use-battery-chemical-ecotoxicological-methods-for-assessment-efficacy

Use of a Battery of Chemical and Ecotoxicological Methods for the Assessment of the Efficacy of Wastewater Treatment Processes to Remove Estrogenic Potency

Endocrine Disrupting Compounds pose a substantial risk to the aquatic environment. Ethinylestradiol (EE2) and estrone (E1) have recently been included in ...

Carnegie Mellon University

We report an enantioselective conjugate addition nitro-Mannich reaction protocol which combines dialkylzinc, aromatic nitro alkene and imine to form two C-C bonds and three contiguous stereocenters in one reaction vessel. Absolute stereochemistry was controlled from the initial 1,4-addition of dialkylzinc to aromatic nitroalkenes by known copper-chiral ligand catalysts. The choice of solvent dictated the formation of either the syn,anti or syn,syn diastereoisomers, two of the four possible diastereoisomers. The syn,syn isomer is a rare example of a syn-selective nitro-Mannich reaction. The diastereoselectivity is dependent upon the presence or not of Zn(O(2)CCF(3))(2) in the reaction mixture and empirical transition state models are proposed to account for the observed stereochemical course of the two reaction conditions. The extent of enantioselectivity and structural diversity of the process is limited by current methodology for the catalytic asymmetric addition of dialkylzincs to nitrostyrenes. The synthetically versatile products are the most complex β-nitro amines prepared using the nitro-Mannich reaction and are formed in high yield and enantioselectivity.

Enantioselective conjugate addition nitro-Mannich reactions: solvent controlled synthesis of acyclic anti- and syn-β-nitroamines with three contiguous stereocenters.

Copper-catalyzed conjugate addition of diorgano zinc reagents to nitroacrylate 1 followed by a subsequent nitro-Mannich reaction and in situ lactamization leads to an efficient one-pot synthesis of 1,3,5-trisubstituted 4-nitropyrrolidin-2-ones (5). The versatility of the reaction is shown for a wide range of N-p-(methoxy)phenyl protected aldimines 3 derived from alkyl, aryl, and heteroaryl aldehydes. The densely functionalized pyrrolidin-2-ones 5 are isolated as single diastereoisomers (40 examples, 33-84% yield). An enantioselective copper-catalyzed conjugate addition of diethylzinc led to highly crystalline products that could be recrystallized to enantiopurity in high yield. A range of successful chemoselective transformations were investigated, which widens the applicability of the pyrrolidn-2-ones as stereochemically pure building blocks for further organic synthesis.

Stereoselective synthesis of densely functionalized pyrrolidin-2-ones by a conjugate addition/nitro-Mannich/lactamization reaction.

The results of low-temperature investigations of the oxidations of 9,10-dihydroanthracene, cumene, ethylbenzene, [D10]ethylbenzene, cyclooctane, and cyclohexane by an iron(V)-oxo TAML complex (2; see Figure 1) are presented, including product identification and determination of the second-order rate constants k2 in the range 233-243 K and the activation parameters (ΔH(≠) and ΔS(≠)). Statistically normalized k2 values (log k2') correlate linearly with the C-H bond dissociation energies DC-H, but ΔH(≠) does not. The point for 9,10-dihydroanthracene for the ΔH(≠) vs. DC-H correlation lies markedly off a common straight line of best fit for all other hydrocarbons, suggesting it proceeds via an alternate mechanism than the rate-limiting C-H bond homolysis promoted by 2. Contribution from an electron-transfer pathway may be substantial for 9,10-dihydroanthracene. Low-temperature kinetic measurements with ethylbenzene and [D10]ethylbenzene reveal a kinetic isotope effect of 26, indicating tunneling. The tunnel effect is drastically reduced at 0 °C and above, although it is an important feature of the reactivity of TAML activators at lower temperatures. The diiron(IV) μ-oxo dimer that is often a common component of the reaction medium involving 2 also oxidizes 9,10-dihydroanthracene, although its reactivity is three orders of magnitude lower than that of 2.

Activation parameters as mechanistic probes in the TAML iron(V)-oxo oxidations of hydrocarbons.

The catalytic activity of the N-tailed ("biuret") TAML (tetraamido macrocyclic ligand) activators [Fe{4-XC6 H3 -1,2-(NCOCMe2 NCO)2 NR}Cl](2-) (3; N atoms in boldface are coordinated to the central iron atom; the same nomenclature is used in for compounds 1 and 2 below), [X, R=H, Me (a); NO2 , Me (b); H, Ph (c)] in the oxidative bleaching of Orange II dye by H2 O2 in aqueous solution is mechanistically compared with the previously investigated activator [Fe{4-XC6 H3 -1,2-(NCOCMe2 NCO)2 CMe2 }OH2 ](-) (1) and the more aggressive analogue [Fe(Me2 C{CON(1,2-C6 H3 -4-X)NCO}2 )OH2 ](-) (2). Catalysis by 3 of the reaction between H2 O2 and Orange II (S) occurs according to the rate law found generally for TAML activators (v=kI kII [Fe(III) ][S][H2 O2 ]/(kI [H2 O2 ]+kII [S]) and the rate constants kI and kII at pH 7 both decrease within the series 3 b>3 a>3 c. The pH dependency of kI and kII was investigated for 3 a. As with all TAML activators studied to-date, bell-shaped profiles were found for both rate constants. For kI , the maximal activity was found at pH 10.7 marking it as having similar reactivity to 1 a. For kII , the broad bell pH profile exhibits a maximum at pH about 10.5. The condition kI ≪kII holds across the entire pH range studied. Activator 3 b exhibits pronounced activity in neutral to slightly basic aqueous solutions making it worthy of consideration on a technical performance basis for water treatment. The rate constants ki for suicidal inactivation of the active forms of complexes 3 a-c were calculated using the general formula ln([S0 ]/[S∞ ])=(kII /ki )[Fe(III) ]; here [Fe(III) ], [S0 ], and [S∞ ] are the total catalyst concentration and substrate concentration at time zero and infinity, respectively. The synthesis and X-ray characterization of 3 c are also described.

Reactivity and operational stability of N-tailed TAMLs through kinetic studies of the catalyzed oxidation of orange II by H2 O2 : synthesis and X-ray structure of an N-phenyl TAML.

Invited for the cover of this issue are Terrence J. Collins and co-workers at Carnegie Mellon University (USA) and the National Chemical Laboratory (India). The image depicts five generations of tetraamido macrocyclic ligand (TAML) activators, which are small molecule, full-functional mimics of oxidizing enzymes that arguably outperform the peroxidase enzymes they mimic. Read the full text of the article at 10.1002/chem.201406061.

Reactivity and operational stability of N-Tailed TAMLs through kinetic studies of the catalyzed oxidation of orange II by H2 O2 : synthesis and X-ray structure of an N-phenyl TAML.

17α-ethinylestradiol (EE2), a synthetic oestrogen in oral contraceptives, is one of many pharmaceuticals found in inland waterways worldwide as a result of human consumption and excretion into wastewater treatment systems. At low parts per trillion (ppt), EE2 induces feminisation of male fish, diminishing reproductive success and causing fish population collapse. Intended water quality standards for EE2 set a much needed global precedent. Ozone and activated carbon provide effective wastewater treatments, but their energy intensities and capital/operating costs are formidable barriers to adoption. Here we describe the technical and environmental performance of a fast- developing contender for mitigation of EE2 contamination of wastewater based upon small- molecule, full-functional peroxidase enzyme replicas called "TAML activators". From neutral to basic pH, TAML activators with H2O2 efficiently degrade EE2 in pure lab water, municipal effluents and EE2-spiked synthetic urine. TAML/H2O2 treatment curtails estrogenicity in vitro and substantially diminishes fish feminization in vivo. Our results provide a starting point for a future process in which tens of thousands of tonnes of wastewater could be treated per kilogram of catalyst. We suggest TAML/H2O2 is a worthy candidate for exploration as an environmentally compatible, versatile, method for removing EE2 and other pharmaceuticals from municipal wastewaters.

Removal of ecotoxicity of 17α-ethinylestradiol using TAML/peroxide water treatment.

The main features of iron-tetra-amido macrocyclic ligand complex (a sub-branch of TAML) catalysis of peroxide oxidations are rationalized by a two-step mechanism: Fe(III) + H2O2 → Active catalyst (Ac) (kI), and Ac + Substrate (S) → Fe(III) + Product (kII). TAML activators also undergo inactivation under catalytic conditions: Ac → Inactive catalyst (ki). The recently developed relationship, ln(S0/S∞) = (kII/ki)[Fe(III)]tot, where S0 and S∞ are [S] at time t = 0 and ∞, respectively, gives access to ki under any conditions. Analysis of the rate constants kI, kII, and ki at the environmentally significant pH of 7 for a broad series of TAML activators has revealed a 6 orders of magnitude reactivity differential in both kII and ki and 3 orders differential in kI. Linear free energy relationships linking kII with ki and kI reveal that the reactivity toward substrates is related to the instability of the active TAML intermediates and suggest that the reactivity in all three processes derives from a common electronic origin. The reactivities of TAML activators and the horseradish peroxidase enzyme are critically compared.

Matthew R. Mills

Department of Chemistry

Carnegie Mellon University

Use of a Battery of Chemical and Ecotoxicological Methods for the Assessment of the Efficacy of Wastewater Treatment Processes to Remove Estrogenic Potency

Matthew R. Mills

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Carnegie Mellon University

Use of a Battery of Chemical and Ecotoxicological Methods for the Assessment of the Efficacy of Wastewater Treatment Processes to Remove Estrogenic Potency

Department of Chemistry