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Search Results: 1 - 10 of 360675 matches for " Cleydson B. R. Santos "
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Application of Hartree-Fock Method for Modeling of Bioactive Molecules Using SAR and QSPR  [PDF]
Cleydson B. R. Santos, Cleison C. Lobato, Francinaldo S. Braga, Sílvia S. S. Morais, Cesar F. Santos, Caio P. Fernandes, Davi S. B. Brasil, Lorane I. S. Hage-Melim, Williams J. C. Macêdo, José C. T. Carvalho
Computational Molecular Bioscience (CMB) , 2014, DOI: 10.4236/cmb.2014.41001
Abstract:
The central importance of quantum chemistry is to obtain solutions of the Schr?dinger equation for the accurate determination of the properties of atomic and molecular systems that occurred from the calculation of wave functions accurate for many diatomic and polyatomic molecules, using Self Consistent Field method (SCF). The application of quantum chemical methods in the study and planning of bioactive compounds has become a common practice nowadays. From the point of view of planning it is important to note, when it comes to the use of molecular modeling, a collective term that refers to methods and theoretical modeling and computational techniques to mimic the behavior of molecules, not intend to reach a bioactive molecule simply through the use of computer programs. The choice of method for energy minimization depends on factors related to the size of the molecule, parameters of availability, stored data and computational resources. Molecular models generated by the computer are the result of mathematical equations that estimate the positions and properties of the electrons and nuclei, the calculations exploit experimentally, the characteristics of a structure, providing a new perspective on the molecule. In this work we show that studies of Highest Occupied Molecular Orbital Energy (HOMO), Low Unoccupied Molecular Orbital Energy (LUMO) and Map of molecular electrostatic potential (MEP) using Hatree-Fock method with different basis sets (HF/3-21G*, HF/3-21G**, HF/6-31G, HF/6-31G*, HF/6-31G** and HF/6-311G), that are of great importance in modern chemistry, biochemistry, molecular biology, and other fields of knowledge of health sciences. In order to obtain a significant correlation, it is essential that the descriptors are used appropriately. Thus, the quantum chemical calculations are an attractive source of new molecular descriptors that can, in principle, express all the geometrical and electronic properties of molecules and their interactions with biological receptor.
Computational Analysis of Physicochemical, Pharmacokinetic and Toxicological Properties of Deoxyhypusine Synthase Inhibitors with Antimalarial Activity  [PDF]
Nayara S. R. Silva, Luana K. S. Gon?alves, Jonatas L. Duarte, Juliane S. Silva, César F. Santos, Francinaldo S. Braga, Raí C. Silva, Josivan S. Costa, Lorane I. S. Hage-Melim, Cleydson B. R. dos Santos
Computational Molecular Bioscience (CMB) , 2014, DOI: 10.4236/cmb.2014.44006
Abstract: Malaria is a parasitic disease which has as etiological agents protozoa of the genus Plasmodium prevalent in tropical countries. The appearance of Plasmodium strains resistant to artemisinin has become necessary the development of new drugs using computational tools to combat this epidemic. Diverse transporter proteins can act as antimalarials targets, thereby being the enzyme deoxyhypusine synthase a promising antimalarial target. The present study aimed to investigate 15 most active inhibitors of deoxyhypusine synthase target, deposited in databases Binding DB, in order to trace a pattern of physicochemical, pharmacokinetic and toxicological properties of the inhibitors for this enzyme and propose new inhibitors of deoxyhypusine synthase target. The physicochemical properties were obtained according to the Lipinski parameters to evaluate oral absorption. Based on the certain properties were proposed three new inhibitors (A, B and C). The ADME/Tox properties were calculated for new inhibitors compared with results of the selected compounds. The fifteen inhibitors for oral administration showed satisfactory results, because they have adapted to the Lipinski parameters. In relation to the penetration of the blood-brain barrier the inhibitors analyzed showed penetration values less than 1, and ranged from 0.0411815 to 0.481764, being that the compound 1 showed value of CBrain/CBlood = 0.135467. Compound B showed a higher strength in plasma protein binding in relation to the compound 1, having a variation be-tween them of ±1.489344. Therefore, the compound B would present a longer halflife compared with compound 1. The proposed compounds showed positive and satisfactory results, being able to reach less adverse effects related to the central nervous system depending of administered dose.
Evaluation of Quantum Chemical Methods and Basis Sets Applied in the Molecular Modeling of Artemisinin  [PDF]
Cleydson B. R. dos Santos, Cleison C. Lobato, Josinete B. Vieira, Davi S. B. Brasil, Alaan U. Brito, Williams J. C. Macêdo, José Carlos T. Carvalho, José C. Pinheiro
Computational Molecular Bioscience (CMB) , 2013, DOI: 10.4236/cmb.2013.33009
Abstract: In this paper, we evaluate semiempirical methods (AM1, PM3, and ZINDO), HF and DFT (B3LYP) in different basis sets to determine which method best describes the sign and magnitude of the geometrical parameters of artemisinin in the region of the endoperoxide ring compared to crystallographic data. We also classify these methods using statistical analysis. The results of PCA were based on three main components, explaining 98.0539% of the total variance, for the geometrical parameters C3O13, O1O2C3, O13C12C12a, and O2C3O13C12. The DFT method (B3LYP) corresponded well with the experimental data in the hierarchical cluster analysis (HCA). The experimental and theoretical angles were analyzed by simple linear regression, and statistical parameters (correlation coefficients, significance, and predictability) were evaluated to determine the accuracy of the calculations. The statistical analysis exhibited a good correlation and high predictive power for the DFT (B3LYP) method in the 6-31G** basis set.
A SAR and QSAR Study of New Artemisinin Compounds with Antimalarial Activity
Cleydson Breno R. Santos,Josinete B. Vieira,Cleison C. Lobato,Lorane I. S. Hage-Melim,Raimundo N. P. Souto,Clarissa S. Lima,Elizabeth V. M. Costa,Davi S. B. Brasil,Williams Jorge C. Macêdo,José Carlos T. Carvalho
Molecules , 2014, DOI: 10.3390/molecules19010367
Abstract: The Hartree-Fock method and the 6-31G** basis set were employed to calculate the molecular properties of artemisinin and 20 derivatives with antimalarial activity. Maps of molecular electrostatic potential (MEPs) and molecular docking were used to investigate the interaction between ligands and the receptor (heme). Principal component analysis and hierarchical cluster analysis were employed to select the most important descriptors related to activity. The correlation between biological activity and molecular properties was obtained using the partial least squares and principal component regression methods. The regression PLS and PCR models built in this study were also used to predict the antimalarial activity of 30 new artemisinin compounds with unknown activity. The models obtained showed not only statistical significance but also predictive ability. The significant molecular descriptors related to the compounds with antimalarial activity were the hydration energy (HE), the charge on the O11 oxygen atom (QO11), the torsion angle O1-O2-Fe-N2 (D2) and the maximum rate of R/Sanderson Electronegativity (RTe +). These variables led to a physical and structural explanation of the molecular properties that should be selected for when designing new ligands to be used as antimalarial agents.
The Molecular Chaperone Binding Protein BiP Prevents Leaf Dehydration-Induced Cellular Homeostasis Disruption
Humberto H. Carvalho, Otávio J. B. Brustolini, Maiana R. Pimenta, Giselle C. Mendes, Bianca C. Gouveia, Priscila A. Silva, José Cleydson F. Silva, Clenilso S. Mota, Juliana R. L. Soares-Ramos, Elizabeth P. B. Fontes
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0086661
Abstract: BiP overexpression improves leaf water relations during droughts and delays drought-induced leaf senescence. However, whether BiP controls cellular homeostasis under drought conditions or simply delays dehydration-induced leaf senescence as the primary cause for water stress tolerance remains to be determined. To address this issue, we examined the drought-induced transcriptomes of BiP-overexpressing lines and wild-type (WT) lines under similar leaf water potential (ψw) values. In the WT leaves, a ψw reduction of ?1.0 resulted in 1339 up-regulated and 2710 down-regulated genes; in the BiP-overexpressing line 35S::BiP-4, only 334 and 420 genes were induced and repressed, respectively, at a similar leaf ψw = ?1.0 MPa. This level of leaf dehydration was low enough to induce a repertory of typical drought-responsive genes in WT leaves but not in 35S::BiP-4 dehydrated leaves. The responders included hormone-related genes, functional and regulatory genes involved in drought protection and senescence-associated genes. The number of differentially expressed genes in the 35S::BiP-4 line approached the wild type number at a leaf ψw = ?1.6 MPa. However, N-rich protein (NRP)- mediated cell death signaling genes and unfolded protein response (UPR) genes were induced to a much lower extent in the 35S::BiP-4 line than in the WT even at ψw = ?1.6 MPa. The heatmaps for UPR, ERAD (ER-associated degradation protein system), drought-responsive and cell death-associated genes revealed that the leaf transcriptome of 35S::BiP-4 at ψw = ?1.0 MPa clustered together with the transcriptome of well-watered leaves and they diverged considerably from the drought-induced transcriptome of the WT (ψw = ?1.0, ?1.7 and ?2.0 MPa) and 35S::BiP-4 leaves at ψw = ?1.6 MPa. Taken together, our data revealed that BiP-overexpressing lines requires a much higher level of stress (ψw = ?1.6 MPa) to respond to drought than that of WT (ψw = ?1.0). Therefore, BiP overexpression maintains cellular homeostasis under water stress conditions and thus ameliorates endogenous osmotic stress.
A Mean Field Theory approach to a model with Dipole-Quadrupole interaction
R. P. B. Santos
Physics , 2002,
Abstract: We study a model initially proposed to describe a mixture of (CO) and (N2) adsorbed on exfoliated graphite. The approach used here is that of mean field theory. The Mean Field equations and the Helmholtz Free Energy are found. Phase diagrams are calculated too, and it is possible to find an analytical expression for the second order phase transition line.
The Self-Force of a Charged Particle in Classical Electrodynamics with a Cut-off
Josif Frenkel,R B Santos
Physics , 1998, DOI: 10.1142/S0217979299000199
Abstract: We discuss, in the context of classical electrodynamics with a Lorentz invariant cut-off at short distances, the self-force acting on a point charged particle. It follows that the electromagnetic mass of the point charge occurs in the equation of motion in a form consistent with special relativity. We find that the exact equation of motion does not exhibit runaway solutions or non-causal behavior, when the cut-off is larger than half of the classical radius of the electron.
A Novel Synthesis Route to Produce Boron Nitride Nanotubes for Bioapplications  [PDF]
T. H. Ferreira, P. R. O. Silva, R. G. Santos, E. M. B. Sousa
Journal of Biomaterials and Nanobiotechnology (JBNB) , 2011, DOI: 10.4236/jbnb.2011.24052
Abstract: Nanostructures of boron nitride have attracted a great deal of interest due to their potential applications that comprise a broad range of topics, including biomedical technology, since it presents good chemical stability and suggests good biological inertia. This paper reports a facile and effective synthesis based on CVD process with new conditions to produce boron nitride nanotubes in higher amount using boron powder, ammonium nitrate and hematite as catalysts in tubular furnace, without using extreme conditions. The characterization of the material was carried out by Fourier transformed infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). From the results, it was possible to verify the production of a hexagonal BN nanotube filled with Fe nanoparticles. It was possible to understand the reactions involved in synthesis process, and also confirm the formation of hexagonal boron nitride nanotubes with iron nanoparticles as catalysts. Depending on the final use, samples need to be purified to analyze their unique properties in some bioapplications. In the other hand, sometimes BNNTs containing Fe nanoparticles have potential for use in therapeutic drug, gene and radionuclide delivery, and radio frequency methods for the catabolism of tumors via hyperthermia. In this sense, some application-related studies on BNNTs such as biocompatibility tests have also been investigated in both pure and BN nanotube filled with Fe.
Study of Calcium and Sodium Behavior to Identify Milk Adulteration Using Flame Atomic Absorption Spectrometry  [PDF]
Poliana M. dos Santos, Lenon F. B. Costa, Edenir R. Pereira-Filho
Food and Nutrition Sciences (FNS) , 2012, DOI: 10.4236/fns.2012.39161
Abstract: A fast and direct method for determination of milk adulteration by monitoring of calcium and sodium concentrations variations was described. Milk samples were furnished by a dairy company located at S?o Carlos (S?o Paulo State, Brazil) and and spiked with tap-water, whey, hydrogen peroxide, synthetic urine, urea and synthetic milk in the ranged from 5% to 50% (v/v), expect for caustic soda. Caustic soda was added in the milk until establish the original pH. The milk samples were analyzed by using flame atomic absorption spectrometry (FAAS) and no acid digestion process was required. Results showed a significant decrease in the Na and Ca concentrations with addition of synthetic milk and tap-water, a nonlinear variation with addition of synthetic urine, whey and hydrogen peroxide and a largest increase in the Na concentration with addition of NaOH. Correlation between Na and Ca concentrations in pure and adulterated milk were evaluated by paired t-test at a 95% confidence level. Results showed that the method proposed is efficient to identify samples adulterated with tap-water, caustic soda, synthetics milk and urine.
Perifíton como alimento da Biomphalaria Tenagophila (Gastropoda, Planorbidae)
Santos, M. B. L.;Freitas, J. R.;
Revista do Instituto de Medicina Tropical de S?o Paulo , 1987, DOI: 10.1590/S0036-46651987000200002
Abstract: snails reared in cages colonized by periphyton grew from 5.0mm to 8.8mm shell diameter, each laid 0.5 batch of eggs per day and the overall survival during the period was 75%
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