Preparação e caracterização do complexo cobaloxima e sua utilização na construção de um eletrodo modificado: um experimento eletroquímico no curso de graduação

The present experiment describes the preparation, characterization of n-butyl(pyridil)cobaloxime complex and its electrochemical property. The infrared and uv-visible absorption spectra were used to characterize the complex obtained. The infrared spectrum of the compound showed characteristics bands that indicated the formation of the Co-C chemical bond formation. The electronic absorption spectrum in acetonitrile showed transition bands attributed to p-p*, metal-to-ligand charge transfer, d-d transitions and charge transfer Co-C. The electrochemical property was investigated by the pulse differential voltammetry technique. Two oxidation processes: Co(I)/Co(II) at -423 mV and Co(II)/Co(III) at 752 mV were observed.

Adaptação no método do peso da gota para determinação da tensão superficial: um método simplificado para a quantificação da CMC de surfactantes no ensino da química

The discussion based on surfactant cleaning action is commonly used in chemistry classrooms for the comprehension of theoretical concepts related to surface tension and micelle formation. The experimental quantification of surface tension of aqueous solutions of surfactants provides the practical instruments for this discussion. The present paper describes a simplification on the common apparatus employed for the drop-weight method, making the determination of surface tension accessible to any chemistry lab. The surface tension of various liquids and the critical micelle concentration, CMC, of three commercial surfactants were measured with this modified method, and proved to be consistent with literature values.

Otimização da preparação de eletrodo de pasta de carbono contendo riboflavina imobilizada em suporte inorgânico

The aim of this work was to optimize the preparation of electrodes with riboflavin (RF) immobilized on a silica surface modified with niobium oxide and carbon paste. Electrode preparation was optimized employing a factorial design consisting of two levels and three factors. The electrochemical properties of immobilized RF were investigated by cyclic voltammetry. The factorial analysis was carried out analysing the current intensity (Ipa). It was possible to optimize the electrode to get the best reversibility in the redox process, i. e. the lowest separation between anodic and cathodic peak potentials and a current ratio close to unity. The concentration of supporting electrolyte has a small effect. The proportion has the highest effect and the interaction factor between proportion and mixture has also a significant effect on the current intensity.

Influência do agente precipitante na preparação do óxido de nióbio (V) hidratado pelo método da precipitação em solução homogênea

This work reports the preparation, characterization and study of the ion exchange behavior of hydrous niobium oxide prepared by a homogeneous precipitation method. The precipitating agent was obtained in aqueous solution by thermal decomposition of urea or ammonium carbonate. The compounds were chemically and physically characterized by X-ray diffractometry, thermal analysis (TG/DTG), surface area measurements and ion exchange behavior with sodium. The materials prepared with ammonium carbonate presented a higher degree of crystallinity and better ion exchange capacity with sodium than materials prepared with urea. In the homogeneous precipitation method, materials were obtained with specific surface area of 123 - 224 m² g-1. A variation of the preparation process produced hydrous niobium oxide with a different degree of hydration and specific surface area. This provided materials with different physico-chemical properties.

Materiais híbridos orgânico-inorgânicos: preparação e algumas aplicações

The preparation and application of organic-inorganic hybrid materials are under fast development and constitute an interesting research topic on account of the versatility and wide range of applications offered by these materials. These properties can be achieved due to the mixture of the components at the molecular level. The present review covers the state of the art, the most useful preparation routes and the potential applications of these materials.

Preparação de eletrodos opticamente transparentes

A simple experiment for the preparation of transparent conducting glass electrodes by deposition of pure and fluorine doped SnO2 films is described. This procedure was tested in the undergraduate inorganic course at IQ-UNICAMP. The success in achieving a conducting layer was easily checked using the standard probes of a volt-ohm meter. The optical transmittance and thickness were studied by UV-vis spectrophotometry. To discuss the experimental results we place significant emphasis on molecular orbital and energy band model theories. The undergraduate students can also discuss the concepts related to the electronic properties of solids and to interesting new materials, such as transparent conducting films, which are the subject of significant current research and technological applications.

Preparação de compostos lamelares: síntese do hidrogenofosfato de zircônio cristalino e sua intercalação com aminas. Um experimento para estudantes de graduação

The present paper describes the synthesis of crystalline zirconium hydrogen phosphate by direct precipitation and its intercalation with pyridine and n-butylamine. The simple experiment was tested in the undergraduate inorganic chemistry laboratory course for chemistry students at IQ-UNICAMP using inexpensive reagents. The materials were characterized by powder X-ray diffraction and infrared analyses in order to obtain detailed information of the solid structure changes as a result of the intercalation process. Pyridine and n-butylamine are focused in this work as clear and elucidative examples leading to acid-base interactive processes that result in the well-formed infinite sequence of inorganic lamellar structures.

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.

Preparação e caracterização óptica de filmes de poli(estireno sulfonados) dopados com neodímio

In this work we describe the processing of poly(styrene sulphonate) films (PSS) doped with neodymium (Nd). Optical density measurements in the UV-Vis-NIR region show the typical bands observed for neodymium chloride (NdCl3) in solution. In the case of films, the intensity ratio between the peaks at 800 nm (4I9/2 -> 4F5/2 + ²H7/2) and 580 nm (4I9/2 -> 4G5/2 + ²G7/2) is equal to 0.83. Infrared spectra present an enhancement in the absorption region of aromatic rings. Site selective luminescence spectroscopy shows that the incorporation of Nd introduces a hipsochromic shift and a line shape definition in UV luminescence compared to PSS film, decreasing the interaction between aromatic groups. In addition, the film exhibits an intense radiative transition at 1061 nm (4F3/2->4I11/2), comparable to the one present in crystalline materials doped with Nd.

Preparação e caracterização de substratos SERS ativos: um estudo da adsorção do cristal violeta sobre nanopartículas de prata

The structural characterization of molecules used in the sterilization of blood for transfusions, such as crystal violet (CV), is relevant for understanding the action of these prophylactic drugs. The characterization is feasible by surface enhanced resonance Raman spectroscopy (SERRS) of CV in solution or on surfaces. The limit of detection of CV by SERRS, in the presence of colloidal particles, using 514.5 nm as excitation radiation, was found to be around 1 ppb. The characterization of CV was also made by SERS, by using different active-particles-containing substrates, proving the versatility of this technique for the study of such structures. The results suggest that the controlled production of highly efficient SERS-active substrates may allow qualitative and quantitative analysis, with high sensitivity, with potential applications in medical and environmental fields.

Estudo do efeito do tratamento superficial por moagem sobre as propriedades das partículas de uma liga de hidreto metálico

This work reports results of studies on the electrochemical and structural properties of a Ti/Zr-based metal hydride alloy covered by Ni and LaNi4,7Sn0,3 powder additives by ball milling. The effect of this treatment is investigated for the activation time, hydrogen storage capacity and equilibrium pressure, cycling stability and the hydration/dehydration kinetics. Charge and discharge cycles show a significant decrease of the activation time due to an increase of the active area caused by the milling treatment, independent of the additive. However, other results have evidenced little effect of the milling surface treatment on the charge storage capacity, hydrogen equilibrium pressure, and hydration/dehydration kinetics, for both the Ni and LaNi4,7Sn0,3 covered materials.

Preparação de amostra de fígado bovino e estudo de micro homogeneidade para a determinação de Cd E Pb por espectrometria de absorção atômica com atomização eletrotérmica e amostragem direta de sólido

This work describes a systematic study for bovine liver sample preparation for Cd and Pb determination by solid sampling electrothermal atomic absorption spectrometry. Samples were prepared using different procedures: (1) drying in a household microwave oven followed by drying in a stove at 60 ºC until constant mass, and (2) freeze-drying. Ball and cryogenic mills were used for grinding. Particle size, sample size and micro sample homogeneity were investigated. All prepared samples showed good homogeneity (He < 10) even for low sample mass, but samples dried in a microwave oven/stove and ground in a ball mill presented the best homogeneity.

Heterociclos 1,2,3-triazólicos: histórico, métodos de preparação, aplicações e atividades farmacológicas

The 1,2,3-triazole, known since the end of 19th century, is a very widely used heterocyclic system present in many synthetic substances and commercial pharmaceutical compounds. In fact, 1,2,3-triazoles show several applications in many areas especially as medicines against many diseases like cancer, AIDS, Parkinson and Alzheimer. Nowadays there is a large variety of known methods to obtain these heterocyclic compounds comprising mainly three synthetic routes. Nevertheless, there is no article that gives an objective overview of the synthetic methods for obtaining these kinds of azoheterocycles. This paper presents a brief history of this class of compounds, and a synthetic discussion concerning the main synthetic methods for its preparation, such as cyclization through hydrazones, concerted cycloadditon [2+3] and pseudopericyclic cyclization - and some others of restricted application, but also important. Finally, this paper also provides a brief overview on pharmacological applications of some 1,2,3-triazoles.

Recentes avanços na preparação de aziridinas. Aplicações sintéticas e implicações mecanísticas

This article surveys a selection of the most recent advances in aziridine synthesis. Novel synthetic methods and new insights into existing methodologies for the selective construction of the title compounds reported in the past decade are discussed in terms of synthetic applicability and environmentally benign conditions. Mechanisms involving stereoselective preparation of structurally diverse aziridines are also presented in order to highlight the most important issues associated with the synthesis of these versatile building blocks.

Compostos organofosforados pentavalentes: histórico, métodos sintéticos de preparação e aplicações como inseticidas e agentes antitumorais

This paper is a review of the history, synthesis and application of organophosphorus compounds, especially of those of pentavalent phosphorus, such as phosphoramidates, phosphorothioates, phosphonates and phosphonic acids with insecticide and anticancer activities. The organophosphorus compounds with agrochemical applications show great structural variety, They include not only insecticides, but also fungicides, herbicides, and others. The large variety of commercially available organophosphorus pesticides is remarkable. Even more interesting is the high efficiency of some organophosphorus compounds as anticancer agents such as cyclophosphamide and its derivatives.