Ispitivanje antioksidativnih mehanizama kempferola sa hidroksi radikalom i superoksid radikal anjonom

Kaempferol, one of the most bioactive plant flavonoids was theoretically (at M05-2X/6-311G(d,p) level of theory) investigated for its ability scavange potentially highly damaging hydroxyl and superoxide anion radicals. Theoretical calculations point to HAT and SPLET mechanisms as operative for kaempferol in all solvents under investigations.Teoretski (na M05-2X/6-311G(d,p) nivou teorije) je ispitivana sposobnost kempferola, važnog bioaktivnog biljnog jedinjenja flavonoida, da reaguje sa potencijalno veoma štetnim hidroksi radikalom i superoksid radikal anjonom. Proračuni su pokazali da su HAT i SPLET mogući mehanizmi u svim rastvaračima

DFT ispitivanje antioksidativne aktivnosti alizarina Red S

Density functional theory calculations were performed to evaluate the antioxidant activity of alizarin red S molecule. The conformational behavior of molecule were analysed at the M06-2X/6-311++G(d,p) method. The most stable conformer of alizarin red S has two IHBs. The expected antioxidant activity of alizarin red S was justified from ionization potential (IPs) and homolytic O-H bond dissociation enthalpy (BDEs) values. Heterolytic O-H bond cleavages (proton dissociation enthalpies, PDEs) were also computed. Calculated IP, BDE, and PA values suggested that one-step H atom transfer (HAT), rather than SPLET or SET-PT, would be the most favored mechanism for explaining the antioxidant activity of alizarin red S in gas phase. In aqueous solution all of three mechanisms were competitive.Upotrebom DFT metode vršena su izračunavanja u cilju određivanja antioksidativne aktivnosti alizarina red S. Konformaciona priroda molekula analizirana ispitana je primenom M06-2X/6-311++G(d,p) metoda. Najstabilniji konformer alizarina red S ima dve unutrašnje vodonične veze. Očekivana antioksidativna aktivnost alizarina red S određena je izračunavanjem vrednosti jonizacionih potencijala (IP) i i vrednosti entalpija homolitičkog raskidanja O-H veza (BDE). Vrednosti entalpije heterolitičkog raskidanja O-H veza (entalpije disocijacije protona, PDE), su takođe izračunate. Izračunate IP, BDE i PA vrednosti ukazuju na to da je jednostepeni transfer H-atoma (HAT), pre nego SPLET ili SET-PT mehanizam, favorizovan u pogledu antioksidativne aktivnosti alizarina red S u gasnoj fazi. U vodenom rastvoru, sva tri mehanizma su konkurentna

Synthesis and dielectric properties of calcium copper titanate (CCTO) based ceramics

The perovskite CaCu3Ti4O12 (CCTO) powders with various oxide phase impurities were synthesized via citric gel combustion method. Influence of citric acid amount used for gel preparation was examined in order to lower CCTO formation temperature to obtain powders with less impurities and better micro structural characteristics. Prepared powders were pressed into pellets and sintered at 1000 °C. Effects of oxide component impurities, such as CuO, rutile, anatase, CaTiO3 were examined on sintering behavior and dielectric properties of ceramics. Phase composition of powders and sintered specimens were determined by XRD, microstructure powders and sintered bodies were observed by SEM, and dielectric constants of sintered ceramics were measured by Wayne-Kerr B224 universal bridge

Synthesis Procedure for the Preparation of CaCu3Ti4O12

Poster presented at the 12th Annual Conference of the Materials Research Society of Serbia - YUCOMAT 2010, Herceg Novi, Montenegro, 6–10. septembar 2010

Transfer Learning with ResNet3D-101 for Global Prediction of High Aerosol Concentrations

In order to better predict the high aerosol concentrations associated with air pollution and climate change, a machine learning model was developed using transfer learning and the segmentation process of global satellite images. The main concept of transfer learning lies on convolutional neural networks and works by initializing the already trained model weights to better adapt the weights when the network is trained on a different dataset. The transfer learning technique was tested with the ResNet3D-101 model pre-trained from a 2D ImageNet dataset. This model has performed well for contrail detection to assess climate impact. Aerosol distributions can be monitored via satellite remote sensing. Satellites can monitor some aerosol optical properties like aerosol optical thickness. Aerosol optical thickness snapshots were the input dataset for the model and were obtained from NASA’s Terra-Modis satellite; the output images were segmented by comparing the pixel values with a threshold value of 0.8 for aerosol optical thickness. Hyperparameter optimization finds a tuple of hyperparameters that yields an optimal model that minimizes a predefined loss function on given independent data. The model structure was adjusted in order to improve the performance of the model by applying methods and hyperparameter optimization techniques such as grid search, batch size, threshold, and input length. According to the criteria defined by the authors, the distance domain criterion and time domain criterion, the developed model is capable of generating adequate data and finding patterns in the time domain. As observed from the comparison of relative coefficients for the criteria metrics proposed by the authors, ddc and dtc, the deep learning model based on ConvLSTM layers developed in our previous studies has better performance than the model developed in this study with transfer learning

The isolation, analytical characterization by HPLC-UV and NMR spectroscopy, cytotoxic and antioxidant activities of baeomycesic acid from Thamnolia vermicularis var. subuliformis

The aim of this work was the analytical characterization of the β-orcinol depside, baeomycesic acid in lichens extracts. The extract of Thamnolia vermicularis var. subuliformis was analyzed by the two different methods, namely HPLC-UV and 1H NMR analysis. The results showed that baeomycesic acid was the most abundant depside in the lichens. These results could be of use for rapid identification of this metabolite in other lichen species. Besides baeomycesic acid, three depsides and one monocyclic phenolic compound were isolated from the lichen extract on the chromatographic column. The structure of baeomycesic acid was confirmed by HPLC-UV and spectroscopic methods. In addition, antioxidant and cytotoxic activities of baeomycesic acid were determined. The result of the testing showed that baeomycesic acid exhibited a moderate radical scavenging activity (IC50 = 602.10 ± 0.54 μg/mL) and good cytotoxic activity. This is the first report of detailed analytical characterization, isolation, as well as antioxidant and cytotoxic activities of baeomycesic acid from Thamnolia vermicularis. These results may be helpful in future industrial production of herbal medicines that include this important natural product

Hydrothermal synthesis of ZnO powders with a tailored particle morphology and improved optical characteristics

ZnO represent one of the most important multifunctional materials. Its properties are well known and confirmed in different application areas such as: gas sensors, UV lasers, solar cells, electroluminescent and optoelectronic devices, piezoelectric transducers, hydrogen-storages, rubber industry and plastic processing, cosmetics and pharmacy, and it is also used as an antibacterial agent. In this work, we propose a low-temperature hydrothermal method for the synthesis of phase-pure ZnO powders with a controlled morphology and narrow particle size distribution. This simple and low-cost method allows tailoring of the shape and size of ZnO particles, from micro-rods via hexagonal prism-like to nano-spheres, by choosing the appropriate pH of the reaction solution, tuned by the varying of [Na+]:[Zn2+] molar ratio. The agglomeration of the powders was prevented with the assistance of PVP as a capping agent. The synthesized powders were characterized by XRD, TEM, SEAD and HRTEM methods to examine the phase purity and crystallinity. FE-SEM measurements were used for the morphology characterization, while the results of Raman and UV-Vis DRS measurements were used for the study of optical properties. The relationship between the particle size and morphology and the optical properties is discussed. Diffuse reflectance spectra of ZnO powders with different size and morphology revealed characteristic R curves with the absorption edge near 380 nm, but with obvious difference in the absorption in the visible region. The micro-sized powder ZnO8 revealed the lowest reflectance (∼70%), compared to submicro- (∼80%) and nano-sized (ZnO12 and ZnO13, ∼90%) powders. Thus, the reflectance of the ZnO powders decreases with the increase in the average particle size

The influence of powder characteristics on two-step sintering behavior of hydroxyapatite

Fabrication of full dense ceramic materials on the basis of hydroxyapatite (HAp) and biphasic calcium phosphate (BCP) with controllable microstructural and compositional characteristics attracts considerable efforts. Various synthesis and sintering methods were applied in order to achieve desirable material properties. In this study different nanopowders were produced and processed via two-step sintering (TSS) approach. Characterization of synthesized nanopowders were done by XRD, BET, FE-SEM, TEM and thermal analysis methods, while microstructural and chemical characterizations of sintered samples were performed through FE-SEM and XRD analysis. A possibility for obtaining full dense ceramics with suppressed grain growth is discussed on the basis of inherent nanopowders characteristics. Certain attention would be paid on thermal behavior of Ca-deficient HAp systems

Tailoring morphology and particle size of ZnO powders

U ovom tekstu objašnjeni su postupci sinteze prahova ZnO i mogućnosti da se tim sintezama morfologija i srednja veličina čestica kreiraju od mikrometarskih štapića do nanometarskih sfernih čestica. Primenjene su dve metode sinteze, niskotemperatursko hidrotermalno (HT) procesiranje i ultrazvučno (UZ) procesiranje. Morfologija i srednja veličina čestica su kreirane podešavanjem molskog odnosa [Zn2+]/[OH-] polaznog (prekurskorskog) rastvora. Aglomeracija čestica je sprečena upotrebom polivinil pirolidona (PVP). Sintetisani prahovi su karakterisani metodom rendgenske difrakcije na prahu (XRD), skanirajuće elektronske mikroskopije (FESEM) i UV-Vis difuzione refleksione spektroskopije (UV-Vis DRS). Na osnovu skanirajućih elektronskih mikrografija predložen je mehanizam rasta čestica ZnO u zavisnosti od molskog odnosa [Zn2+]/[OH-] polaznog rastvora. Takođe, ispitan je i uticaj veličine i morfologije čestica na optičke karakteristike prahova ZnO; uočeno je da veličina i morfologija čestica utiču kako na apsorpciju vidljive svetlosti (%) tako i na pomeraj energetskog procepa (eV).Different ZnO powders synthesis methods as well as possibilities to obtain particles with controlled morphology and average particle size from micro- to nano-level were discussed. Two synthesis methods were applied, low-temperature hydrothermal (HT) and ultrasound processing (UZ). Morphology and average particle size were tailored by adjusting of initial solution [Zn2+]/[OH-]molar ratio. Particles agglomeration is suppressed by polyvinylpyrrolidone (PVP). Synthesized powders were characterized by X-ray diffraction method (XRD), field emission scanning electron microscopy (FESEM) and UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS). Considering FESEM micrographs the ZnO particles growth mechanism depending on initial solution [Zn2+]/[OH-] molar ratio is proposed. Furthermore, influence of average particle size and morphology on ZnO optical properties is studied; it is observed that both average particle size and morphology affect visible light absorption (%) as well as shift of Ebg (eV)