Reaction Of Dioxygen Research Articles

Computational Study on Flavin-Catalyzed Aerobic Dioxygenation of Alkenyl Thioesters: Decomposition of Anionic Peroxides.

Flavin-dependent catalysts are widely applied to aerobic monooxygenation/oxidation reactions. In contrast, flavin-catalyzed aerobic dioxygenation reactions exhibit higher atomic economy but are less reported, not to mention the relevant mechanistic studies. Herein, a density functional theory study on flavin-catalyzed aerobic epoxidation-oxygenolysis of alkenyl thioesters was performed for the first time. Different from the previous mechanistic proposal, a pathway featuring two catalytic stages, monoanionic flavin-C(4a)-peroxide/oxide intermediates, and a reverse reaction sequence (epoxidation goes prior to oxygenolysis) was revealed. In comparison, the pathways involving dianionic flavin catalysts, monoanionic flavin-N(5)-(hydro)peroxide/C(10a)-peroxide, or neutral flavin-C(4a)-hydroperoxide/hydroxide/N(5)-oxide, and the pathways where oxygenolysis goes prior to epoxidation are less favored. Epoxidation goes through intramolecular substitution of the O-O bond of anionic flavin-C(4a)-peroxide by β-carbon, while the resulting flavin-C(4a)-oxide accomplishes the oxygenolysis. Furthermore, two other reaction modes, i.e., concerted O-O cleavage/1,2-shift of α-substituents and dyotropic rearrangement were discovered for the decomposition of other anionic peroxides, and preliminary rules were summarized for understanding the chemoselectivity for this process. This study sheds light on the different reaction features of numerous flavin-dioxygen derivatives, providing deeper insights into flavin-catalyzed dioxygenation reactions, and is expected to inspire experimental design based on unconventional anionic peroxides.

Consecutive one-pot alkyne semihydrogenation/alkene dioxygenation reactions by Pt(II)/Cu(II) single-chain nanoparticles in green solvent.

Heterobimetallic Pt(II)/Cu(II) single-chain polymer nanoparticles (SCNPs) were sequentially synthesized from a polymeric precursor featuring both α-diazo-β-ketoester and naked β-ketoester functional groups. Photoactivated carbene generation at λexc = 365 nm from α-diazo-β-ketoester moieities was triggered for bonding Pt(II) ions from dichloro(1,5-cyclooctadiene)Pt(II) to the polymeric precursor, whereas Cu(II) ions were subsequently incorporated via Cu(II)-(β-ketoester)2 complex formation using Cu(II) acetate. Both intrachain Pt(II) bonding and Cu(II) complexation were found to contribute to the folding of the polymeric precursor generating Pt(II)/Cu(II)-SCNPs as evidenced by infrared spectroscopy, size exclusion chromatography and dynamic light scattering. These heterobimetallic SCNPs proved highly efficient as soft nanocatalysts for the consecutive one-pot alkyne semihydrogenation/alkene dioxygenation reactions at room temperature in N-butylpyrrolidone, as a non-toxic alternative solvent to N,N-dimethylformamide.

HCO3−-mediated highly efficient photoelectrochemical dioxygenation of arylalkenes: triple roles of HCO3−-derived radicals

HCO3−-mediated highly efficient photoelectrochemical dioxygenation of arylalkenes coupled with the hydrogen evolution reaction: triple roles of HCO3−-derived radicals.

Copper-Catalyzed Enantioselective Aerobic Alkene Aminooxygenation and Dioxygenation: Access to 2-Formyl Saturated Heterocycles and Unnatural Proline Derivatives.

Alkene aminooxygenation and dioxygenation reactions that result in carbonyl products are uncommon, and protocols that control absolute stereochemistry are rare. We report herein catalytic enantioselective alkene aminooxygenation and dioxygenation that directly provide enantioenriched 2-formyl saturated heterocycles under aerobic conditions. Cyclization of substituted 4-pentenylsulfonamides, catalyzed by readily available chiral copper complexes and employing molecular oxygen as both oxygen source and stoichiometric oxidant, directly provides chiral 2-formyl pyrrolidines efficiently. Reductive or oxidative workup of these aldehydes provides their respective amino alcohols or amino acids (unnatural prolines). Enantioselective synthesis of an indoline and isoquinolines is also demonstrated. Concurrently, cyclization of various alkenols under similar conditions provides 2-formyl tetrahydrofurans, phthalans, isochromans, and morpholines. The nature of the copper ligands, the concentration of molecular oxygen, and the reaction temperature all impact the product distribution. Chiral nitrogen and oxygen heterocycles are common components of bioactive small molecules, and these enabling technologies provide access to saturated heterocycles functionalized with ready-to-use carbonyl electrophiles.

Selective Control and Characteristics of Water Oxidation and Dioxygen Reduction in Environmental Photo(electro)catalytic Systems.

ConspectusEmploying semiconductor materials is a popular engineering method to harvest solar energy, which is widely investigated for photocatalysis (PC) and photoelectrocatalysis (PEC) that convert solar light to chemical energy. In particular, environmental photo(electro)catalysis has been extensively studied as a sustainable method for water treatment, air purification, and resource recovery. Environmental PC/PEC processes working in ambient conditions are initiated mainly through hole transfer to water (water oxidation) and electron transfer to dioxygen (O2 reduction) and the subsequent photoredox transformation of water and dioxygen serves as a base of various PC/PEC systems. Through the redox transformations, different products can be generated depending on the number of transferred electrons and holes. The single electron/hole transfer generates radical species and reactive oxygen species (ROS) which initiate the degradation/transformation of various pollutants in water and air, while the multicharge transfer can generate energy-rich chemicals (e.g., H2, H2O2). Therefore, understanding the characteristics of the photoredox reactions of water and dioxygen on the semiconductor surface is critically important in controlling the selectivity and efficiency of photoconversion processes.In this Account, we describe various environmental PC/PEC conversions with a particular focus on how the phototransformation of dioxygen and water is related to the overall processes occurring on diverse semiconductor materials. The activation of water or dioxygen can be controlled by modifying the properties of semiconductors, changing the kind of counterpart half-reaction and the experimental conditions. If water can be used as a ubiquitous reductant under solar irradiation, many kinds of reductive transformations can be carried out under ambient environmental conditions. For example, various toxic oxyanions (or metal ions) can be reductively transformed to harmless or less harmful species or useful chemicals/fuels can be synthesized under ambient conditions if water can provide electrons and protons via solar water oxidation. On the other hand, dioxygen can turn into reactive oxygen species (ROS) as a versatile oxidant or to a chemical like H2O2. There should be many more possibilities of utilizing the photoconversion of water and dioxygen for environmentally significant purposes, which are yet to be further developed and demonstrated. In this Account, we highlight the recent strategies and the novel functional materials for effective activation of water and dioxygen in environmental PC/PEC systems. Design of environmentally functional PC/PEC systems should be based on better understanding of water and dioxygen activation.

Exploring the nitric oxide dioxygenation (NOD) reactions of manganese-peroxo complexes.

Here, we report the nitric oxide dioxygenation (NOD) reactions of two MnIII-peroxo (MIII-O22-) complexes, [(3PYENMe)MnIII(O22-)]+ (1) and [(N3PY)MnIII(O22-)]+ (2), bearing pentadentate ligands. Complexes 1 and 2 give MnII-nitrate (MnII-NO3-) complexes (3 and 4) when reacted with nitric oxide (NO), respectively. The mechanistic study explored by using 2,4-di-tert-butylphenol (2,4-DTBP) suggested that the NOD reaction of 1 and 2 occurs via a presumed Mn-peroxynitrite ([Mn-PN]+, [Mn-ONOO-]+) intermediate. Tracking the source of N atoms using 15NO revealed that the N-atoms in MnII-NO3- (3 and 4) are derived from the 15NO moiety. Furthermore, we have explored the MIII-O22- regeneration from NOD products (3 and 4), and we have observed the formation of MIII-O22- complexes (1 and 2) upon treatment with KO2 or H2O2/triethylamine (TEA), respectively.

Flavonol dioxygenation catalysed by cobalt(II) complexes supported with 3N(COO) and 4N donor ligands: a comparative study to assess the carboxylate effects on quercetin 2,4-dioxygenase-like reactivity.

Two new cobalt(II)-acetato complexes, [CoII(L3NCOO)(OAc)]·0.5H2O (1OAc·0.5H2O) and [CoII(L4N)(OAc)](PF6) (2OAc(PF6)), were synthesised using ligands L3NCOO- (Li+L3NCOO- = lithium 2-(benzyl((6'-methyl-[2,2'-bipyridin]-6-yl)methyl)amino)acetate) and L4N (N-benzyl-1-(6'-methyl-[2,2'-bipyridin]-6-yl)-N-(pyridin-2-ylmethyl)methanamine), respectively, to mimic the functional activity of cobalt(II)-quercetin-2,4-dioxygenase (CoII-2,4-QD). Additionally, Co(II)-flavonolato ternary complexes, [CoII(L3NCOO)(fla)]·H2O (1fla·H2O) and [CoII(L4N)(fla)](PF6) (2fla(PF6)), were synthesised as enzyme-substrate models. All four complexes were thoroughly characterised by elemental analyses and spectroscopic methods. Structural characterisation was performed for 1OAc·0.5H2O, 2OAc(PF6)·CH2Cl2 and 2fla+ with a perchlorate counter anion, 2fla(ClO4)·1.5H2O. Furthermore, density functional theory (DFT) calculations, time-dependent DFT (TD-DFT) and molecular orbital (MO) analysis were performed for the flavonolato adducts 1fla and 2fla+. The catalytic activities of complexes 1OAc·0.5H2O and 2OAc(PF6) in the oxygenative degradation of flavonol (multiple-turnover reactions) were investigated at 70 °C in DMF to determine the effect of the carboxylate substituent over a pyridyl donor residue on reactivity. Complex 1OAc·0.5H2O showed a higher catalytic rate than complex 2OAc(PF6). The same reactivity order was observed for single-turnover dioxygenation reactions with ternary complexes (1fla > 2fla+). The formation constants (Kf) of 1fla and 2fla+ species are comparable, implying that catalyst-substrate adduct formation occurs in similar amounts for both catalytic reactions. Therefore, the Kf values have a similar impact on reactivities. However, the oxidation potential of the bound fla-/fla˙ couple in 1fla is considerably lower than that in 2fla+. DFT calculations predicted that the negatively charged carboxylate group of ligand L3NCOO- determines the higher reactivity of 1fla with dioxygen by decreasing the oxidation potential of the bound fla-/fla˙ couple. During the dioxygenation process, the reactive Co(II)-bound flavonoxy radical was generated via single-electron transfer from the coordinated fla- to dioxygen, simultaneously forming a superoxide ion. The anionic carboxylate group improves the stability of the bound flavonoxy radical by providing substantial electron density to the electron-deficient fla˙ through the Co(II) centre, allowing the reactive fla˙ species to accumulate at an optimal concentration for effective catalysis. EPR spectroscopy successfully detected the cobalt-bound fla˙ species formed through the dioxygenation of 1fla. NBT2+ and EPR spin-trapping experiments confirmed superoxide formation during the dioxygenation process. So, the present work describes CoII-2,4-QD model studies and clarifies the function of carboxylate in quercetinase-like reactivity.

Investigations on the Reactivity of Copper(I) Complexes with a N3S Thioether Ligand System

AbstractIn the active site of several copper monooxygenases, thioether residues are coordinated through the sulfur atom, e. g. dopamine‐β‐monooxygenase (DβM). The reaction of dioxygen with a series of copper(I) complexes with thioether groups in tripodal ligands based on either derivatives of tris(2‐pyridylmethyl)amine (TMPA) or a guanidine system were investigated by low‐temperature stopped‐flow measurements. The formation of labile intermediates, an end‐on superoxido complex, and μ‐1,2‐trans‐peroxido copper(II) complexes were spectroscopically detected and a kinetic analysis allowed the calculation of activation parameters for these reactions supporting the postulated mechanism. Most interesting was the finding that replacing the ethyl group in the tren‐guanidine derivative (TMGEt)2(SEtEt)N with a methyl group allowed a dramatic increase in the stability of the formed superoxido copper complex. Measurements with ozone were performed in order to find an alternative way to obtain and stabilize the labile intermediates.

Reactivity of Copper Complexes with Tripodal Tetradentate Ligands based on Camphoric Acid towards Dioxygen

AbstractThe reaction of dioxygen with copper(I) complexes containing camphor‐derived ligands was investigated. Stopped‐flow measurements revealed the formation of bis(μ‐oxido) copper complexes at low temperatures. However, these intermediates were not stable enough to be isolated and decomposed quickly. Sterically more demanding alkyl groups slowed the formation of the bis(μ‐oxido) copper complexes. A kinetic analysis was performed and showed ‐ in line with previous reports ‐ that the rate‐determining step could be assigned to forming a mononuclear superoxido copper complex. For one of the reactions investigated, a product could be structurally characterized and turned out to be a copper(II) complex with an additional hydroxide as a ligand (most likely caused by a C−H abstraction from the solvent acetone). One of the complexes oxidized thioanisole to the corresponding sulfoxide (conversion of 34 % according to GC‐MS) with no byproducts. Chiral GC gave an enantiomeric excess of 14 %.

Rieske Oxygenase Catalyzed C–H Bond Functionalization Reactions in Chlorophyll b Biosynthesis

Rieske oxygenases perform precise C–H bond functionalization reactions in anabolic and catabolic pathways. These reactions are typically characterized as monooxygenation or dioxygenation reactions, but other divergent reactions are also catalyzed by Rieske oxygenases. Chlorophyll(ide) a oxygenase (CAO), for example is proposed to catalyze two monooxygenation reactions to transform a methyl-group into the formyl-group of Chlorophyll b. This formyl group, like the formyl groups found in other chlorophyll pigments, tunes the absorption spectra of chlorophyllb and supports the ability of several photosynthetic organisms to adapt to environmental light. Despite the importance of this reaction, CAO has never been studied in vitro with purified protein, leaving many open questions regarding whether CAO can facilitate both oxygenation reactions using just the Rieske oxygenase machinery. In this study, we demonstrated that four CAO homologues in partnership with a non-native reductase convert a Chlorophyll a precursor, chlorophyllidea, into chlorophyllideb in vitro. Analysis of this reaction confirmed the existence of the proposed intermediate, highlighted the stereospecificity of the reaction, and revealed the potential of CAO as a tool for synthesizing custom-tuned natural and unnatural chlorophyll pigments. This work thus adds to our fundamental understanding of chlorophyll biosynthesis and Rieske oxygenase chemistry.

Gold‐Catalyzed Regioselective Oxyfluorination/Oxydifluorination vs. Diketonization of Phthalimido‐Protected Propargylamines with Selectfluor

AbstractAlkyl‐ and aryl‐substituted N‐propargyl phthalimides were used as valuable building blocks for the selective formation of the corresponding α‐fluoro, β‐phthalimido ketones, α,α‐difluoro, β‐phthalimido ketones or β‐phthalimido α‐diketones by means of gold‐catalyzed oxyfluorination/oxydifluorination or dioxygenation reactions. The key factors addressing the product selectivity control were determined. The simultaneous assembly of the quinoxaline nucleus and the removal of the phthalimido‐protecting group were tested. Reaction mechanisms of the different reaction pathways are assumed.

Oxygenolysis of a series of copper(II)-flavonolate adducts varying the electronic factors on supporting ligands as a mimic of quercetin 2,4-dioxygenase-like activity.

Four copper(II)-flavonolate compounds of type [Cu(LR)(fla)] {where LR = 2-(p-R-benzyl(dipyridin-2-ylmethyl)amino)acetate; R = -OMe (1), -H (2), -Cl (3) and -NO2 (4)} have been developed as a structural and functional enzyme-substrate (ES) model of the Cu2+-containing quercetin 2,4-dioxygenase enzyme. The ES model complexes 1-4 are synthesized by reacting 3-hydroxyflavone in the presence of a base with the respective acetate-bound copper(II) complexes, [Cu(LR)(OAc)]. In the presence of dioxygen the ES model complexes undergo enzyme-type oxygenolysis of flavonolate (dioxygenase type bond cleavage reaction) at 80 °C in DMF. The reactivity shows a substituent group dependent order as -OMe (1) > -H (2) > -Cl (3) > -NO2 (4). Experimental and theoretical studies suggest a single-electron transfer (SET) from flavonolate to dioxygen, rather than valence tautomerism {[CuII(fla-)] ↔ [CuI(fla˙)]}, to generate the reactive flavonoxy radical (fla˙) that reacts further with the superoxide radical to bring about the oxygenative ring opening reaction. The SET pathway has been further verified by studying the dioxygenation reaction with a redox-inactive Zn2+ complex, [Zn(LOMe)(fla)] (5).

The Regulation of O2 Spin State and Direct Oxidation of CO at Room Temperature Using Triboelectric Plasma by Harvesting Mechanical Energy.

Oxidation reactions play a critical role in processes involving energy utilization, chemical conversion, and pollutant elimination. However, due to its spin-forbidden nature, the reaction of molecular dioxygen (O2) with a substrate is difficult under mild conditions. Herein, we describe a system that activates O2 via the direct modulation of its spin state by mechanical energy-induced triboelectric corona plasma, enabling the CO oxidation reaction under normal temperature and pressure. Under optimized reaction conditions, the activity was 7.2 μmol h−1, and the energy consumption per mole CO was 4.2 MJ. The results of kinetic isotope effect, colorimetry, and density functional theory calculation studies demonstrated that electrons generated in the triboelectric plasma were directly injected into the antibonding orbital of O2 to form highly reactive negative ions O2−, which effectively promoted the rate-limiting step of O2 dissociation. The barrier of the reaction of O2− ions and CO molecular was 3.4 eV lower than that of O2 and CO molecular. This work provides an effective strategy for using renewable and green mechanical energy to realize spin-forbidden reactions of small molecules.

Characterization of copper complexes with derivatives of the ligand (2-aminoethyl)bis(2-pyridylmethyl)amine (uns-penp) and their reactivity towards oxygen

A series of copper(I) complexes with ligands derived from the tripodal ligand (2-aminoethyl)bis(2-pyridylmethyl)amine (uns-penp) have been structurally characterized and their redox chemistry analyzed by cyclic voltammetry. While the redox potentials of most of the complexes were similar their reactivity towards dioxygen was quite different. While the complex with a ferrocene derived ligand of uns-penp reacted in solution at low temperatures in a two-step reaction from the preliminary formed mononuclear end-on superoxido complex to a quite stable dinuclear peroxido complex it did not react with dioxygen in the solid state. Other complexes also did not react with dioxygen in the solid state while some showed a reversible formation to a green compound, indicating formation of an end-on superoxido complex that unfortunately so far could not be characterized. In contrast, copper complexes with the Me2uns-penp and Et-iProp-uns-penp formed dinuclear peroxido complexes in a solid-state reaction. While the reaction of dioxygen with the [Cu(Me2uns-penp]BPh4 was quite slow an instant reaction took place for [Cu(Et-iProp-uns-penp]BPh. Very unusual, it turned out that crystals of the copper(I) complex that could be structurally characterized still were crystalline when reacted with dioxygen. Therefore, it was possible to solve the structure of the corresponding dinuclear peroxido complex directly from the same batch of crystals. The crystalline structures of the copper(I) and copper(II) complex revealed that the reason for this is the fact, that the copper(I) complex is kind of preorganized for the uptake of dioxygen and does not really change in its overall structure when being oxidized.

Dioxygen Activation and Pyrrole α-Cleavage with Calix[4]pyrrolato Aluminates: Enzyme Model by Structural Constraint.

The present work describes the reaction of triplet dioxygen with the porphyrinogenic calix[4]pyrrolato aluminates to alkylperoxido aluminates in high selectivity. Multiconfigurational quantum chemical computations disclose the mechanism for this spin‐forbidden process. Despite a negligible spin–orbit coupling constant, the intersystem crossing (ISC) is facilitated by singlet and triplet state degeneracy and spin–vibronic coupling. The formed peroxides are stable toward external substrates but undergo an unprecedented oxidative pyrrole α‐cleavage by ligand aromatization/dearomatization‐initiated O−O σ‐bond scission. A detailed comparison of the calix[4]pyrrolato aluminates with dioxygen‐related enzymology provides insights into the ISC of metal‐ or cofactor‐free enzymes. It substantiates the importance of structural constraint and element–ligand cooperativity for the functions of aerobic life.

Reaction of ammonia and dioxygen in solid neon excited with far-ultraviolet radiation investigated with electronic and vibrational spectra

Irradiation of dilute mixtures of NH3 and O2 dispersed in solid Ne at 3.6 K with light of wavelengths 200, 192.5, 173, and 143 nm from a synchrotron initiated photochemical dissociation of those precursors and the production of N, NH, NH2, O, O3, HO2, NO, NO2, N2O, H2O, HONO in both s-cisoid and s-transoid rotational isomers, and HONO2, detected according to their spectra in mid-infrared absorption from 450 to 4000 cm−1 and in absorption and emission from 200 to 1100 nm.

A Dynamic Substrate is Required for MhuD-Catalyzed Degradation of Heme to Mycobilin.

The noncanonical heme oxygenase MhuD from Mycobacterium tuberculosis binds a heme substrate that adopts a dynamic equilibrium between planar and out-of-plane ruffled conformations. MhuD degrades this substrate to an unusual mycobilin product via successive monooxygenation and dioxygenation reactions. This article establishes a causal relationship between heme substrate dynamics and MhuD-catalyzed heme degradation, resulting in a refined enzymatic mechanism. UV/vis absorption (Abs) and electrospray ionization mass spectrometry (ESI-MS) data demonstrated that a second-sphere substitution favoring the population of the ruffled heme conformation changed the rate-limiting step of the reaction, resulting in a measurable buildup of the monooxygenated meso-hydroxyheme intermediate. In addition, UV/vis Abs and ESI-MS data for a second-sphere variant that favored the planar substrate conformation showed that this change altered the enzymatic mechanism resulting in an α-biliverdin product. Single-turnover kinetic analyses for three MhuD variants revealed that the rate of heme monooxygenation depends upon the population of the ruffled substrate conformation. These kinetic analyses also revealed that the rate of meso-hydroxyheme dioxygenation by MhuD depends upon the population of the planar substrate conformation. Thus, the ruffled heme conformation supports rapid heme monooxygenation by MhuD, but further oxygenation to the mycobilin product is inhibited. In contrast, the planar substrate conformation exhibits altered heme monooxygenation regiospecificity followed by rapid oxygenation of meso-hydroxyheme. Altogether, these data yielded a refined enzymatic mechanism for MhuD where access to both substrate conformations is needed for rapid incorporation of three oxygen atoms into heme yielding mycobilin.

MCPBA-mediated dioxygenation of unactivated alkenes for the synthesis of 5-imino-2-tetrahydrofuranyl methanol derivatives

A mCPBA-mediated, metal-free, intramolecular dioxygenation reaction of unactivated alkenes is reported. In the presence of m-chlorobenzoic peracid, different unsaturated amide substrates could be cyclized via epoxide intermediates, producing the corresponding 5-imino-2-tetrahydrofuranyl methanol products in up to 94% yield at room temperature.

Unusual Nitrene Oxidation Product Formation by Metathesis Involving the Dioxygen O-O and Borylnitrene B-N Bonds.

The reaction of dioxygen with nitrenes can have significant energy barriers, although both reactants are triplet diradicals and the formation of nitroso‐O‐oxides is spin‐allowed. By means of matrix‐isolation infrared spectroscopy in solid argon, nitrogen, and neon, and through high‐level computational quantum chemistry, it is shown herein that a 3‐nitreno‐1,3,2‐benzodioxaborole CatBN (Cat=catecholato) reacts with dioxygen under cryogenic conditions thermally at temperatures as low as 7 K to produce two distinct products, an anti‐nitroso‐O‐oxide and a nitritoborane CatBONO. The computed barriers for the formation of nitroso‐O‐oxide isomers are very low. Whereas anti‐nitroso‐O‐oxide is kinetically trapped, its bisected isomer has a very low barrier for metathesis, yielding the CatBO+NO radicals in a strongly exothermic reaction; these radicals can combine under matrix‐isolation conditions to give nitritoborane CatBONO. The trapped isomer, anti‐nitroso‐O‐oxide, can form the nitritoborane CatBONO only after photoexcitation, possibly involving isomerization to the bisected isomer of anti‐nitroso‐O‐oxide.

Reducing Agent-Mediated Nonenzymatic Conversion of 2-Oxoglutarate to Succinate: Implications for Oxygenase Assays.

l‐Ascorbate (l‐Asc) is often added to assays with isolated FeII‐ and 2‐oxoglutarate (2OG)‐dependent oxygenases to enhance activity. l‐Asc is proposed to be important in catalysis by some 2OG oxygenases in vivo. We report observations on the nonenzymatic conversion of 2OG to succinate, which is mediated by hydrogen peroxide generated by the reaction of l‐Asc and dioxygen. Slow nonenzymatic oxidation of 2OG to succinate occurs with some, but not all, other reducing agents commonly used in 2OG oxygenase assays. We intend these observations will help in the robust assignment of substrates and inhibitors for 2OG oxygenases.