scholarly journals Dissecting the low catalytic capability of flavin-dependent halogenases

2020 ◽  
pp. jbc.RA120.016004 ◽  
Author(s):  
Aisaraphon Phintha ◽  
Kridsadakorn Prakinee ◽  
Aritsara Jaruwat ◽  
Narin Lawan ◽  
Surawit Visitsatthawong ◽  
...  
Keyword(s):  
Reaction Mechanisms ◽  
Energy Barrier ◽  
Catalytic Efficiency ◽  
Proton Donor ◽  
Saturation Mutagenesis ◽  
X Ray ◽  
Practical Applications ◽  
Rapid Quench ◽  
Computational Calculations ◽  
First Time

Although flavin-dependent halogenases (FDHs) are attractive biocatalysts, their practical applications are limited because of their low catalytic efficiency. Here, we investigated the reaction mechanisms and structures of tryptophan 6-halogenase (Thal) from Streptomyces albogriseolususing stopped-flow, rapid-quench flow, QM/MM calculations, crystallography and detection of intermediate (hypohalous acid (HOX)) liberation. We found that the key flavin intermediate, C4a-hydroperoxyflavin (C4aOOH-FAD), formed by Thal and other FDHs(tryptophan 7-halogenase (PrnA) and tryptophan 5-halogenase (PyrH)), can react with I-, Br-, and Cl-but not F-, to form C4a-hydroxyflavin and HOX. Our experiments revealed that I-reacts with C4aOOH-FAD the fastest with the lowest energy barrier, and have shown for the first time that a significant amount of the HOX formed leaks out as free HOX.  This leakage is probably a major cause of low product coupling ratios in all FDHs. Site-saturation mutagenesis of Lys79 showed that changing Lys79 to any other amino acid resulted in an inactive enzyme. However, the levels of liberated HOX of these variants are all similar, implying that Lys79 probably does not form a chloramine or bromamine intermediateas previously proposed. Computational calculations revealed that Lys79 has an abnormally lower pKa compared to other Lys residues, implying that the catalytic Lys may act as a proton donor in catalysis. Analysis of new X-ray structures of Thal also explains why pre-mixing of FDHs with FADH- generally results in abolishment of C4aOOH-FAD formation. These findings reveal the hidden factors restricting FDHs capability which should be useful for future development of FDHs applications.

scholarly journals Magnetic Chitosan-Supported Silver Nanoparticles: A Heterogeneous Catalyst for the Reduction of 4-Nitrophenol

Catalysts ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 839 ◽  
Author(s):  
Hasan ◽  
Shehadi ◽  
Al-Bab ◽  
Elgamouz
Keyword(s):  
Silver Nanoparticles ◽  
Heterogeneous Catalyst ◽  
Active Catalyst ◽  
Low Cost ◽  
Catalytic Efficiency ◽  
Magnetic Chitosan ◽  
X Ray ◽  
Surface Modified ◽  
First Time ◽  
Magnetic Fe3o4

Developing heterogeneous catalyst using chitosan (CS) and magnetic Fe3O4 as support has been remarkably attractive due to their availability, low cost and non-toxicity. In this work, a heterogeneous catalyst (denoted as Fe3O4@CS@MS@Ag) was fabricated by the deposition of silver nanoparticles on magnetic chitosan via an easy and facile modification of its surface with methyl salicylate (MS). The catalyst was characterized using Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), X-ray diffractometer (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). To the best of our knowledge, for the first time, CS decorated Fe3O4 (Fe3O4@CS) has shown the catalytic activity for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in presence of NaBH4. Surface modified magnetic chitosan (Fe3O4@CS@MS) also acts as active catalyst towards the reduction of 4-NP. However, catalytic efficiency has increased fourfold when silver-nanoparticles-deposited magnetic chitosan (Fe3O4@CS@MS@Ag) used as our target catalyst. The catalyst was separated with external magnet after each cycle of catalytic reaction and reused effectively five times with almost 90% efficiency.

scholarly journals New iron-cobalt clusters with silicon-containing dicarboxylic acids

2012 ◽  
Vol 10 (4) ◽  
pp. 1079-1086 ◽  
Author(s):  
Maria Cazacu ◽  
Angelica Vlad ◽  
Constantin Turta ◽  
Gabriela Lisa
Keyword(s):  
Thermal Stability ◽  
Fourier Transform ◽  
Thermogravimetric Analysis ◽  
Elemental Analysis ◽  
Dicarboxylic Acids ◽  
High Spin State ◽  
Iron Cobalt ◽  
X Ray ◽  
Practical Applications ◽  
First Time

AbstractFor the first time, silicon-containing dicarboxylic acids were used to prepare two new heterotrinuclear carboxylates of the composition [Fe2IIICoIIO(Bcpdps)3(H2O)3], I, where H2Bcpdps ≡ HOOC-C6H4-Si(C6H5)2-C6H4COOH, and [Fe2IIICoIIO(Ipds)3(H2O)3], II, where H2Ipds ≡ [HOOC-C6H3(CO)2N-(CH2)3-(CH3)2Si]2O. The precursor for these two complexes was trinuclear µ3-oxo-hexaacetate triaqua diiron(III)cobalt(II) cluster, {Fe 2 CoO}, in which the acetate anions were subsequently substituted by silicon-containing dianions. The resulting products were characterized by elemental analysis, thermogravimetry, Fourier Transform Infrared (FTIR), Energy-Dispersive X-ray Fluorescence (EDXRF), and Mossbauer spectroscopies (MS). The investigation by MS revealed the presence of the iron(3+) ions in high spin state and having the close environment. Thermogravimetric analysis results indicated an improving in the thermal stability by replacing acetate anions with silicon-containing carboxyl ligands. This widens the temperature range in which such compounds can be used in practical applications.

Mo coordination and Thermal Stability of the Mo–Si3N4 Absorbers for Solar Selective Coatings

MRS Advances ◽  
2017 ◽  
Vol 2 (53) ◽  
pp. 3061-3068 ◽  
Author(s):  
C. Prieto ◽  
E. Céspedes ◽  
D. Hernández-Pinilla ◽  
A. Rodríguez-Palomo ◽  
O. Sánchez ◽  
...  
Keyword(s):  
Concentrated Solar Power ◽  
Edge Structure ◽  
X Ray ◽  
Practical Applications ◽  
Design And Optimization ◽  
Structural Correlation ◽  
First Time ◽  
X Ray Absorption ◽  
Optical Behavior ◽  
Thermal Stability Of

ABSTRACTThe study of the chemical stability of solar selective coatings (SSC) for concentrated solar power (CSP) becomes essential for their use at high temperatures. In this paper, the short range order around Mo in Mo-Si3N4 cermets is studied for the first time by X-ray absorption spectroscopy. The information obtained by extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) spectroscopies gives new insights of the origin of the optical behavior of the cermets cermets after vacuum and air annealing treatments. The established optical and structural correlation becomes of great importance for the design and optimization of SSC for practical applications.

scholarly journals Comparative study between the Titanium Phosphate TiP2O7 and the Phosphate Fertilizers in the catalysis of the Quinazolin-4(3H)-one derivatives synthesis

2020 ◽  
Vol 10 (6) ◽  
pp. 553
Author(s):  
Youssef Merroun ◽  
Soukaina Chehab ◽  
Tourya Ghailane ◽  
Rachida Ghailane ◽  
Said Boukhris ◽  
...  
Keyword(s):  
Reaction Times ◽  
Catalytic Efficiency ◽  
Titanium Phosphate ◽  
Triple Superphosphate ◽  
X Ray Diffraction ◽  
Phosphate Fertilizers ◽  
X Ray ◽  
High Yields ◽  
First Time

A simple and efficient method for the synthesis of quinazolin-4(3H)-one derivatives via condensation of anthranilamide with aromatic aldehyde catalyzed by monoammonium phosphate (MAP), diammonium phosphate (DAP), and triple superphosphate (TSP), were developed.  The modification of these three phosphate fertilizers using titanium tetrachloride (TiCl<sub>4</sub>) has increased their catalytic efficiency. The prepared titanium phosphate (TiP<sub>2</sub>O<sub>7</sub>) was characterized using microscopic and spectroscopic methods, namely X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and infrared spectroscopy (IR). The TiP<sub>2</sub>O<sub>7</sub> was applied for the first time as a heterogeneous catalyst in quinazolin-4(3H)-ones synthesis. High yields and short reaction times were observed in the determined optimal condition (solvent nature, volume, and catalyst amount). This study shows that the TiP<sub>2</sub>O<sub>7</sub> presents an exciting catalytic activity and long-term durability compared to those of MAP, DAP, and TSP.

A NEW 1212-TYPE PHASE: Cr-SUBSTITUTED TlSr2CaCu2O7 WITH Tc UP TO ABOUT 110 K

1991 ◽  
Vol 05 (09) ◽  
pp. 635-642 ◽  
Author(s):  
Z.Z. SHENG ◽  
D.X. GU ◽  
Y. XIN ◽  
D.O. PEDERSON ◽  
L.W. FINGER ◽  
...  
Keyword(s):  
Ac Susceptibility ◽  
Single Element ◽  
X Ray Diffraction ◽  
X Ray ◽  
Practical Applications ◽  
Element Substitution ◽  
Type Phase ◽  
First Time

Superconductivity up to about 110 K in the CrTlSrCaCuO system was observed by resistance and ac susceptibility measurements. Powder X-ray diffraction analyses showed that a 1212-type phase, Cr -substituted TlSr 2 CaCu 2 O 7, is responsible for the observed superconductivity. This is the first time that single-element substitution for TlSr 2 CaCu 2 O 7 increases Tc of the 1212 phase to above 100 K. The Cr -substituted TlSr 2 CaCu 2 O 7 is easily prepared and has very good quality suitable for practical applications.

X-Ray Microanalysis of Nickel and Cobalt Intensified Peroxidase- Antiperoxidase For Verification of Reaction Sites

1985 ◽  
Vol 43 ◽  
pp. 468-469
Author(s):  
A. Angel ◽  
K. Miller ◽  
V. Seybold ◽  
R. Kriebel
Keyword(s):  
Reaction Mechanisms ◽  
Visual Discrimination ◽  
Osmium Tetroxide ◽  
Ultrastructural Level ◽  
Microscopic Level ◽  
Electron Microscopic Level ◽  
Electron Microscopic ◽  
X Ray ◽  
Insoluble Polymer ◽  
Cytochemical Reaction

Localization of specific substances at the ultrastructural level is dependent on the introduction of chemicals which will complex and impart an electron density at specific reaction sites. Peroxidase-antiperoxidase(PAP) methods have been successfully applied at the electron microscopic level. The PAP complex is localized by addition of its substrate, hydrogen peroxide and an electron donor, usually diaminobenzidine(DAB). On oxidation, DAB forms an insoluble polymer which is able to chelate with osmium tetroxide becoming electron dense. Since verification of reactivity is visual, discrimination of reaction product from osmiophillic structures may be difficult. Recently, x-ray microanalysis has been applied to examine cytochemical reaction precipitates, their distribution in tissues, and to study cytochemical reaction mechanisms. For example, immunoreactive sites labelled with gold have been ascertained by means of x-ray microanalysis.

Diphosphinoazine Rhodium(I) and Iridium(I) Complexes

2006 ◽  
Vol 71 (2) ◽  
pp. 197-206 ◽  
Author(s):  
Martin Pošta ◽  
Jan Čermák ◽  
Pavel Vojtíšek ◽  
Ivana Císařová
Keyword(s):  
Rhodium Complexes ◽  
Iridium Complexes ◽  
X Ray ◽  
First Time

The first rhodium complexes of diphosphinoazines [{RhCl(1,2-η:5,6-η-CH=CHCH2CH2CH=CHCH2CH2)}2 {μ-R2PCH2C(But)=NN=C(But)CH2PR2] (R = Ph, Cy, Pri) were prepared by cleavage of the bridge in chloro(cycloocta-1,5-diene)rhodium(I) dimer, the analogous iridium(I) complexes were also prepared for the first time. The X-ray structures of isostructural rhodium and iridium complexes with bis(dicyclohexylphosphino)pinacoloneazine were determined. Diphosphinoazine ligands in the complexes remained in (Z,Z) configuration bridging two RhCl(C8H12) units.

scholarly journals Quartz Crystallite Size and Moganite Content as Indicators of the Mineralogical Maturity of the Carboniferous Chert: The Case of Cherts from Eastern Asturias (Spain)

Minerals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 611
Author(s):  
Celia Marcos ◽  
María de Uribe-Zorita ◽  
Pedro Álvarez-Lloret ◽  
Alaa Adawy ◽  
Patricia Fernández ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Crystallite Size ◽  
Archaeological Sites ◽  
X Ray Diffraction ◽  
X Ray ◽  
Transmission Electron ◽  
Infrared And Raman Spectroscopy ◽  
First Time ◽  
Geological Formations

Chert samples from different coastal and inland outcrops in the Eastern Asturias (Spain) were mineralogically investigated for the first time for archaeological purposes. X-ray diffraction, X-ray fluorescence, transmission electron microscopy, infrared and Raman spectroscopy and total organic carbon techniques were used. The low content of moganite, since its detection by X-ray diffraction is practically imperceptible, and the crystallite size (over 1000 Å) of the quartz in these cherts would be indicative of its maturity and could potentially be used for dating chert-tools recovered from archaeological sites. Also, this information can constitute essential data to differentiate the cherts and compare them with those used in archaeological tools. However, neither composition nor crystallite size would allow distinguishing between coastal and inland chert outcrops belonging to the same geological formations.

scholarly journals First Report on the Geologic Occurrence of Natural Na–A Zeolite and Associated Minerals in Cretaceous Mudstones of the Paja Formation of Vélez (Santander), Colombia

Crystals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 218
Author(s):  
Carlos Alberto Ríos-Reyes ◽  
German Alfonso Reyes-Mendoza ◽  
José Antonio Henao-Martínez ◽  
Craig Williams ◽  
Alan Dyer
Keyword(s):  
Natural Zeolite ◽  
Scanning Electron Micrographs ◽  
Total Sulfur ◽  
Zeolite A ◽  
X Ray Diffraction ◽  
X Ray ◽  
Mineral Phases ◽  
The World ◽  
Porosity And Permeability ◽  
First Time

This study reports for the first time the geologic occurrence of natural zeolite A and associated minerals in mudstones from the Cretaceous Paja Formation in the urban area of the municipality of Vélez (Santander), Colombia. These rocks are mainly composed of quartz, muscovite, pyrophyllite, kaolinite and chlorite group minerals, framboidal and cubic pyrite, as well as marcasite, with minor feldspar, sulphates, and phosphates. Total organic carbon (TOC), total sulfur (TS), and millimeter fragments of algae are high, whereas few centimeters and not biodiverse small ammonite fossils, and other allochemical components are subordinated. Na–A zeolite and associated mineral phases as sodalite occur just beside the interparticle micropores (honeycomb from framboidal, cube molds, and amorphous cavities). It is facilitated by petrophysical properties alterations, due to processes of high diagenesis, temperatures up to 80–100 °C, with weathering contributions, which increase the porosity and permeability, as well as the transmissivity (fluid flow), allowing the geochemistry remobilization and/or recrystallization of pre-existing silica, muscovite, kaolinite minerals group, salts, carbonates, oxides and peroxides. X-ray diffraction analyses reveal the mineral composition of the mudstones and scanning electron micrographs show the typical cubic morphology of Na–A zeolite of approximately 0.45 mμ in particle size. Our data show that the sequence of the transformation of phases is: Poorly crystalline aluminosilicate → sodalite → Na–A zeolite. A literature review shows that this is an unusual example of the occurrence of natural zeolites in sedimentary marine rocks recognized around the world.

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