Search query: general oxidation reduction redox 2018

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abstract: Low cost semiconductor photocatalysts offer unique possibilities for industrial chemical transformations and energy conversion applications. We report that a range of organic semiconductors are capable of efficient photocatalytic oxygen reduction to H2O2 in aqueous conditions. These semiconductors, in the form of thin films, support a 2 electron/2 proton redox cycle involving photoreduction of dissolved O2 to H2O2, with the concurrent photooxidation of organic substrates: formate, oxalate, and phenol. Photochemical oxygen reduction is observed in a pH range from 2 to 12. In cases where valence band energy of the semiconductor is energetically high, autoxidation competes with oxidation of the donors, and thus turnover numbers are low. Materials with deeper valence band energies afford higher stability and also oxidation of H2O to O2. We found increased H2O2 evolution rate for surfactant stabilized nanoparticles versus planar thin films. These results evidence that photochemical O2 reduction may be a widespread feature of organic semiconductors, and open potential avenues for organic semiconductors for catalytic applications.
author_names: Maciej Gryszel

Mykhailo Sytnyk

Marie Jakesova

Giuseppe Romanazzi

Roger Gabrielsson

Wolfgang Heiss

Eric Daniel Glowacki
title: General Observation of Photocatalytic Oxygen Reduction to Hydrogen Peroxide by Organic Semiconductor Thin Films and Colloidal Crystals.
venue: ACS applied materials interfaces
year: 2018

abstract: Oxygenic photosynthesis gave rise to a regulatory mechanism based on reversible redox modifications of enzymes. In chloroplasts, such on off switches separate metabolic pathways to avoid futile cycles. During illumination, the redox interconversions allow for rapidly and finely adjusting activation states of redox regulated enzymes. Noncovalent effects by metabolites binding to these enzymes, here addressed as 'small molecules' affect the rates of reduction and oxidation. The chloroplast enzymes provide an example for a versatile regulatory principle where small molecules govern thiol switches to integrate redox state and metabolism for an appropriate response to environmental challenges. In general, this principle can be transferred to reactive thiols involved in redox signaling, oxidative stress responses, and in disease of all organisms.
author_names: Johannes Knuesting

Renate Scheibe
title: Small Molecules Govern Thiol Redox Switches.
venue: Trends in plant science
year: 2018

abstract: Abstract Iron redox transformations by five representative Sulfolobus strains (S. metallicus Kra23, S. tokodaii 7, S. acidocaldarius 98 3, S. solfataricus P1, S. shibatae B12) were studied to clarify the general trend of Fe metabolism across different species of the genus Sulfolobus. Negligible to major Fe(II) oxidation was detected in cell suspensions of the strains. Fe(III) reducing ability was differently expressed in each strain with dependence on the oxygen level and growth status; growth uncoupled cell suspensions of all strains reduced Fe(III) under either anaerobic or microaerobic conditions, or under both conditions. A linear correlation between cell growth and Fe(III) reduction was also found in S. tokodaii 7, S. solfataricus P1, and S. shibatae B12. In addition to Fe redox behaviors, the strains were also tested for reduction of highly toxic Cr(VI) to less toxic and soluble Cr(III) as an application possibility; the trend in degree of Cr(V) reduction did not necessarily correspond to that of Fe(III) reduction, suggesting the involvement of different reduction mechanisms.
author_names: Yusei Masaki

Katsutoshi Tsutsumi

Naoko Okibe
title: Iron Redox Transformation by the Thermo Acidophilic Archaea from the Genus Sulfolobus
year: 2018

abstract: Abstract Cross coupling reactions catalyzed by transition metals are among the most influential in modern synthetic chemistry. The vast majority of transition metal catalyzed cross couplings rely on a catalytic cycle involving alternating oxidation and reduction of the metal center and are generally limited to forging just one type of new bond per reaction (e.g. the biaryl linkage formed during a Suzuki cross coupling) This work presents an Isohypsic Redox Sequence (IRS) that uses one metal to effect two catalytic cycles, thereby generating multiple new types of bonds from a single catalyst source. We show that the IRS strategy is amenable to several widely used transformations including the Suzuki Miyaura coupling, Buchwald Hartwig amination, and Wacker oxidation. Furthermore, each of these reactions generates value added heterocycles with significant sp3 C (3 dimensional) content. Our results provide a general framework for generating complex products by using a single metal to fulfill multiple roles. By uniting different combinations of reactions in the isohypsic and redox phases of the process, this type of catalytic multiple bond forming platform has the potential for wide applicability in the efficient synthesis of functional organic molecules.
author_names: Craig D Smith

David E Phillips

Alina Tirla

David J France
title: Catalytic Isohypsic Redox Sequences for the Rapid Generation of Csp3 Containing Heterocycles
venue: Chemistry
year: 2018

abstract: A new redox active, diarylamido based ligand (LN3P2) capable of k5 N,N,N,P,P chelation has been used to prepare a series of complexes with the general formula [MII(LN3P2)]X, where M Fe (1; X OTf) Co (2; X ClO4) or Ni (3; X ClO4) The diarylamido core of monoanionic LN3P2 is derived from bis(2 amino 4 methylphenyl)amine, which undergoes condensation with two equivalents of 2 (diphenylphosphanyl)benzaldehyde to provide chelating arms with both arylphosphine and imine donors. X ray structural, magnetic, and spectroscopic studies indicate that the N3P2 coordination environment generally promotes low spin configurations. Three quasi reversible redox couples between +1.0 and 1.5 V (vs. Fc+/Fc) were observed in voltammetric studies of each complex, corresponding to MII/MIIIoxidation, LN3P2 based oxidation, and MII/MI reduction (in order of highest to lowest potential) Spectroscopic and computational analyses of 3ox generated via chemical one electron oxidation of 3 revealed that a stable diarylaminyl radical (LN3P2* is formed upon oxidation. The ability of the CoII complex (2) to function as an electrocatalyst for H2generation was evaluated in the presence of weak acids. Moderate activity was observed using 4 tert butylphenol as the proton source at potentials below 2.0 V. The insights gained here will assist in the future design of pentadentate mixed N/P based chelates for catalytic processes.
author_names: Denan Wang

Danushka M Ekanayake

Sergey V Lindeman

Claudio N Verani

Adam T Fiedler
title: Multielectron Redox Chemistry of Transition Metal Complexes Supported by a Non Innocent N3P2 Ligand: Synthesis, Characterization, and Catalytic Properties
year: 2018

abstract: In this report, we identify the relevant factors to increase production of medium chain n alcohols through an expanded view of the reverse b oxidation pathway. We began by creating a base strain capable of producing medium chain n alcohols from glucose using a redox balanced and growth coupled metabolic engineering strategy. By dividing the heterologous enzymes in the pathway into different modules, we were able to identify and evaluate homologs of each enzyme within the pathway and identify several capable of enhancing medium chain alcohol titers and/or selectivity. In general, the identity of the trans 2 enoyl CoA reductase (TER) and the direct overexpression of the thiolase (FadA) and b hydroxy acyl CoA reductase (FadB) improved alcohol titer and the identity of the FadBA complex influenced the dominant chain length. Next, we linked the anaerobically induced VHb promoter from Vitreoscilla hemoglobin to each gene to remove the need for chemical inducers and ensure robust expression. The highest performing strain with the autoinduced reverse b oxidation pathway produced n alcohols at titers of 1.8 g/L with an apparent molar yield of 0.2 on glucose consumed in rich medium (52% of theoretical yield)
author_names: Christopher R Mehrer

Matthew R Incha

Mark C Politz

Brian F Pfleger
title: Anaerobic production of medium chain fatty alcohols via a b reduction pathway.
venue: Metabolic engineering
year: 2018

abstract: Oxidation and reduction cycles are used in the regeneration of nanoparticle catalysts that have deactivated due to sintering or poisoning. Nickel oxidation and reduction cycles for the redispersion of nickel nanoparticles were studied via in situ high angle annular dark field environmental scanning transmission electron microscopy. Cycling the Ni/NiO system through successive redox cycles shows that the particles retain the same general size distributions even though Ostwald ripening and particle migration and coalescence is occurring. The regeneration of the smallest nanoparticle sizes, which disappear due to sintering processes, occur by the ejection of small (2 3 nm) nickel particles during the reduction of the hollow nickel oxide nanostructures. The nickel nanoparticles above ~3.5 nm in size form hollow polycrystalline nickel oxide nanostructures upon oxidation. Upon reduction, the grains making up the shell of the hollow nickel oxide reduce separately at the grains surface and at the grain boundaries.
author_names: Alec P LaGrow

David C Lloyd

Pratibha L Gai

Edward D Boyes
title: In Situ Scanning Transmission Electron Microscopy of Ni Nanoparticle Redispersion via the Reduction of Hollow NiO
year: 2018

abstract: Our society's current energy demands are largely met by the exploitation of fossil fuels, which are unsustainable and environmentally harmful resources. However, Nature has provided us with a clean and virtually limitless alternative in the form of solar energy. This abundant resource is utilized constantly by photosynthetic organisms, which has in turn motivated decades of research in our quest to create artificial counterparts of comparable scales. In this feature article, we will highlight some of the recent novel approaches in the field of artificial photosynthesis (AP) which we define by a more general term as a process that stores energy overall by generating fuels and chemicals using light. We will particularly emphasize on the potential of a highly modular plug and play concept that we hope will persuade the community to explore a more inclusive variety of multielectron redox catalysis to complement the proton reduction and water oxidation half reactions in traditional solar water splitting systems. We discuss some of the latest developments in the vital functions of light harvesting, charge separation, and multielectron reductive and oxidative catalysis, as well as their optimization, to achieve the ultimate goal of storing sunlight in chemical bonds. Specific attention is dedicated to the use of earth abundant elements and molecular catalysts that offer greater product selectivity and more intricate control over the reactivity than heterogeneous systems. In this context, we showcase our team's contributions in presenting a unique oxidative carbon carbon bond cleavage reaction in aliphatic alcohols and biomass model compounds, under ambient atmospheric conditions, facilitated by vanadium photocatalysts. We offer this discovery as a promising alternative to water oxidation in an integrated AP system, which would concurrently generate both solar fuels and valuable solar chemicals.
author_names: Milos Dokic

Han Sen Soo
title: Artificial photosynthesis by light absorption, charge separation, and multielectron catalysis.
venue: Chemical communications
year: 2018

abstract: An extensive study of the electrochemical and spectroelectrochemical properties of 14 boron subphthalocyanine (BsubPc) derivatives with various axial and peripheral substituents was performed in 1,2 dichloromethane (CH2Cl2) containing 0.1 M tetra n butyl ammonium perchlorate (TBAP) as the supporting electrolyte. From the cyclic voltammetry results, all compounds exhibit one oxidation and at least two reduction processes within the solvent potential window of +1.6 to 1.8 V vs SCE. It was found that the reversibility of the redox reactions depends on the axial and peripheral substituents and the dipole moment of the boron to axial substituent. In general, UV vis absorption spectra of the singly reduced BsubPc derivatives exhibit three equal intensity peaks in the 450 to 650 nm region that are derived from the maximum BsubPc absorbance peak upon reduction. Axial substituents affect the intensity of the three peaks upon reduction, while peripheral substituents shift the position of the peaks to higher wavelengths. Upon oxidation, the UV vis absorption profile flattens considerably with only a single broad ~300 nm) band apparent. Understanding the effect of substituents on the stability of the redox processes of BsubPcs will aid in further development of these materials for applications in organic electronic devices.
author_names: Kathleen L Sampson

Xiaoqin Jiang

Esmeralda Bukuroshi

Aleksa Dovijarski

Hasan Raboui

Timothy P Bender

Karl M Kasdish
title: A Comprehensive Scope of Peripheral and Axial Substituent Effect on the Spectroelectrochemistry of Boron Subphthalocyanines.
venue: The journal of physical chemistry. A
year: 2018

abstract: Homoleptic platinum azo iminate complexes are formed when triarylformazans are treated with Pt(DMSO)2Cl2 under reducing conditions. The transformation represents a three proton, three electron reduction of each formazan and offers a new route for accessing this class of redox active ligands. The reaction is general for triarylformazans with both electron donating and electron withdrawing substituents, and four complexes in total are described. X ray crystal structures of all four complexes are presented and are consistent with an electronic structure consisting of a formal Pt(II) center, where each azo iminate is in a monoanionic radical form and contributes five p electrons. The complexes are all diamagnetic, indicating delocalization of the p system over both ligands. The complexes are further characterized by cyclic voltammetry, which shows multiple ligand centered redox events, including proton coupled oxidation waves. UV vis spectroelectrochemistry provides further insight into the nature of the redox events. UV vis absorption spectroscopy shows strong visible absorption bands attributed to HOMO LUMO transitions, which is corroborated by time dependent DFT computations on representative examples.
author_names: Ge Mu

Lei Cong

Zhili Wen

Judy I-Chia Wu

Karl M Kadish

Thomas S Teets
title: Homoleptic Platinum Azo iminate Complexes via Hydrogenative Cleavage of Formazans.
venue: Inorganic chemistry
year: 2018