Oxidative Oligomerization Research Articles

Oxidative oligomerization of a synthetic fraction of hydrocarbons from the Fischer-Tropsch synthesis

The work investigated the process of oxidative oligomerization of Fischer-Tropsch synthesis products - a fraction of C10-C15 hydrocarbons with a total content of alkenes (mainly β- and γ-alkenes) of 64.7 wt. % using zirconium octoate as a catalyst. The hydrocarbon fraction was obtained on a zeolite-containing catalyst at a pressure of 2.0 MPa, a temperature of 250 °C, H2/CO ratio at the reactor inlet of 1.70, a gas space velocity of 1000 h-1 and circulation mode ratio range 0-16. It was found that at a temperature of 160 °C the catalyst content is 5.0 wt. %, process duration 6 hours and pressure (air) - 2.5 MPa, target fraction yield - 52.7 %. It was found that the oligomerization product has a low pour point of minus 31 °C. It was proposed to improve the viscosity characteristics of the oligomerization product by introducing additives into its composition, for example, polymethacrylates or polyisobutylene.

An investigation of the enzymatic oligomerization of nitro-substituted phenylene diamine: Thermal and fluorescence properties

2-nitro-p-phenylenediamine, an aromatic diamine, was studied for its oxidative oligomerization with H2O2 using enzyme-catalyzed oligomer synthesis. Characterization of molecular structures was performed utilizing ultraviolet-visible (UV-Vis) spectrophotometer, Fourier-transform infrared spectroscopy (FT-IR), and nuclear magnetic resonance (NMR) techniques, identifying phenazine-bridged oligomer resulting from the enzymatic oligomerization process. Based on the results of gel permeation chromatography (GPC) analysis, the synthesized compound was identified as being in an oligomeric form. Conversely, the number of repeating units, as determined by Mw, was found to be 28. The solvent effect on the optical features of the synthesized oligomer in polar solvents was analyzed. The degradation of phenazine-type structures in the oligomer occurred at higher temperatures than that of the monomer. Under visible light excitation, the oligomer exhibited green light emission with a quantum yield (QY) of 6.2% in N,N-dimethylformamide (DMF). 2-nitro-p-phenylenediamine was readily oxidized into an oligomer with ortho-coupled constitutional units, having a lower electrochemical band gap than the monomer, via the enzymatic oligomerization route. Scanning electron microscopy revealed that enzyme-catalyzed oxidation of monomers exhibited a spongy morphology with some pores

Full-length GSDME mediates pyroptosis independent from cleavage.

Gasdermin (GSDM) family proteins, known as the executors of pyroptosis, undergo protease-mediated cleavage before inducing pyroptosis. We here discovered a form of pyroptosis mediated by full-length (FL) GSDME without proteolytic cleavage. Intense ultraviolet-C irradiation-triggered DNA damage activates nuclear PARP1, leading to extensive formation of poly(ADP-ribose) (PAR) polymers. These PAR polymers are released to the cytoplasm, where they activate PARP5 to facilitate GSDME PARylation, resulting in a conformational change in GSDME that relieves autoinhibition. Moreover, ultraviolet-C irradiation promotes cytochrome c-catalysed cardiolipin peroxidation to elevate lipid reactive oxygen species, which is then sensed by PARylated GSDME, leading to oxidative oligomerization and plasma membrane targeting of FL-GSDME for perforation, eventually inducing pyroptosis. Reagents that concurrently stimulate PARylation and oxidation of FL-GSDME, synergistically promoting pyroptotic cell death. Overall, the present findings elucidate an unreported mechanism underlying the cleavage-independent function of GSDME in executing cell death, further enriching the paradigms and understanding of FL-GSDME-mediated pyroptosis.

Investigation of electrochemical, optical, and thermal properties via oligomerization of aminophenol monomer containing halogen and nitro groups using two distinct oxidants

In this study, two different oligomers of 2-amino-4-chloro-5-nitrophenol (ACNP) with incorporated halogen atom and nitro groups were synthesized by oxidative oligomerization method using two different oxidants, namely H2O2 and ammonium persulfate (APS). Structural characterizations of the obtained products were elucidated by 1H NMR, 13C NMR, FT-IR, UV–Vis spectroscopy methods. The molecular masses of the oligomers were determined through the utilization of Gel Permeation Chromatography (GPC). The analysis revealed that the Mw values of the oligomers synthesized via the oxidative oligomerization method using H2O2 and APS, denoted as OACNP-1 and OACNP-2 were 4150 Da and 2800 Da, respectively. Using the UV–vis spectrophotometer, the optical band gaps were calculated as 2.64 eV, 1.95 eV and 2.14 eV for ACNP, OACNP-1 and OACNP-2, respectively. Thermal properties of the oligomers were investigated using Thermal Gravimetric Analysis-Differential Thermal Analysis (TGA-DTA) and Differential Scanning Calorimetry (DSC). The results demonstrated that OACNP-1 exhibited significantly higher thermal stability when compared to both the monomer and OACNP-2. In addition, Fluorescence Spectroscopic analysis of the oligomers revealed that OACNP-1 emitted blue light at 440 nm when excited with light of a wavelength of 370 nm, exhibiting fluorescent characteristics. Furthermore, the surface properties and morphologies of the oligomers were analyzed with the help of Scanning Electron Microscopy (SEM), revealing a flower-like structure for the oxidative oligomerization product, OACNP-1, in the presence of H2O2. In course of a change in the oxidant, the oligomer, OACNP-2, had rough and spongy surface morphology with some pores.

Yellow pigments produced by oxidative oligomerization of dihydrochalcone glucoside and the reaction mechanism.

From the dried leaves of Lithocarpus polystachyus, yellow pigments, lithocarputins B (11) and C (12), were isolated with a colorless dihydrochalcone dimer, lithocarputin A (10). The pigments 11 and 12 are dimeric dihydrochalcone glycosides with bicyclo[3.2.1]octane structures. Each pigment is a diastereomeric mixture with enantiomeric aglycones that could not be separated. The production mechanisms of the pigments were proposed based on the in vitro enzymatic preparation from trilobatin (1), the major dihydrochalcone glucoside of L. polystachyus. The majority of the pigments in the dried leaves were the oligomers of the dihydrochalcone glycosides generated by a mechanism similar to dimerization. The pigments are probably artifacts produced in the drying process. This is the first report disclosing a detailed chemical mechanism for pigment formation from dihydrochalcone.

Plasmon Energy Transfer Driven by Electrochemical Tuning of Methylene Blue on Single Gold Nanorods.

Plasmonic photocatalysis has attracted interest for its potential to generate energy-efficient reactions, but ultrafast internal conversion limits efficient plasmon-based chemistry. Resonance energy transfer (RET) to surface adsorbates offers a way to outcompete internal conversion pathways and also eliminate the need for sacrificial counter-reactions. Herein, we demonstrate RET between methylene blue (MB) and gold nanorods (AuNRs) using in situ single-particle spectroelectrochemistry. During electrochemically driven reversible redox reactions between MB and leucomethylene blue (LMB), we show that the homogeneous line width is broadened when spectral overlap between AuNR scattering and absorption of MB is maximized, indicating RET. Additionally, electrochemical oxidative oligomerization of MB allowed additional dipole coupling to generate RET at lower energies. Time-dependent density functional theory-based simulated absorption provided theoretical insight into the optical properties, as MB molecules were electrochemically oligomerized. Our findings show a mechanism for driving efficient plasmon-assisted processes by RET through the change in the chemical states of surface adsorbates.

Injectable gelatin-oligo-catechol conjugates for tough thermosensitive bioadhesion

Extracellular matrix-derived biomaterials, such as gelatin-based hydrogels, are attractive candidates for sealing internal leakages. However, gelatin derivatives are brittle and suffer from poor adhesion. Modifications of gelatin with adhesive catechol moieties have been limited to low degrees of substitution. Here, we propose oxidative oligomerization of catecholic compounds (namely, caffeic acid [CA]) prior to the coupling reaction to augment the number and availability of grafted catechol groups per carbodiimide conjugation reaction, thereby achieving robust bioadhesion. Ex vivo adhesion tests on pig lungs suggests ∼3× improvement in adhesion strength compared with gelatin methacryloyl controls due to their enhanced cohesion (i.e., ∼5.3× and ∼11.5× improvements in stretchability and toughness, respectively). Functionalization of gelatin with CA oligomers enables rapid formation of physical gels upon exposure to room temperature, tunes the viscosity of the gelatin-caffeic acid pre-gel solution for controllable injectability onto multiply curved tissues, and boosts the antioxidant effects of CA.

Interfacial Oxidative Oligomerization of Catechol.

The heterogeneous reaction between thin films of catechol exposed to O3(g) creates hydroxyl radicals (HO•) in situ, which in turn generate semiquinone radical intermediates in the path to form heavier polyhydroxylated biphenyl, terphenyl, and triphenylene products. Herein, the alteration of catechol aromatic surfaces and their chemical composition are studied during the heterogeneous oxidation of catechol films by O3(g) molar ratios ≥ 230 ppbv at variable relative humidity levels (0% ≤ RH ≤ 90%). Fourier transform infrared micro-spectroscopy, atomic force microscopy, electrospray ionization mass spectrometry, and reverse-phase liquid chromatography with UV–visible and mass spectrometry detection provide new physical insights into understanding the surface reaction. A Langmuir–Hinshelwood mechanism is accounted to report reaction rates, half-lives, and reactive uptake coefficients for the system under variable relative humidity levels. The reactions reported explain how the oligomerization of polyphenols proceeds at interfaces to contribute to the formation of brown organic carbon in atmospheric aerosols.

Reactivity of aminophenols in forming nitrogen-containing brown carbon from iron-catalyzed reactions

Nitrogen-containing organic carbon (NOC) in atmospheric particles is an important class of brown carbon (BrC). Redox active NOC like aminophenols received little attention in their ability to form BrC. Here we show that iron can catalyze dark oxidative oligomerization of o- and p-aminophenols under simulated aerosol and cloud conditions (pH 1–7, and ionic strength 0.01–1 M). Homogeneous aqueous phase reactions were conducted using soluble Fe(III), where particle growth/agglomeration were monitored using dynamic light scattering. Mass yield experiments of insoluble soot-like dark brown to black particles were as high as 40%. Hygroscopicity growth factors (κ) of these insoluble products under sub- and super-saturated conditions ranged from 0.4–0.6, higher than that of levoglucosan, a prominent proxy for biomass burning organic aerosol (BBOA). Soluble products analyzed using chromatography and mass spectrometry revealed the formation of ring coupling products of o- and p-aminophenols and their primary oxidation products. Heterogeneous reactions of aminophenol were also conducted using Arizona Test Dust (AZTD) under simulated aging conditions, and showed clear changes to optical properties, morphology, mixing state, and chemical composition. These results highlight the important role of iron redox chemistry in BrC formation under atmospherically relevant conditions.

Diindolylamine Preparation and Stability Investigations.

The synthesis of diindolylamines via the palladium-catalyzed cross-coupling of aminoindoles and bromoindoles has been investigated, and efficient coupling conditions using BrettPhos, Pd(OAc)2, K2CO3, and tBuOH have been identified. The diindolylamines were found to be unstable in ambient conditions. Blocking the reactive 3-position of the bromoindole coupling partner with a tert-butyl group results in a diindolylamine with improved air stability. NMR, CV, and UV–vis studies on an asymmetrically substituted 3-tert-butyl-3′H-diindolylamine indicate that the instability of the diindolylamine substrates is likely due to oxidative oligomerization. Literature conditions used for the preparation of 3-tert-butylindoles afforded only the indole tetramer. The presence of water during the alkylation reaction was identified as the cause of the formation of the tetramer. Replacing hygroscopic tBuOH with nonhygroscopic tBuCl as the alkylating reagent provided access to 7-bromo-3-tert-butyl indole.

Vitis OneGenE: A Causality-Based Approach to Generate Gene Networks in Vitis vinifera Sheds Light on the Laccase and Dirigent Gene Families.

The abundance of transcriptomic data and the development of causal inference methods have paved the way for gene network analyses in grapevine. Vitis OneGenE is a transcriptomic data mining tool that finds direct correlations between genes, thus producing association networks. As a proof of concept, the stilbene synthase gene regulatory network obtained with OneGenE has been compared with published co-expression analysis and experimental data, including cistrome data for MYB stilbenoid regulators. As a case study, the two secondary metabolism pathways of stilbenoids and lignin synthesis were explored. Several isoforms of laccase, peroxidase, and dirigent protein genes, putatively involved in the final oxidative oligomerization steps, were identified as specifically belonging to either one of these pathways. Manual curation of the predicted sequences exploiting the last available genome assembly, and the integration of phylogenetic and OneGenE analyses, identified a group of laccases exclusively present in grapevine and related to stilbenoids. Here we show how network analysis by OneGenE can accelerate knowledge discovery by suggesting new candidates for functional characterization and application in breeding programs.

Investigation of horseradish peroxide and hydrogen peroxide mediated synthesis of amino-functional oligomers: Characterization and fluorescence study

The insightful mechanism of two oligomerization methods using either horseradish peroxide (HRP)/hydrogen peroxide (H2O2) (enzymatic approach), or H2O2 (35% aqueous) (chemical approach) on 4-phenoxy aniline (PA) and 4-(4-chlorophenoxy)aniline (PACl) as two amino-functional monomers was studied. Four oligomers synthesized were described by FT-IR, UV-Vis, 1H-NMR and 13C-NMR techniques for the molecular structure analysis. The oligomers substituted with chlorine had stronger electron acceptor ability, which enhanced the intramolecular charge transfer between the donating moiety and chlorine acceptor substituent, resulting in a 48 nm red shift of the λmax for the n→π* electronic transition. Oligomers prepared by horseradish peroxidase shows better fluorescence properties than the monomers. The use of oxidoreductase enzyme (HRP) as the catalyst, for the one-step oligomerization of the monomers demonstrated to yield fluorescent products. Photoluminescence (PL) measurements enlightened that emission quantum yields of PACl-E in DMF were found to be 18% and 4.2% at the maximum emission wavelength of 412 nm and 482 nm, respectively. it is considered as green oligomerization/polymerization method Since HRP catalysis provided a green oxidative oligomerization method of aniline and their derivatives, four oligomers were produced by peroxidase-catalyzed oxidation oligomerization in relation to their electronic properties. HOMO-LUMO energy levels were calculated to make comments about electrochemical (E′g) band gaps of the oligomers which were lower than those of their regarding monomers. SEM images were provided to study the morphology of the oligomers. Intermolecular dihydrophenazine formation in the course of enzymatic oligomerization would eventuate in highly ordered structures.

Polymerization of furan by a sequential liquid crystal W-STEP method

Chemical oxidative oligomerization of furan as a monomer in helical twisted liquid crystal field and subsequently electrochemical polymerization were carried out with convenient one-pot process, referred to as double step (W-STEP) polymerization in liquid crystal. The pre-alignment of linear formed oligo-furan in the liquid crystal matrix and electrochemical polymerization affords to yield electo-optically active π-conjugate polymer with beautiful finger print pattern.

Oxidative Oligomerization of DBL Catechol, a potential Cytotoxic Compound for Melanocytes, Reveals the Occurrence of Novel Ionic Diels-Alder Type Additions.

The exposure of human skin to 4-(4-hydroxyphenyl)-2-butanone (raspberry ketone, RK) is known to cause chemical/occupational leukoderma. RK is a carbonyl derivative of 4-(4-hydroxyphenyl)-2-butanol (rhododendrol), a skin whitening agent that was found to cause leukoderma in skin of many consumers. These two phenolic compounds are oxidized by tyrosinase and the resultant products seem to cause cytotoxicity to melanocytes by producing reactive oxygen species and depleting cellular thiols through o-quinone oxidation products. Therefore, it is important to understand the biochemical mechanism of the oxidative transformation of these compounds. Earlier studies indicate that RK is initially oxidized to RK quinone by tyrosinase and subsequently converted to a side chain desaturated catechol called 3,4-dihydroxybenzalacetone (DBL catechol). In the present study, we report the oxidation chemistry of DBL catechol. Using UV–visible spectroscopic studies and liquid chromatography mass spectrometry, we have examined the reaction of DBL catechol with tyrosinase and sodium periodate. Our results indicate that DBL quinone formed in the reaction is extremely reactive and undergoes facile dimerization and trimerization reactions to produce multiple isomeric products by novel ionic Diels-Alder type condensation reactions. The production of a wide variety of complex quinonoid products from such reactions would be potentially more toxic to cells by causing not only oxidative stress, but also melanotoxicity through exhibiting reactions with cellular macromolecules and thiols.

Reversible Oxygen Sensing Based on Multi-Emission Fluorescence Quenching.

Oxygen is ubiquitous in nature and it plays a key role in several biological processes, such as cellular respiration and food deterioration, to name a few. Currently, reversible and non-destructive oxygen sensing is usually performed with sensors produced by photosensitization of phosphorescent organometallic complexes. In contrast, we propose a novel route of optical oxygen sensing by fluorescence-based quenching of oxygen. We hereby developed for the first time a set of multi-emissive purely organic emitters. These were produced through a one-pot hydrothermal synthesis using p-phenylenediamine (PPD) and urea as starting materials. The origin of the multi-emission has been ascribed to the diversity of chemical structures produced as a result of oxidative oligomerization of PPD. A Bandrowski’s base (BB, i.e., trimer of PPD) is reported as the main component at reaction times higher than 8 h. This indication was confirmed by electrospray-ionization quadrupole time-of-flight (ESI-QTOF) and liquid chromatography-mass spectrometry (LC-MS) analysis. Once the emitters are embedded within a high molecular weight poly (vinyl alcohol) matrix, the intensities of all three emission centers exhibit a non-linear quenching provoked by oxygen within the range of 0–8 kPa. The detection limit of the emission centers are 0.89 kPa, 0.67 kPa and 0.75 kPa, respectively. This oxygen-dependent change in fluorescence emission is reversible (up to three tested 0–21% O2 cycles) and reproducible with negligible cross-interference to humidity. The cost-effectiveness, metal-free formulation, cross-referencing between each single emission center and the relevant oxygen range are all appealing features, making these sensors promising for the detection of oxygen, e.g., in food packaged products.

Oxidative Oligomerization of Phenolic Endocrine Disrupting Chemicals Mediated by Mn(III)-L Complexes and the Role of Phenoxyl Radicals in the Enhanced Removal: Experimental and Theoretical Studies.

Soluble manganese(III), stabilized by ligands as Mn(III)-L complexes, are ubiquitous in natural waters and wastewaters and can potentially serve as both the oxidant and reductant in one-electron transfer reactions with organic contaminants. In this study, the oxidative transformations of 14 phenolic endocrine disrupting chemicals (EDCs) by in situ-formed Mn(III)-L complexes, generated from irradiated water containing Mn(II) and humic acid, were investigated. The pseudo-first-order rate constants (kobs, h-1) of these phenols varied from 1.0 × 10-4 to 5.9 × 10-2. A quantitative structure-activity relationship model was developed, which suggests that the electron-donating ability (EHOMO) of phenolic chemicals was the most important molecular characteristic for the Mn(III)-L-mediated oxidative transformation. Phenol transformation was initiated by the generation of a phenoxyl radical through electron transfer to Mn(III)-L. Subsequent self-coupling reactions between phenoxyl radicals resulted in the formation of self-coupling dimers and trimers. With the addition of simple phenol as a cosubstrate, enhanced transformations of these phenolic EDCs were clearly observed, and cross-coupling products of simple phenol and the substrates were also detected. In addition, a reaction activation energy calculation based on the transition-state theory indicated that the cross-coupling reaction was more likely than the self-coupling reaction to occur in the presence of phenol. This work provides new insights into the environmental fate of phenolic compounds.

Injury-Triggered Blueing Reactions of Psilocybe "Magic" Mushrooms.

Upon injury, psychotropic psilocybin‐producing mushrooms instantly develop an intense blue color, the chemical basis and mode of formation of which has remained elusive. We report two enzymes from Psilocybe cubensis that carry out a two‐step cascade to prepare psilocybin for oxidative oligomerization that leads to blue products. The phosphatase PsiP removes the 4‐O‐phosphate group to yield psilocin, while PsiL oxidizes its 4‐hydroxy group. The PsiL reaction was monitored by in situ 13C NMR spectroscopy, which indicated that oxidative coupling of psilocyl residues occurs primarily via C‐5. MS and IR spectroscopy indicated the formation of a heterogeneous mixture of preferentially psilocyl 3‐ to 13‐mers and suggest multiple oligomerization routes, depending on oxidative power and substrate concentration. The results also imply that phosphate ester of psilocybin serves a reversible protective function.

Injury‐Triggered Blueing Reactions of Psilocybe “Magic” Mushrooms

AbstractUpon injury, psychotropic psilocybin‐producing mushrooms instantly develop an intense blue color, the chemical basis and mode of formation of which has remained elusive. We report two enzymes from Psilocybe cubensis that carry out a two‐step cascade to prepare psilocybin for oxidative oligomerization that leads to blue products. The phosphatase PsiP removes the 4‐O‐phosphate group to yield psilocin, while PsiL oxidizes its 4‐hydroxy group. The PsiL reaction was monitored by in situ 13C NMR spectroscopy, which indicated that oxidative coupling of psilocyl residues occurs primarily via C‐5. MS and IR spectroscopy indicated the formation of a heterogeneous mixture of preferentially psilocyl 3‐ to 13‐mers and suggest multiple oligomerization routes, depending on oxidative power and substrate concentration. The results also imply that phosphate ester of psilocybin serves a reversible protective function.

Artificial Allomelanin Nanoparticles

Allomelanin is a type of nitrogen-free melanin most commonly found in fungi. Its existence enhances resistance of the organisms to environmental damage and helps fungi survive harsh radiation conditions such as those found on spacecraft and inside contaminated nuclear power plants. We report the preparation and characterization of artificial allomelanin nanoparticles (AMNPs) via oxidative oligomerization of 1,8-dihydroxynaphthalene (1,8-DHN). We describe the resulting morphological and size control of AMNPs and demonstrate that they are radical scavengers. Finally, we show that AMNPs are taken up by neonatal human epidermal keratinocytes and packaged into perinuclear caps where they quench reactive oxygen species generated following UV exposure.

Improve Plant Photosynthesis by a New Slow-Release Carbon Dioxide Gas Fertilizer.

In the natural state, the concentration of carbon dioxide in the atmosphere is about 300 μmol mol–1. Plants need a suitable balance of CO2 to achieve optimal growth. The optimum CO2 content corresponding to a high photosynthesis rate is between 0.1 and 1.0% by volume. However, air has only a CO2 content of 0.03% by volume, so plants cannot use all of their growth potential. The use of fertilizer to assist in the supply of CO2 increases the rate of photosynthesis. In this work, a slow-release CO2 gas fertilizer inspired by polyphenol chemistry was prepared to provide sustainable CO2 that could improve plant photosynthetic capacity and get a higher crop yield. The core–shell structure was designed to confer gas fertilizers slow-release property. Micron-sized calcium carbonate particles with uniform particle size and regularity morphology, as carbon sources for plant photosynthesis, was a core, and tannic acid was coated on it as a shell via oxidative oligomerization and cross-linked by polyetherimide. The structure and morphology of fertilizers were characterized by scanning electron microscopy, X-ray energy dispersive spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis. In vitro experiments, the prepared fertilizers were proved to have slow-release properties. And then through net photosynthesis rate, chlorophyll fluorescence parameters, chlorophyll content, leaf area, leaf mass per area, and dry matter to study the effects of slow-release CO2 gas fertilizers on plant physiology of Brassica chinensis. The results revealed that the slow-release CO2 gas fertilizers not only had good slow-release properties but also can well improve plant photosynthesis.