Glifosato: propriedades, toxicidade, usos e legislação

This paper supplies a compact revision on the herbicide glyphosate physic-chemistry characteristic mains, including toxicity and valid Brazilian legislation for its use.

Biossurfactantes: propriedades e aplicações

Chemically synthesized surfactants are widely used for many purposes in almost every sector of modern industry. Surface-active compounds of biological origin (biosurfactants) have been gaining attention in recent years because of some advantages such as biodegradability, low toxicity, diversity of applications and functionality under extreme conditions. Microbial biosurfactants are useful in bioremediation of water and soil, enhanced oil recovery, and in many formulations of petrochemical, chemical, pharmaceutical, food, cosmetic and textile industries. The importance of biosurfactants, their characteristics and industrial applications are discussed.

Síntese, caracterização e estudo das propriedades catalíticas e magnéticas de nanopartículas de Ni dispersas em matriz mesoporosa de SiO2

Nickel nanoparticles supported on amorphous silica ceramic matrix were synthesized by the polymeric precursor method. The nanostructure was characterized by NMR, BET, XRD, SEM, TEM, and flame atomic absorption spectrometry techniques. It was observed a dependence of the crystallite size on the thermal annealing, under a N2 atmosphere. The materials presented a high catalytic activity and selectivity upon the beta-pinene hydrogenation reaction. The magnetic hystereses were also correlated with the morphology of the processed material.

Proteínas tirosina fosfatases: propriedades e funções biológicas

Protein phosphorylation-dephosphorylation catalyzed by the opposing and dynamic action of protein kinases and phosphatases probably, is the most crucial chemical reaction taking place in living organisms. Protein phosphatases are classified according to their substrate specificity and sensitivity to inhibitory or activator agents, into two families of protein phosphatases: serine/threonine phosphatases and tyrosine phosphatases (PTPs). PTPs can be divided into 3 groups: tyrosine specific phosphatases, dual and low molecular weight phosphatases. The role of tyrosine phosphorylation in mitogenic signaling is well documented, and one would predict that vanadate, pervanadate and other oxidant agents (protein tyrosine phosphatase inhibitors) may act as a growth stimulator.

Propriedades espectroscópicas e parâmetros ópticos-eletrônicos dos complexos Ln(NO3)3.2DTPO.4H2O (Ln = Nd e Er)

Complexes with the composition Ln(NO3)3.2DTPO.4H2O (Ln = Nd and Er) were synthesized and characterized by infrared and visible absorption spectra (solid state and solution). The results of the absorption spectra in the solid state suggest that metal-ligand bonds are essentially electrostatic in all complexes. The absorption spectra of the nitrate salt solution presented smaller values of the oscillator strength when compared to the spectra of the complexes in the same solvent.

Aplicação da equação de Poisson-Boltzmann ao cálculo de propriedades dependentes do pH em proteínas

The ability of biomolecules to catalyze chemical reactions is due chiefly to their sensitivity to variations of the pH in the surrounding environment. The reason for this is that they are made up of chemical groups whose ionization states are modulated by pH changes that are of the order of 0.4 units. The determination of the protonation states of such chemical groups as a function of conformation of the biomolecule and the pH of the environment can be useful in the elucidation of important biological processes from enzymatic catalysis to protein folding and molecular recognition. In the past 15 years, the theory of Poisson-Boltzmann has been successfully used to estimate the pKa of ionizable sites in proteins yielding results, which may differ by 0.1 unit from the experimental values. In this study, we review the theory of Poisson-Boltzmann under the perspective of its application to the calculation of pKa in proteins.

Síntese, caracterização e propriedades espectroscópicas de criptatos de lantanídeo do tipo [LnÌ(bipy)2py(CO2Et) 2(3+)]

This work reports on the synthesis, characterization (infrared and hidrogen nmr spectra) and photophysical properties (luminescence spectra and emission quantum yield) of the lanthanide cryptates [LnÌ(bipy)2py(CO2Et) 2]3+ with Ln = Eu3+, Tb3+ or Gd3+, which can be applied as efficient Light-Conversion-Molecular-Devices. From emission spectra of [EuÌ(bipy)2py(CO2Et) 2]3+ it was possible to assign C3 symmetry to the metal ion. The spectroscopic studies show a higher emission quantum yield (q=25%) for [TbÌ(bipy)2py(CO2Et) 2]3+ in aqueous solution, whereas the europium cryptate presents q=14%. This is justified by a more efficient energy transfer between triplet and emission levels of terbium (T->5D4).

Estudo de efeito dos sais precursores sobre as propriedades eletrocatalíticas de eletrodos de Ti-SnO2/Sb preparados por decomposição térmica

The physical and electrochemical properties of Ti-SnO2/Sb electrodes obtained by the thermal decomposition of solutions of the precursor salts SnCl2×2H2O/SbCl3 and SnSO4/Sb2(SO4)3 were investigated. The reversibility of the cyclic voltammetric response of the Fe(CN)6(4-)/Fe(CN)6(3-) redox couple was assessed using the obtained electrodes. Their catalytic activity for the oxygen-evolving reaction and maximum capacity for electronic transfer were also evaluated by potential and current linear scans in 0.5 mol L-1 H2SO4. Additionally, scanning electron microscopy analyses allowed the visualization of the morphology of the oxide films obtained. The best results were presented by the electrodes obtained from the chloride salt precursors.

Conformações distorcida e planar do anel porfirínico em complexos e hemoproteínas: propriedades físico-químicas e implicações espectroscópicas

The different conformations of porphyrin rings are strongly related with the electronic configurations of the metallic center in the ferriheme coordination compounds and heme proteins. The usual electronic configuration, (d xy)²(d xz,d yz )³ presents a planar conformation of the porphyrin ring and the less common electronic configuration (d xz,d yz)4(d xy )¹ occurs in the case of a strongly ruffled ring. These states are responsible for distinct chemical and spectroscopic properties of the porphyrin systems. The importance of the ring conformations, their characteristics, implications and applications are discussed.

Propriedades eletrônicas e estruturais do PbTiO3: teoria do funcional de densidade aplicada a modelos periódicos

Calculations based on density functional theory at the B3LYP hybrid functional level applied to periodic models have been performed to characterize the structural and electronic properties of PbTiO3. Two different slab terminations (PbO and TiO2) have been considered to obtain and discuss the results of band structure, density of states, charge distribution on bulk and surface relaxation. It is observed that the relaxation processes are most prominent for the Ti and Pb surface atoms. The electron density maps confirm the partial covalent character of the Ti-O bonds. The calculated optical band gap and other results are in agreement with experimental data.

Estrutura e propriedades de elipticinas

The ellipticines constitute a broad class of molecules with antitumor activity. In the present work we analyzed the structure and properties of a series of ellipticine derivatives in the gas phase and in solution using quantum mechanical and Monte Carlo methods. The results showed a good correlation between the solvation energies in water obtained with the continuum model and the Monte Carlo simulation. Molecular descriptors were considered in the development of QSAR models using the DNA association constant (log Kapp) as biological data. The results showed that the DNA binding is dominated by electronic parameters, with small contributions from the molecular volume and area.

Efeito do cromo nas propriedades catalíticas da MCM-41

The effect of chromium on the catalytic properties of MCM-41 was evaluated in order to develop new catalysts for the trimethylbenzene transalkylation with benzene to produce ethylbenzene, a high-value aromatic in the industry. It was found that chromium decreases the specific surface area but increases the acidity, turning MCM-41 into an active and selective catalyst for ethylbenzene and toluene production. The coke produced on the catalyst is hydrogenated and mainly located outside the pores and thus can be easily removed. The catalyst is more active and selective than mordenite, a commercial catalyst, and thus more promising for commercial applications.

Resina de Protium heptaphyllum: isolamento, caracterização estrutural e avaliação das propriedades térmicas

Three mixtures of triterpenes (maniladiol and breine; alpha and beta-amyrin; lupenone, alpha and beta-amyrinone) were isolated from Protium heptaphyllum March resin. The structural identification was based on NMR and mass spectrometry data. Lupenone, and alpha and beta-amyrinone were not reported before as constituents of this resin. The resin was submitted to methylation and acetylation reactions. The pure and derivatized resins and the mixtures (maniladiol and breine; alpha and beta-amyrin) were analyzed by TG and DSC. The TG curves revealed that the derivatization decreases the thermal stability of the resin. The DSC curves showed peaks that can be assigned to evaporation and phase transitions processes.

Lipossomas: propriedades físico-químicas e farmacológicas, aplicações na quimioterapia à base de antimônio

The use of organoantimonial complexes in the therapeutic of leishmaniasis and schistosomiasis has been limited mainly by the need for daily parenteral administration, their adverse side-effects and the appearance of drug resistance. Liposome encapsulation has been so far the most effective means to improve the efficacy of pentavalent antimonials against visceral leishmaniasis. Pharmacologically- and pharmaceutically-acceptable liposomal compositions are still being investigated through manipulation of preparation method, lipid composition and vesicle size. Recently, the encapsulation of a trivalent antimonial within "stealth" liposomes was found to reduce its acute toxicity and effectively deliver this compound to the parasite in experimental schistosomiasis.

Pilarização de uma argila brasileira com poliidroxications de alumínio: preparação, caracterização e propriedades catalíticas

Montmorillonite clay from Brazil was pillared with aluminium polyhydroxications. The influence of aging of the pillaring solution and the concentration of the clay suspension on the properties of the prepared materials was studied. The materials were characterized by chemical analysis, XRD and pore analysis by N2 adsorption. The catalytic properties were evaluated in the cumene cracking reaction. Results showed that the pillarization process increases the basal spaces of natural clay from 9.7 to 18.5 Å and the surface area from 41 to 300 m²/g.