scholarly journals Synthesis and Structure of Copper Complexes of a N6O4 Macrocyclic Ligand and Catalytic Application in Alcohol Oxidation

Catalysts ◽  
2019 ◽  
Vol 9 (5) ◽  
pp. 424 ◽  
Author(s):  
Zhen Ma ◽  
Qijun Wang ◽  
Elisabete C. B. A. Alegria ◽  
M. Fátima C. Guedes da Silva ◽  
Luísa M. D. R. S. Martins ◽  
...  
Keyword(s):  
Copper Complexes ◽  
Electron Paramagnetic Resonance Spectroscopy ◽  
Aerobic Oxidation ◽  
Electrochemical Techniques ◽  
Macrocyclic Ligand ◽  
Copper Cation ◽  
Molecular Structures ◽  
Resonance Spectroscopy ◽  
Copper Salts ◽  
Paramagnetic Resonance

Reactions between N6O4 macrocyclic 1,4,19,22,25,40-hexaaza-10,13,31,34-tetraoxa-6,14,27,35(1,4)-tetrabenzenacyclopentacontane (L) and several copper salts (viz. trifuoromethane and toluene sulfonates, nitrate, perchlorate, benzoate, and acetate) led to the formation of dinuclear compounds [Cu2(OSO2CF3)2(DMF)2L](SO3CF3)2 (1), [Cu2(p-OSO2C6H4Me)2L(DMF)2](SO3C6H4Me)2 (2), [Cu2(ONO2)2L(DMF)2](NO3)2 (3), [Cu2(OClO3)2(DMF)2L](ClO4)2 (4), [Cu2(OOCPh)2L(H2O)2](O2CPh)2 (5), and [Cu2(OOCMe)4L] (6), which were characterized by IR, elemental analysis and TG-DTA (thermogravimetric-differential thermal analysis), as well as by single-crystal X-ray diffraction, EPR (electron paramagnetic resonance) spectroscopy, and electrochemical techniques (cyclic voltammetry and controlled potential electrolysis). The molecular structures of compounds 1–6 reveal a considerable conformational flexibility of the ligand L, which allowed its readjustment for the formation of the metal compounds and confirmed the presence of dinuclear endo macrocyclic species. In every case, the L ligand coordinates to each copper cation via three nitrogen atoms, with the remaining coordination positions of the metal square pyramid environment being accomplished by neutral or anionic ligands. The macrocyclic cavities appear to be adequate for the enclosure of a neutral species as proved by compound 6 with 1,4-dioxane. The compounds, in combination with the TEMPO (2,2,6,6-tetramethyl-piperidinyloxyl) radical and in alkaline aqueous solution, act as efficient catalysts in the aerobic oxidation of different alcohols to the corresponding aldehydes (yields up to 99% and TON up 232) after 20 h at 70 °C. In addition, the microwave-assisted solvent-free peroxidative oxidation (by tert-butylhydroperoxide, TBHP) of 1-phenylethanol led to acetophenone yields up to 99% and TOF of 1.1 × 103 after 0.5 h, without any additive.

Electron Paramagnetic Resonance Spectroscopic (EPR) Study of Copper Amine Treated Southern Pine in Wood Preservation

Holzforschung ◽  
2000 ◽  
Vol 54 (4) ◽  
pp. 343-348 ◽  
Author(s):  
J. Zhang ◽  
D. P. Kamdem
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Copper Complexes ◽  
Electron Paramagnetic Resonance Spectroscopy ◽  
Treated Wood ◽  
Wood Preservation ◽  
Resonance Spectroscopy ◽  
Paramagnetic Resonance ◽  
Electronic Parameters ◽  
Electron Paramagnetic ◽  
Copper Amine

Summary The structure of copper complexes in copper amine treated wood samples were elucidated by the application of electron paramagnetic resonance spectroscopy (EPR). EPR axial spectra were observed for all Cu-amine treated samples irrespective of the formulations. The values of A∥ and g∥ of the axial spectra indicate that the stereo-structure of copper complexes in copper amine treated wood was either tetragonal-based octahedral or square-based pyramidal. Comparison of electronic parameters of A∥ and g∥ in Cu-amine treated wood with those of the Cu-amine treating solution and the values in literature suggests that the interaction of wood with copper amine is through complexation in which wood functional groups are complexed with copper amine perpendicularly. The copper complexes in both treating solution and treated wood are in the form of CuN2O2, where copper is ligated with 2 nitrogen and 2 oxygen.

Effect of Sweeteners on Radical Formation in Starch Studied by Electron Paramagnetic Resonance Spectroscopy

2009 ◽  
Vol 15 (4) ◽  
pp. 357-365 ◽  
Author(s):  
M. Łabanowska ◽  
K. Dyrek ◽  
E. Bidzińska ◽  
T. Fortuna ◽  
S. Pietrzyk ◽  
...  
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Corn Starch ◽  
Electron Paramagnetic Resonance Spectroscopy ◽  
Molecular Structures ◽  
Radical Formation ◽  
Resonance Spectroscopy ◽  
Paramagnetic Resonance ◽  
Oh Groups ◽  
Radical Processes ◽  
Electron Paramagnetic

The process of radical generation occurring upon thermal treatment of potato and corn starch containing sweeteners: saccharose, acesulfam K, aspartame, and sorbitol was investigated by electron paramagnetic resonance spectroscopy, using Cu2+ ions as a paramagnetic probe. It was found that the influence of acesulfam K and sorbitol on radical formation is stronger than that of other additives. Acesulfam K increased the amount of radicals in the starch compared to native starch, whereas sorbitol significantly decreased their concentration. The influence of sweeteners on radical processes in the starch is because of differences in their molecular structures and presence or absence of OH groups.

scholarly journals Tauroursodeoxycholic Acid (TUDCA)—Lipid Interactions and Antioxidant Properties of TUDCA Studied in Model of Photoreceptor Membranes

Membranes ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 327
Author(s):  
Michał J. Sabat ◽  
Anna M. Wiśniewska-Becker ◽  
Michał Markiewicz ◽  
Katarzyna M. Marzec ◽  
Jakub Dybas ◽  
...  
Keyword(s):  
Antioxidant Activity ◽  
Plasma Membranes ◽  
Electron Paramagnetic Resonance Spectroscopy ◽  
Protective Action ◽  
Antioxidant Properties ◽  
Model Membranes ◽  
Dynamics Simulation ◽  
Resonance Spectroscopy ◽  
Paramagnetic Resonance ◽  
Tauroursodeoxycholic Acid

Tauroursodeoxycholic acid (TUDCA), a hydrophilic bile acid containing taurine conjugated with the ursodeoxycholic acid (UDCA), has been known and used from ancient times as a therapeutic compound in traditional Chinese medicine. TUDCA has recently been gaining significant interest as a neuroprotective agent, also exploited in the visual disorders. Among several mechanisms of TUDCA’s protective action, its antioxidant activity and stabilizing effect on mitochondrial and plasma membranes are considered. In this work we investigated antioxidant activity of TUDCA and its impact on structural properties of model membranes of different composition using electron paramagnetic resonance spectroscopy and the spin labeling technique. Localization of TUDCA molecules in a pure POPC bilayer has been studied using a molecular dynamics simulation (MD). The obtained results indicate that TUDCA is not an efficient singlet oxygen (1O2 (1Δg)) quencher, and the determined rate constant of its interaction with 1O2 (1Δg) is only 1.9 × 105 M−1s−1. However, in lipid oxidation process induced by a Fenton reaction, TUDCA reveals substantial antioxidant activity significantly decreasing the rate of oxygen consumption in the system studied. In addition, TUDCA induces slight, but noticeable changes in the polarity and fluidity of the investigated model membranes. The results of performed MD simulation correspond very well with the experimental results.

scholarly journals Ambient base-free glycerol oxidation over bimetallic PdFe/SiO2 by in situ generated active oxygen species

2021 ◽  
Author(s):  
Ricci Underhill ◽  
Mark Douthwaite ◽  
Richard J. Lewis ◽  
Peter J. Miedziak ◽  
Robert D. Armstrong ◽  
...  
Keyword(s):  
Heterogeneous Catalysts ◽  
Bimetallic Catalyst ◽  
Electron Paramagnetic Resonance Spectroscopy ◽  
Active Oxygen Species ◽  
Catalytic Performance ◽  
Resonance Spectroscopy ◽  
Oxygen Species ◽  
Paramagnetic Resonance ◽  
Temperature Oxidation

AbstractLow temperature oxidation of alcohols over heterogeneous catalysts is exceptionally challenging, particularly under neutral conditions. Herein, we report on an efficient, base-free method to oxidise glycerol over a 0.5%Pd-0.5%Fe/SiO2 catalyst at ambient temperature in the presence of gaseous H2 and O2. The exceptional catalytic performance was attributed to the in situ formation of highly reactive surface-bound oxygenated species, which promote the dehydrogenation on the alcohol. The PdFe bimetallic catalyst was determined to be significantly more active than corresponding monometallic analogues, highlighting the important role both metals have in this oxidative transformation. Fe leaching was confirmed to occur over the course of the reaction but sequestering experiments, involving the addition of bare carbon to the reactions, confirmed that the reaction was predominantly heterogeneous in nature. Investigations with electron paramagnetic resonance spectroscopy suggested that the reactivity in the early stages was mediated by surface-bound reactive oxygen species; no homogeneous radical species were observed in solution. This theory was further evidenced by a direct H2O2 synthesis study, which confirmed that the presence of Fe in the bimetallic catalyst neither improved the synthesis of H2O2 nor promoted its decomposition over the PdFe/SiO2 catalyst.

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