 nm TiO2 nanoparticles or TiO2 nanosheets supported onto monodispersed SiO2 Stöber spheres. Visible excitation (λ > 400 nm) resulted in oxidation of the thioether sulfur of 2-CEES. The highest reaction rate of 56.2 μmol/g/h (quantum yield (QY) of 1.64 × 10−5 molecules/photon) was obtained for the SiO2-TiO2 5 nm composite vs. 16.5 μmol/g/h (1.20 × 10−5 molecules/photon) for the SiO2-TiO2 nanosheets. Neat TiO2 nanoparticles and nanosheets displayed lower photocatalytic reactivity with reaction rates of 8.1 µmol/g/h (QY of 1.77 × 10−5 molecules/photon) and 5.1 µmol/g/h (1.20 × 10−5 molecules/photon), respectively. The reactivity of TiO2 nanostructures is due to surface defects/states. SiO2 support promotes the homogenous distribution of TiO2 nanoparticles allowing most of the active surface to remain available.

Synthesis, Crystal Structure and Physicochemical Characterization of Two Ni(II)-Famotidine Metal Complexes

The coordination ability of the antisecretor agent Famotidine (FMT) was explored using Ni(II) as central ion. [NiFMTH-2] and [Ni(FMT)2]Cl2 were obtained by the solvent evaporation method from the corresponding starting solutions at pH 8 and 4, respectively; the crystal structure was elucidated by single crystal X-ray diffraction in both cases.[NiFMTH-2] resulted in a distorted square-planar geometry, where FMT acts as a tetradentate dianionic ligand through nitrogen atoms belonging to the guanidine group, the thiazolic ring and the side chain, and a sulfur atom from the thioether moiety. [Ni(FMT)2]Cl2 exhibits an octahedral environment composed by two FMT molecules that coordinate by nitrogen atoms deriving from guanidine and thiazole ring moieties, and the thioether sulfur atom. The physicochemical characterization was completed by means of FTIR and UV–Vis spectroscopies, and thermal analysis. Solubility measurements were performed and the results could be satisfactorily correlated with the solvation Gibbs free energy (ΔGsolv) values in aqueous solution obtained using the SDM model by DFT calculations. Ni(II) and famotidine form an octahedral complex at pH 4 where famotidine acts as a tridentate neutral ligand. In basic medium, it behaves as a tetradentate dianion, resulting in a quasi-planar complex. Spectroscopic and thermal data are consistent with single crystal X-ray diffraction structural elucidation. The relative stabilities were assessed by theoretical studies.

Rapid oxidation of histamine H2-receptor antagonists by peroxymonosulfate during water treatment: Kinetics, products, and toxicity evaluation

Peroxymonosulfate (PMS) is an appealing oxidant for organic contaminant destruction relying on radical generation after activation. Herein, we report PMS-promoted rapid degradation of histamine H2-receptor antagonists (HRAs) through non-radical process for the first time. Five commonly used HRAs, i.e., ranitidine (RNTD), cimetidine (CMTD), famotidine (FMTD), nizatidine (NZTD) and roxatidine (RXTD), were examined their reactivity towards PMS. Results show that HRAs (except RXTD) exhibit high reactivity towards PMS, with apparent second-order rate constants from 403 to 872 M−1s−1 at pH 7.0. Radical scavenging experiments excluded the contribution of radicals to PMS-promoted degradation of HRAs, and this non-radical process was unaffected by the real water matrices. Structure-activity assessment and theoretical calculation indicated that the thioether sulfur in HRAs (except RXTD) was the main reactive site for PMS oxidation. Transformation product analysis further elucidated oxidation of the thioether sulfur to sulfoxide product through an oxygen atom transfer process. Moreover, the thioether sulfur on the straight chain was more susceptible to oxygen transfer with PMS than that on the thiazole ring of HRAs. Toxicity evaluation indicated the ecotoxicity of HRAs could be remarkably reduced after PMS oxidation. Hence, this work provides a promising strategy to rapidly remove HRAs and significantly reduce their toxicity in water treatment.

Corrigendum: Entrapment of a Pseudo-Tetrahedral CoII Center by Thioether Sulfur Bound {Co2 (μ-L)} Fragments: Synthesis, Field-Induced Single-Ion Magnetism and Catechol Oxidase Mimicking Activity.

It has come to the attention of the authors that Figure 6, the values of effective magnetic moments for complexes 1 and 2, giso, E/D values in Abstract section and in the Magnetic properties sections, giso and E/D values in Table 1, and D value for complex 2 in Conclusions section were changed mistakenly in the final stage of manuscript preparation. The data published in Figure 6 reveal the results obtained for older measurement on different batches of the complexes. The correct values, corresponding to the results obtained for the same batches of complexes for which the DC and AC magnetic measurements were done, are presented below. These mistakes do not affect the integrity of the research and overall conclusions of the published paper. The corrected Figure 6 and corresponding text are given below. Magnetic properties. Investigation of the magnetic features of complexes 1 and 2 proceeded using a PPMS device on which the temperature (1.9–300 K) and field (0–9 T) dependent magnetic data were obtained (Figure 6). Figure 6 Temperature dependence of the effective magnetic moment (inset: temperature dependence of the molar magnetic susceptibility) for complexes 1 and 2 (Left). The isothermal magnetizations measured in the range of B=0–9 T and at T=2, 5 and 10 K (Right). The magnetic properties of the complexes are primarily due to the presence of central tetrahedral CoII ion since octahedral LS-CoIII ions are diamagnetic. The value of effective magnetic moment (μeff) of complex 1 at 300 K is 3.5 μB, slightly lower than the spin-only value of 3.9 μB for S=3/2, g=2.0. Thereafter upon cooling the μeff value raises slightly up to ca 75 K and then, it drops sharply to a minimum at 1.9 K, where it adopts the value of 3.2 μB. In the case of complex 2, the μeff value at 300 K is 5.0 μB which is again much higher that the calculated value for isotropic S=3/2 spin. It decreases gradually upon cooling up to ca 50 K and then, it declines sharply to a minimum at 4.4 K reaching the value of 4.2 μB. The high μeff value at 300 K indicates considerable contribution of a spin-orbit coupling to the ground state in the complex 2. Isothermal magnetization experiments (Figure 6) for 1 and 2 in the applied field range of B=0–9 T at different constant temperatures T=2, 5 and 10 K reveal that the magnetization does not show saturation suggesting the presence of magnetic anisotropy. To extract the parameters affected by magnetic anisotropy arising from crystal field effects (g, D), both the susceptibility and magnetization data were fitted simultaneously. The best fit parameters were calculated using the PHI program package[26] for S=3/2 and they are as follows: giso=2.05, D=−23.6 cm−1, E/D=0, zJ/hc=0 cm−1, χTIP=−13.0×10−4 cm3 mol−1 for 1 and giso=2.61, D=−24.3 cm−1, E/D=0.01, zJ/hc=0.05 cm−1, χTIP=2.0×10−4 cm3 mol−1 for 2. The presence of temperature-independent paramagnetism (TIP) term accounts for the four surrounding CoIII ions. The observed D values for 1 and 2 are relatively close compared to those (−31.31 cm−1 and −21.88 cm−1) obtained in our previous investigations with complexes having similar molecular structures.[10] The authors wish to emphasize that with these corrections, the reported ZFS parameters relevant for the discussion of single molecule magnetism (i.e. the D values) did not change at all and the overall conclusions published in the original version of the article are not affected.

One- and Two-Electron Oxidations of β-Amyloid25-35 by Carbonate Radical Anion (CO3•-) and Peroxymonocarbonate (HCO4-): Role of Sulfur in Radical Reactions and Peptide Aggregation.

The β-amyloid (Aβ) peptide plays a key role in the pathogenesis of Alzheimer’s disease. The methionine (Met) residue at position 35 in Aβ C-terminal domain is critical for neurotoxicity, aggregation, and free radical formation initiated by the peptide. The role of Met in modulating toxicological properties of Aβ most likely involves an oxidative event at the sulfur atom. We therefore investigated the one- or two-electron oxidation of the Met residue of Aβ25-35 fragment and the effect of such oxidation on the behavior of the peptide. Bicarbonate promotes two-electron oxidations mediated by hydrogen peroxide after generation of peroxymonocarbonate (HCO4−, PMC). The bicarbonate/carbon dioxide pair stimulates one-electron oxidations mediated by carbonate radical anion (CO3•−). PMC efficiently oxidizes thioether sulfur of the Met residue to sulfoxide. Interestingly, such oxidation hampers the tendency of Aβ to aggregate. Conversely, CO3•− causes the one-electron oxidation of methionine residue to sulfur radical cation (MetS•+). The formation of this transient reactive intermediate during Aβ oxidation may play an important role in the process underlying amyloid neurotoxicity and free radical generation.

Degradation of thiacloprid via unactivated peroxymonosulfate: The overlooked singlet oxygen oxidation

Unactivated peroxymonosulfate (PMS) degrading organic contaminants has been reported. Previous studies have focused on direct PMS oxidation, while the role of singlet oxygen (1O2) is often overlooked. Here, we studied the oxidation of thiacloprid (THIA) of the neonicotinoid insecticides by PMS without explicit activation. According to electron spin resonance spectroscopy and quenching experiments, the nonradical mechanism (i.e., direct PMS oxidation and 1O2 oxidation) was responsible for the THIA degradation. There are two pathways to generate 1O2. The pyridine nitrogen of THIA structure can combine with PMS to produce epoxide, which is beneficial to generation of 1O2. However, the contribution of 1O2 from PMS self-decomposition can be ignored. According to kinetic solvent isotropic effect analysis, the overall THIA degradation was attributed to 36.5% 1O2 oxidation and 63.5% direct PMS oxidation. A structure-activity assessment and density functional theory suggested that thioether sulfur, amidine nitrogen and the cyanoimino groups were the main reaction sites. Product analysis further confirmed the involvement of 1O2 and PMS. Moreover, three major THIA degradation pathways were proposed, including (i) heterolytic cleavage of peroxo bonds and transfer of oxygen atoms, (ii) electron transfer and (iii) oxidation of cyanoimino groups to generate nitroso/nitro-THIA. In addition, identification byproducts (Except for TP141) had lower ecotoxicity toxicity (using ECOSAR) in fish, daphnid and green algae. Effects of pH and natural water matrices on THIA oxidation via PMS were further evaluated. This study investigated the overlooked 1O2 oxidation reaction to elucidate the mechanism. The new mechanistic knowledge has important implications for other contaminants for their interactions with PMS.

Palladium(II) Extraction by 4-[(Hexylsulfanyl)methyl]-3,5-dimethyl-1-phenyl-1Н-pyrazole from Hydrochloric Acid Solutions

Palladium(II) extraction from hydrochloric acid solutions by 4-[(hexylsulfanyl)methyl]-3,5-dimethyl-1-phenyl-1Н-pyrazole, a new complexing reagent dissolved in toluene or chloroform, was studied. The reagent showed high efficiency in palladium(II) recovery from 0.1–(5–6) М HCl. Palladium(II) is recovered from 1 М HCl by the nonprotonated reagent species according to the coordination mechanism to form the extracted compound [PdCl2μ-L]n (n > 2). The reagent is coordinated to metal ions via the nitrogen atom and the thioether sulfur atom as shown by 1H and 13С NMR spectroscopy. In the temperature range 10–40°С, palladium(II) extraction from 1 M HCl is an endothermic process. The palladium(II) can be quantitatively stripped by a hydrochloric acid solution of thiourea. The reagent (with toluene as diluent) may be recommended for use in palladium(II) concentration from hydrochloric acid solutions and for palladium(II) selective separation from platinum(IV), copper(II), nickel(II), iron(III), and aluminum(III).

Dinuclear Molybdenum(II) Complexes with Thioether Functionalized Silylamide Ligands

Treatment of molybdenum(II) acetate with thioether functionalized silylamides R2Si(NLi‐C6H4–2‐SR')2 leads to the formation of dinuclear MoII complexes [Mo2{R2Si(NC6H4‐2‐SR')2}2]. According to X‐ray crystal structure analyses the complexes [Mo2{Me2Si(NC6H4‐2‐SMe)2}2] and [Mo2{Ph2Si(NC6H4‐2‐SPh)2}2] comprise a Mo2‐unit which is coordinated by two μ‐κ‐N,N' silylamide ligands. The coordination sphere around the molybdenum atoms consists of two amide nitrogen atoms and two thioether sulfur atoms in a distorted square‐planar arrangement. The Mo‐Mo distances are 211.0(1) and 211.7(1) pm, resp. In the complex [Mo2{Ph2Si(NC6H4‐2‐SMe)2}2] the silyl amide units act as tetradentate κ‐N,N',S,S'chelating ligands and the Mo‐Mo distance is 218.6(1) pm.

CNS and CNP Iron(II) Mono-Iron Hydrogenase (Hmd) Mimics: Role of Deprotonated Methylene(acyl) and the trans-Acyl Site in H2 Heterolysis.

We report syntheses and H2 activation involving model complexes of mono-iron hydrogenase (Hmd) derived from acyl-containing pincer ligand precursors bearing thioether (CNSPre) or phosphine (CNPPre) donor sets. Both complexes feature pseudo-octahedral iron(II) dicarbonyl units. While the CNS pincer adopts the expected mer-CNS (pincer) geometry, the CNP ligand unexpectedly adopts the fac-CNP coordination geometry. Both complexes exhibit surprisingly acidic methylene C-H bond (reversibly de/protonated by a bulky phenolate), which affords a putative dearomatized pyridinate-bound intermediate. Such base treatment of Fe-CNS also results in deligation of the thioether sulfur donor, generating an open coordination site trans from the acyl unit. In contrast, Fe-CNP maintains a CO ligand trans from the acyl site both in the parent and dearomatized complexes (the -PPh2 donor is cis to acyl). The dearomatized mer-Fe-CNS was competent for H2 activation (5 atm D2(g) plus phenolate as base), which is attributed to both the basic site on the ligand framework and the open coordination site trans to the acyl donor. In contrast, the dearomatized fac-Fe-CNP was not competent for H2 activation, which is ascribed to the blocked coordination site trans from acyl (occupied by CO ligand). These results highlight the importance of both (i) the open coordination site trans to the organometallic acyl donor and (ii) a pendant base in the enzyme active site.

EPR-Derived Structure of a Paramagnetic Intermediate Generated by Biotin Synthase BioB.

Biotin (vitamin B7) is an enzyme cofactor required by organisms from all branches of life but synthesized only in microbes and plants. In the final step of biotin biosynthesis, a radical S-adenosyl-l-methionine (SAM) enzyme, biotin synthase (BioB), converts the substrate dethiobiotin to biotin through the stepwise formation of two C-S bonds. Previous electron paramagnetic resonance (EPR) spectroscopic studies identified a semistable intermediate in the formation of the first C-S bond as 9-mercaptodethiobiotin linked to a paramagnetic [2Fe-2S] cluster through one of its bridging sulfides. Herein, we report orientation-selected pulse EPR spectroscopic results that reveal hyperfine interactions between the [2Fe-2S] cluster and a number of magnetic nuclei (e.g., 57Fe, 15N, 13C, and 2H) introduced in a site-specific manner via biosynthetic methods. Combining these results with quantum chemical modeling gives a structural model of the intermediate showing that C6, the target of the second hydrogen-atom abstraction, is now in close proximity to the nascent thioether sulfur and is ideally positioned for the second C-S bond forming event.

Oxidation of Cefalexin by Permanganate: Reaction Kinetics, Mechanism, and Residual Antibacterial Activity.

The oxidation of cefalexin (CFX), a commonly used cephalosporin antibiotic, was investigated by permanganate (PM) in water. Apparent second-order rate constant of the reaction between CFX and PM was determined to be 12.71 ± (1.62) M−1·s−1 at neutral pH. Lower pH was favorable for the oxidation of CFX by PM. The presence of Cl− and HCO3− could enhance PM-induced oxidation of CFX, whereas HA had negligible effect on CFX oxidation by PM. PM-induced oxidation of CFX was also significant in the real wastewater matrix. After addition of bisulfite (BS), PM-induced oxidation was significantly accelerated owing to the generation of Mn(III) reactive species. Product analysis indicated oxidation of CFX to three products, with two stereoisomeric sulfoxide products and one di-ketone product. The thioether sulfur and double bond on the six-membered ring were the reactive sites towards PM oxidation. Antibacterial activity assessment indicated that the activity of CFX solution was significantly reduced after PM oxidation.

Palladium(II) Extraction from Hydrochloric Acid Solutions with 4-[(Hexylsulfanyl)methyl]-3,5-Dimethyl-1H-Pyrazole

Palladium(II) extraction from hydrochloric acid solutions with a novel weakly basic complexing reagent, 4-[(hexylsulfanyl)methyl]-3,5-dimethyl-1H-pyrazole, dissolved in chloroform was studied. Palladium(II) was found to be highly efficiently extracted from 0.1–3 mol/L HCl solutions. A coordination mechanism of palladium(II) extraction with a protonated form of the reagent via fast interphase transfer of ion associates was proposed. The composition of the extracted compound, [PdCl2μ-L]n (n > 2), was found, and the way of coordination of the reagent to metal ions through N(2) nitrogen atom and thioether sulfur atom was determined. The reagent can be recommended for concentrating palladium(II) and selectively separating it from platinum(IV), copper(II), nickel(II), and iron(III).

Oxidation of cefalexin by thermally activated persulfate: Kinetics, products, and antibacterial activity change

While the widely used β-lactam antibiotics, such as cephalosporins, are known to be susceptible to oxidation by sulfate radical (SO4−), comprehensive study about SO4−-induced oxidation of cephalosporins is still limited, such as the impact of water matrices, and the structure and antibacterial activity of transformation products. Herein, the oxidation of cefalexin (CFX), a most frequently detected cephalosporin, was systematically investigated by thermally activated persulfate (PS). CFX oxidation followed pseudo-first-order kinetics, and SO4− dominantly contributed to the overall oxidation of CFX. The impact of water matrices, such as Cl−, HCO3− and natural organic matter, on CFX degradation was predicted using a pseudo-steady-state kinetic model. The secondary reactive species, such as chlorine and carbonate radicals, were found to contribute to CFX degradation. Product analysis indicated oxidation of CFX to six products (molecular weight of 363), with two stereoisomeric sulfoxides as the primary oxidation products. It was thus suggested that the primary amine on the side chain, and the thioether sulfur and double bond on the six-membered ring were the reactive sites of CFX towards SO4− oxidation. Antibacterial activity assessment showed that the biological activity of CFX solution was significantly diminished after treatment by the thermally activated PS.

Degradation mechanism and kinetic modeling for UV/peroxydisulfate treatment of penicillin antibiotics

The widespread occurrence of penicillin antibiotics (PENs) in natural environment has raised increasing concerns due to their potential to induce antibiotic-genes. In this study, the degradation of PENs by UV/peroxodisulfate (PDS) process was investigated to determine the reaction kinetics, transformation mechanism and energy efficiency. The second-order rate constants for sulfate radical (SO4−) and hydroxyl radical (HO) with PENs, including, pencillin G (PG), amoxicillin (AMX) and carbenicillin (CBN), were determined to be (3.90–9.32) × 109 M−1·s−1 and (6.67–9.86) × 109 M−1·s−1, respectively. A pseudo steady-state kinetic model was employed and successfully predicted the degradation of PENs in ultrapure water. The modeling results revealed that both direct and indirect photolysis contributed to PENs degradation, and the contribution of indirect photolysis increased with the increase of PDS dosage. SO4− was the major contributor to PENs indirect photolysis. The effect of pH and water matrices, including HCO3−, Cl− and natural organic matter were evaluated and modeled. Combined with the modeling results, the derived radicals and excited species were likely generated and involved in the overall degradation of PENs. Based on the developed model, we gave a roughly calculation of electrical energy per order (EE/O) to evaluate the energy efficiency of PDS treatment processes. Finally, the transformation product analysis indicated that the thioether sulfur on the five-membered ring and the side chain, e.g., benzene ring on PG and CBN were the reactive sites for SO4−, while the primary amine was another reactive site for SO4− on AMX.