Dans cette thèse nous avons évalué l'effet de la substitution partielle du cobalt par des éléments non-magnétiques de type p (M) sur les propriétés structurales et magnétiques des composés RCo5. Les ...échantillons ont été synthétisées par fusion dans un four à induction, puis caractérisés en utilisant des nombreuses techniques expérimentales: diffraction de rayons X et de neutrons, microscopie électronique à balayage, magnétométrie, susceptométrie en courant alternatif et spectroscopie photoélectronique par rayons X.Tous les composés de type RCo5-xMx (R= Pr, Sm, Tb, Er et Tm; M= Si, Ge, Al, Ga; x=0,5 et x=1) étudiés gardent la structure cristalline de type CaCu5 des composés de départ RCo5, mais les paramètres de la maille cristalline sont modifiés par la présence des éléments M. Le domaine de stabilité thermique des phases RCo5-xMx est notablement modifié par la présence d'élément métalloïde en substitution sur les sites du cobalt. Il peut être étendu pour Al et Ga et réduit pour Si et Ge. Les atomes de l'élément M sont localisés préférentiellement sur le site cristallographique Co 3g. La solubilité des éléments Ge et Si dans la structure RCo5 est trouvée être inférieure à celle des métalloïdes ayant un électron de moins tels que Al et Ga.La substitution M/Co a une influence importante sur les propriétés magnétiques des composés RCo5. La température d'ordre et l'aimantation spontanée diminuent significativement après le remplacement partiel du cobalt par l'élément métalloïde. Ces modifications sont induites par l'évolution des interactions d'échange en particulier Co-Co mais aussi par la réduction de l'aimantation du Co liée à sa sensibilité au voisinage atomique et magnétique local. La direction de facile aimantation à la température ambiante est préservée le long de l'axe cristallographique c pour tous les échantillons étudiés. Dans quelques composés RCo5-xMx (R = Sm, Er et Tm) la substitution de M au cobalt change le mécanisme de coercitivité par rapport aux composés de départ RCo5. Une coercitivité élevée a été détectée à basse température, surtout pour les composés SmCo4Al et SmCo4Ga, qui présentent aussi des champs d'anisotropie énormes, bien supérieurs à ceux de phase SmCo5.Les expériences XPS sur les composés de type RCo5-xMx ont détecté la réduction de la densité d'états électroniques au niveau de Fermi par rapport aux composés de type RCo5. La bande 3d du cobalt est remplie lors de la substitution M/Co et conduit à un moment magnétique du cobalt réduit.
In this work we have evaluated the effect of the partial substitution of cobalt with non-magnetic p-type elements (M) on the structural and magnetic properties of RCo5 compounds. The samples were prepared by alloying in an induction furnace and were characterized using various experimental techniques: X-ray and neutron diffraction, scanning electron microscopy, magnetometry, AC susceptometry and X-ray photoelectron spectroscopy.All of the studied RCo5-xMx compounds (R=Pr, Sm, Tb, Er and Tm; M=Si, Ge, Al and Ga; x=0.5 and x=1) maintain the CaCu5 crystal structure of the RCo5 compounds, however the lattice parameters are modified due to the presence of M elements. The thermal stability range of the RCo5-xMx phases is modified significantly due to the Co site substitutions. The thermal stability increases for Al and Ga substitutions and decreases when M is Si or Ge. The M atoms were found to preferentially occupy the Co 3g site. The solubility of Ge and Si in the RCo5 structure is inferior to that of metalloid elements with one less electron, such as Al and Ga. The M/Co substitution has an important influence on the magnetic properties of RCo5 compounds. The ordering temperature and the spontaneous magnetization are significantly reduced after the partial substitution of cobalt by the metalloid elements. These changes are induced in particular by the evolutions of the Co-Co exchange interactions and also by the reduction of the Co magnetization due to the sensitivity of Co to the local atomic and magnetic vicinity. The easy magnetization direction at room temperature is preserved along the c-axis for all of the studied samples. In several RCo5-xMx (R = Sm, Er and Tm) compounds the substitution of Co with M atoms changes the coercivity mechanism compared to RCo5. A higher coercivity was found at low temperatures, especially for SmCo4Al and SmCo4Ga compounds, which also show huge values of the anisotropy field, well above the ones found in SmCo5.The XPS measurements on RCo5-xMx compounds show a reduction of the density of states at the Fermi level compared to the RCo5 compounds. There is a filling of the Co 3d band following the M/Co substitution, leading to a lower Co moment.
•Biogenic production of Se NPs by L. casei.•Cd bio-adsorption and remediation by lactic acid bacteria.•Better stimulation of endogenous SeNPs in L. fermentum evidenced by FT-Raman ...spectroscopy.•Synergic effect of biogenic SeNPs and lactic acid bacteria against Cd toxicity.
Cadmium is a heavy metal, environmental pollutant and toxic for organisms. Lactic acid bacteria (LAB) and nanoparticles represent useful tools to remove heavy metals from different environments. The main goal of our study was to develop a novel experimental design for cadmium (Cd) disposal using L. casei or L. fermentum and exogenous selenium nanoparticles. The experimental design was developed in two steps. In the first step, bio-synthesis, morphological and chemical characterization of selenium nanoparticles (SeNPs) produced by L. casei was performed. In the next step, L. casei and L. fermentum were used to evidence their binding ability toward Cd, highlighting the role of SeNPs against Cd-induced toxicity. Homogenous, spherical shape SeNPs and sharp size distribution with maximum 200 nm were obtained via reduction route, using L. casei and Na2SeO3. Addition of Cd to LAB culture medium strongly inhibits both bacteria growth. SeNPs, in contrast to sodium selenite, clearly demonstrates the protective effect against Cd toxicity, as evidenced by dynamic growth curves of both bacteria. A better stimulation of endogenous SeNPs production was noticed for L. fermentum compared to L. casei. The efficiency of Cd bio-absorption by LAB was in the range 43.78% - 50.87%, the ratio of 1:2 LAB/SeNPs showing the best results for both bacteria. The synergic effect of biogenic SeNPs and LAB against Cd toxicity was demonstrated. The combination of FTIR (Fourier Transform Infrared), FT Raman (Fourier Transformed Raman) and ICP-OES (Inductively Coupled Plasma Optical Emission Spectroscopy) techniques provides specific qualitative and quantitative information on the behavior of probiotic species with respect to SeNPs synthesis and Cd disposal.
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Since cadmium is a toxic metal that can cause serious health problems for humans, it is necessary to find bioremediation solutions to reduce its harmful effects. The main goal of our work was to ...develop a functional food based on elemental selenium nanoparticles (SeNPs) obtained by green synthesis using
and to validate their ability to annihilate the hepatic toxic effects induced by cadmium. The characterization of SeNPs was assessed by UV-Vis spectroscopy, FTIR, XRD, DLS and TEM. In order to investigate the dose-dependent protective effects of SeNPs on Cd liver toxicity, mice were assigned to eight experimental groups and fed by gavage, with 5 mg/kg b.w. cadmium, respectively, with co-administration with SeNPs or lacto-SeNPs (LSeNPs) in 3 doses (0.1, 0.2 and 0.4 mg/kg b.w.) for 30 days. The protective effect was demonstrated by the restoration of blood hepatic markers (AST, ALT, GGT and total bilirubin) and antioxidant enzymes, such as catalase (CAT) and glutathione peroxidase (GPx). Moreover, the antioxidant capacity of mice plasma by the FRAP assay, revealed the highest antioxidant capacity for the 0.2 mg/kg LSeNPs group. Histopathological analysis demonstrated the morphological alteration in the group that received only cadmium and was restored after the administration of SeNPs or LSeNPs, while the immunohistochemical analysis of the
family revealed anti-apoptotic effects; the Q-PCR analysis showed an upregulation of hepatic inflammatory markers for the group exposed to Cd and a decreased value for the groups receiving oral SeNPs/ LSeNPs in a dose-dependent manner. The best protective effects were obtained for LSeNPs. A functional food that includes both probiotic bacteria and elemental SeNPs could be successfully used to annihilate Cd-induced liver toxicity, and to improve both nutritional values and health benefits.
The LULUCF sector (land use, land use change and forestry) can act as a carbon dioxide (CO2) sink, either by increasing the removal of greenhouse gasses from the atmosphere or by reducing their ...current emissions. This paper intends to analyze the results of the CO2 monitoring methodology by the chamber method in order to estimate the effect of different land use cover and management techniques. For this purpose, seasonal CO2 efflux field measurements were conducted in two types of ecosystems (forested land and wheat crop) located in the adjacent area of Bucharest. CO2 efflux was analysed for each land cover in relation to the physical characteristics of the soil, respectively soil temperatures and humidity, but also together with the main weather parameters. The measurements were performed simultaneously in both land covers at relevant time intervals. The difference in measured values between the two ecosystems was recorded but the results of the statistical analysis showed a lack of differences in the correlation between the CO2 efflux. This indicates that the CO2 efflux can be affected by particular elements of the environment which facilitates differences in soil temperature and humidity in the same weather conditions.
Natural compounds are used in modern dermal treatments to avoid side effects commonly associated with conventional treatments. The aim of our study was to develop a liposomal formulation including ...black mulberry extract and to highlight its potential on the healing of normal human dermal fibroblasts (NHDF) in vitro using the scratch test. Mulberry-loaded liposomes (MnL) were prepared using a thin-film hydration method based on cholesterol (C) and phosphatidylcholine (PC) in a 1:3 (w/w) ratio. The liposomal formulation was characterized by analyzing its size, electric surface potential, morphology, entrapment efficiency, and in vitro healing effects. Also, the black mulberry fruits (Morus nigra L.) were characterized from point of view of polyphenolic compounds and antioxidant capacity by Ferric-Reducing Antioxidant Power (FRAP) assay. HPLC-DAD-MS (ESI+) (high performance liquid chromatography-photodiode array detection-mass spectrometry (electrospray ionization)) analysis indicated the presence of phenolic compounds namely from hydroxybenzoic and hydroxycinnamic acids and flavonols. Among flavonols, quercetin-glucoside represented 50.56%, and chlorogenic acid was the predominant compound among hydroxycinnamic acids (37.06%). In vitro fibroblast wound closure was more effective with mulberry-loaded liposomes (MnL) than extracts of mulberries. According to our study, mulberry-loaded liposomes have been shown to be effective in wound healing and can be used as a natural treatment.
The healing of skin wounds remains an important concern in medicine, especially in chronic wounds caused by various diseases such as diabetes. Using herbs or herbal products to heal skin wounds is a ...therapeutic challenge for traditional medicine. In this context, the main aim of our work was to highlight the in vitro healing potential of Stellaria media (L.) Vill. (SM) extract using the scratch assay on normal human dermal fibroblasts (NHDF). The ability to stimulate cell migration and proliferation under the influence of different concentrations of SM extract (range between 12.5 and 200 µg/mL) was determined compared to the control (untreated in vitro-simulated wound) and positive control (allantoin 50 µg/mL). Our results showed that the concentration of 100 µg/mL SM extract applied on the simulated wound recorded the strongest and fastest (24 h) migration (with wound closure) and proliferation of NHDF compared with the control. In addition, the SM extract was characterized in terms of bioactive compounds (total phenols and flavonoids content), antioxidant capacity (FRAP (The Ferric-Reducing Antioxidant Power) assay and electrochemical method), and antimicrobial activity. The results show that the SM extract contains a considerable amount of polyphenols (17.19 ± 1.32 mg GAE/g dw and 7.28 ± 1.18 mg QE/g dw for total phenol and flavonoid content, respectively) with antioxidant capacity. Antimicrobial activity against Gram-positive bacteria (S. aureus) is higher than E. coli at a dose of 15 µg/mL. This study showed that Stellaria media is a source of polyphenols compounds with antioxidant capacity, and for the first time, its wound healing potential was emphasized.
With the expansion of urban areas, the amount of sludge produced by sewage treatment plants is increasing, raising big problems regarding the reintroduction of this sludge into nature in order to ...fully solve the wastewater problem. The application of sludge to agricultural surfaces or degraded land is a controversial solution since, despite the well-known benefits, sludge can, in certain cases, represent a real threat to both human health and the environment, with long-term harmful effects. The present study evaluates the potential genotoxicity of sludge using the Comet Test and three cellular bioindicators (lymphocytes, coelomocytes, and Allium cepa L.) for its quantification. To perform the tests, the soluble fraction of the sludge was used at concentrations of 25%, 50%, 75%, and 100%, as well as a negative control (Hsub.2O) and a positive control (Hsub.2Osub.2). The Comet test indicated an increase in DNA damage among cells exposed for 4 h in the following order: coelomocytes, lymphocytes, and Allium cepa L. cells. Our results indicate that Allium cepa L. nuclei are more sensitive, with genotoxic effects being evident at concentrations as low as 25%. In coelomocytes, we recorded nuclear damage starting at a concentration of 75%. These results indicate the necessity of using multiple genotoxicity tests, combined in a test battery, to achieve a greater level of relevance. The concentration of the soluble fraction of the sludge has an inverse relationship with the auxin content in leaves and roots, suggesting varying levels of stress. The results of this study can contribute to the creation of a genotoxic profile of sewage sludge, facilitating decisions related to reducing its negative impact.
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