scholarly journals Three Manganese Complexes of Anionic N4-Donor Schiff-Base Macrocycles: Monomeric MnII and MnIII, and dimeric MnIV

2019 ◽  
Vol 72 (10) ◽  
pp. 805 ◽  
Author(s):  
Rajni K. Wilson ◽  
Sébastien Dhers ◽  
Stephen Sproules ◽  
Eric J. L. McInnes ◽  
Sally Brooker
Keyword(s):  
Schiff Base ◽  
Magnetic Measurements ◽  
Electron Paramagnetic Resonance Spectroscopy ◽  
Building Blocks ◽  
Macrocyclic Complexes ◽  
Resonance Spectroscopy ◽  
Original Design ◽  
Paramagnetic Resonance ◽  
Supramolecular Architectures ◽  
Schiff Base Macrocycles

Three manganese macrocyclic complexes of two anionic N4-donor [1+1] Schiff-base macrocycles that differ in ring size (14 versus 16 membered), HLEt and HLPr (obtained from condensation of diphenylamine-2,2′-dicarboxaldehyde and either diethylenetriamine or dipropylenetriamine), are reported. Specifically, a pair of monomeric complexes MnIILEt(NCS)(H2O) and [MnIIILPr(NCS)2]·0.5H2O, plus a dimeric complex [MnIV2LEt2(O)2](ClO4)2·3DMF have been synthesised and characterised. Single crystal structure determinations on [MnIIILPr(NCS)2]·0.5H2O and [MnIV2LEt2(O)2](ClO4)2·3DMF revealed octahedral manganese centres in both cases: N6-coordinated Jahn–Teller distorted MnIII in the former and a pair of N4O2-coordinated MnIV in the latter. UV-Vis, IR, and electron paramagnetic resonance spectroscopy as well as magnetic measurements are reported. These macrocyclic complexes feature a simple and original design, and could find future uses as models for manganese catalase or as building blocks for the assembly of larger supramolecular architectures.

A Novel µ1,1-Azido-, µ2-Alkoxo-, and µ2-Phenoxo-Bridged Tetranuclear Copper(II) Complex with a Quinquedentate Schiff-Base Ligand: Magneto-Structural and DFT Studies

2009 ◽  
Vol 62 (4) ◽  
pp. 366 ◽  
Author(s):  
Subhra Basak ◽  
Soma Sen ◽  
Georgina Rosair ◽  
Cédric Desplanches ◽  
Eugenio Garribba ◽  
...  
Keyword(s):  
Schiff Base ◽  
Schiff Base Ligand ◽  
Density Functional ◽  
Electron Paramagnetic Resonance Spectroscopy ◽  
Variable Temperature ◽  
Density Functional Theory Calculations ◽  
Magnetic Interactions ◽  
Resonance Spectroscopy ◽  
Paramagnetic Resonance ◽  
Ft Ir

A novel tetranuclear copper(ii) complex [Cu4L2(μ1,1- N3)2]·CH3CN (1) has been synthesized using a symmetrical quinquedentate N2O3-donor Schiff-base ligand H3L (N,N′-(2-hydroxypropane-1,3-diyl)bis(2- hydroxyacetophenimine)) and characterized by elemental analysis, Fourier-transform (FT)-IR, UV-visible, electron paramagnetic resonance spectroscopy, and cyclic voltammetry. The X-ray single-crystal structure of 1 reveals three kinds of bridges among the four metal centres: one from the exogenous azido ligand and two from the phenoxo and alkoxo moieties of the Schiff base. The same structure highlights the remarkable versatility of copper(ii) to adopt an array of stereochemistries. Four unusual eight-membered metallacycles exist in 1. The μ1,1-azido, μ2-alkoxo, and μ2-phenoxo bridges among the four copper centres have facilitated interesting magnetic interactions that have been elucidated by variable-temperature magnetic susceptibility measurements and backed up by density functional theory calculations. Detailed analyses have shown that the antiferromagnetic effect through the alkoxo-bridged CuII centres combined with the ferromagnetic interaction through the azido-bridged metal centres results in an S = 0 ground state.

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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