scholarly journals Birnessite: A New Oxidant for Green Rust Formation

Materials ◽  
2020 ◽  
Vol 13 (17) ◽  
pp. 3777
Author(s):  
Amira Doggaz ◽  
Romain Coustel ◽  
Pierrick Durand ◽  
François Humbert ◽  
Christian Ruby

Iron and manganese are ubiquitous in the natural environment. FeII-FeIII layered double hydroxide, commonly called green rust (GR), and MnIII-MnIV birnessite (Bir) are also well known to be reactive solid compounds. Therefore, studying the chemical interactions between Fe and Mn species could contribute to understanding the interactions between their respective biogeochemical cycles. Moreover, ferromanganese solid compounds are potentially interesting materials for water treatment. Here, a {Fe(OH)2, FeIIaq} mixture was oxidized by Bir in sulphated aqueous media in the presence or absence of dissolved O2. In oxic conditions for an initial FeII/OH− ratio of 0.6, a single GR phase was obtained in a first step; the oxidation kinetics being faster than without Bir. In a second step, GR was oxidised into various final products, mainly in a spinel structure. A partial substitution of Fe by Mn species was suspected in both GR and the spinel. In anoxic condition, GR was also observed but other by-products were concomitantly formed. All the oxidation products were characterized by XRD, XPS, and Mössbauer spectroscopy. Hence, oxidation of FeII species by Bir can be considered as a new chemical pathway for producing ferromanganese spinels. Furthermore, these results suggest that Bir may participate in the formation of GR minerals.

2021 ◽  
Vol 152 (10) ◽  
pp. 1231-1239
Author(s):  
Anjan Patel ◽  
Thomas Rosenau

AbstractTocopherols are a mixture of antioxidants which are commonly referred to as vitamin E. Tocopheramines differ from tocopherols by an amino function in lieu of the phenolic OH group. They are potent antioxidants which are used in biomedical scenarios as well as stabilizers for polymers against aging. While in aqueous media α-tocopheramine is mainly oxidized to α-tocopherylquinone and N-oxidized by-products, oxidation in apolar media or in polymeric matrices mainly leads to dimeric compounds of hitherto unknown structure. In the present study, we synthesized the whole array of N,N-dimerization product of α-tocopheramine, including the hydrazo, azo, and azoxy derivatives for the first time, and provided comprehensive analytical data as well as general protocols to access the compounds in straightforward syntheses. These results can now be used to identify the common oxidation by-products of α -tocopheramine in different reaction systems. Graphic abstract


Nanomaterials ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 514
Author(s):  
David Medina-Cruz ◽  
Ada Vernet-Crua ◽  
Ebrahim Mostafavi ◽  
María Ujué González ◽  
Lidia Martínez ◽  
...  

Cancer and antimicrobial resistance to antibiotics are two of the most worrying healthcare concerns that humanity is facing nowadays. Some of the most promising solutions for these healthcare problems may come from nanomedicine. While the traditional synthesis of nanomaterials is often accompanied by drawbacks such as high cost or the production of toxic by-products, green nanotechnology has been presented as a suitable solution to overcome such challenges. In this work, an approach for the synthesis of tellurium (Te) nanostructures in aqueous media has been developed using aloe vera (AV) extracts as a unique reducing and capping agent. Te-based nanoparticles (AV-TeNPs), with sizes between 20 and 60 nm, were characterized in terms of physicochemical properties and tested for potential biomedical applications. A significant decay in bacterial growth after 24 h was achieved for both Methicillin-resistant Staphylococcus aureus and multidrug-resistant Escherichia coli at a relative low concentration of 5 µg/mL, while there was no cytotoxicity towards human dermal fibroblasts after 3 days of treatment. AV-TeNPs also showed anticancer properties up to 72 h within a range of concentrations between 5 and 100 µg/mL. Consequently, here, we present a novel and green approach to produce Te-based nanostructures with potential biomedical applications, especially for antibacterial and anticancer applications.


2009 ◽  
Vol 73 (12) ◽  
pp. 3579-3592 ◽  
Author(s):  
B.C. Christiansen ◽  
T. Balic-Zunic ◽  
P.-O. Petit ◽  
C. Frandsen ◽  
S. Mørup ◽  
...  

1967 ◽  
Vol 20 (10) ◽  
pp. 2151
Author(s):  
JW Clark-Lewis ◽  
LR Williams

Epimerization and solvolysis of the benzylic 4-hydroxyl group is shown to be a general property of flavan-3,4-diols, and the diols give 4- ethoxyflavan-3-ols with ethanolic hydrochloric acid (1%). The diols are first converted into epimeric mixtures of 3,4-cis- and 3,4-trans-diols and in aqueous media cis-cis-flavan-3,4-diols yield mainly 2,3-cis-3,4- trans-diols. These 2,3-cis-3,4-diols undergo solvolysis to yield 2,3- cis-3,4-trans-4-ethoxyflavan-3-ols in which the 3,4-trans- stereochemistry is controlled by participation of the neighbouring 3ax- hydroxyl group. 2,3-trans-Flavan-3,4-diols give mixtures of trans- trans-diols and 2,3-trans-3,4-cis-diols and solvolysis first yields 2.3-trans-3,4-cis-4-ethoxyflavan-3-ols and then mixtures of the 3,4- cis- and 3,4-trans-ethers; the final proportion of these two ethers is controlled by thermodynamic factors. Solvolysis under mild conditions gives minor products considered to be 3-oxoflavans (or their enols) because of their immediate conversion into antho-cyanidins by cold acids in the presence of air, and from the formation of an enol-ether on prolonged solvolysis under more vigorous conditions. The relevance of these observations to the mechanism of formation of anthocyanidins from flavan-3,4-diols is discussed. Other by-products of solvolysis reactions include a dimeric cyclic ether (dioxan derivative) of 2,3- trans-3,4-cis-7,8,4?-trimethoxyflavan-3,4-diol. The structure and stereochemistry of solvolysis products were established by N.M.R. data; the 4-ethoxyl group in the ethers generally gave rise to an ABX3 multiplet.


1996 ◽  
Vol 465 ◽  
Author(s):  
V. A. Sinitsyn ◽  
D. A. Kulik ◽  
M. Skhodorivski ◽  
V. A. Kurepin ◽  
A. Y. Abramis ◽  
...  

ABSTRACTA special geochemical environment exists within the Shelter (”Sarcophagus”) erected in 1986 over the destroyed Unit-4 of Chernobyl nuclear power plant (NPP). Based upon the available in situ and compositional data, thermodynamic models of solid-aqueous interactions were developed to clarify the leaching behaviour of various materials within the Shelter. The “Selektor-A” code, based on a convex programming approach to Gibbs free energy minimization, was used for the calculations. A built-in flexible hybrid thermodynamic database for the system Na-K-Ca-Mg-Cl-S-N-H-O-Si-P-Fe-Al-Sr-Cs was extended with the critically selected and matched parameters for aqueous species and solid phases in the U-Zr-Si-O-H subsystem, secondary U-minerals, mineral phases of fully hydrated Portland cements and U-bearing zircons. Modeling results show that the “Shelter waters” can selectively leach a significant quantity of U and Si from the fuel-containing masses, while Zr, Fe, Ca, Mg and some other components are rather insoluble. Serpentinite, assemblages of fully-hydrated phases of Portland cements, and oxidation products of steel structural elements are estimated to be sufficiently stable in the aqueous environment of the Shelter. Our calculations also define some feasible pathways for secondary mineral formation from evaporation of Shelter water solutions and interactions between these waters with the mineral matter inside the Shelter.


1995 ◽  
Vol 73 (8) ◽  
pp. 1298-1304 ◽  
Author(s):  
Paul-Louis Fabre ◽  
Paule Castan ◽  
Diane Deguenon ◽  
Nicole Paillous

Croconic acid, H2C5O5, is readily oxidized. This may be attested by decolorization of the solutions and by observation of oxalic acid complexes. The oxidation products are identified by 13C NMR spectroscopy as oxalic and mesoxalic acids, and experimental conditions are specified. The oxidation process requires dioxygen and photons. In parallel, the electrochemical oxidation of croconic acid is studied in aqueous media and in acetonitrile. A potential–pH diagram is drawn. Keywords: croconic acid, oxalic acid, oxidation, electrochemistry, photochemistry.


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