Helio Salim de Amorim

Pyrite Suspended in Artificial Sea Water Catalyzes Hydrolysis of Adsorbed ATP: Enhancing Effect of Acetate

Minerals have been implicated in different catalytic processes during chemical evolution. It has been proposed that exergonic synthesis of pyrite (FeS2) could have served to promote the endergonic synthesis of biomonomers in early stages of life formation on Earth. The present study was aimed to investigate whether pyrite can adsorb nucleotides and oxo acids in the potentially mild prebiotic conditions found away from the hot hydrothermal vents. It is shown that pyrite strongly adsorbs adenosine 5′-triphosphate in an artificial medium that simulates primordial aqueous environments, and that adsorption is enhanced in the presence of acetate and in an oxygen-free atmosphere. Moreover, the mineral catalyzes the sequential hydrolysis of the γ and β phosphoanhydride bonds of the nucleotide.

A placa Arduino: uma opção de baixo custo para experiências de física assistidas pelo PC

We present the Arduino board as a very low cost option for data acquisition with a PC. Two simple applications that demonstrate the potential of this board are briefly discussed.

Adsorption of 5′-AMP and catalytic synthesis of 5′-ADP onto phosphate surfaces: Correlation to solid matrix structures

A non-enzymatic formation of 5′-ADP starting from phosphorylation of 5′-AMP in the presence of either calcium phosphate or calcium pyrophosphate precipitates is reported. This reaction is taken as a model for the study of heterogeneous catalysis of transphosphorylation in prebiotic conditions. Experiments were performed in completely aqueous media and in media containing dimethyl sulfoxide (Me2S0), to simulate periods of dehydration in primitive aquatic environments. It has been observed that the nucleotide is adsorbed onto both calcium phosphate and calcium pyrophosphate in accordance with Langmuir isotherms. Adsorptive capacity and affinity of the precipitates for nucleotide are changed by the presence of Me2SO, suggesting that the interaction between biomonomers and surfaces can be modulated by the degree of hydration of the anionic components of these compounds. In completely aqueous environments, formation of 5′-ADP from 5′-AMP adsorbed on precipitates of calcium phosphate and calcium pyrophosphate is very small. However, in the presence of 60% Me2SO this synthesis increases by factors of 3 and 6 for surfaces of calcium phosphate and calcium pyrophosphate, respectively, and follows first-order kinetics. Determinations of free energy changes show that phosphorylation of 5′-AMP adsorbed to these precipitates is thermodynamically favorable. Depending on the precipitation time of the samples and the composition of the medium, structural analysis of these precipitates by electron and X-ray diffraction shows changes in their cristallinity grade. It is proposed that these changes are responsible for the modulation of the quantity of adsorbed nucleotides to the surface of solid matrices as well as the catalytic activity of the precipitates.

Influence of different surface treatments on the fracture toughness of a commercial ZTA dental ceramic

The objective of this study was to investigate how mechanical surface treatments performed for removal of excess of molten glass, influence the fracture toughness of a dental zirconia toughened alumina (In-Ceram® Zirconia). Infiltrated ZTA disks were submitted to three different surface treatments (grinding, sandblasting and grinding + sandblasting + annealing). Fracture toughness was accessed through indentation strength test (IS). X ray diffraction was used to investigate the metastability of tetragonal zirconia particles under all treatments proposed. Kruskall-Wallis non-parametrical test and Weibull statistics were used to analyze the results. Grinding (group 1) introduced defects which decreased the fracture toughness and reliability, presenting the lowest KIC. On the other hand, grinding followed by sandblasting and annealing (group 3) presented the highest KIC. Sandblasting (group 2) presented the highest reliability but lower KIC compared to group 3.

Observando as marés atmosféricas: uma aplicação da placa Arduino com sensores de pressão barométrica e temperatura

We present a simple experimental apparatus for studying the atmospheric tide based on the use of Arduino Uno board. With this apparatus, the physics teacher in high school can present to your students barometric oscillations, an effect mainly of thermal origin, due to the warming of the atmosphere produced by solar radiation. We also present a comparison between atmospheric tide and the gravitational effect of ocean tide, with emphasis on the differences between the two phenomena.

Estatística de contagem com a plataforma Arduino

We describe simple didactic experiments on radiation detection and statistics counts using the Arduino platform for application in secondary and higher education. The experiments illustrate the binominal nature of the radioactive decay process. The setup enables the students to measure the distributions of Poisson and Gauss.

Investigação do fenômeno ilha de calor urbana através da utilização da placa Arduíno e de um sítio oficial de meteorologia

Studies of phenomena related to climate are often great opportunities to contextualize the teaching of physics, especially the Thermal Physics. Two activities are proposed: i) Construction of small weather stations, based on the Arduino board, produced with PVC (polyvinyl chloride), which can be easily reproduced at a low cost and ii) Obtainment of meteorological data via the Alerta Rio website. The activities proposed are designed to enable, through knowledge of physics, that students understand the phenomenon of urban heat island and are aware of its serious implications for the welfare of urban populations and the environment.

Adsorption and Catalysis of Nucleotide Hydrolysis by Pyrite in Media Simulating Primeval Aqueous Environments

Metal sulfides have been proposed as physical support for primitive bidimensional metabolism and chiral discriminators. There are controversial data about the possibly coupling between the exergonic pyrite syntheses and the endergonic amino acids syntheses in pyrite pulled metabolic-like processes. However, a role in adsorption and catalysis involving biomonomers — such as nucleotides — cannot be ruled out in an especial aqueous scenario. In an aqueous environment with a vast reservoir of reducing power in the form of, especially, iron (II) and sulfide within and beneath the crust. Our hypothesis is that ancient minerals such as pyrite could have played a role in concentrating mononucleotides and in determining their catalytic routes in later periods, when polynucleotides appeared and evolved (Tessis et al., 1999). Pyrite — as well as other sulfides — could have participated in nucleotide adsorption and in primitive phosphoryl transfer reactions in the less drastic conditions that prevail away from the hot hydrothermal vents, the big sources of starting molecules. In this presentation, we shall briefly comment about our results on the following themes: 1) Adsorption of mononucleotides (AMP and ADP) onto untreated and acetate-treated samples of pyrite in which soluble Fe3+ ions were removed; 2) The influence — on nucleotide adsorption — of the previous adsorption onto the crystal of an oxo acid that could have appeared near the mineral and modified its surface properties (acetate can be formed onto the surface of mixed iron nickel sulfides at high temperature and pressure [Huber and Wachtershauser, 1997]); 3) The role of the interface. In some models, the two-dimensional system represented by a mineral surface would be in a seawater environment having a passive role. The actual conditions prevailing when sulfur materials are in contact with salt solutions are quite complex. The very reactive iron-sulfide immersed in a solution resembling a primitive ocean generates a continuously changing interface with ionic gradients and formation of different oxide layers; 4) Hydrolysis of ATP adsorbed onto pyrite.

Effect of ionising radiation on potassium pentacyanonitrosylruthenate(II): an Electron Spin Resonance study

O sal pentacianonitrosilrutenato(II) de potassio, em forma amorfa, foi sintetizado e caracterizado por espectroscopias UV, IR, difracao de raios X e analise termogravimetrica. Amostras irradiadas por raios X revelam, por espectroscopia de Ressonância Paramagnetica Eletronica, a presenca de complexos paramagneticos de rutenio (I) e de radicais NO2. Os parâmetros do hamiltoniano de spin medidos para o complexo [Ru(CN)5NO]3- ( g^= 2.0064, A^(14N) = 60.7 MHz, g||= 1.999, A|| (14N) = 77.3 MHz ) indicam uma captura eletronica em um orbital molecular p* do grupo nitrosil com a participacao de orbitais dxz and dyz do rutenio, como recentemente previsto por calculos teoricos. Ions de prata, presentes como impurezas oriundas da rota sintetica, sao reduzidos a Ag(0) durante a irradiacao e interagem com quatro nitrogenios equivalentes em um sitio distorcido, originando um espectro de RPE anisotropico.