Publicações 2021

Por Ardiley Torres Avelar Em 29/07/21 12:05 Atualizada em 29/07/21 12:05

Flavor-dependent U(3) Nambu-Jona-Lasinio coupling constant

May 24 2021 | 

A nonperturbative one-gluon exchange quark-antiquark interaction is considered to compute flavordependent U(3) Nambu-Jona-Lasinio-type (NJL-type) interactions of the form G(ij,Gamma)((psi) over bar lambda i Gamma(psi))((psi) over bar lambda i Gamma(psi))for i, j = 0.8 and Gamma = I; i gamma(5) from the one-loop polarization process with nondegenerate u-d-s quark effective masses. The resulting NJL-type coupling constants in all channels are resolved in the long-wavelength limit and the numerical results are presented for different choices of an effective gluon propagator. Leading deviations with respect to a flavor symmetric coupling constant are found to be of the order (M*(f2) - M*(f1))(n)/(M*(f2) + M*f1)(n) for n = 1, 2, where M*(fi) are the effective masses of quarks f(1), f(2) = u, d and s. The scalar channel coupling constants Gij; s can be considerably smaller than the pseudoscalar ones. The effect of the flavor-dependence of coupling constants for the masses of pions and kaons may be nearly of the same order of magnitude as the effect of the u, d, and s quark mass nondegeneracy. The effect of these coupling constants is also verified for some of the light scalar meson masses, usually described by quark-antiquark states, and for some observables of the pseudoscalar mesons.

Updating atomic charge parameters of aliphatic amino acids: a quest to improve the performance of molecular modeling via sequential molecular dynamics and DFT-GIAO-NMR calculations dagger

Apr 14 2021 | Mar 2021 (Early Access) | 

In this work, we observe the behavior of the dipole moment, atomic charges, solute-solvent interactions and NMR spectroscopy of aliphatic amino acids in a water solution via the computational simulations of classical molecular dynamics and DFT quantum calculations. Our results indicate that the convergence of the atomic charge of the solute, from an iterative process, together with the dipole moment of the amino acid, alters the lifetime of hydrogen bonds present in the first solvation shell, resulting in the modification of its structure and dynamics. Using GIAO-DFT-NMR calculations, we assessed the impact of these structural solute-solvent modifications on the magnetic shielding constants of the solute carbon atoms. In this sense, we evaluate the importance of an update in parameters that describe atomic charges present in the CHARMM36 force field.

Hopf-Like Bifurcations and Asymptotic Stability in a Class of 3D Piecewise Linear Systems with Applications

Aug 2021 | 

The main purpose of this paper is to analyze the Hopf-like bifurcations in 3D piecewise linear systems. Such bifurcations are characterized by the birth of a piecewise smooth limit cycle that bifurcates from a singular point located at the discontinuity manifold. In particular, this paper concerns systems of the form (x) over dot = Ax + b(+/-) which are ubiquitous in control theory. For this class of systems, we show the occurrence of two distinct types of Hopf-like bifurcations, each of which gives rise to a crossing limit cycle (CLC). Conditions on the system parameters for the coexistence of two CLCs and the occurrence of a saddle-node bifurcation of these CLCs are provided. Furthermore, the local asymptotic stability of the pseudo-equilibrium point is analyzed and applications in discontinuous control systems are presented.

Anderson localization induced by interaction in linearly coupled binary Bose-Einstein condensates

May 14 2021 | 

In this paper we investigate the existence of Anderson localization induced by one specific component of a binary Bose-Einstein condensate (BEC). We use a mean-field approach, in which each type of particle of the BEC is considered as a specific field, and we consider that only one kind of particle is subject to a quasiperiodic potential, which induces a localization in the partner field. We assume the system is under a Rabi coupling, i.e., a linear coupling mixing the two-field component, and we investigate the conditions associated with the parameter values of the system for observing the localization. Numerical simulations are performed, confirming the existence of Anderson localization in the partner field.

Update of CHARMM36's atomic charges for aromatic amino acids in water solution simulations and spectroscopy analysis via sequential molecular dynamics and DFT calculations

Jan 1 2021 | 

In this theoretical work we develop simulations of classical molecular dynamics sequentially combined with quantum calculations to obtain an update of the atomic charges of the aromatic amino acids: Phenylalanine, Tryptophan and Tyrosine in water solution. The charge point model was used to describe the solvent medium and obtain new atomic charges as the aromatic amino acids' dipole moment convergence into solution. Additionally, we developed quantum calculations for GIAO-NMR and absorption spectrum (TD-DFT) spectroscopy to verify the influence of electrical distribution adjustment on the spectroscopic properties of these amino adds in water. Our results show that, in fact, a new electronic distribution of the amino acids is obtained and updates the CHARMM36's atomic charges. In this way the solute-solvent interaction is modified and indicates deviations on the magnetic shielding spectroscopy signature up to -6.9 ppm for carbon atoms, -4.4 ppm for nitrogen atoms and -13.4 ppm for oxygen atoms. Electronic absorption spectrum demonstrates a change in the distribution of electronic transitions. (C) 2020 Elsevier B.V. All rights reserved.


Two-level quantum Otto heat engine operating with unit efficiency far from the quasi-static regime under a squeezed reservoir

May 5 2021 | 

Recent theoretical and experimental studies in quantum heat engines show that, in the quasi-static regime, it is possible to have higher efficiency than the limit imposed by Carnot, provided that engineered reservoirs are used. The quasi-static regime, however, is a strong limitation to the operation of heat engines, since an infinitely long time is required to complete a cycle. In this paper we propose a two-level model as the working substance to perform a quantum Otto heat engine surrounded by a cold thermal reservoir and a squeezed hot thermal reservoir. Taking advantage of this model we show a striking achievement, that is to attain unity efficiency even at non-null power.

Self-consistent statistical thermodynamics of an anharmonic one-dimensional crystal surface under pressure

Sep 15 2021 | 

In this work, we use the unsymmetrized self-consistent field theory and the Gibbs's method of excess functions to calculate surface thermodynamic properties of an anharmonic one-dimensional crystal surface under pressure. We find an overall decrease in the anharmonicity while increasing the pressure. Using some specific interatomic potential functions, we are able to corroborate the analytical results. (C) 2021 Elsevier B.V. All rights reserved.

Relativistic spin operator must be intrinsic

Mar 15 2021 | 

Although there are many proposals of relativistic spin observables, there is no agreement about the adequate definition of this quantity. This problem arises from the lack of consensus concerning the properties that such an operator should satisfy. Here we present how to overcome this problem by imposing an unquestionable condition about the nature of the relativistic spin observable: it must be intrinsic. The intrinsicality concept is analyzed in the relativistic classical limit and then it is extended to the quantum regime to approach the relativistic spin problem. This approach rules out three-vector proposals of relativistic spin observables and leads to a unique satisfactory definition that, besides being intrinsic, also possesses interesting physical features such as covariance and consistency of predictions in the non-relativistic limit. To support the results from an operational perspective, a consistent observer-independent model for the electromagnetic-spin interaction is also presented. (C) 2021 Elsevier B.V. All rights reserved.


Applicability of DFT functionals for evaluating the first hyperpolarizability of phenol blue in solution

Mar 7 2021 | 

The first electronic hyperpolarizability (beta) of phenol blue (PB) in several solvents in a wide range of dielectric constants is investigated using the density functional theory (DFT). The reliability of various exchange-correlation functionals is assessed by a comparison to reference MOller-Plesset second-order perturbation theory (MP2) calculations. The equilibrium geometry of PB in each solvent is obtained by using the average solvent electrostatic configuration/free energy gradient method, which performs optimizations on the free energy hyper-surface by employing iteratively the sequential quantum mechanics/molecular mechanics methodology. The dependence of beta on the bond length alternation (BLA) coordinate is rationalized by means of the two-level model. Within the employed exchange-correlation functionals, the LC-BLYP functional shows the best performance for describing the static and dynamic MP2 results of beta, which increases as the BLA diminishes, reaching a maximum in an intermediate value of BLA. The results also illustrate the role played by the difference between the ground- and excited-state dipole moments (Delta mu) in determining the hyperpolarizability behavior in solution. Particularly, in the aqueous solution case, Delta mu goes to around zero when BLA is near zero, leading to an abrupt decline in the beta value. The DFT results of this study, therefore, indicate a clear relationship between the first hyperpolarizability and the BLA coordinate for the PB in solution, in agreement with experiment.

Proper-time approach to localization

Jun 28 2021 | 

The causality issues concerning the localization of relativistic quantum systems, as evidenced by Hegerfeld's paradox, are addressed through a proper-time relativistic formalism of single-particle operators. Starting from the premise that physical variables associated with the proper-time gauge have a prominent role in the specification of position, since they do not depend on classical parameters connected to an external observer, we obtain a single-particle formalism in which localization is described by explicitly covariant four-vector operators associated with POVM measurements parametrized by the system's proper time. Among the consequences of this result, we emphasize that physically acceptable states are necessarily associated with the existence of a temporal uncertainty and their proper-time evolution is not subject to the causality violation predicted by Hegerfeldt.

Nanostructured lipid carriers for hair follicle-targeted delivery of clindamycin and rifampicin to hidradenitis suppurativa treatment

Jan 2021 | 

Hidradenitis suppurativa is a chronic and debilitating inflammatory condition related to a permanent obstruction of the pilosebaceous units. Until nowadays, therapeutic options are unsatisfactory. Here, we propose nano structured lipid carriers (NLC) entrapping an association of clindamycin phosphate (CDM) and rifampicin (RIF) as a topical alternative for the treatment of the disease. Chemical compatibility between the drugs was demonstrated using thermal analysis combined with ATR-FTIR and X-ray powder diffraction assays. Nano carriers' diameter was narrowly distributed (polydispersity index = 0.2) around 400 +/- 14 nm, they possess a negative surface charge (-48.9 +/- 0.7 mV) and high drug entrapment efficiencies (80.2 +/- 0.4 % and 93.4 +/- 0.7 % for CDM and RIF, respectively). The formulation proved to be safe for the topical application, as it was nonirritant on both HET-CAM and reconstructed human epidermis (RHE) assays. Spin-label EPR indicated an NLC affinity for the lipidic domains of stratum corneum, which could benefit the targeting of the sebaceous units. Indeed, when applied on the skin in vitro, even when mimicking the sebaceous condition, NLC accumulated into the hair follicles openings, not altering the amount of accumulated CDM and significantly increasing by 12-fold the uptake of RIF in these structures. In conclusion, developed NLC formulation incorporating the antibiotics CDM and RIF is a promising strategy for the topical treatment of hidradenitis suppurativa or other infections that may affect the pilosebaceous units.

Propagation of Solitons in Quasi-periodic Nonlinear Coupled Waveguides

Apr 2021 | Jan 2021 (Early Access) | 

This paper is a tribute to Professor Mahir Saleh Hussein. It is motivated by two works which we published in collaboration in Cardoso et al. (Phys. Lett. A 374, 2356 2010, 374, 4594 2010). Here, we study the propagation of solitons in nonlinear coupled waveguides described by coupled nonlinear Schrodinger equations. In a specific case, these coupled equations behave as an exactly integrable nonlinear system known as the Manakov model. We introduce quasi-periodic nonlinear couplings by merging the components that allow changing the nonlinearities of the system, and study how the quasi-periodic nonlinearities modify the behavior of the solutions.

A structure-based approach for the discovery of inhibitors against methylcitrate synthase of Paracoccidioides lutzii

May 2021 (Early Access) | 

Paracoccidioidomycosis (PCM) is a systemic mycosis, endemic in Latin America, caused by fungi of the genus Paracoccidioides. The treatment of PCM is complex, requiring a long treatment period, which often results in serious side effects. The aim of this study was to screen for inhibitors of a specific target of the fungus that is absent in humans. Methylcitrate synthase (MCS) is a unique enzyme of microorganisms and is responsible for the synthesis of methylcitrate at the beginning of the propionate degradation pathway. This pathway is essential for several microorganisms, since the accumulation of propionyl-CoA can impair virulence and prevent the development of the pathogen. We performed the modeling and molecular dynamics of the structure of Paracoccidioides lutzii MCS (PlMCS) and performed a virtual screening on 89,415 compounds against the active site of the enzyme. The compounds were selected according to the affinity and efficiency criteria of in vitro tests. Six compounds were able to inhibit the enzymatic activity of recombinant PlMCS but only the compound ZINC08964784 showed fungistatic and fungicidal activity against Paracoccidioides spp. cells. The analysis of the interaction profile of this compound with PlMCS showed its effectiveness in terms of specificity and stability when compared to the substrate (propionyl-CoA) of the enzyme. In addition, this compound did not show cytotoxicity in mammalian cells, with an excellent selectivity index. Our results suggest that the compound ZINC08964784 may become a promising alternative antifungal against Paracoccidioides spp. Communicated by Ramaswamy H. Sarma


Quantifying electron-correlation effects in small coinage-metal clusters via ab initio calculations

Apr 28 2021 | Mar 2021 (Early Access) | 

We investigate many-electron correlation effects in neutral and charged coinage-metal clusters Cu-n, Ag-n, and Au-n (n = 1-4) via ab initio calculations using fixed-node diffusion Monte Carlo (FN-DMC) simulations, density functional theory (DFT), and the Hartree-Fock (HF) method. From very accurate FN-DMC total energies of the clusters and the HF results in the infinity large complete-basis-set limit, we obtain correlation energies in these strongly correlated many-electron clusters involving d orbitals. The obtained bond lengths of the clusters, atomic binding and dissociation energies, ionization potentials, and electron affinities are in satisfactory agreement with the available experiments. In the analysis, the electron correlation effects on these observable physical quantities are quantified by relative correlation contributions determined by the difference between the calculated FN-DMC and HF results. We show that the correlation contribution is not only significant for the quantities related to electronic structures of the coinage-metal clusters, such as electron affinity, but it is also essential for the stability of the atomic structures of these clusters. For example, the electron correlation contribution is responsible for more than 90% of the atomic binding energies of the small neutral copper clusters. We also demonstrate the orbital-occupation dependence of the correlation energy and electron pairing of the valence electrons in these coinage-metal clusters from the electron correlation-energy gain and spin-multiplicity change in the electron addition processes, which are reflected in their ionization potentials and electron affinities.

Membrane interactions of the anuran antimicrobial peptide HSP1-NH2: Different aspects of the association to anionic and zwitterionic biomimetic systems

Jan 1 2021 | 

Studies have suggested that antimicrobial peptides act by different mechanisms, such as micellisation, self-assembly of nanostructures and pore formation on the membrane surface. This work presents an extensive investigation of the membrane interactions of the 14 amino-acid antimicrobial peptide hylaseptin P1-NH2 (HSP1-NH2), derived from the tree-frog Hyla punctata, which has stronger antifungal than antibacterial potential. Biophysical and structural analyses were performed and the correlated results were used to describe in detail the interactions of HSP1-NH2 with zwitterionic and anionic detergent micelles and phospholipid vesicles. HSP1-NH2 presents similar well-defined helical conformations in both zwitterionic and anionic micelles, although NMR spectroscopy revealed important structural differences in the peptide N-terminus. H-2 exchange experiments of HSP1-NH2 indicated the insertion of the most N-terminal residues (1-3) in the DPC-d(38) micelles. A higher enthalpic contribution was verified for the interaction of the peptide with anionic vesicles in comparison with zwitterionic vesicles. The pore formation ability of HSP1-NH2 (examined by dye release assays) and its effect on the size and surface charge as well as on the lipid acyl chain ordering (evaluated by Fourier-transform infrared spectroscopy) of anionic phospholipid vesicles showed membrane disruption even at low peptide-to-phospholipid ratios, and the effect increases proportionately to the peptide concentration. On the other hand, these biophysical investigations showed that a critical peptide-to-phospholipid ratio around 0.6 is essential for promoting disruption of zwitterionic membranes. In conclusion, this study demonstrates that the binding process of the antimicrobial HSP1-NH2 peptide depends on the membrane composition and peptide concentration.

Interaction between TPPS4 porphyrin and CdTe-3-MPA quantum dot: Proton and energy transfer

Sep 2021 | 

Interaction between meso-tetrakis(p-sulfonato-phenyl)porphyrin (TPPS4) and cadmium telluride QD functionalized by 3-Mercaptopropionic Acid (CdTe-3-MPA QD) in water solution was investigated using the optical absorption and fluorescence spectroscopies. TPPS4 and QD spectral and temporal characteristics were studied separately and at their interaction at pH 4.0, where TPPS4 possesses charge 2- and QD are neutral, and at pH 7.0, where TPPS4 charge is 4- and QD are negatively charged. The analysis of quenching of the TPPS4 fluorescence by QD and QD luminescence by TPPS4 shows that the interaction reduces the intensities and lifetimes of the porphyrin fluorescence and QD luminescence. The interaction of TPPS4 with QD at pH 4.0 occurs via two mechanisms: proton transfer from the porphyrin to QD and the energy transfer from QD to porphyrin, while at pH 7.0 just energy transfer takes place. The CdTe-3-MPA QD luminescence has two components, which differ by their spectral position and lifetimes. These components are associated with the electron-hole annihilation in the QD CdTe core and in 3-MPA functionalization layer. Higher value of the accessibility factor at pH 4.0 (f(1) = 0.95 +/- 0.06) than that at pH 7.0 (f(3) = 0.37 +/- 0.03) shows that electrostatic interaction is important at the TPPS4 - QD interaction.

Biomimetic electrochemical sensors: New horizons and challenges in biosensing applications

Aug 1 2021 | 

The urge to meet the ever-growing needs of sensing technology has spurred research to look for new alternatives to traditional analytical methods. In this scenario, the glucometer is the flagship of commercial electrochemical sensing platforms, combining selectivity, reliability and portability. However, other types of enzyme-based biosensors seldom achieve the market, in spite of the large and increasing number of publications. The reasons behind their commercial limitations concern enzyme denaturation, and the high costs associated with procedures for their extraction and purification. In this sense, biomimetic materials that seek to imitate the desired properties of natural enzymes and biological systems have come out as an appealing path for robust and sensitive electrochemical biosensors. We herein portray the historical background of these biomimicking materials, covering from their beginnings until the most impactful applications in the field of electrochemical sensing platforms. Throughout the discussion, we present and critically appraise the major benefits and the most significant drawbacks offered by the bioinspired systems categorized as Nanozymes, Synzymes, Molecularly Imprinted Polymers (MIPs), Nanochannels, and Metal Complexes. Innovative strategies of fabrication and challenging applications are further reviewed and evaluated. In the end, we ponder over the prospects of this emerging field, assessing the most critical issues that shall be faced in the coming decade.

Thorough Analysis of the Phase Diagram for the Bell-Lavis Model: An Entropic Simulational Study

Jun 2021 | Mar 2021 (Early Access) | 

In this work, we investigate the Bell-Lavis model using entropic simulations for several values of the energy parameters. The T x mu phase diagram and the ground state configurations are analyzed thoroughly. Besides, we examine the particle density and specific heat behavior for different values of the chemical potential mu as functions of temperature. We also obtain configurations that maximize the canonical probability for several values of chemical potential and temperature, enabling the identification of the low-density (LDL) and high-density liquid (HDL) phases, among others, in the critical regions. We found a second-order phase transition from the LDL-HDL0 to LDL-HDL coexistence in the range of 0 < mu < 1.05503. In the 1.05503 < mu < 1.48024 range, the transition between the LDL-HDL0 and LDL-HDL0-empty coexistence presents discontinuous and continuous transitions characteristics. Finally, for 1.48024 < mu < 1.5, the phase transition between LDL and empty phases is of first order.


Ground states for fractional linear coupled systems via profile decomposition *

Jul 2021 | 

In this work we study existence and nonexistence of weak and ground state (least energy) solutions for a class of nonlocal linearly coupled elliptic systems. We deal with nonautonomous nonlinearities that may not satisfy any kind of monotonicity, also the related potentials may not have any kind of smoothness. In order to obtain ground states, instead of applying the well known methods of Nehari-Pohozaev manifold, we introduce new arguments and techniques whose are based on a Pohozaev type identity, a concentration-compactness principle and a profile decomposition type result.

Atomistic molecular dynamics study on the influence of high temperatures on the structure of peptide nanomembranes candidates for organic supercapacitor electrode

Jul 15 2021 | 

Recently, a series of organic structures formed by peptide self-assembly have been reported, among which stand out the peptide nanomembranes with promising applications in the energy storage field. In these applications, the nanomembranes can be subjected to high temperatures. Although the effects of temperature are well known in lipid membranes, in peptide ones they lack further investigation. In this sense, we present a study based on fully atomistic molecular dynamics simulation, which demonstrates the behavior of peptide membranes formed by Alanine (A) and Arginine (R) electrically charged and uncharged, A(6)R(1+) and A(6)R, at temperatures of 300 K, 320 K, 340 K, 360 K, 380 K, 400 K, 420 K, 440 K, 460 K, 480 K, and 500 K. We report a detailed analysis based on the total average number of Hydrogen Bonds (HBs) between the residues and between the residues with the water molecules, as well as the average lifetime of each of these interactions. Our results demonstrate that a hydrogen-bond network is maintained in the range of temperature evaluated contributing to the stability of the peptide nanomembranes. The increase in temperature causes only a small variation in the total number of HBs, however, the HBs lifetime of these interactions is drastically affected by temperature, providing greater dynamics in the peptide-peptide interaction, favoring greater mobility of these molecules as the temperature rises, as confirmed by the Einstein's diffusion coefficient, also obtained in this study. The HBs results together with the Coulomb and vdW interactions, show that the membrane structures are quite stable in withstanding high temperatures, which may indicate a potential application in coatings, liquid separation, and especially in supercapacitors since the nanomembranes formed by A(6)R(1+) and A(6)R peptide present pores in all 2D-material favoring a slight infiltration of ionic liquid in the material surface, which directly impacts energy storage efficiency. (C) 2021 Elsevier B.V. All rights reserved.

Membrane dynamics in Leishmania amazonensis and antileishmanial activities of beta-carboline derivatives

Jan 1 2021 | 

Two beta-carboline compounds, 8i and 6d, demonstrated in vitro antileishmanial activity against Leishmania (L.) amazonensis promastigotes similar to that of miltefosine (MIL). Estimates of the membrane-water partition coefficient (K-M/W) and the compound concentrations in the membrane (c(m50)) and aqueous phase (c(w50)) for half maximal inhibitory concentration were made. Whereas these biophysical parameters for 6d were not significantly different from those reported for MIL, 8i showed lower affinity for the parasite membrane (lower KM/W) and a lower concentration of the compound in the membrane required to inhibit the growth of the parasite (lower c(m50)). A 2-hour treatment of Leishmania promastigotes with the compounds 8i and 6d caused membrane rigidity in a concentration-dependent manner, as demonstrated by the electron paramagnetic resonance (EPR) technique and spin label method. This increased rigidity of the membrane was interpreted to be associated with the occurrence of cross-linking of oxidized cytoplasmic proteins to the parasite membrane skeleton. Importantly, the two beta-carboline-oxazoline derivatives showed low hemolytic action, both in experiments with isolated red blood cells or with whole blood, denoting their great Leishmania/erythrocyte selectivity index. Using electron microscopy, changes in the membrane of both the amastigote and promastigote form of the parasite were confirmed, and it was demonstrated that compounds 8i and 6d decreased the number of amastigotes in infected murine macrophages. Furthermore, 8i and 6d were more toxic to the protozoa than to J774A.1 macrophages, with treated promastigotes exhibiting a decrease in cell volume, mitochondrial membrane potential depolarization, accumulation of lipid bodies, increased ROS production and changes in the cell cycle.

Thermoelectric and thermal properties of the weakly disordered non-Fermi liquid phase of Luttinger semimetals

Aug 16 2021 | 

We compute the thermoelectric and thermal transport coefficients in the weakly disordered non-Fermi liquid phase of the Luttinger semimetals at zero doping, where the decay rate associated with the (strong) Coulomb interactions is much larger than the electron-impurity scattering rate. To this end, we implement the Mori-Zwanzig memory matrix method, that does not rely on the existence of long-lived quasiparticles in the system. We find that the thermal conductivity at zero electric field scales as (kappa) over bar similar to T-n (with 0 less than or similar to n less than or similar to 1) at low temperatures, whereas the thermoelectric coefficient has the temperature dependence given by alpha similar to T-p (with 1/2 less than or similar to p less than or similar to 3/2). These unconventional properties turn out to be key signatures of this long sought-after non-Fermi liquid state in the Luttinger semimetals, which is expected to emerge in strongly correlated spin-orbit coupled materials like the pyrochlore iridates. Finally, our results indicate that these materials might be good candidates for achieving high figure-of-merit for thermoelectric applications. (C) 2021 Elsevier B.V. All rights reserved.

Density functional theory for the thermodynamic gas-phase investigation of butanol biofuel and its isomers mixed with gasoline and ethanol

Feb 11 2021 | 

Herein, we present the results of our study on the thermodynamic properties of the isomers of butanol (n-butanol, 2-butanol, i-butanol, and t-butanol) to evaluate their thermodynamic potential as a complementary biofuel and/or substitute for ethanol and gasoline. The Gaussian09W software was used to perform molecular geometry optimization calculations using density functional theory with the B3lyp hybrid function using the base set 6-311++g(d,p) and the compound methods G3, G4, and CBS-QB3. Calculations of the fundamental frequency of the molecules were performed to obtain the molecular vibration modes for the respective frequencies. These calculations provided thermodynamic parameters such as the entropy, enthalpy, and specific molar heat at constant pressure, all as a function of the temperature. The parameter values obtained by each method were compared to the experimental values available in the literature. The results showed good accuracy, especially those obtained at the B3lyp/6-311++g(d,p) level for n-butanol. The error between the theoretical and experimental values for the combustion enthalpy of n-butanol was less than 4% at 298.15 K; due to the good prediction of its thermodynamic properties, we used n-butanol as a model for the prediction of other thermodynamic properties. We started a molecular docking study of four ligands, namely, n-butanol, ethanol, propanol, heptane, isooctane, and methanol interacting with butanol isomers. The highest values of affinity energy found were for N-butanol. The possible formation of hydrogen bonds, associations by means of London forces, hydrogen, and alkyl interactions were analyzed. n-Butanol was added to ethanol-gasoline mixtures in the temperature range of 298.15 to 600 K and the results suggest that n-butanol has a higher calorific value than gasoline-ethanol mixtures in G30E, G40E, G50E, G60E, G70E, G80E, G90E, and E100 blends. As such, n-butanol releases greater amounts of heat during combustion and is thus a viable alternative to biofuels.

Poly(Alizarin Red S) on pyrolytic graphite electrodes as a new multi-electronic system for sensing oxandrolone in urine

Aug 1 2021 | 

This study presents a new polymeric and multielectronic system, the poly-Alizarin Red S (PARS), obtained from the electropolymerization of Alizarin Red S (ARS) dye on an edge-plane pyrolytic graphite electrode (EPPGE) surface. During EPPGE/PARS electrochemical characterization, we identified seven stable and reversible redox peaks in acidic medium (0.10 mol L-1, pH 1.62 KH2PO4), which indicated its mechanisms underlying electropolymerization and electrochemical behavior. To the best of our knowledge, this is the first study to use an EPPGE/PARS electrode to detect oxandrolone (OXA) in artificial urine, where PARS acts as a synthetic receptor for OXA. The interactions of OXA with EPPGE/PARS as well as the properties of PARS were investigated using density functional theory (DFT). Atomic force microscopy (AFM) was used to characterize EPPGE/PARS, and it was found that the PARS polymer formed a semi-globular phase on the EPPGE surface. The limit of detection for OXA found by the sensor was close to 0.50 nmol L-1, with a recovery rate of approximately 100% in artificial urine. In addition to the application proposed in this study, EPPGE/PARS is a low-cost product that could be applied in several devices and processes, such as supercapacitors and electrocatalysis.

The interaction of a thiosemicarbazone derived from R - (+) - limonene with lipid membranes

Jan 2021 | 

As a potential drug, 2-nitrobenzaldehyde-thiosemicarbazone (2-TSC), a thiosemicarbazone derived from the terpene R-(+)-limonene, was studied through calorimetric and spectroscopic techniques. Differential Scanning Calorimetry (DSC) data showed that 2-TSC causes structural changes in a 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DMPC) membrane, strongly decreasing the cooperativity of the bilayer gel-fluid thermal transition. Optical absorption spectroscopy showed that 2-TSC is more soluble in ethanol and lipids than in water medium, and that the drug displays different structures in the different environments. Though 2-TSC displays no fluorescence, time resolved fluorescence showed that the drug is an effective quencher of the fluorescent probe 6-dodecanoyl-2-dimethylaminonaphthalene (Laurdan). As it is well accepted that Laurdan is positioned into the bilayer close to the membrane surface, that is possibly the localization of 2-TSC in a bilayer. Electron spin resonance (ESR) of the probe 1-palmitoyl-2-stearoyl-(14-doxyl)-sn-glycero-3-phosphocholine (14-PCSL) revealed that 2-TSC is inserted into the hydrocarbon part of the bilayer, fluidizing the lipid bilayer gel phase and rigidifying or organizing the bilayer fluid phase. Similar effects are found for other lipophilic molecules, including cholesterol. These results are useful to improve the understanding of the processes that govern the interaction of thiosemicarbazones with cell membranes, related to the activity of the drugs and their cytotoxicity.

Margins of stability of persons with transtibial or transfemoral amputations walking on sloped surfaces

Jun 23 2021 | 

Gait is a complex motor skill. However, most falls in humans occur during gait, and people with lower limb amputation have an increased risk of falls. Thus, this study evaluated the stability of persons with unilateral amputation by quantifying the margin of stability (MoS) during gait, to contribute to understanding the strategies adopted by these people to reduce falls. The participants were divided into 3 groups: persons with transtibial amputations (n = 12, 32.27 +/- 10.10 years, 76.9 +/- 10.3 kg, 1.74 +/- 0.06 m ); persons with transfemoral amputations (n = 13, 32.21 +/- 8.34 years, 72.55 +/- 10.23 kg, 1.73 +/- 0.05 m); and controls (n = 15, 32.2 +/- 10.17 years, 75.4 +/- 9.25 kg, 1.75 +/- 0.05 m), who walked for 4 min on a level and sloped (8% down and up) treadmill. The pelvic and foot marker kinematic data were used to estimate the center of mass and base of support, and from these, the MoS was estimated. Although both groups of persons with amputations showed higher values for the ML MoS than did the control group (transtibial: 8.81 +/- 1.79, 8.97 +/- 1.74, 8.79 +/- 1.76, transfemoral: 10.15 +/- 2.03, 10.60 +/- 1.98, 10.11 +/- 1.75, control: 8.13 +/- 1.30, 7.18 +/- 1.85, 8.15 +/- 1.57, level, down, and up, respectively), only the transfemoral group presented a significant higher value compared to the control group. Our findings suggest that the documented limitations in persons with amputations, especially with transfemoral amputation, are exacerbated in situations that require more skills, such as walking on sloped surfaces, triggering protective mechanisms.

(c) 2021 Elsevier Ltd. All rights reserved.

Bounding generalized relative entropies: Nonasymptotic quantum speed limits

Mar 5 2021 | 

Information theory has become an increasingly important research field to better understand quantum mechanics. Noteworthy, it covers both foundational and applied perspectives, also offering a common technical language to study a variety of research areas. Remarkably, one of the key information-theoretic quantities is given by the relative entropy, which quantifies how difficult is to tell apart two probability distributions, or even two quantum states. Such a quantity rests at the core of fields like metrology, quantum thermodynamics, quantum communication, and quantum information. Given this broadness of applications, it is desirable to understand how this quantity changes under a quantum process. By considering a general unitary channel, we establish a bound on the generalized relative entropies (Renyi and Tsallis) between the output and the input of the channel. As an application of our bounds, we derive a family of quantum speed limits based on relative entropies. Possible connections between this family with thermodynamics, quantum coherence, asymmetry, and single-shot information theory are briefly discussed.

A new isostructural halogenated chalcone with optical properties

Jan 27 2021 | 

Chalcones are organic compounds that present a number of properties. This study presents a comprehensive structural description of a new derivative of a chlorine-substituted chalcone in comparison with a bromine chalcone. Also, supermolecule and sum-over-state approach were used to describe the optical properties of these structures regarding the substitution of the bromine by the chlorine atom. In addition, the electrical properties, dipole moment, linear polarizability, and second IDRI hyperpolarizability were calculated. The linear refractive index and the third-order nonlinear macroscopic susceptibility were evaluated as a function of the applied electric field frequency. Furthermore, the quantum mechanics calculations that were implemented at the M06-2X/6-311++G(d,p) level of the theory for these isostructural chalcones indicate that the change in halogen atoms does not cause meaningful changes in their conformation. Finally, we can postulate that side-to-side and the antiparallel interactions are the interaction forces that drive the crystal growth for new isostructural chalcones. The NLO properties showed title compounds that are good candidates for use as NLO materials.

An entropic simulational study of the spin-1 Baxter-Wu model in a crystal field

Aug 15 2021 | 

We investigate the critical behavior of the two-dimensional spin-1 Baxter-Wu model in a crystal field using entropic sampling simulations, based on the Wang-Landau method, with the joint density of states. We obtain the temperature-crystal field phase diagram, which includes a tetracritical line ending at a pentacritical point. A finite-size scaling analysis of the maximum of the specific heat, while changing the crystal field anisotropy, is used to obtain a precise location of the pentacritical point. Our results give the critical temperature and crystal field as T-pc = 0.98030(10) and D-pc = 1.68288(62). We also detect that at the first-order region of the phase diagram, the specific heat exhibits a double peak structure as in the Schottky-like anomaly, which is associated with an order-disorder transition. (C) 2021 Elsevier B.V. All rights reserved.

Second-order nonlinear optical properties of two chalcone derivatives: insights from sum-over-states

Mar 14 2021 | 

In this study, a combined experimental and theoretical study of the nonlinear optical properties (NLO) of two chalcone derivatives, (E)-3-(2-methoxyphenyl)-1-(2-(phenylsulfonylamine)phenyl)prop-2-en-1-one (MPSP) and (E)-3-(3-nitrophenyl)-1-(2-(phenylsulfonylamine)phenyl)prop-2-en-1-one (NPSP), in DMSO is reported. The single crystal structures of the compounds, which differ only by the type and position of one substituent, were grown using the slow evaporation technique, and the main structural differences are discussed. The two-photon absorption and first-order hyperpolarizability measurements were performed via the Z-scan technique and hyper-Rayleigh scattering experiment in DMSO. The theoretical calculations were performed using the Density Functional Theory (DFT) at the CAM-B3LYP/6-311++G(d,p) level, and the sum-over-states (SOS) approach in both static and dynamic cases. Besides the electron conjugation achieved by the aromatic rings, olefins, and carbonyl groups, both compounds have a nearly flat chalcone backbone, which is believed to contribute to the nonlinear optical properties. MPSP and NPSP have different positions, even though they have roughly the same conformation and form C-HMIDLINE HORIZONTAL ELLIPSISO interactions. For several studied frequencies, the HRS first hyperpolarizability values for MPSP are greater than those for NPSP, indicating that in most cases the NLO properties of MPSP are better. The comparison among the theoretical and experimental HRS first hyperpolarizability results showed a good agreement. In addition, the two-dimensional second order nonlinear optical spectra obtained from the sum-over-states model indicate good second-order NLO responses of the two chalcone derivatives under external fields. Our findings are important not only to show the potential nonlinear optical application of the two new compounds but also to gain an insight into how different chemical compositions might affect the crystal structures and physico-chemical properties.

Insights on a new sulfonamide chalcone with potential antineoplastic application

Jul 2021 | 

Chalcones (E)-1,3-diphenyl-2-propene-1-ones, a class of biosynthetic precursor molecules of flavonoids, have a wide variety of biological applications. Besides the natural products, many synthetic derivatives and analogs became an object of continued interest in academia and industry. In this work, a synthesis and an extensive structural study were performed on a sulfonamide chalcone 1-Benzenesulfonyl-3-(4-bromobenzylidene)-2-(2-chlorophenyl)-2,3-dihydro-1H-quinolin-4-one with potential antineoplastic application. In addition, in silico experiments have shown that the sulfonamide chalcone fits well in the ligand-binding site of EGFR with seven mu-alkyl binding energy interactions on the ligand-binding site. Finally, the kinetic stability and the pharmacophoric analysis for EGFR indicated the necessary spatial characteristics for potential activity of sulfonamide chalcone as an antagonist.

Transport Barriers in Symplectic Maps

Jun 2021 | Apr 2021 (Early Access) | 

Chaotic transport is a subject of paramount importance in a variety of problems in plasma physics, specially those related to anomalous transport and turbulence. On the other hand, a great deal of information on chaotic transport can be obtained from simple dynamical systems like two-dimensional area-preserving (symplectic) maps, where powerful mathematical results like KAM theory are available. In this work, we review recent works on transport barriers in area-preserving maps, focusing on systems which do not obey the so-called twist property. For such systems, usual KAM theory no longer holds everywhere and novel dynamical features show up as non-resistive reconnection, shearless curves, and shearless bifurcations. After presenting some general features using a standard nontwist mapping, we consider magnetic field line maps for magnetically confined plasmas in tokamaks.

Attritional evaluation of lipophilic and hydrophilic metallated phthalocyanines for oncological photodynamic therapy

Mar 2021 | 

Background and aim: Oncological photodynamic therapy (PDT) relies on photosensitizers (PSs) to photo-oxidatively destroy tumor cells. Currently approved PSs yield satisfactory results in superficial and easy-to -access tumors but are less suited for solid cancers in internal organs such as the biliary system and the pancreas. For these malignancies, second-generation PSs such as metallated phthalocyanines are more appro-priate. Presently it is not known which of the commonly employed metallated phtahlocyanines, namely aluminum phthalocyanine (AlPC) and zinc phthalocyanine (ZnPC) as well as their tetrasulfonated derivatives AlPCS4 and ZnPCS4, is most cytotoxic to tumor cells. This study therefore employed an attritional approach to ascertain the best metallated phthalocyanine for oncological PDT in a head-to-head comparative analysis and standardized experimental design.

Methods: ZnPC and AlPC were encapsulated in PEGylated liposomes. Analyses were performed in cultured A431 cells as a template for tumor cells with a dysfunctional P53 tumor suppressor gene and EGFR overexpression. First, dark toxicity was assessed as a function of PS concentration using the WST-1 and sulforhodamine B assay. Second, time-dependent uptake and intracellular distribution were determined by flow cytometry and confocal microscopy, respectively, using the intrinsic fluorescence of the PSs. Third, the LC50 values were established for each PS at 671 nm and a radiant exposure of 15 J/cm(2) following 1-h PS exposure. Finally, the mode of cell death as a function of post-PDT time and cell cycle arrest at 24 h after PDT were analyzed.

Results: In the absence of illumination, AlPC and ZnPC were not toxic to cells up to a 1.5-mu M PS concentration and exposure for up to 72 h. Dark toxicity was noted for AlPCS4 at 5 mu M and ZnPCS4 at 2.5 mu M. Uptake of all PSs was observed as early as 1 min after PS addition to cells and increased in amplitude during a 2-h incubation period. After 60 min, the entire non-nuclear space of the cell was photosensitized, with PS accumulation in multiple subcellular structures, especially in case of AlPC and AlPCS4. PDT of cells photosensitized with ZnPC, AlPC, and AlPCS4 yielded LC50 values of 0.13 mu M, 0.04 mu M, and 0.81 mu M, respectively, 24 h post-PDT (based on sulfo-rhodamine B assay). ZnPCS4 did not induce notable phototoxicity, which was echoed in the mode of cell death and cell cycle arrest data. At 4 h post-PDT, the mode of cell death comprised mainly apoptosis for ZnPC and AlPC, the extent of which was gradually exacerbated in AlPC-photosensitized cells during 8 h. ZnPC-treated cells seemed to recover at 8 h post-PDT compared to 4 h post-PDT, which had been observed before in another cell line. AlPCS4 induced considerable necrosis in addition to apoptosis, whereby most of the cell death had already manifested at 2 h after PDT. During the course of 8 h, necrotic cell death transitioned into mainly late apoptotic cell death. Cell death signaling coincided with a reduction in cells in the G(0)/G(1) phase (ZnPC, AlPC, AlPCS4) and cell cycle arrest in the S-phase (ZnPC, AlPC, AlPCS4) and G2 phase (ZnPC and AlPC). Cell cycle arrest was most profound in cells that had been photosensitized with AlPC and subjected to PDT.

Conclusions: Liposomal AlPC is the most potent PS for oncological PDT, whereas ZnPCS4 was photodynamically inert in A431 cells. AlPC did not induce dark toxicity at PS concentrations of up to 1.5 mu M, i.e., > 37 times the LC50 value, which is favorable in terms of clinical phototoxicity issues. AlPC photosensitized multiple intracel-lular loci, which was associated with extensive, irreversible cell death signaling that is expected to benefit treatment efficacy and possibly immunological long-term tumor control, granted that sufficient AlPC will reach the tumor in vivo. Given the differential pharmacokinetics, intracellular distribution, and cell death dynamics, liposomal AlPC may be combined with AlPCS4 in a PS cocktail to further improve PDT efficacy.


Search for slow magnetic monopoles with the NOvA detector on the surface

Jan 11 2021 | 

We report a search for a magnetic monopole component of the cosmic-ray flux in a 95-day exposure of the NOvA experiment's Far Detector, a 14 kt segmented liquid scintillator detector designed primarily to observe GeV-scale electron neutrinos. No events consistent with monopoles were observed, setting an upper limit on the flux of 2 x 10(-14) cm(-2) s(-1) sr(-1) at 90% C.L. for monopole speed 6 x 10(-4) < beta < 5 x 10(-3) and mass greater than 5 x 10(8) GeV. Because of NOvA's small overburden of 3 meters-water equivalent, this constraint covers a previously unexplored low-mass region.

Supernova neutrino burst detection with the Deep Underground Neutrino Experiment

May 2021 | 

The Deep Underground Neutrino Experiment (DUNE), a 40-kton underground liquid argon time projection chamber experiment, will be sensitive to the electron-neutrino flavor component of the burst of neutrinos expected from the next Galactic core-collapse supernova. Such an observation will bring unique insight into the astrophysics of core collapse as well as into the properties of neutrinos. The general capabilities of DUNE for neutrino detection in the relevant few- to few-tens-of-MeV neutrino energy range will be described. As an example, DUNE's ability to constrain the nu(e) spectral parameters of the neutrino burst will be considered.

Prospects for beyond the Standard Model physics searches at the Deep Underground Neutrino Experiment DUNE Collaboration

Apr 2021 | 

The Deep Underground Neutrino Experiment (DUNE) will be a powerful tool for a variety of physics topics. The high-intensity proton beams provide a large neutrino flux, sampled by a near detector system consisting of a combination of capable precision detectors, and by the massive far detector system located deep underground. This configuration sets up DUNE as a machine for discovery, as it enables opportunities not only to perform precision neutrino measurements that may uncover deviations from the present three-flavor mixing paradigm, but also to discover new particles and unveil new interactions and symmetries beyond those predicted in the Standard Model (SM). Of the many potential beyond the Standard Model (BSM) topics DUNE will probe, this paper presents a selection of studies quantifying DUNE's sensitivities to sterile neutrino mixing, heavy neutral leptons, non-standard interactions, CPT symmetry violation, Lorentz invariance violation, neutrino trident production, dark matter from both beam induced and cosmogenic sources, baryon number violation, and other new physics topics that complement those at high-energy colliders and significantly extend the present reach.