Oligomerization of humic phenolic monomers by oxidative coupling under biomimetic catalysis

Unraveling Multiple Pathways of Electron Donation from Phenolic Moieties in Natural Organic Matter

Natural organic matter (NOM) exhibits a distinctive electron-donating capacity (EDC) that serves a pivotal role in the redox reactions of contaminants and minerals through the transformation of electron-donating phenolic moieties. However, the ambiguity of the molecular transformation pathways (MTPs) that engender the EDC during NOM oxidation remains a significant issue. Here, MTPs that contribute to EDC were investigated by identifying the oxidized products of phenolic model compounds and NOM samples in direct or mediated electrochemical oxidation (DEO or MEO, respectively) using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). It was found that the oxidation of newly formed phenolic-OH (ArOH) and the oxidative coupling reaction of the phenoxy radical are the main MTPs that directly contribute to EDC, in addition to the transformation of hydroquinones to quinones. Notably, the oxidative coupling reaction of ArOH contributed at least 22-42% to the EDC. Ferulic acid-like structures can also directly contribute to EDC by incorporating H2O into their acrylic substituents. Furthermore, the opening of C rings can indirectly attenuate the EDC through structural alterations in the electron-donating process of NOM. Decarboxylation can either weaken or enhance the EDC depending on the structure of the phenolic moieties in NOM. These findings suggest that the EDC of NOM is a comprehensive result of multiple NOM MTPs, involving not only ArOH oxidation but also the addition of H2O to olefinic bonds and bond-breaking reactions. Our work provides molecular evidence that aids in the comprehension of the multiple EDC-associated transformation pathways of NOM.

Scavengome of an antioxidant

The term "scavengome" refers to the chemical space of all the metabolites that may be formed from an antioxidant upon scavenging reactive oxygen or nitrogen species (ROS/RNS). This chemical space covers a wide variety of free radical metabolites with drug discovery potential. It is very rich in structures representing an increased chemical complexity as compared to the parent antioxidant: a wide range of unusual heterocyclic structures, new CC bonds, etc. may be formed. Further, in a biological environment, this increased chemical complexity is directly translated from the localized conditions of oxidative stress that determines the amounts and types of ROS/RNS present. Biomimetic oxidative chemistry provides an excellent tool to model chemical reactions between antioxidants and ROS/RNS. In this chapter, we provide an overview on the known metabolites obtained by biomimetic oxidation of a few selected natural antioxidants, i.e., a stilbene (resveratrol), a pair of hydroxycinnamates (caffeic acid and methyl caffeate), and a flavonol (quercetin), and discuss the drug discovery perspectives of the related chemical space.

Oxidative Oligomerization of Phenolic Endocrine Disrupting Chemicals Mediated by Mn(III)-L Complexes and the Role of Phenoxyl Radicals in the Enhanced Removal: Experimental and Theoretical Studies

Soluble manganese(III), stabilized by ligands as Mn(III)-L complexes, are ubiquitous in natural waters and wastewaters and can potentially serve as both the oxidant and reductant in one-electron transfer reactions with organic contaminants. In this study, the oxidative transformations of 14 phenolic endocrine disrupting chemicals (EDCs) by in situ-formed Mn(III)-L complexes, generated from irradiated water containing Mn(II) and humic acid, were investigated. The pseudo-first-order rate constants (k_obs, h^-1) of these phenols varied from 1.0 × 10^-4 to 5.9 × 10^-2. A quantitative structure-activity relationship model was developed, which suggests that the electron-donating ability (E_HOMO) of phenolic chemicals was the most important molecular characteristic for the Mn(III)-L-mediated oxidative transformation. Phenol transformation was initiated by the generation of a phenoxyl radical through electron transfer to Mn(III)-L. Subsequent self-coupling reactions between phenoxyl radicals resulted in the formation of self-coupling dimers and trimers. With the addition of simple phenol as a cosubstrate, enhanced transformations of these phenolic EDCs were clearly observed, and cross-coupling products of simple phenol and the substrates were also detected. In addition, a reaction activation energy calculation based on the transition-state theory indicated that the cross-coupling reaction was more likely than the self-coupling reaction to occur in the presence of phenol. This work provides new insights into the environmental fate of phenolic compounds.

UV-Vis Spectroelectrochemistry of Oleuropein, Tyrosol, and p-Coumaric Acid Individually and in an Equimolar Combination. Differences in LC-ESI-MS2 Profiles of Oxidation Products and their Neuroprotective Properties

Major phenolic compounds from olive oil (ArOH-EVOO), oleuropein (Ole), tyrosol (Tyr), and p-coumaric acid (p-Cou), are known for their antioxidant and neuroprotective properties. We previously demonstrated that their combination could potentiate their antioxidant activity in vitro and in cellulo. To further our knowledge of their electron-transfer properties, Ole, Tyr, and p-Cou underwent a spectroelectrochemical study, performed either individually or in equimolar mixtures. Two mixtures (Mix and Mix-seq) were prepared in order to determine whether distinct molecules could arise from their simultaneous or sequential oxidation. The comparison of Liquid Chromatography-Electrospray Ionization-Tandem Mass Spectrometry (LC-ESI-MS2) profiles highlighted the presence of specific oxidized products found in the mixes. We hypothesized that they derived from the dimerization between Tyr and Ole or p-Cou, which have reacted either in their native or oxidized forms. Moreover, Ole regenerates when the Mix undergoes oxidation. Our study also showed significant neuroprotection by oxidized Ole and oxidized Mix against H2O2 toxicity on SK-N-SH cells, after 24 h of treatment with very low concentrations (1 and 5 nM). This suggests the putative relevant role of oxidized Ole products to protect or delay neuronal death.

Recent advances in metalloporphyrins for environmental and energy applications

Porphyrin-based chemistry has reached an unprecedented period of rapid development after decades of study. Due to attractive multifunctional properties, porphyrins and their analogues have emerged as multifunctional organometals for environmental and energy purposes. In particular, pioneer works have been conducted to explore their application in pollution abatement, energy conversion and storage and molecule recognition. This review summarizes recent advances of porphyrins chemistry, focusing on elucidating the nature of catalytic process. The Fenton-like redox chemistry and photo-excitability of porphyrins and their analogues are discussed, highlighting the generation of high-valent iron oxo porphyrin species. Finally, challenges in current research are identified and perspectives for future development in this area are presented.

Transformation and toxicity evaluation of tetracycline in humic acid solution by laccase coupled with 1-hydroxybenzotriazole

Enzyme-based catalyzed oxidative coupling reactions (E-COCRs) are considered as viable technologies to transform a variety of pharmaceutical antibiotics. This study indicated that the extracellular fungal laccase from Pleurotus ostreatus was effective in transforming tetracycline (TC) with 1-hydroxybenzotriazole (HBT) present at varying conditions during E-COCRs. The presence of humic acid (HA) showed suppressive effect on the transformation rate constants (k) of TC, and the k values for TC decreased as HA concentration increased. It was ascribed primarily to the covalent binding between TC and HA, which reduced the apparent concentration and availability of TC in water. It is noted that TC molecules from the cross-coupling products were likely re-released under extreme conditions (pH<2.0). The intermediate products were identified regardless of HA presence by high-resolution mass spectrometry (HRMS). A possible reaction pathway of TC in HA solution including electron transfer, hydroxylation, dehydrogenation, oxidation, radical reaction, decomposition, and covalent binding was proposed. The growth inhibition assays of Escherichia coli (E. coli) confirmed that the antimicrobial activity of TC was remarkably reduced with an increasing reaction time. These findings provide novel insights into the decomposition and cross-coupling of TC in a multi-solute natural aquatic environment by laccase-based catalyzed oxidative processes.

Transformation and products of captopril with humic constituents during laccase-catalyzed oxidation: Role of reactive intermediates

The transformation of captopril (CAP), a widely-used thiol drug, was studied with the presence of dissolved model humic constituents (HCs) in a laccase-catalyzed system. Reaction products were analyzed by ultra-performance liquid chromatography coupled to time-of-flight mass spectrometry and condensed fukui function computation. CAP reacted with different model HCs in the enzymatic system for 1 h, ranging from 75% (syringic acid) to 96% (p-coumaric acid). In the absence of HCs, only 15% of CAP was removed through self-coupling. The presence of HCs apparently changed the transformation of CAP in aqueous environment, and the HC reactive intermediates played an important role. First, during laccase catalysis, HCs with different structures were oxidized to produce reactive intermediates, including phenoxyl radical cation, ortho-, and para-quinone intermediates. Second, these intermediates were readily attacked by CAP via nucleophilic reactions, forming C-S-C covalent conjugates. More importantly, the standard reduction potential of these intermediates is a critical parameter, as PCA showed the highest reactivity to the nucleophilic addition reaction with CAP by forming phenoxy radical cations. While SYR showed the least reactivity due to the formation of para-quinone intermediates. Therefore, the functional groups on HCs could greatly influence the cross-coupling with CAP, as well as the type and stability of the coupling products. This work clearly demonstrated the transformation of CAP and other thiol drugs with the presence of HCs in aqueous environment, which is similar to the natural humification process.

Catechol degradation on hematite/silica-gas interface as affected by gas composition and the formation of environmentally persistent free radicals

Environmentally persistent free radicals (EPFRs) formed on a solid particle surface have received increasing attention because of their toxic effects. However, organic chemical fate regulated by EPFRs has rarely been investigated, and this information may provide the missing link in understanding their environmental behavior. Previous studies have suggested that the reduction of transition metals is involved in EPFRs formation. We thus hypothesize that an oxidative environment may inhibit EPFRs formation in particle-gas interface, which will consequently release free radicals and accelerate organic chemical degradation. Our result indicates that a 1% hematite coating on a silica surface inhibited catechol degradation in N₂, especially at low catechol loadings on solid particles (S_CT). However, under an O₂ environment, catechol degradation decreased when S_CT was <1 μg/mg but increased when S_CT was >1 μg/mg. Stable organic free radicals were observed in the N₂ system with g factors in the 2.0035–2.0050 range, suggesting the dominance of oxygen-centered free radicals. The introduction of O₂ into the catechol degradation system substantially decreased the free radical signals and decreased the Fe(II) content. These results were observed in both dark and light irradiation systems, indicating the ubiquitous presence of EPFRs in regulating the fate of organic chemicals.

Enzymes as Green Catalysts for Precision Macromolecular Synthesis

The present article comprehensively reviews the macromolecular synthesis using enzymes as catalysts. Among the six main classes of enzymes, the three classes, oxidoreductases, transferases, and hydrolases, have been employed as catalysts for the in vitro macromolecular synthesis and modification reactions. Appropriate design of reaction including monomer and enzyme catalyst produces macromolecules with precisely controlled structure, similarly as in vivo enzymatic reactions. The reaction controls the product structure with respect to substrate selectivity, chemo-selectivity, regio-selectivity, stereoselectivity, and choro-selectivity. Oxidoreductases catalyze various oxidation polymerizations of aromatic compounds as well as vinyl polymerizations. Transferases are effective catalysts for producing polysaccharide having a variety of structure and polyesters. Hydrolases catalyzing the bond-cleaving of macromolecules in vivo, catalyze the reverse reaction for bond forming in vitro to give various polysaccharides and functionalized polyesters. The enzymatic polymerizations allowed the first in vitro synthesis of natural polysaccharides having complicated structures like cellulose, amylose, xylan, chitin, hyaluronan, and chondroitin. These polymerizations are "green" with several respects; nontoxicity of enzyme, high catalyst efficiency, selective reactions under mild conditions using green solvents and renewable starting materials, and producing minimal byproducts. Thus, the enzymatic polymerization is desirable for the environment and contributes to "green polymer chemistry" for maintaining sustainable society.

Oxidation of catechols during positive ion electrospray mass spectrometric analysis: evidence for in-source oxidative dimerization

RATIONALE

Catechols are an important class of analytes occurring in many natural and synthetic products. Electrospray ionization in negative mode is the preferred way of ion generation for these compounds; however, studies in positive ion mode can reveal their potential for in-source oxidation and further structural changes, some of which may also occur in the solution phase. Therefore in-source oxidation can provide a forward look into the potential for solution oxidation.

METHODS

1:1 Acetonitrile/water solutions of catechol (Cat), 4,5-dichlorocatechol (4,5-DCC), 3,4-dichlorocatechol (3,4-DCC) and tetrachlorocatechol (TCC) were analyzed by positive ion ultrahigh-performance liquid chromatography (UHPLC/ESI-MS) and UHPLC/ESI-MS/MS under various emitter voltages to assess their liability towards in-source oxidation. Structural information for in-source generated compounds was obtained through the use of product ion scans.

RESULTS

Using catechols as probe compounds, we have demonstrated that under the conditions used in many analytical laboratories in-source oxidation can severely affect the sensitivity and response functions of an analyte. Under standard UHPLC conditions (300 μL/min flow rate), Cat, 3,4-DCC, 4,5-DCC and TCC can undergo in-source oxidation. The extent of oxidation is dependent either on the instrument or on the characteristics of the emitter. This is evident by a change in the isotopic pattern of these compounds and the generation of ions at lower m/z values due to a loss of 1 and/or 2 hydrogens and electrons. In the case of catechol, the formation of a dimer resulting from in-source oxidation reactions was observed. This dimer has the same fragmentation pattern as the dimer generated by oxidation in the solution phase.

CONCLUSIONS

The present work demonstrates the potential of positive ion ESI for oxidizing electroactive compounds during regular analytical operation using commercially available mass spectrometers. Using Cat and some of its chlorinated analogues as probe compounds, we have demonstrated that under the conditions used in many analytical laboratories in-source oxidation and dimerization can and does take place.

Adsorption of uranium composites onto saltrock oxides - experimental and theoretical study

The study encompassed experimental mass spectrometric and theoretical quantum chemical studies on adsorption of uranium species in different oxidation states of the metal ion, and oxides of UxOy(n+) type, where x = 1 or 3, y = 2 or 8, and n = 0, 1 or 2 onto nanosize-particles of saltrock oxides MO (M = Mg(II), Ca(II), Ni(II), Co(II), Sr(II) or Ba(II)), M2Oy (M = Au(III) or Ag(I), y = 3 or 1) silicates 3Al2O3.2SiO2, natural kaolinite (Al2O2·2SiO2·2H2O), illite (K0.78Ca0.02Na0.02(Mg0.34Al1.69Fe(III)0.02)[Si3.35Al0.65]O10(OH)2·nH2O), CaSiO3, 3MgO·4SiO2,H2O, and M(1)M(2)(SiO4)X2 (M(1) = M(2) = Al or M(1) = K, M(2) = Al, X = F or Cl), respectively. The UV-MALDI-Orbitrap mass spectrometry was utilized in solid-state and semi-liquid colloidal state, involving the laser ablation at λex = 337.2 nm. The theoretical modeling and experimental design was based on chemical-, physico-chemical, physical and biological processes involving uranium species under environmental conditions. Therefore, the results reported are crucial for quality control and monitoring programs for assessment of radionuclide migration. They impact significantly the methodology for evaluation of human health risk from radioactive contamination. The study has importance for understanding the coordination and red-ox chemistry of uranium compounds as well. Due to the double nature of uranium between rare element and superconductivity like materials as well as variety of oxidation states ∈ (+1)-(+6), the there remain challenging areas for theoretical and experimental research, which are of significant importance for management of nuclear fuel cycles and waste storage.

Copolymerization of 2,4-dichlorophenol with humic substances by oxidative and photo-oxidative biomimetic catalysis

We evaluated the catalytic activity of a water-soluble iron-porphyrin in an oxidative coupling reaction to form covalent bonds between 2,4-dichlorophenol (2,4-DCP) and humic molecules. The biomimetic catalysis in the presence of H₂O₂ was tested in the dark and in daylight, and changes in reaction products were revealed by high-performance liquid chromatography (HPLC) and nuclear magnetic resonance (NMR) spectroscopy. In all conditions, iron-porphyrin was effective in promoting complete disappearance of 2,4-DCP, although catalyst activity was enhanced in daylight (with a maximum turnover number of 85.13). Further evidence of the occurred covalent coupling between 2,4-DCP and humic molecules was revealed by diffusion-ordered nuclear magnetic resonance (DOSY-NMR) spectroscopy that showed a reduced diffusivity of 2,4-DCP after the catalytic reaction. These findings indicate that iron-porphyrin is an efficient catalyst for the covalent binding of polyhalogenated phenols to humic molecules, thereby suggesting that the copolymerization reactions may become a useful technology to remediate soils and waters contaminated by halogenated phenols and their analogues.

Remediation of highly contaminated soils from an industrial site by employing a combined treatment with exogeneous humic substances and oxidative biomimetic catalysis

Remediation of two polluted soils from a northern Italian industrial site heavily contaminated with organic contaminants was attempted here by subjecting soils first to addition with an exogenous humic acid (HA), and, then, to an oxidation reaction catalyzed by a water-soluble iron-porphyrin (FeP). An expected decrease of detectable organic pollutants (>50%) was already observed when soils were treated only with the H2O2 oxidant. This reduction was substantially enhanced when oxidation was catalyzed by iron-porphyrin (FeP+H2O2) and the largest effect was observed for the most highly polluted soil. Even more significant was the decrease in detectable pollutants (70-90%) when soils were first amended with HA and then subjected to the FeP+H2O2 treatment. This reduction in extractable pollutants after the combined HA+FeP+H2O2 treatment was due to formation of covalent CC and COC bonds between soil contaminants and amended humic molecules. Moreover, the concomitant detection of condensation products in soil extracts following FeP addition confirmed the occurrence of free-radical coupling reactions catalyzed by FeP. These findings indicate that a combined technique based on the action of both humic matter and a metal-porhyrin catalyst, may become useful to quantitatively reduce the toxicity of heavily contaminated soils and prevent the environmental transport of pollutants.

Quantitative Analysis of Substituted -Dimethyl-tryptamines in the Presence of Natural Type XII Alkaloids

This paper reports the qualitative and quantitative analysis (QA) of mixtures of hallucinogens, N,N-dimethyltryptamine (DMT) (1), 5-methoxy- (1a) and 5-hydroxy- N,N-dimethyltryptamine (1b) in the presence of β-carbolines (indole alkaloids of type XII) {(2), (3) and (5)}. The validated electronic absorption spectroscopic (EAs) protocol achieved a concentration limit of detection (LOD) of 7.2.10-7 mol/L {concentration limit of quantification (LOQ) of 24.10-7mol/L} using bands (λmax) within 260±0.23-262±0.33 nm. Metrology, including accuracy, measurement repeatability, measurement precision, trueness of measurement,and reproducibility of the measurements are presented using N,N- dimethyltryptamine (DMA) as standard. The analytical quantities of mixtures of alkaloids 4, 6 and 7 are: λmax 317±0.45, 338±0.69 and 430±0.09 for 4 (LOD, 8.6.10-7 mol/L; LOQ, 28.666, mol/L), as well as 528±0.75 nm for 6 and 7 (LOD, 8.2. 10-7 mol/L; LOQ, 27.333, mol/L), respectively. The partially validated protocols by high performance liquid chromatography (HPLC), electrospray ionization (ESI), mass spectrometry (MS), both in single and tandem operation (MS/MS) mode, as well as matrix/assisted laser desorption/ionization (MALDI) MS are elaborated. The Raman spectroscopic (RS) protocol for analysis of psychoactive substances, characterized by strong fluorescence RS profile was developed, with the detection limits being discussed. The known synergistic effect leading to increase the psychoactive and hallucinogenic properties and the reported acute poisoning cases from 1-7, make the present study emergent, since as well the current lack of analytical data and the herein metrology obtained contributed to the elaboration of highly selective and precise analytical protocols, which would be of interest in the field of criminal forensic analysis.

Co-polymerization of penta-halogenated phenols in humic substances by catalytic oxidation using biomimetic catalysis

INTRODUCTION

A synthetic water-soluble meso-tetra(2,6-dichloro-3-sulfonatophenyl)porphyrinate of iron(III) chloride, Fe-(TDCPPS)Cl, was employed to catalyze the oxidative co-polymerization of penta-halogenated phenols in two humic materials of different origin.

MATERIALS AND METHODS

Co-polymerization of pentachlorophenol (PCP) was followed by high-performance size-exclusion chromatography (HPSEC), the unbound PCP recovered from reacting humic solutions was evaluated by gas-chromatography/electron capture detector, and the oxidative catalyzed coupling of pentafluorophenol (PFP) into humic matter was assessed by liquid-state (19)F-NMR spectroscopy. HPSEC showed that the catalyzed oxidative coupling between PCP and humic molecules increased the apparent weight-average molecular weight (M(w)) values in both humic substances.

RESULTS AND DISCUSSION

HPSEC further indicated that the co-polymerization reaction turned the loosely bound humic supramolecular structures into more stable conformations, which could no longer be disrupted by the disaggregating effect of acetic acid. The occurrence of covalent linkages established between PCP and humic molecules was also suggested by the very little amount of PCP found free in solution after the catalyzed co-polymerization. (19)F-NMR spectroscopy suggested that also PFP could be oxidatively coupled to humic materials. PFP-humic co-polymerization reaction produced (19)F-spectra with many more (19)F signals and wider chemical shifts spread than for PFP alone or PFP subjected to catalyzed coupling without humic matter.

CONCLUSIONS

These findings show that biomimetic iron-porphyrin is an efficient catalyst for the covalent binding of polyhalogenated phenols to humic molecules, thereby suggesting that the co-polymerization reaction may become a useful technology to remediate soils and waters contaminated by polyhalogenated phenols and their analogues.

Carbon sequestration in soil by in situ catalyzed photo-oxidative polymerization of soil organic matter

Here we describe an innovative mechanism for carbon sequestration in soil by in situ photopolymerization of soil organic matter under biomimetic catalysis. Three different Mediterranean soils were added with a synthetic water-soluble iron-porphyrin, irradiated by solar light, and subjected first to 5 days incubation and, then, 15, and 30 wetting and drying (w/d) cycles. The in situ catalyst-assisted photopolymerization of soil organic carbon (SOC) increased water stability of soil aggregates both after 5 days incubation and 15 w/d cycles, but not after 30 w/d cycles. Particle-size distribution of all treated soils confirmed the induced soil physical improvement, by showing a concomitant lower yield of the clay-sized fraction and larger yields of either coarse sand- or fine sand-size fractions, depending on soil texture, though only after 5 days incubation. The gain in soil physical quality was reflected by the shift of OC content from small to large soil aggregates, thereby suggesting that photopolymerization stabilized OC by both chemical and physical processes. A further evidence of the carbon sequestration capacity of the photocatalytic treatment was provided by the significant reduction of CO(2) respired by all soils after both incubation and w/d cycles. Our findings suggest that "green" catalytic technologies may potentially be the bases for future practices to increase soil carbon stabilization and mitigate CO(2) emissions from arable soils.

Effect of extremely high specific flow rates on the removal of NOM and arsenic from groundwater with an ion-exchange resin: a pilot-scale study in Northern Serbia

A pilot-scale study was performed to explore the possibility of the removal of natural organic matter (NOM) and arsenic from groundwater in the village of Melenci (Northern Serbia) using strongly basic, macroporous ion-exchange resin, commercially available as Amberlite IRA 958-Cl. The influences of the specific flow rate (SFR) and a broad range of contact times were studied using native groundwater and the same water pretreated with sodium hypochlorite (NaClO) for the oxidation of As(III) to As(V) and the degradation of NOM. The investigated SFR exceeded the manufacturer's recommended maximum value by up to ten times. In the range of SFR from 50 to 300 bed volumes per hour (BV/h), a higher efficiency of NOM removal was achieved in the absence of the oxidant, whereas at lower SFR and shorter contact times, the efficiency was higher when the water was pretreated. The arsenic removal from the oxidant-pretreated water was equally efficient at all SFR, whereas in the absence of the oxidant the efficiency was significantly lower and did not depend on SFR. The effectiveness of the resin illustrates the fact that the experimentally determined optimum SFR value of 30 BV/h is stated as the maximum in the manufacturer's specifications.

Formation of chlorinated biphenyls, diphenyl ethers and benzofurans as a result of Fenton-driven oxidation of 2-chlorophenol

Homogeneous catalytic Fenton oxidation proved to be very efficient in the degradation of high concentrations (3.9 mM) of 2-chlorophenol (2-CP) in aqueous matrices. When using [H(2)O(2)](0)/[2-CP](0) substoichiometric molar ratios of 4 and 16, the detected aromatic intermediates included mainly chlorinated benzenediols, with the virtual absence of condensation products of higher molecular weight. At even lower substoichiometric ratios of [H(2)O(2)](0)/[2-CP](0) (< or =2.2), hydroxylated chlorobiphenyls, hydroxylated chlorodiphenyl ethers and hydroxylated chlorinated dibenzofurans were formed in addition to chlorinated benzenediols. The aromatic intermediates were identified as trimethylsilyl ethers and dimethyl-t-butyl silyl ethers. A reaction scheme was proposed to describe the formation of aromatic intermediates based on coupling reactions of resonance-stabilized 2-CP radicals generated by electrophilic attack of reactive hydroxyl radicals. The pattern of aromatic intermediates identified in the Fenton solutions coincided well with that predicted on the basis of oxidative coupling reactions. In addition to coupling of stabilized radicals, aromatic intermediates can be formed by addition of organoradicals onto neutral analyte molecules. The findings presented in this contribution are considered crucial for the design and optimization of Fenton-based remediation devoted either to wastewater treatment under economically feasible conditions or to in situ groundwater treatment where poorly controlled reaction conditions prevail.

Reduced toxicity of olive mill waste waters by oxidative coupling with biomimetic catalysis

Large quantities of environmentally toxic olive mill waste waters (OMWW) result from olive oil production worldwide. A synthetic water-soluble meso-tetra(2,6-dichloro-3-sulfonatophenyl)porphyrinate of iron(III) chloride (FePha) was used as biomimetic catalystto oxidatively couple toxic phenols in OMWW fractions obtained by micro-, ultra-, and nanofiltration, and reverse osmosis. The occurrence of oxidative coupling in different OMWW size-fractions was assessed by high performance size exclusion chromatography (HPSEC), before and after conformational disruption with acetic acid, and measurements of proton spin-lattice relaxation time in the rotating frame (T1(rho)H) through 13C-CPMAS-NMR spectroscopy. The concurrent reduction in toxicity of OMWW size-fractions brought about by the FePha treatment was monitored by an algal bioassay. HPSEC chromatograms of OMWW samples subjected to catalyzed coupling showed apparent weight-average molecular weight (Mwa) values varying from 18 to 185% larger than for control. Moreover, when such FePha-treated fractions were added to acetic acid prior to HPSEC, the Mwa values still ranged from 14 to 162% larger than for control fractions similarly treated with acetic acid. This evidence of polymerization among toxic phenols was confirmed by T1(rho)(H) values which were significantly enhanced by the FePha treatment, thereby indicating an increased conformational rigidity of OMWW materials. These molecular changes were reflected in a significantly reduced toxicity exerted on microalgae by the OMWW size-fractions subjected to catalyzed oxidative couplings. Our results suggest that OMWW can be effectively treated with a biomimetic catalyst to induce oxidative phenol polymerization and reduce their toxicity before amendments to soils or other disposal means.