Phase-Vanishing Methodology for Efficient Bromination, Alkylation, Epoxidation, and Oxidation Reactions of Organic Substrates

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.

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Photocatalytic Oxygenation by Water-Soluble Metalloporphyrins as a Pathway to Functionalized Polycycles

International Journal of Photoenergy ◽

10.1155/2018/1017957 ◽

2018 ◽

Vol 2018 ◽

pp. 1-8

Author(s):

Ivana Šagud ◽

Irena Škorić

Keyword(s):

Water Soluble ◽

Synthetic Methods ◽

Reaction Pathways ◽

Organic Substrates ◽

Free Base ◽

Oxidation Reactions ◽

Good Tool ◽

Vast Number ◽

Heteroaromatic Compounds ◽

Photocatalytic Reactions

Photocatalytic processes are present in natural biochemical pathways as well as in the organic synthetic ones. This minireview will cover the field of photocatalysis that uses both the free-base and specially metallated porphyrins as catalysts. While free-base porphyrins are valuable sensitizers to output singlet oxygen, metalloporphyrins are even more adjustable as photocatalysts because of their coordination capacity, generating a wider range of oxidation reactions. They can be applied in autooxidation reactions, hydroxylations, or direct oxygen transfer producing epoxides. This review will mainly focus on how manganese and some iron porphyrins can be utilized for the functionalization of compounds that have a polycyclic skeleton in their structure. These kinds of compounds are notoriously taxing to obtain and difficult to further functionalize by conventional organic synthetic methods. We have focused on photocatalytic oxygenation reactions in mild conditions with the use of water-soluble porphyrins, as this has been proven to be a good tool for these transformations. In the photocatalytic reactions of some polycyclic heteroaromatic compounds, new polycyclic epoxides, enediones, ketones, alcohols, and/or hydroperoxides are yielded, depending on the catalyst applied. The application of anionic and cationic Mn(III) porphyrins under different reaction parameters results in different reaction pathways generating a vast number of photocatalytic products. Recently, Co and Ni complexes have been also photophysically investigated and confirmed as potential photocatalysts for the functionalization of organic substrates.

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Exploring the Role of Phenylalanine Residues in Modulating the Flexibility and Topography of the Active Site in the Peroxygenase Variant PaDa-I

International Journal of Molecular Sciences ◽

10.3390/ijms21165734 ◽

2020 ◽

Vol 21 (16) ◽

pp. 5734

Author(s):

Joaquin Ramirez-Ramirez ◽

Javier Martin-Diaz ◽

Nina Pastor ◽

Miguel Alcalde ◽

Marcela Ayala

Keyword(s):

Hydrogen Peroxide ◽

Cytochrome P450 ◽

Active Site ◽

Bulk Solution ◽

Computational Studies ◽

Organic Substrates ◽

Oxidation Reactions ◽

Heme Group ◽

Wide Range

Unspecific peroxygenases (UPOs) are fungal heme-thiolate enzymes able to catalyze a wide range of oxidation reactions, such as peroxidase-like, catalase-like, haloperoxidase-like, and, most interestingly, cytochrome P450-like. One of the most outstanding properties of these enzymes is the ability to catalyze the oxidation a wide range of organic substrates (both aromatic and aliphatic) through cytochrome P450-like reactions (the so-called peroxygenase activity), which involves the insertion of an oxygen atom from hydrogen peroxide. To catalyze this reaction, the substrate must access a channel connecting the bulk solution to the heme group. The composition, shape, and flexibility of this channel surely modulate the catalytic ability of the enzymes in this family. In order to gain an understanding of the role of the residues comprising the channel, mutants derived from PaDa-I, a laboratory-evolved UPO variant from Agrocybe aegerita, were obtained. The two phenylalanine residues at the surface of the channel, which regulate the traffic towards the heme active site, were mutated by less bulky residues (alanine and leucine). The mutants were experimentally characterized, and computational studies (i.e., molecular dynamics (MD)) were performed. The results suggest that these residues are necessary to reduce the flexibility of the region and maintain the topography of the channel.

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Enzyme Electrochemistry — Biocatalysis on an Electrode

Australian Journal of Chemistry ◽

10.1071/ch05340 ◽

2006 ◽

Vol 59 (4) ◽

pp. 233 ◽

Cited By ~ 54

Author(s):

Paul V. Bernhardt

Keyword(s):

Electron Transfer ◽

Small Molecule ◽

Electrode Surface ◽

Catalytic Mechanism ◽

Organic Substrates ◽

Oxidation Reactions ◽

Accurate Analysis ◽

Practical Applications ◽

Redox Partner ◽

Oxidoreductase Enzymes

Oxidoreductase enzymes catalyze single- or multi-electron reduction/oxidation reactions of small molecule inorganic or organic substrates, and they are integral to a wide variety of biological processes including respiration, energy production, biosynthesis, metabolism, and detoxification. All redox enzymes require a natural redox partner such as an electron-transfer protein (e.g. cytochrome, ferredoxin, flavoprotein) or a small molecule cosubstrate (e.g. NAD(P)H, dioxygen) to sustain catalysis, in effect to balance the substrate/product redox half-reaction. In principle, the natural electron-transfer partner may be replaced by an electrochemical working electrode. One of the great strengths of this approach is that the rate of catalysis (equivalent to the observed electrochemical current) may be probed as a function of applied potential through linear sweep and cyclic voltammetry, and insight to the overall catalytic mechanism may be gained by a systematic electrochemical study coupled with theoretical analysis. In this review, the various approaches to enzyme electrochemistry will be discussed, including direct and indirect (mediated) experiments, and a brief coverage of the theory relevant to these techniques will be presented. The importance of immobilizing enzymes on the electrode surface will be presented and the variety of ways that this may be done will be reviewed. The importance of chemical modification of the electrode surface in ensuring an environment conducive to a stable and active enzyme capable of functioning natively will be illustrated. Fundamental research into electrochemically driven enzyme catalysis has led to some remarkable practical applications. The glucose oxidase enzyme electrode is a spectacularly successful application of enzyme electrochemistry. Biosensors based on this technology are used worldwide by sufferers of diabetes to provide rapid and accurate analysis of blood glucose concentrations. Other applications of enzyme electrochemistry are in the sensing of macromolecular complexation events such as antigen–antibody binding and DNA hybridization. The review will include a selection of enzymes that have been successfully investigated by electrochemistry and, where appropriate, discuss their development towards practical biotechnological applications.

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A Bpp-based dinuclear ruthenium photocatalyst for visible light-driven oxidation reactions

Catalysis Science & Technology ◽

10.1039/c9cy01796h ◽

2019 ◽

Vol 9 (23) ◽

pp. 6760-6768 ◽

Cited By ~ 1

Author(s):

Seán Hennessey ◽

Pau Farràs ◽

Jordi Benet-Buchholz ◽

Antoni Llobet

Keyword(s):

Visible Light ◽

Photocatalytic Oxidation ◽

Organic Substrates ◽

Oxidation Reactions ◽

Bridging Ligand ◽

Visible Light Driven ◽

Dinuclear Ruthenium

The photocatalytic oxidation of organic substrates in water using a diruthenium chromophore-catalyst dyad molecule can be tuned by the nature of the bridging ligand.

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Reduced Molecular Flavins as Single-Electron Reductants after Photo-Excitation

10.26434/chemrxiv-2021-n0n8c ◽

2021 ◽

Author(s):

Richard Foja ◽

Alexandra Walter ◽

Christian Jandl ◽

Erling Thyrhaug ◽

Jürgen Hauer ◽

...

Keyword(s):

Organic Substrates ◽

Oxidation Reactions ◽

Catalytic Method ◽

Dna Photolyase ◽

Rapid Reduction ◽

Catalytically Active ◽

Organic Laboratory ◽

Covalent Adducts ◽

Site Selective ◽

Barbituric Acid Derivatives

Flavoenzymes mediate a multitude of chemical reactions and are catalytically active both in different oxidation states and in covalent adducts with reagents. The transfer of such reactivity to the organic laboratory using simplified molecular flavins is highly desirable and such applications in (photo-)oxidation reactions are already established. However, molecular flavins have not been used for the reduction of organic substrates yet, although this activity is known and well-studied for DNA photolyase enzymes. We report a catalytic method using reduced, molecular flavins as photo-reductants and γ-terpinene as sacrificial reductant. Additionally, we present our design for air-stable, reduced flavin catalysts, which is based on a conformational bias strategy and circumvents the otherwise rapid reduction of O2 from air. Using our catalytic strategy, we were able to replace super-stoichiometric amounts of the rare-earth reductant SmI2 in a 5-exo-trig cyclization of substituted barbituric acid derivatives. Such flavin-catalyzed reductions are anticipated to be of broad applicability and their straightforward synthesis indicates future use in stereo- as well as site-selective transformations.

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Fractionation of polymethylene chains: An electron crystallographic investigation

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100145315 ◽

1986 ◽

Vol 44 ◽

pp. 794-795

Author(s):

Douglas L. Dorset

Keyword(s):

Cross Section ◽

Binary Systems ◽

Linear Chain ◽

Pure Component ◽

Organic Substrates ◽

Crystallographic Investigation ◽

X Ray Diffraction ◽

X Ray ◽

Molecular Sizes ◽

The Stability

A variety of linear chain materials exist as polydisperse systems which are difficultly purified. The stability of continuous binary solid solutions assume that the Gibbs free energy of the solution is lower than that of either crystal component, a condition which includes such factors as relative molecular sizes and shapes and perhaps the symmetry of the pure component crystal structures.Although extensive studies of n-alkane miscibility have been carried out via powder X-ray diffraction of bulk samples we have begun to examine binary systems as single crystals, taking advantage of the well-known enhanced scattering cross section of matter for electrons and also the favorable projection of a paraffin crystal structure posited by epitaxial crystallization of such samples on organic substrates such as benzoic acid.

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