Uma metodologia para o projeto teórico de conversores moleculares de luz

Recentlly, we have proposed the representation of lanthanides within AM1 as sparkles for the purpose of obtaing ground state geometries of their complexes. We tested our quantum chemical sparkle model (SMLC/AM1) for the prediction of the crystallographic structure of complexes with coordination number nine, eight and seven. A technique is introduced for the theoretical prediction of eletronic spectra of the organic part of lanthanide complexes by replacing the metal ion by a point charge with the ligands held in their positions as determined by the SMLC/AM1, and by computing the theoretical spectra via the intermediate neglect of differential overlap/spectroscopic-configuration interaction (INDO/S-CI).

Adsorção do complexo H[Ru(III)Cl2(H2EDTA)] sobre a superfície da sílica gel modificada com [3-(2-aminoetil) aminopropil]trimetoxissilano em soluções etanólicas

Silica gel was functionalized with [3-(2-aminoethyl)aminopropyl]trimethoxysilane group (SF-AEATS) and the characterization by chemical analysis (N) and infrared spectroscopy confirmed the functionalization. The capacity of the modified silica to adsorb the complex Ru(III)-EDTA from ethanolic solution was studied. The selectivity coefficients of the complex formed on the support obtained was (Gñ), 2,07 x 10(4) L/mol and the average number of ligand bonded by one metal ion on the support (ñ) was ~ 1.

Cinética e mecanismo da reação de auto-oxidação de S(IV) catalisada por íons metálicos de transição

The oxidation process of sulfur (IV) species (SO2, HSO3- e SO32-) by oxygen, catalysed by trace metal ion and complexes, can play an important role in atmospheric, analytical and bioinorganic chemistry. An overview of the most important reactions in these fields is presented. A fascinating redox cycling of the metal ions and complexes during such autoxidation process was revealed by the combination of kinetics and coordination chemistry studies.

Obtenção de um material adsorvente para íons de metais pesados, através da eletropolimerização de 2-mercaptobenzimidazol à superfície de carbono vítreo reticulado

Electrochemical methods applied to organic species transformation has been used as excellent synthesis tools. C-C bonds can be established, making possible polymer synthesis by both anodic and cathodic reactions of suitable monomer species at the working electrode surface. In this study, anodic procedure was used to electropolymerization of 2-mercaptobenzimidazole at reticulated glassy carbon (RGC) surface. 2-mercaptobenzimidazole presents ligand sites towards Hg2+, Ag+ and Cu2+ ions. The obtained material has been able to adsorb the above mentioned ions in aqueous solution.

Caracterização de amostras comerciais de vermicomposto de esterco bovino e avaliação da influência do pH e do tempo na adsorção de Co(II), Zn(II) and Cu(II)

Some commercial samples of vermicompost from bovine manure (humus) were characterized by thermogravimetry with respect to humidity, organic matter and ash contents, the percentages of which range from 6.55 to 5.35%, 53.01 to 69.96% and 46.44 to 66,14%, respectively. The capacity of adsorption of Cu2+, Zn2+ and Co2+ ions by these samples has been evaluated as a function of pH and time. The contents of several metal ions in the original vermicompost samples have been determined by flame atomic absorption spectrometry after digestion in a microwave oven. The high nitrogen content suggests that the earthworms used in the maturation procedure lead to an efficient degradation of organic matter. The metal retention was affected by both pH and adsorption time. The results also show that adsorption follows the order Cu2+ > Zn2+ > Co2+.

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).

Materiais magnéticos baseados em diferentes zeólitas para remoção de metais em água

In this work the adsorption features of zeolites (NaY, Beta, Mordenite and ZSM-5) have been combined with the magnetic properties of iron oxides in a composite to produce a magnetic adsorbent. These magnetic composites can be used as adsorbents for contaminants in water and subsequently removed from the medium by a simple magnetic process. The magnetic zeolites were characterized by XRD, magnetization measurements, chemical analyses, N2 adsorption isotherms and Mössbauer spectroscopy. These magnetic adsorbents show remarkable adsorption capacity for metal ion contaminants in water.

Sistema aquoso bifásico: uma alternativa eficiente para extração de íons

Solvent extraction has been successfully applied to metal ion preconcentration and often meant the use of toxic organic diluents. However, regulatory pressure is increasingly focusing on the use and disposal of organic solvents, and thus the development of nonhazardous alternatives is important. In this review, we examine the application of aqueous biphasic systems (ABS) to extraction of ions, analyzing their potential and limitations and suggest that ABSs could be an efficient substitute for oil/water biphasic systems. ABSs are formed by mixing certain inorganic salts and water-soluble polymers, or by mixing two water-soluble polymers.

Avaliação da concentração de alguns íons metálicos em diferentes espécies de líquens do cerrado Sul-Mato-Grossense

Concentrations of Fe, Mn, Co, Cr, Zn and Cu were determinated using flame atomic absorption spectrometry in nine lichen species of the Sul-Mato-Grossense cerrado. The average metal ion concentrations varied in the following ranges: Fe, 248.41-1568.01; Mn, 98.50-397.33; Co, 10.08-24.81; Cr, 18.24-44.26; Zn, 14.62-34.79 and Cu, 3.23-7.57 mg kg-1. Statistical analysis (Pearson and Cluster) applied to the metal ion concentrations indicated that the accumulation of these ions can be due to several anthropogenic sources including agricultural activities, mineral exploration, biomass burning, soil mineral composition and leather tanning processes by chromium.

Cromatografia de afinidade por íons metálicos imobilizados (IMAC) de biomoléculas: aspectos fundamentais e aplicações tecnológicas

Immobilized Metal Ion Affinity Cromatography - IMAC - is a group-specific based adsorption applied to the purification and structure-function studies of proteins and nucleic acids. The adsorption is based on coordination between a metal ion chelated on the surface of a solid matrix and electron donor groups at the surface of the biomolecule. IMAC is a highly selective, low cost, and easily scaled-up technique being used in research and commercial operations. A separation process can be designed for a specific molecule by just selecting an appropriate metal ion, chelating agent, and operational conditions such as pH, ionic strength, and buffer type.

Preconcentration, determination and speciation of iron by solid-phase extraction using dimethyl (E)-2-[(Z)-1-acetyl)-2-hydroxy-1-propenyl]-2-butenedioate

A new sensitive and selective procedure for speciation of trace dissolved Fe(III) and Fe(II), using modified octadecyl silica membrane disks and determination by flame atomic absorption spectrometry was developed. A ML3 complex is formed between the ligand and Fe(III) responsible for extraction of metal ion on the disk. Various factors influencing the separation of iron were investigated and the optimized operation conditions were established. Under optimum conditions, an enrichment factor of 166 was obtained for Fe3+ ions. The calibration graph using the preconcentration system for Fe3+ was linear between 40.0 and 1000.0 μg L-1.

Polímeros impressos com íons: fundamentos, estratégias de preparo e aplicações em química analítica

Chemical imprinting technology has been widely used as a valuable tool in selective recognition of a given target analyte (molecule or metal ion), yielding a notable advance in the development of new analytical protocols. Since their discovery, molecularly imprinted polymers (MIPs) have been extensively studied with excellent reviews published. However, studies involving ion imprinted polymers (IIPs), in which metal ions are recognized in the presence of closely related inorganic ions, remain scarce. Thus, this review involved a survey of different synthetic approaches for preparing ion imprinted adsorbents and their application for the development of solid phase extraction methods, metal ion sensors (electrodes and optodes) and selective membranes.

Lability of Cd, Cr, Cu, Mn and Pb complexed by aquatic humic substances

The lability of Cd(II), Cr(III), Cu(II), Mn(II) and Pb(II) complexed by humic substances (HSs) was investigated by means of ion exchange on cellulose modified with p-aminobenzoic groups (Cell-PAB), using a batch procedure. The HSs were extracted from water samples using adsorption in a column packed with XAD 8 resin. The metal-HS complexes were prepared by adding solutions containing all the aforementioned metal ions ( Cd(II), Cr(III), Cu(II), Mn(II) and Pb(II) ). The results indicated that the distribution coefficients (Kd) of Cell-PAB decreased with the presence of HSs, and that the lability of metal fractions complexed by HSs decreases in pH values > 4.0, complexation time > 10 h and HS concentration > 500 mg L-1. The metal exchange between HSs and Cell-PAB exhibited the following order of metal ion lability: Cd < Pb < Mn @ Cr < Cu.

Magnetic, thermal and spectral behaviour of 3-chloro-2-nitrobenzoates of Co(II), Ni(II), and Cu(II)

Physico-chemical properties of 3-chloro-2-nitrobenzoates of Co(II), Ni(II) and Cu(II) were synthesized and studied. The complexes were obtained as mono- and dihydrates with a metal ion to ligand ratio of 1 : 2. All analysed 3-chloro-2-nitrobenzoates are polycrystalline compounds with colours depending on the central ions: pink for Co(II), green for Ni(II) and blue for Cu(II) complexes. Their thermal decomposition was studied in the range of 293 ­ 523 K, because it was found that on heating in air above 523 K 3-chloro-2-nitrobenzoates decompose explosively. Hydrated complexes lose crystallization water molecules in one step and anhydrous compounds are formed. The final products of their decomposition are the oxides of the respective transition metals. From the results it appears that during dehydration process no transformation of nitro group to nitrite takes place. The solubilities of analysed complexes in water at 293 K are of the order of 10-4 ­ 10-2 mol / dm³. The magnetic moment values of Co2+, Ni2+ and Cu2+ ions in 3-chloro-2-nitrobenzoates experimentally determined at 76 ­ 303 K change from 3.67µB to 4.61µB for Co(II) complex, from 2.15µB to 2.87µB for Ni(II) 3-chloro-2-nitrobenzoate and from 0.26µB to 1.39µB for Cu(II) complex. 3-Chloro-2-nitrobenzoates of Co(II) and Ni(II) follow the Curie-Weiss law. Complex of Cu(II) forms dimer.

Spectrophotometric study of the chromium(III)/azide system in the ultraviolet region and its analytical application

A sensitive and alternative method for the spectrophotometric determination of chromium(III) based on the formation of chromium(III)/azide complexes was established by investigating a new band in the ultraviolet region. The best experimental conditions for the analytical determination of this metallic ion were: ligand and perchloric acid analytical concentration = 493 and 12.0 mmol L-1, respectively; aqueous medium; T = 25.0 ºC; contact time = 1 hour. The maximum molar absorptivity coefficient occurred at 287 nm (average 1.481 ± 0.008 ´ 10(4) L mol-1 cm-1), leading to the determination of metal ion concentrations one hundred times lower than the ones formerly determined in the visible region. The system obeys Beer's Law and is suitable for chromium determination in the 0.702-2.81 mg L-1 concentration range (15-65% T, 1.00 cm-width quartz cells). Analytical applications of the current method were tested with a nutritional supplement containing chromium. Results were compared with those obtained with atomic absorption spectrometry.