Alencar AB, de Oliveira A, Chacham H. Crystal reorientation and plastic deformation of single-layer MoS2 and MoSe2 under uniaxial stress. Journal of Physics: Condensed Matter [Internet]. 2020. Publisher's VersionAbstract
We investigate theoretically, through of first-principles calculations, the effect of the application of large in-plane uniaxial stress on single-layer of MoS2, MoSe2, and MoSSe alloys. For stress applied along the zigzag direction, we predict an anomalous behavior near the point fracture. This behavior is characterized by the reorientation of the MoS2 structure along the applied stress from zigzag to armchair due to the formation of transient square-lattice regions in the crystal, with an apparent (although not real) crystal rotation of 30 degrees. After reorientation, a large plastic deformation √3-1 remains after the stress is removed. This behavior is also observed in MoSe2 and in MoSSe alloys. This phenomenon is observed both in stress-constrained geometry optimizations and in ab initio molecular dynamics simulations at finite temperature and applied stress.
Velten H, Dito G. Post-Editorial of the Special Issue “Estate Quantistica Conference—Recent Developments in Gravity, Cosmology, and Mathematical Physics”. Universe [Internet]. 2020;6 (12) :240. Publisher's Version
de Santos ABS, Manfredi AM, Salla CAM, Farias G, Girotto E, Eccher J, Westphal E, Curcio SF, Cazati T, Malvestiti I, et al. Highly luminescent liquid crystals by connecting 1,3,4-oxadiazole with thiazolo[5,4-d]thiazole units. Journal of Molecular Liquids [Internet]. 2020 :114887. Publisher's VersionAbstract
The direct bonding between a thiazolo[5,4-d]thiazole and two 1,3,4-oxadiazole units allowed us to create a new and versatile rigid core for luminescent liquid crystal, which showed interesting and variable mesomorphic and photophysical properties. From the 5-bis(5-phenyl-1,3,4-oxadiazol-2-yl)thiazolo[5,4-d]thiazole new core, three molecules with different number of alkoxy chains were synthesized and had their properties correlated with the molecular structure. The molecule with two chains showed a smectic C mesophase, while the mesogens with four and six chains presented hexagonal columnar mesomorphism, which was confirmed by POM and XRD measurements. In addition, the molecule with six chains presented liquid crystalline behavior close to room temperature. In solution, the molecules presented strong photoluminescence ranging from blue to yellow, with quantum yields higher than 0.6. Excited state lifetimes allowed to correlate the fluorescence component associated to the different emitting species to the molecular organization in spin coated films. The molecular energy levels, together with thermal stability and possible charge carrier transport due to molecular packing, suggest that these molecules are promising for optoelectronic applications. Overall, this work contributes to the development of the use of thiazolo[5,4-d]thiazole in liquid crystals, demonstrating its great efficiency and versatility.
Batista RJC, Dias RF, Barboza APM, de Oliveira AB, Manhabosco TM, Gomes-Silva TR, Gadellha AC, Rabelo C, Cançado LGL, Jorio A, et al. Nanomechanics of few-layer materials: do individual layers slide upon folding?. Beilstein J. Nanotechnol. 2020;11 :1801–1808.
Diniz MO, Coelho RS, Bianchi RF, Guerra EM. Electrical Impedance of V 2 O 5/POMA Hybrid Film Deposited by Casting for Application in Ammonia Gas Sensor. Journal of Electronic Materials. 2020 :1–6.
Martins LGP, Silva DL, Smith JS, Lu A-Y, Su C, Hempel M, Occhialini C, Ji X, Pablo R, Alencar RS, et al. Hard, transparent, sp3-containing 2D phase formed from few-layer graphene under compression. Carbon [Internet]. 2020. Publisher's VersionAbstract
Despite several theoretically proposed two-dimensional (2D) diamond structures, experimental efforts to obtain such structures are in initial stage. Recent high-pressure experiments provided significant advancements in the field, however, expected properties of a 2D-like diamond such as sp3 content, transparency and hardness, have not been observed together in a compressed graphene system. Here, we compress few-layer graphene samples on SiO2/Si substrate in water and provide experimental evidence for the formation of a quenchable hard, transparent, sp3-containing 2D phase. Our Raman spectroscopy data indicates phase transition and a surprisingly similar critical pressure for two-, five-layer graphene and graphite in the 4-6 GPa range, as evidenced by changes in several Raman features, combined with a lack of evidence of significant pressure gradients or local non-hydrostatic stress components of the pressure medium up to ≈ 8 GPa. The new phase is transparent and hard, as evidenced from indentation marks on the SiO2 substrate, a material considerably harder than graphene systems. Furthermore, we report the lowest critical pressure (≈ 4 GPa) in graphite, which we attribute to the role of water in facilitating the phase transition. Theoretical calculations and experimental data indicate a novel, surface-to-bulk phase transition mechanism that gives hint of diamondene formation.
Farias G, Salla CAM, da Silva Heying R, Bortoluzzi AJ, Curcio S, Cazati T, dos Santos PL, Monkman AP, de Souza B, BECHTOLD IVANH. Reducing Lifetime in Cu(I) Complexes with Thermally Activated Delayed Fluorescence and Phosphorescence promoted by Chalcogenolate-Diimine Ligand. J. Mater. Chem. C [Internet]. 2020 :-. Publisher's VersionAbstract
Luminescent copper(I) complexes have drawn attention due to their promising performance as alternative optoelectronic materials to the well-known heavy transition metals complexes. Herein, we report the synthesis of six luminescent Cu(I) complexes with phosphines and 1,10-phenanthroline-derived ligands with thiadiazole and selenodiazole groups in order to evaluate the effect of heavy atom on their photophysical properties. Steady-state and time-resolved spectroscopy confirmed delayed fluorescence emission via a thermally activated delayed fluorescence mechanism in all cases. The experimental spectroscopic data was analyzed with detailed quantum-chemical calculations. Interestingly, these complexes did not show the expected “heavy atom effect”, that enhances the spin-orbit coupling matrix elements, but nevertheless the addition of the heavier chalcogens contributed to reduce the photoluminescence lifetime to roughly 800 ns, which is the lowest reported so far for such TADF materials.
dos Teixeira AR, Teixeira RR, Ribeiro IML, Pereira WL, Manhabosco TM, de Brito ACF, Oliveira LAM, de Oliveira K, Nogueira PC. Association of electroanalytical and spectrophotometric methods to evaluate the antioxidant activity of isobenzofuranone in primary cultures of hippocampal neurons. Toxicology in Vitro [Internet]. 2020 :104970. Publisher's VersionAbstract
The isobenzofuran-1(3H)-ones (phthalides) exhibit various biological activities, including antioxidant activity on reactive oxygen species (ROS). An excess of ROS that cannot be naturally contained by cellular enzymatic systems is called redox imbalance, which damage cell membranes, proteins, and DNA, thereby possibly triggering neuronal death in several neurodegenerative diseases. Considering our ongoing efforts to find useful compounds to control redox imbalance, herein we evaluated the antioxidant activity of two phtalides (compounds 3 and 4), using primary cultures of hippocampal neurons. Spectrophotometric assays showed that compound 3 significantly reduced (p ≤ 0.05) ROS levels and lipid peroxidation compared to the control treatment, while compound 4 was unable at any of the tested concentrations. Despite their structural similarity, these compounds behave differently in the intracellular environment, which was reliably corroborated by the determination of oxidation potentials via cyclic voltammetry. It was demonstrated that compound 3 presents a lower oxidation potential. The combination of the mentioned methods allowed us to find a strong correlation between the chemical structure of compounds and their biological effects. Taking together, the results indicate that compound 3 presents desirable characteristics to act as a candidate pharmacological agent for use in the prevention and treatment of neurodegenerative diseases.
Paez EBA, Curcio S, Neme N, Matos M, Correa RS, Pereira FJ, Hilário FF, Cazati T, Taylor JG. Synthesis, Photophysical and Electrochemical Properties of Novel and Highly Fluorescent Difluoroboron Flavanone β-Diketonate Complexes. New J. Chem. [Internet]. 2020 :-. Publisher's VersionAbstract
Difluoroboron β-diketonates complexes are highly luminescent with extensive properties such as their fluorescence both in solution and in solid state and their high molar extinction coefficients. Due to their rich optical properties, these compounds have been studied for their applications in organic electronics such as in self-assembly and applications in biosensors, bio-imaging and optoelectronic devices. The easy and fast synthesis of difluoroboron β-diketonate (BF2dbm) complexes makes their applications even more attractive. Although many different types of difluoroboron β-diketonates complexes have been studied, the cyclic flavanone analogues of these compounds have never been reported in the literature. Therefore, the present work aims to synthesize difluouroboron flavanone β-diketonate complexes, study their photophysical and electrochemical properties and assess their suitability for applications in optoelectronic devices. The synthesis was based on a Baker–Venkataraman reaction which initially provided substituted diketones, which were subsequently reacted with aldehydes to afford the proposed flavanones. The complexation was achieved by reacting flavanones and BF3. Et2O and in total 9 novel compounds were obtained. A representative difluoroboron flavanone complex was subjected to single crystal X-ray diffraction to unequivocally confirm the chemical structure. A stability study indicated only partial degradation of these compounds over a few days in a protic solvent at elevated temperatures. Photophysical studies revealed that the substituent groups and the solvent media significantly influence the electrochemical and photophysical properties of the final compounds, especially the molar absorption coefficient, fluorescence quantum yields, and the band gap. Moreover, the compounds exhibited a single excited-state lifetime in all studied solvent. Computational studies were employed to evaluate ground and excited states properties and carry out DFT and TDDFT level analysis. These studies clarify the role of each state in the experimental absorption spectra as well as the effect of the solvent.
Velten H. Matéria escura, energia escura e a busca por uma nova teoria para a gravitação. Cadernos de Astronomia [Internet]. 2020;1 (1) :40-51. Publisher's Version
Pinheiro CFS, Castro e Silva A, Velten H. Astrobiologia: como modelar o crescimento de organismos na Terra e em exoplanetas. Cadernos de Astronomia [Internet]. 2020;1 (1) :116-122. Publisher's Version
Nascimento LÃ\textordmasculinebia G, Lopes SA, Teodolino ABL, Novack KÃ!`tia M, Barboza APM, Neves BRA, Azevedo MLS, Sousa LRD, M. R. dos Santos V. Novel PEG 4000 derivatives and its use in controlled release of drug indomethacin. QuÃ\-mica Nova [Internet]. 2020;43 :685 - 691. Publisher's Version
Zimdahl W, Fabris JC, Velten H, Herrera R. On (non-)dynamical dark energy. Physics of the Dark Universe [Internet]. 2020;30 :100681. Publisher's VersionAbstract
The current Universe is composed by a mixture of relativistic species, baryonic matter, dark matter and dark energy which evolve in a non-trivial way at perturbative level. An advanced description of the cosmological dynamics should include non-standard features beyond the simplistic approach idealized by the standard cosmology in which cosmic components do not interact, are adiabatic and dissipationless. We promote a full perturbative analysis of linear scalar perturbations of a non-interacting cosmological model containing baryons, dark matter (both pressureless) and a scalar field allowing for the presence of relative entropic perturbations between the three fluids. Assuming an effective scalar-field sound speed equal to one and neglecting anisotropic stresses we establish a new set of equations for the scalar cosmological perturbations. As a consequence of this new approach, we show that tiny departures from a constant scalar field equation of state wS=−1 damage structure formation in a non-acceptable manner. Hence, by strongly constraining wS our results provide compelling evidence in favor of the standard cosmological model and rule out a large class of dynamical dark energy models.
Cipreste MF, Mussel] W [da N, da Silva] J [B, de Marques] M [BF, Batista] RJ [C, Gastelois PL, de Macedo] W [AA, de Sousa] EM [B. A new theranostic system for bone disorders: Functionalized folate-MDP hydroxyapatite nanoparticles with radiolabeled copper-64. Materials Chemistry and Physics [Internet]. 2020 :123265. Publisher's VersionAbstract
Hydroxyapatite nanoparticles have been investigated as biological agents for the treatment and diagnosis of bone diseases due to their properties, providing high affinity to bone tissues and also due to the possibility to chemically modify the surfaces of these nanoparticles to provide active targeting to bone tumors or other bone disorders. In this work, synthetic hydroxyapatite nanoparticles and their surface modifications with folic and medronic acid were studied. Copper-64 was produced by neutron irradiation in a TRIGA MARK I nuclear reactor, and the functionalized nanoparticles radiolabeled with this radioisotope. The multi-technique characterization includes FTIR, PXRD, TGA, DSC, CHN, Zeta potential, XPS, SEM, TEM, and Gamma spectroscopy. Furthermore, the evaluation of the chemical interaction stability was through leaching tested for efficiency. The results indicate that folic and medronic acids can be covalently bonded to HA surface, producing a new material not yet described in the literature, been stably attached to hydroxyapatite nanoparticle surfaces, able to provide active targeting for bone disorders. The complexation of copper-64 provides high radiochemistry purity, although the specific activity must be improved.
Pacheco TS, Ludwig ZMC, Sant’Anna DR, Perpétuo GJ, Franco CJ, Paiva EC, Ghosh S. Growth and vibrational spectroscopy of K2LiyNixCo1-xSO42.6H2O (y=0.1;0.2;0.3;0.4) crystals. Vibrational Spectroscopy [Internet]. 2020;109 :103093. Publisher's VersionAbstract
The mixed crystals of the Tutton’s salt doped with Li following the empirical formula K2LiyNixCo1-x (SO4)2.6H2O, were synthesized from the slow evaporation of the solvent at constant temperature. The presence of K, S, Ni, Co and O elements in the studied crystalline structure was confirmed by EDS spectroscopy using a scanning electron microscope and their quantification including Li was carried out with the help of ICP-OES technique. Raman spectroscopy in the range 100−3600 cm−1, confirmed the presence of tetrahedral (SO4), octahedral complexes Ni(H2O)6, Co(H2O)6, and H2O molecules in the crystal structure. Our UV–vis studies have shown that the mixed crystals have good optical transparency in the ultraviolet (200−350 nm) and infrared (750−1000 nm) region. The direct and indirect optical energy gap of the synthesized crystals were determined from the Tauc’s plot. XRD diffractograms of the sample crystals do not show any specific changes due to the presence of Li ion in the crystalline network.
Ribeiro SP, Castro e Silva A, Dáttilo W, Reis AB, Góes-Neto A, Alcantara LCJ, Giovanetti M, Coura-vital W, Fernandes GW, Azevedo VAC. Severe airport sanitarian control could slow down the spreading of COVID-19 pandemics in Brazil. PeerJ [Internet]. 2020;8 :e9446. Publisher's VersionAbstract
Background We investigated a likely scenario of COVID-19 spreading in Brazil through the complex airport network of the country, for the 90 days after the first national occurrence of the disease. After the confirmation of the first imported cases, the lack of a proper airport entrance control resulted in the infection spreading in a manner directly proportional to the amount of flights reaching each city, following the first occurrence of the virus coming from abroad. Methodology We developed a Susceptible-Infected-Recovered model divided in a metapopulation structure, where cities with airports were demes connected by the number of flights. Subsequently, we further explored the role of the Manaus airport for a rapid entrance of the pandemic into indigenous territories situated in remote places of the Amazon region. Results The expansion of the SARS-CoV-2 virus between cities was fast, directly proportional to the city closeness centrality within the Brazilian air transportation network. There was a clear pattern in the expansion of the pandemic, with a stiff exponential expansion of cases for all the cities. The more a city showed closeness centrality, the greater was its vulnerability to SARS-CoV-2. Conclusions We discussed the weak pandemic control performance of Brazil in comparison with other tropical, developing countries, namely India and Nigeria. Finally, we proposed measures for containing virus spreading taking into consideration the scenario of high poverty.
da Almeida WAS, Sousa LRD, dos Santos Antunes A, de Azevedo AS, do Nascimento Aéa M, Amparo TR, de Souza GHB, dos Santos ODH, Andrade �ngela Lão, Cazati T, et al. Green Propolis: In Vitro Photoprotective and Photostability Studies of Single and Incorporated Extracts in a Sunscreen Formulation. Revista Brasileira de Farmacognosia [Internet]. 2020. Publisher's VersionAbstract
Propolis is a natural, non-toxic resin produced by honey bees that has been used for hundreds of years for its biological activities, such as antimicrobial, anti-inflammatory, anesthetic, cytostatic, and cariostatic properties. Currently, it is used in food, pharmaceutical, and cosmetic industries. The aim of this work was to evaluate the antioxidant activity, sun protection factor, and photostability of different hydroalcoholic extracts of green propolis. All extracts prepared presented high absorption in the UVB region. The extract of 70% green propolis (high temperature) was incorporated into Gel Permulen TR-1. This new formulation presented a higher value of sun protection factor. Besides that, the formulation developed with Gel Permulen TR-1 and the hydroalcoholic extract of 70% green propolis (high temperature) showed good photostability and it was safe to be applied on the skin according the HET-CAM test. These results indicated the potential of hydroalcoholic extracts of 70% green propolis (high temperature) for use in sunscreen.
Faria AMA, Miranda MA, Gonçalves GE, Bianchi RF, Bianchi AGC, Cuba C, Neves BRA, Pinto ES. Partially ordered porous structures on layer-by-layer polyaniline/poly(vinyl sulfate sodium) ultrathin films: Easy fabrication of robust submicroscopic patterning. Journal of Applied Polymer Science [Internet]. 2020;137 (17) :48597. Publisher's VersionAbstract
ABSTRACT The use of polyaniline (PANI) as a conductive material has steadily increased in recent years due to its interesting physicochemical properties, low manufacturing cost, and easy processing. This conductive material, associated with the diffraction properties of organized nanostructures in thin films, has excellent application potential in microelectronics and photonic devices. Initially, this work presents improvement routes for the breath figure method (a nanopatterning technique) in polystyrene (PS) films through the control of film deposition parameters and the presence of water in the polymer solution. Such improvements are then extended to the production of PANI nanostructures, in the form of pores, from patterned porous PS films. Consequently, PANI films with a partially ordered pore structure (mean pore diameter of  100 nm) are produced in a facile and easily scalable method. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48597.
Antoniazzi I, Chagas T, Matos MJS, Marçal LAB, Soares EA, Mazzoni MSC, Miwa RH, Lopes JMJ, Malachias Â, Magalhães-Paniago R, et al. Oxygen intercalated graphene on SiC(0001): Multiphase SiOx layer formation and its influence on graphene electronic properties. Carbon [Internet]. 2020. Publisher's VersionAbstract
Low-dimensionality materials are highly susceptible to interfaces. Indeed, intercalation of different chemical species in between epitaxial graphene and silicon carbide (SiC), for instance, may decouple the graphene with respect to the substrate due to the conversion of the buffer layer into a graphene layer. O-intercalation is known to release the strain of such 2D material and to lead to the formation of high structural quality AB-stacked bilayer graphene. Nonetheless, this interface transformation concomitantly degrades graphene electronic transport properties. In this work we employed different techniques in order to better understand the structure of the graphene/SiC interface generated by O-intercalation and to elucidate the origin of the poor electronic properties of graphene. Experimental results revealed the formation of a SiO2 rich layer with a defective transition layer in between it and the SiC, which is characterized by the existence of silicon oxycarbide structures. Scanning tunneling spectroscopy measurements revealed an extensive presence of electronic states just around the Fermi level all over the sample surface, which may suppress the charge carriers mobility around this region. According to theoretical calculations, such states are mainly due to the formation of silicon oxicarbides within the interfacial layer.
Freitas] DN [de, Mendonça BHS, Köhler MH, Barbosa MC, Matos MJS, Batista RJC, Oliveira] AB [de. Water Diffusion in Carbon Nanotubes Under Directional Electric Fields: Coupling Between Mobility and Hydrogen Bonding. Chemical Physics [Internet]. 2020 :110849. Publisher's VersionAbstract
Molecular Dynamics simulations of water confined in carbon nanotubes subjected to external electric fields show that water mobility strongly depends on the confining geometry, the intensity and directionality of the electric field. While fields forming angles of 0° and 45° slow down the water dynamics by increasing organization, perpendicular fields can enhance water diffusion by decreasing hydrogen bond formation. For 1.2 diameter long nanotubes, the parallel field destroys the ice-like water structure increasing mobility. These results indicate that the structure and dynamics of confined water are extremely sensitive to external fields and can be used to facilitate filtration processes.