Daniel Menezes Silvestre

Cell Penetrating Peptide (CPP)-Conjugated Desferrioxamine for Enhanced Neuroprotection: Synthesis and in Vitro Evaluation

Iron overload causes progressive and sometimes irreversible damage due to accelerated production of reactive oxygen species. Desferrioxamine (DFO), a siderophore, has been used clinically to remove excess iron. However, the applications of DFO are limited because of its inability to access intracellular labile iron. Cell penetrating peptides (CPPs) have become an efficient delivery vector for the enhanced internalization of drugs into the cytosol. We describe, herein, an efficient method for covalently conjugating DFO to the CPPs TAT(47-57) and Penetratin. Both conjugates suppressed the redox activity of labile plasma iron in buffered solutions and in iron-overloaded sera. Enhanced access to intracellular labile iron compared to the parent siderophore was achieved in HeLa and RBE4 (a model of blood-brain-barrier) cell lines. Iron complexes of both conjugates also had better permeability in both cell models. DFO antioxidant and iron binding properties were preserved and its bioavailability was increased upon CPP conjugation, which opens new therapeutic possibilities for neurodegenerative processes associated with brain iron overload.

Direct Determination of Potentially Toxic Elements in Rice by SS-GF AAS: Development of Methods and Applications

The development of methods for direct determinations of Al, Cd, and Pb in rice by SS-GF AAS is presented. Heating program optimization associated with the use of an adequate chemical modifier containing Pd + Mg allowed direct analysis against aqueous calibrations. The obtained LOD values were 114.0, 3.0, and 16.0 μg kg⁻¹ for Al, Cd, and Pb, respectively. Important parameters associated with a solid sampling analysis were investigated, such as minimum and maximum sample mass size and analyte segregation. Seventeen rice samples available in São Paulo City were analyzed, and all of them presented analyte mass fractions less than the maximum allowed by legislation. The influences of rice washing and the cooking procedure were also investigated. The washing procedure diminished the Al and Pb total mass fractions, indicating an exogenous grain contamination. The cooking procedure diminished the Cd total mass fraction. Rice cooking using an aluminum container did not cause a significant increase in the Al mass fraction in the rice, indicating no translocation of this element from container to food. In general, coarse rice presented higher levels of Al when compared to polished or parabolized rice.

Desferrioxamine-caffeine (DFCAF) as a cell permeant moderator of the oxidative stress caused by iron overload

Desferrioxamine (DFO) is a potent iron chelator used in the treatment of iron overload (IO) disorders. However, due to its low cell permeability and fast clearance, DFO administration is usually prolonged and of limited use for the treatment of IO in tissues such as the brain. Caffeine is a safe, rapidly absorbable molecule that can be linked to other compounds to improve their cell permeability. In this work, we successfully prepared and described DFO-caffeine, a conjugate with iron scavenging ability, antioxidant properties and enhanced permeation in the HeLa cell model.

Template coexistence in prebiotic vesicle models

Abstract.The coexistence of distinct templates is a common feature of the diverse proposals advanced to resolve the information crisis of prebiotic evolution. However, achieving robust template coexistence turned out to be such a difficult demand that only a class of models, the so-called package models, seems to have met it so far. Here we apply Wrights Island formulation of group selection to study the conditions for the coexistence of two distinct template types confined in packages (vesicles) of finite capacity. In particular, we show how selection acting at the level of the vesicles can neutralize the pressures towards the fixation of any one of the template types (random drift) and of the type with higher replication rate (deterministic competition). We give emphasis to the role of the distinct generation times of templates and vesicles as yet another obstacle to coexistence.

Deferasirox-TAT(47–57) peptide conjugate as a water soluble, bifunctional iron chelator with potential use in neuromedicine

Deferasirox (DFX), an orally active and clinically approved iron chelator, is being used extensively for the treatment of iron overload. However, its water insolubility makes it cumbersome for practical use. In addition to this, the low efficacy of DFX to remove brain iron prompted us to synthesize and evaluate a DFX-TAT(47–57) peptide conjugate for its iron chelation properties and permeability across RBE4 cell line, an in vitro model of the blood–brain barrier. The water-soluble conjugate was able to remove labile iron from buffered solution as well as from iron overloaded sera, and the permeability of DFX-TAT(47–57) conjugate into RBE4 cells was not affected compared to parent deferasirox. The iron bound conjugate was also able to translocate through the cell membrane.

Feasibility of using laser induced breakdown spectroscopy for quantitative measurement of calcium, magnesium, potassium and sodium in meat

The aim of this work is to demonstrate the potential of a commercial laser induced breakdown spectroscopy (LIBS) system for quantitative determination of calcium, magnesium, potassium and sodium in bovine and chicken meat. Bovine and chicken meat are important sources of nutrients in the human diet, and Brazil is one of the major producers and exporters in the world. Measurements were performed using a commercial LIBS system designed with a Q-switched laser (Nd:YAG, 10 Hz, λ = 266 nm) and a 6 channel-CCD spectrometer. Calibration standards were produced from a selected beef and chicken sample either diluted with high-purity cellulose or spiked with increasing amounts of standard solutions of analytes. After acid decomposition, inductively coupled plasma optical emission spectroscopy (ICP OES) was used to obtain the mass fraction of each analyte in calibration standards. The accuracy of the method was checked by analysis of certified reference materials and comparison of LIBS results with ICP OES data. By applying a t-test at the 95% confidence level, LIBS results and ICP OES data presented no significant differences. The metrological figures of merit indicate the potential of a commercial LIBS system for the intended purposes and can be recommended for the analysis of beef and chicken meat aiming at the determination of Ca, Mg, K and Na.

Experimento utilizando grãos para explorar a calibração em análises químicas

The conventional curriculum of Analytical Chemistry undergraduate courses emphasizes the introduction of techniques, methods and procedures used for instrumental analysis. All these concepts must be integrated into a sound conceptual framework to allow students to make appropriate decisions. Method calibration is one of the most critical parameters that has to be grasped since most analytical techniques depend on it for quantitative analysis. The conceptual understanding of calibration is not trivial for undergraduate students. External calibration is widely discussed during instrumental analysis courses. However, the understanding of the limitations of external calibration to correct some systematic errors is not directly derived from laboratory examples. The conceptual understanding of other calibration methods (standard addition, matrix matching, and internal standard) is imperative. The aim of this work is to present a simple experiment using grains (beans, corn and chickpeas) to explore different types of calibration methods.

Determination of Metal Loading in Heterogeneous Catalyst by Slurry Sampling Flame Atomic Absorption Spectrometry

Quantification of metal loading in supported catalysts is imperative; however, the analytical methods are usually time-consuming, expensive, and require sophisticated equipment and sample extraction with hazardous and corrosive strong acids. Herein, we report a new method for quantification of metal in supported catalysts using slurry sampling flame atomic absorption spectrometry. The slurry sampling method was used for determination of gold and the results were similar to those obtained with the traditional extraction method using aqua regia; however, it overcomes the main drawbacks associated with sample digestion by avoiding the use of concentrated toxic reagents, minimizing sample manipulation, and consequently, reducing the risks of contamination and the sample preparation time. Ultrasound radiation optimization associated with the solvent, mass of sample, concentration, and matrix effect in the slurry analysis allowed direct analysis by using the calibration in aqueous medium. The slurry sampling procedure could be applied to other catalysts with different supports and in bimetallic systems.