scholarly journals Deciphering Evolution Pathway of Supported NO3• Enabled via Radical Transfer from •OH to Surface NO3– Functionality for Oxidative Degradation of Aqueous Contaminants

JACS Au ◽  
2021 ◽  
Author(s):  
Jongsik Kim ◽  
Yun Jeong Choe ◽  
Sang Hoon Kim ◽  
In-Suk Choi ◽  
Keunhong Jeong
Keyword(s):  
Oxidative Degradation ◽  
Radical Transfer ◽  
Aqueous Contaminants

scholarly journals Does Tyrosine Protect S. Coelicolor Laccase from Oxidative Degradation?

2020 ◽  
Author(s):  
Patrycja Kielb ◽  
Harry B. Gray ◽  
Jay R. Winkler
Keyword(s):  
Streptomyces Coelicolor ◽  
Aerobic Oxidation ◽  
Oxidative Degradation ◽  
Protein Damage ◽  
Normal Flow ◽  
Wild Type ◽  
Radical Transfer ◽  
Electron Reduction ◽  
Reducing Equivalents

We have investigated the roles of tyrosine (Tyr) and tryptophan (Trp) residues in the four-electron reduction of oxygen catalyzed by <i>Streptomyces coelicolor</i> laccase (SLAC). During normal enzymatic turnover in laccases, reducing equivalents are delivered to a type 1 Cu center (Cu<sub>T1</sub>) and then are transferred over 13 Å to a trinuclear Cu site (TNC: (Cu<sub>T3</sub>)<sub>2</sub>Cu<sub>T2</sub>) where O<sub>2</sub> reduction occurs. The TNC in SLAC is surrounded by a large cluster of Tyr and Trp residues that can provide reducing equivalents when the normal flow of electrons is disrupted. Canters and coworkers have shown that when O<sub>2</sub> reacts with a reduced SLAC variant lacking the Cu<sub>T1</sub> center, a Tyr108<sup>·</sup> radical near the TNC forms rapidly. We have found that ascorbate reduces the Tyr108<sup>·</sup><sup> </sup>radical in wild-type SLAC about 10 times faster than it reacts with the Cu<sub>T1</sub><sup>2+</sup> center, possibly owing to radical transfer along a Tyr/Trp chain. Aerobic oxidation of two reduced SLAC mutants (Y108F and W132F) leads to the formation of a long-lived (~15 min) Tyr<sup>·</sup><sup> </sup>radical with distinct absorption at 408 nm. The diffusion of redox equivalents away from the primary enzymatic pathway in SLAC may indicate a poorly optimized enzyme or a mechanism to protect against protein damage.

scholarly journals Does Tyrosine Protect S. Coelicolor Laccase from Oxidative Degradation?

2020 ◽  
Author(s):  
Patrycja Kielb ◽  
Harry B. Gray ◽  
Jay R. Winkler
Keyword(s):  
Streptomyces Coelicolor ◽  
Aerobic Oxidation ◽  
Oxidative Degradation ◽  
Protein Damage ◽  
Normal Flow ◽  
Wild Type ◽  
Radical Transfer ◽  
Electron Reduction ◽  
Reducing Equivalents

We have investigated the roles of tyrosine (Tyr) and tryptophan (Trp) residues in the four-electron reduction of oxygen catalyzed by <i>Streptomyces coelicolor</i> laccase (SLAC). During normal enzymatic turnover in laccases, reducing equivalents are delivered to a type 1 Cu center (Cu<sub>T1</sub>) and then are transferred over 13 Å to a trinuclear Cu site (TNC: (Cu<sub>T3</sub>)<sub>2</sub>Cu<sub>T2</sub>) where O<sub>2</sub> reduction occurs. The TNC in SLAC is surrounded by a large cluster of Tyr and Trp residues that can provide reducing equivalents when the normal flow of electrons is disrupted. Canters and coworkers have shown that when O<sub>2</sub> reacts with a reduced SLAC variant lacking the Cu<sub>T1</sub> center, a Tyr108<sup>·</sup> radical near the TNC forms rapidly. We have found that ascorbate reduces the Tyr108<sup>·</sup><sup> </sup>radical in wild-type SLAC about 10 times faster than it reacts with the Cu<sub>T1</sub><sup>2+</sup> center, possibly owing to radical transfer along a Tyr/Trp chain. Aerobic oxidation of two reduced SLAC mutants (Y108F and W132F) leads to the formation of a long-lived (~15 min) Tyr<sup>·</sup><sup> </sup>radical with distinct absorption at 408 nm. The diffusion of redox equivalents away from the primary enzymatic pathway in SLAC may indicate a poorly optimized enzyme or a mechanism to protect against protein damage.

Controlled Injection of Holes into ALQ3 Based Oleds by Means of An Oxidized Transport Layer

2001 ◽  
Vol 708 ◽  
Author(s):  
Mathew K. Mathai ◽  
Keith A. Higginson ◽  
Bing R. Hsieh ◽  
Fotios Papadimitrakopoulos
Keyword(s):  
Indium Tin Oxide ◽  
Oxidative Degradation ◽  
Transport Layer ◽  
Hole Injection ◽  
Carrier Injection ◽  
Salt Loading ◽  
Light Emitting ◽  
Hole Transporting ◽  
Intrinsic Degradation ◽  
Variable Conductivity

ABSTRACTIn this paper we report a method for tuning the extent of hole injection into the active light emitting tris- (8-hydroxyquinoline) aluminum (Alq3) layer in organic light emitting diodes (OLEDs). This is made possible by modifying the indium tin oxide (ITO) anode with an oxidized transport layer (OTL) comprising a hole transporting polycarbonate of N,N'-bis(3-hydroxymethyl)-N,N'-bis(phenyl) benzidine and diethylene glycol (PC-TPB-DEG) doped with varying concentrations of antimonium hexafluoride salt of N,N,N',N'-tetra-p-tolyl-4,4'-biphenyldiamine (TMTPD+ SbF6-). The conductivity of the OTL can be changed over three orders of magnitude depending on salt loading. The analysis of hole and electron current variations in these devices indicates that optimizing the conductivity of the OTL enables the modulation of hole injection into the Alq3 layer. The bipolar charge transport properties for OLEDs in which the interfacial carrier injection barriers have been minimized, are governed by the conductivities of the respective layers and in this case it is shown that the variable conductivity of the OTL does allow for better control of the same. Accordingly, varying the concentration of holes in the device indicates that beyond an optimum concentration of holes, further hole injection results in the formation of light quenching cationic species and the initiation of oxidative degradation processes in the Alq3 layer, thus accelerating the intrinsic degradation of these devices. The variable conductivity of the OTL can hence be used to minimize the occurrence of these processes.

Simple Modification Measurement of Photodegradability of Polymers by using Photo-induced Chemiluminescence Technique

2013 ◽  
Vol 10 (2) ◽  
pp. 51
Author(s):  
Siti Farhana Zakaria ◽  
Keith R Millington
Keyword(s):  
Free Radicals ◽  
Organic Materials ◽  
Oxidative Degradation ◽  
Working Life ◽  
Bimolecular Reaction ◽  
Synthetic Polymers ◽  
Accelerated Weathering ◽  
Simple Modification ◽  
Uv Absorbers ◽  
Irradiation Period

Polymers and organic materials that are exposed to sunlight undergo photooxidation, which leads to deterioration of their physical properties. To allow adequate performance under outdoor conditions, synthetic polymers require additives such as antioxidants and UV absorbers. A major problem with optimising polymer formulations to maximise their working life span is that accelerated weathering tests are empirical. The conditions differ significantly from real weathering situations, and samples require lengthy irradiation period. Degradation may not be apparent in the early stages of exposure, although this is when products such as hydroperoxides are formed which later cause acceleration of oxidation. A simple way of quantifying the number of free radicals presents in organic materials following exposure to light or heat is by measuring chemiluminescence (CL) emission. Most polymers emit CL when they undergo oxidative degradation, and it originates from the bimolecular reaction of macroperoxy radicals which creates an excited carbonyl.

KINETICS CONSIDERATIONS CONCERNING THE OXIDATIVE DEGRADATION BY PHOTO-FENTON PROCESS OF SOME ANTIBIOTICS

2010 ◽  
Vol 9 (1) ◽  
pp. 1-5 ◽  
Author(s):  
Ion Untea ◽  
Cristina Orbeci ◽  
Madelene Dancila ◽  
Daniela Simina Stefan
Keyword(s):  
Oxidative Degradation ◽  
Fenton Process

A NEW PHOTO-FENTON PROCEDURE APPLIED IN OXIDATIVE DEGRADATION OF ORGANIC COMPOUNDS FROM WASTEWATER

2012 ◽  
Vol 11 (1) ◽  
pp. 141-146
Author(s):  
Ion Untea ◽  
Cristina Orbeci ◽  
Rodica Stanescu ◽  
Adina Elena Segneanu ◽  
Mihaela Emanuela Craciun
Keyword(s):  
Organic Compounds ◽  
Oxidative Degradation

CHEMICAL PULPING. Oxidative degradation of AOX in softwood-based kraft mill effluents from E C F bleachin g

2012 ◽  
Vol 27 (4) ◽  
pp. 707-713 ◽  
Author(s):  
Jukka Pekka lsoaho ◽  
Suvi Tarkkanen ◽  
Raimo Alen ◽  
Juha Fiskari
Keyword(s):  
Reaction Time ◽  
Oxidative Degradation ◽  
Cost Effective ◽  
Process Conditions ◽  
Main Process ◽  
Chemical Pulping ◽  
Kraft Mill ◽  
Organic Halogens ◽  
Aox Removal ◽  
Adsorbable Organic Halogens

Abstract Softwood-based kraft mill bleaching effluents from the initial bleaching stages D0 and E1 (the bleaching sequence being D0E 1D 1 E2D2) were treated by the oxidative Fenton method (H20rFeS04) to decompose organic pollutants contammg adsorbable organic halogens (AOX). Experiments designed using the Taguchi method were applied to predict the process conditions that would result in a cost-effective and adequate removal of AOX. In addition to the composition and concentration of the reagents (H202 and Fe2+), the main process parameters selected were temperature and reaction time, while pH was adj usted to an approximate value of 4 (the volumetric ratio of the mixed effluents D0:E 1 was 3 :2). The results indicated that an AOX removal of about 70% for this mixture ( corresponding to about 50% for the mill) was achieved when the eftluent samples were treated for 60 min at 70°C with H202 and Fe2+ at a concentration of 1 600 mg/1 and 28 mg/1, respectively.

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