Oxidation Of Organic Substrates Research Articles

Heterogeneous catalysis with encapsulated haem and other synthetic porphyrins: Harnessing the power of porphyrins for oxidation reactions

AbstractEncapsulated metalloporphyrins have been widely studied for their use as efficient heterogeneous catalysts, inspired by the known catalytic activity of porphyrins in haemoproteins. The oxidation of organic substrates by haemoproteins is one of the well-known roles of these proteins, in which the haem (ferriprotoporphyrin IX = FePPIX) cofactor is the centre of reactivity. While these porphyrins are highly efficient catalysts in the protein environment, once removed, they quickly lose their reactivity. It is for this reason that they have garnered much interest in the field of heterogeneous catalysis of oxidation reactions. This review details current research in the field, focusing on the application of encapsulated haem, and other synthetic metalloporphyrins, applied to oxidation reactions.

Bioinspired Olefin cis-Dihydroxylation and Aliphatic C-H Bond Hydroxylation with Dioxygen Catalyzed by a Nonheme Iron Complex.

A mononuclear iron(II)-α-hydroxy acid complex [(TpPh,Me)FeII(benzilate)] (TpPh,Me = hydrotris(3-phenyl-5-methylpyrazol-1-yl)borate) of a facial tridentate ligand has been isolated and characterized to explore its catalytic efficiency for aerial oxidation of organic substrates. In the reaction between the iron(II)-benzilate complex and O2, the metal-coordinated benzilate is stoichiometrically converted to benzophenone with concomitant reduction of dioxygen on the iron center. Based on the results from interception experiments and labeling studies, different iron-oxygen oxidants are proposed to generate in situ in the reaction pathway depending upon the absence or presence of an external additive (such as protic acid or Lewis acid). The five-coordinate iron(II) complex catalytically cis-dihydroxylates olefins and oxygenates the C-H bonds of aliphatic substrates using O2 as the terminal oxidant. The iron(II) complex exhibits better catalytic activity in the presence of a Lewis acid.

Vanadium Complexes Based Polymer Supported Catalysts: A Brief Account of Research from Our Group

Solid supported catalysts can go a long way in developing catalyst based technology because of their high efficiency with recyclability and easy separation from the reaction mixture. Immobilizations of homogeneous catalysts through covalent bond with chloromethylated polystyrene cross-linked with divinylbenzene and develop them as environmentally safe heterogeneous catalysts for oxidation reaction have attracted attention in recent years. Recently, effort from our research laboratory was to synthesize new recyclable polymer-supported vanadium complexes based heterogeneous catalysts. Thus, chloromethylated polystyrene cross linked with 5% divinylbenzene was used as support to prepare variety of polymer supported vanadium catalysts. These catalysts have successfully been used for the oxidation and oxidative bromination of various organic substrates. Keeping in mind the industrial usage of these heterogeneous catalysts, the leaching and recycle ability of all polymer-supported catalysts have also been tested. Most catalysts are stable and do not leach during the catalytic reactions.

From model compounds to applications: Kinetic studies on the activation of dioxygen using an iron complex in a SuperFocus mixer

It was demonstrated previously that a system consisting of a dinuclear iron complex with the ligand HPTB (N,N,N′,N′-tetrakis[2-benzimidazolylmethyl]-1,3-diamino-2-propanol) reacts with dioxygen to form a peroxido complex that may be used for the oxidation of organic substrates. Detailed kinetic studies using stopped-flow techniques and a SuperFocus mixer clearly demonstrate that this complex has a high potential for future applications in catalytic selective oxidation processes in industry. Especially for that reason a reaction KIT system for easy handling was developed that allows to start with a stable iron(III) complex that is reduced (activated) prior to its oxidation with dioxygen.This work has been selected by the Editors as a Featured Cover Article for this issue.

Harnessing the power of microbial nanowires.

SummaryThe reduction of iron oxide minerals and uranium in model metal reducers in the genus Geobacter is mediated by conductive pili composed primarily of a structurally divergent pilin peptide that is otherwise recognized, processed and assembled in the inner membrane by a conserved Type IVa pilus apparatus. Electronic coupling among the peptides is promoted upon assembly, allowing the discharge of respiratory electrons at rates that greatly exceed the rates of cellular respiration. Harnessing the unique properties of these conductive appendages and their peptide building blocks in metal bioremediation will require understanding of how the pilins assemble to form a protein nanowire with specialized sites for metal immobilization. Also important are insights into how cells assemble the pili to make an electroactive matrix and grow on electrodes as biofilms that harvest electrical currents from the oxidation of waste organic substrates. Genetic engineering shows promise to modulate the properties of the peptide building blocks, protein nanowires and current‐harvesting biofilms for various applications. This minireview discusses what is known about the pilus material properties and reactions they catalyse and how this information can be harnessed in nanotechnology, bioremediation and bioenergy applications.

Dabco Ammonium Halochromates, $$ {\text{C}}_{6} {\text{H}}_{14} {\text{N}}_{2}\,^{ + } $$ C 6 H 14 N 2 + $$ {\text{Cr}}_{2} {\text{F}}_{2} {\text{O}}_{6}\,^{ - } $$ Cr 2 F 2 O 6 - (DAXC, X = F, Cl), Reagents for Efficient and Mild Oxidation of Organic Substrates

New orange solid dabco ammonium halochromates, \( {\text{C}}_{6} {\text{H}}_{14} {\text{N}}_{2}\,^{ + } \) \( {\text{Cr}}_{2} {\text{F}}_{2} {\text{O}}_{6}\,^{ - } \), DAXC (X = F, Cl) are easily synthesized by the reaction of dabco (1,4-diaza-bicyclo[2.2.2] octane) with CrO3 in a 1:2 molar ratio in the presence of HF or HCl. Dabco ammonium halochromates(VI) are versatile reagents for the effective and selective oxidation of organic substrates to carbonyl derivatives.

(Invited) Charge Transfer Behaviour of Modified Titania Nanotube Arrays Transplanted on Transparent Conducting Oxides

Free-standing, one-dimensional TiO2 nanotube arrays (TNAs) with disordered surface structure are synthesized on transparent conducting substrates, and their opto-physicochemical properties and photoelectrocatalytic (PEC) performances are examined in detail. TNAs grown on titanium foils are transplanted onto fluorine-doped SnO2 substrates via a two-step anodization process (denoted W-TNAs), followed by being reduced electrochemically for 20 and 90 s (denoted B-TNAs-20 and 90, respectively). As-transplanted W-TNAs exhibit the low PEC activities in terms of photocurrent, and oxygen evolution reaction (OER), and oxidations of inorganic and organic substrates (iodide and urea, respectively) under simulated sunlight (AM 1.5; 100 mW×cm- 2) primarily because of sluggish charge transfers through low electrical conductive TNAs framework. The quick electrochemical reduction of W-TNAs leads to 8-fold larger photocurrent, while significantly accelerating the OER by three times, and the oxidations of iodide and urea by 2 and ~20 times, respectively. Such enhanced PEC activity of B-TNAs is attributed to creation of Ti3+ and associated oxygen vacancy (examined with XPS, EPR, and Raman), strengthening n-type character and thereby increasing electrical conductivity (examined with Mott-Schottky and Nyquist). Time-resolved photoluminescence spectra further reveal that the lifetime (t) of photogenerated charge carriers in B-TNAs (t = 0.33 ns) is an order of magnitude shorter than that of W-TNAs (t = 3.63 ns). The disordered surface exhibits lower Faradaic efficiency for multi-electron transferred oxidation reactions whereas higher Faradaic efficiency for single-electron transfer oxidations compared to W-TNAs. Detailed surface characterization and PEC mechanism are discussed.

Bio-electro-Fenton process for the degradation of Non-Steroidal Anti-Inflammatory Drugs in wastewater

Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) are ubiquitous municipal wastewater pollutants of which several are resistant to degradation in conventional wastewater treatment, and represent a major environmental health concern worldwide. An alternative treatment, the bio-electro-Fenton process, has received increasing attention in past years. In this process the strong oxidant HO is formed using the electrons derived from bacterial oxidation of organic substrate. In this work, a laboratory scale microbial electrolysis cell based bio-electro-Fenton process was developed for the treatment of four different NSAIDs. The system was demonstrated to remove low concentration NSAIDs from water and wastewater and all tested parameters (cathode pH, cathode air-flow, cathode Fe2+ concentration, applied voltage, NSAIDs concentration and reaction time) were found to affect the apparent first order rate constant and removal efficiency for NSAIDs. Optimum parameter values were found to be pH = 2, Fe+2 = 7.5 mM, air-flow = 8 mL min−1, applied voltage = 0.3 V; the apparent rate constant was higher for higher NSAIDs initial concentration. For reaction times of 5 h removal efficiencies were 59–61% for Ketoprofen, 87–97% for Diclofenac, 80–86% for Ibuprofen and 75–81% for Naproxen. Prolonged reaction times lead to substantial increase in removal efficiencies for Ketoprofen and Naproxen. Finally results obtained with real wastewater show lower removal rate constants than with distilled water matrices suggesting interference from wastewater components in the NSAIDs oxidation process. The results offer insight into future developments of an efficient platform for wastewater treatment technology targeting micropollutants.

Thermal and photocatalytic oxidation of organic substrates by dioxygen with water as an electron source

This critical review discusses the thermal and photocatalytic mechanisms of the oxidation of organic substrates by transition metal catalysts and O2, which is the greenest oxidant.

A supramolecular photocatalyst composed of a polyoxometalate and a photosensitizing water-soluble porphyrin diacid for the oxidation of organic substrates in water

A water-soluble porphyrin (H416+) forms stable supramolecular assemblies with polyoxometalates to show photocatalytic substrate oxidation.

Highly dispersed Mo-doped graphite carbon nitride: potential application as oxidation catalyst with hydrogen peroxide

A novel Mo-doped g-C3N4 catalyst exhibits high efficiency for selective oxidation of organic substrates with H2O2 or TBHP.

High efficiency solar chemical conversion using electrochemically disordered titania nanotube arrays transplanted onto transparent conductive oxide electrodes

Free-standing, one-dimensional TiO2 nanotube arrays (TNAs) with a disordered surface structure are synthesized on transparent conducting substrates, and their opto-physicochemical properties and photoelectrocatalytic (PEC) performances are examined in detail. A two-step anodization process is used to transplant TNAs grown on titanium foils onto fluorine-doped SnO2 substrates (denoted as W-TNAs), after which they are electrochemically reduced for 20 and 90 s (denoted as B-TNAs-20 and 90, respectively). The as-transplanted W-TNAs exhibit low PEC activities in terms of their photocurrent, oxygen evolution reaction (OER), and oxidations of inorganic and organic substrates (iodide and urea, respectively) under simulated sunlight (AM 1.5; 100 mW cm−2), primarily because of the sluggish charge transfer through the poor electrically conductive TNA framework. The quick electrochemical reduction of the W-TNAs leads to an 8-fold larger photocurrent, while significantly accelerating the OER (by three times) and iodide and urea oxidation reactions (by 2 and ∼20 times, respectively). These enhanced PEC activities of the B-TNAs are attributed to the creation of Ti3+ and associated oxygen vacancies which strengthen their n-type characteristics and thereby increase their electrical conductivity. The time-resolved photoluminescence spectra further reveal that the lifetime (τ) of the photogenerated charge carriers in the B-TNAs (τ = 0.33 ns) is an order of magnitude shorter than that of the W-TNAs (τ = 3.63 ns). The disordered surface exhibits a lower Faradaic efficiency for multi-electron transfer oxidation reactions and a higher Faradaic efficiency for single-electron transfer oxidation reactions compared to the W-TNAs. The detailed surface characterization and PEC mechanism are discussed.

Cytochrome c as a Peroxidase: Activation of the Precatalytic Native State by H2O2-Induced Covalent Modifications.

In addition to serving as respiratory electron shuttle, ferri-cytochrome c (cyt c) acts as a peroxidase; i.e., it catalyzes the oxidation of organic substrates by H2O2. This peroxidase function plays a key role during apoptosis. Typical peroxidases have a five-coordinate heme with a vacant distal coordination site that permits the iron center to interact with H2O2. In contrast, native cyt c is six-coordinate, as the distal coordination site is occupied by Met80. It thus seems counterintuitive that native cyt c would exhibit peroxidase activity. The current work scrutinizes the origin of this structure-function mismatch. Cyt c-catalyzed peroxidase reactions show an initial lag phase that is consistent with the in situ conversion of a precatalyst to an active peroxidase. Using mass spectrometry, we demonstrate the occurrence of cyt c self-oxidation in the presence of H2O2. The newly generated oxidized proteoforms are shown to possess significantly enhanced peroxidase activity. H2O2-induced modifications commence with oxidation of Tyr67, followed by permanent displacement of Met80 from the heme iron. The actual peroxidase activation step corresponds to subsequent side chain carbonylation, likely at Lys72/73. The Tyr67-oxidized/carbonylated protein has a vacant distal ligation site, and it represents the true peroxidase-active structure of cyt c. Subsequent self-oxidation eventually causes deactivation. It appears that this is the first report that identifies H2O2-induced covalent modifications as an essential component for the peroxidase activity of "native" cyt c.

Gas diffusion electrodes improve hydrogen gas mass transfer for a hydrogen oxidizing bioanode.

BackgroundBioelectrochemical systems (BESs) are capable of recovery of metals at a cathode through oxidation of organic substrate at an anode. Recently, also hydrogen gas was used as an electron donor for recovery of copper in BESs. Oxidation of hydrogen gas produced a current density of 0.8 A m‐2 and combined with Cu2+ reduction at the cathode, produced 0.25 W m‐2. The main factor limiting current production was the mass transfer of hydrogen to the biofilm due to the low solubility of hydrogen in the anolyte. Here, the mass transfer of hydrogen gas to the bioanode was improved by use of a gas diffusion electrode (GDE).ResultsWith the GDE, hydrogen was oxidized to produce a current density of 2.9 A m‐2 at an anode potential of –0.2 V. Addition of bicarbonate to the influent led to production of acetate, in addition to current. At a bicarbonate concentration of 50 mmol L‐1, current density increased to 10.7 A m‐2 at an anode potential of –0.2 V. This increase in current density could be due to oxidation of formed acetate in addition to oxidation of hydrogen, or enhanced growth of hydrogen oxidizing bacteria due to the availability of acetate as carbon source. The effect of mass transfer was further assessed through enhanced mixing and in combination with the addition of bicarbonate (50 mmol L‐1) current density increased further to 17.1 A m‐2.ConclusionHydrogen gas may offer opportunities as electron donor for bioanodes, with acetate as potential intermediate, at locations where excess hydrogen and no organics are available. © 2017 The Authors. Journal of Chemical Technology & Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Photoelectrochemical oxidation of organic substrates in organic media

There is a global effort to convert sunlight into fuels by photoelectrochemically splitting water to form hydrogen fuels, but the dioxygen byproduct bears little economic value. This raises the important question of whether higher value commodities can be produced instead of dioxygen. We report here photoelectrochemistry at a BiVO4 photoanode involving the oxidation of substrates in organic media. The use of MeCN instead of water enables a broader set of chemical transformations to be performed (e.g., alcohol oxidation and C-H activation/oxidation), while suppressing photocorrosion of BiVO4 that otherwise occurs readily in water, and sunlight reduces the electrical energy required to drive organic transformations by 60%. These collective results demonstrate the utility of using photoelectrochemical cells to mediate organic transformations that otherwise require expensive and toxic reagents or catalysts.

Dioxygen Activation: Potential Future Technical Applications in Reactive Bubbly Flows

AbstractA dinuclear iron complex reacts with dioxygen to form a peroxido complex which has the potential to be used in homogeneous catalysis for selective oxidation of organic substrates. Previously, this complex has been investigated in organic solvents that seem less likely to be used on a larger scale in chemical industry. Transferring the reaction from organic solvents to aqueous solutions is difficult; however, first results indicated that derivatives of this complex should lead to the formation of a reactive oxidant from air in water. So far, the complexes investigated do not fulfill the requirements for their usage in a reactive bubbly flow system, but results of this work are promising for future applications.

Electrolytic CO2 Reduction in Tandem with Oxidative Organic Chemistry.

Electrochemical reduction of CO2 into carbon-based products using excess clean electricity is a compelling method for producing sustainable fuels while lowering CO2 emissions. Previous electrolytic CO2 reduction studies all involve dioxygen production at the anode, yet this anodic reaction requires a large overpotential and yields a product bearing no economic value. We report here that the cathodic reduction of CO2 to CO can occur in tandem with the anodic oxidation of organic substrates that bear higher economic value than dioxygen. This claim is demonstrated by 3 h of sustained electrolytic conversion of CO2 into CO at a copper–indium cathode with a current density of 3.7 mA cm–2 and Faradaic efficiency of >70%, and the concomitant oxidation of an alcohol at a platinum anode with >75% yield. These results were tested for four alcohols representing different classes of alcohols and demonstrate electrolytic reduction and oxidative chemistry that form higher-valued carbon-based products at both electrodes.

Atomically Precise Clusters of Noble Metals: Emerging Link between Atoms and Nanoparticles.

Atomically precise pieces of matter of nanometer dimensions composed of noble metals are new categories of materials with many unusual properties. Over 100 molecules of this kind with formulas such as Au25(SR)18, Au38(SR)24, and Au102(SR)44 as well as Ag25(SR)18, Ag29(S2R)12, and Ag44(SR)30 (often with a few counterions to compensate charges) are known now. They can be made reproducibly with robust synthetic protocols, resulting in colored solutions, yielding powders or diffractable crystals. They are distinctly different from nanoparticles in their spectroscopic properties such as optical absorption and emission, showing well-defined features, just like molecules. They show isotopically resolved molecular ion peaks in mass spectra and provide diverse information when examined through multiple instrumental methods. Most important of these properties is luminescence, often in the visible-near-infrared window, useful in biological applications. Luminescence in the visible region, especially by clusters protected with proteins, with a large Stokes shift, has been used for various sensing applications, down to a few tens of molecules/ions, in air and water. Catalytic properties of clusters, especially oxidation of organic substrates, have been examined. Materials science of these systems presents numerous possibilities and is fast evolving. Computational insights have given reasons for their stability and unusual properties. The molecular nature of these materials is unequivocally manifested in a few recent studies such as intercluster reactions forming precise clusters. These systems manifest properties of the core, of the ligand shell, as well as that of the integrated system. They are better described as protected molecules or aspicules, where aspis means shield and cules refers to molecules, implying that they are "shielded molecules". In order to understand their diverse properties, a nomenclature has been introduced with which it is possible to draw their structures with positional labels on paper, with some training. Research in this area is captured here, based on the publications available up to December 2016.

Multi-electrode bioelectrochemical system for the treatment of high total dissolved solids bearing chemical based wastewater

Multi-electrode bioelectrochemical treatment system (ME-BET; membrane less) consisting of six electrode assemblies (E1–E6) was designed and fabricated for the treatment of complex chemical based wastewater with high salt concentration. The performance was compared with single electrode assembly BET reactor (SE-BET). Enhanced TDS and COD removal was observed in ME-BET (32%; 56%) compared to SE-BET (15%; 23%) as a result of in situ bio-potential from multi-electrodes through the oxidation of organic substrate in the wastewater. Inorganic pollutants viz., nitrates (28%; 8%), sulphates (25%; 9%) and phosphates (20%; 7%) removal was higher in ME-BET in comparison with SE-BET and this was also supported with bioelectrogenic activity (584; 160mW/m3). The study infers that designing of compact reactors with multiple electrodes in a single system enhances the anodic reactions and enable effective treatment of complex wastewaters with simultaneous power production.

Highly crystalline poly(heptazine imides) by mechanochemical synthesis for photooxidation of various organic substrates using an intriguing electron acceptor – Elemental sulfur

Low-defect potassium poly(heptazine imide) (PHIK-BM) was engineered for application in photocatalytic oxidation of organic substrates. Mechanochemical pretreatment of a mixture of 5-aminotetrazole in LiCl/KCl eutectics using high-energy ball milling afforded a highly homogeneous mixture that, upon sequential thermolysis at 600°C, gave nanosized particles of PHIK–BM. The photocatalytic activity of the free-standing PHIK–BM plates was assessed in the oxidation of benzyl alcohol to benzaldehyde under visible light irradiation using elemental sulfur as an electron acceptor. Both quantitative conversion (>99%) of benzyl alcohol and selectivity (>98%) with respect to benzaldehyde were achieved. The developed method was extended to aliphatic alcohol oxidation coupled with multicomponent Hantzsch 1,4-dihydropyridine synthesis. These 1,4-dihydropyridines were also photocatalytically oxidized by PHIK–BM to the corresponding substituted pyridines, with very good yields and under mild metal-free conditions.