Aplicação do modelo geométrico no estudo dos efeitos glory e rainbow em colisões atômicas

A simple analysis of glory and rainbow effects, together with the description of their trajectories is given by the geometric model. The energy dependence of glory and rainbow impact parameters and the energy dependence of the rainbow angle are determined analytically within the model. An universal function for glory and rainbow trajectories can be easily determined.

Construção de modelos para ilustração de estruturas moleculares em aulas de química

This paper describes the construction of a kit of molecular model for illustration of molecular structure in chemical class using cheap materials. The atoms were represented by plastic spheres and the bonds between the atoms were made from plastic straws which were cut in the required length using a scale of 1.6 cm corresponding to 100 pm. Examples of adaptations made in this kit for didactical application are given.

Economia de átomos, engenharia molecular e catálise organometálica bifásica: conceitos moleculares para tecnologias limpas

For economical and ecological reasons, synthetic chemists are confronted with the increasing obligation of optimizing their synthetic methods. Maximizing efficiency and minimizing costs in the production of molecules and macromolecules constitutes, therefore, one of the most exciting challenges of synthetic chemistry. The ideal synthesis should produce the desired product in 100% yield and selectivity, in a safe and environmentally acceptable process. In this highlight the concepts of atom economy, molecular engineering and biphasic organometallic catalysis, which address these issues at the molecular level for the generation of "green" technologies, are introduced and discussed.

Distribuição de metais e caracterização das constantes de troca entre espécies metálicas e frações húmicas aquáticas de diferentes tamanhos moleculares

In this work the metal distribution and exchange constants between metal species and aquatic humic fractions with different molecular sizes were studied. The aquatic humic substances (AHS) were extracted by XAD-8 resin from water sample collected from Itapitanguí river, São Paulo State, Brazil. The AHS were fractionated in six fractions with different molecular sizes (>100 - <5 kDa) and characterized by several techniques. Molar ratios H/C suggested higher aromaticity for fractions F1 and F6 whereas molar ratios C/N didn´t show any differences regarding the humification degree between the fractions. The UV-Vis absorbance a254/a436 ratio showed higher results for F4 and F5, probably by less condensed features. FTIR studies showed high similarity in the functional groups in the fractions. The highest percentage of traces of Co, Al, Fe, Mn, Cu, Zn and Ni (determined by ICP-AES) was preferably complexed by fractions F3 and F4 with a greater amount of dissolved organic carbon (DOC). In addition, the exchange constants, determined by ultrafiltration method, showed complexes AHS-Fe and AHS-Al with higher stability than complexes AHS-Co in all fractions.

O método das trajectórias clássicas: colisões coplanares do tipo A+BC

The general methodology of classical trajectories as applied to elementary chemical reactions of the A+BC type is presented. The goal is to elucidate students about the main theoretical features and potentialities in applying this versatile method to calculate the dynamical properties of reactive systems. Only the methodology for two-dimensional (2D) case is described, from which the general theory for 3D follows straightforwardly. The adopted point of view is, as much as possible, that of allowing a direct translation of the concepts into a working program. An application to the reaction O(¹D)+H2->O+OH with relevance in atmospheric chemistry is also presented. The FORTRAN codes used are available through the web page www.qqesc.qui.uc.pt.

Aplicação catalítica de peneiras moleculares básicas micro e mesoporosas

Catalysis by solid acids has received much attention due to its importance in petroleum refining and petrochemical processes. Relatively few studies have focused on catalysis by bases and even les on using basic molecular sieves. This paper deals with the potential application of micro and mesoporous molecular sieves in base catalysis reactions. The paper is divided in two parts, the first one dedicated to the design of the catalysts and the second to some relevant examples of catalytic reactions, which find a huge field of applications essentially in the synthesis of fine chemicals. Here, recent developments in catalysis by basic molecular sieves and the perspectives of applications in correlated catalytic processes are described.

alfa e b-glucosidases como alvos moleculares para desenvolvimento de fármacos

Glucosidases are involved in key steps in the processing of oligosaccharides by cleaving O-glucose residues. Since they catalyze breaking and transfer reactions of glucosidic groups for the normal growth and development of all the cells, defects or genetic deficiencies in these enzymes are associated with serious disorders of the carbohydrate metabolism. Thus, glucosidases represent important targets to develop inhibitors, owing to their potential activities against viruses, tumoral growth and metastasis, diabetes, Gaucher's disease and other syndromes associated with the lisosomal storage of glucoesphingolipids, and osteoarthritis. This paper presents a description of the biochemical pathways and mechanisms of alpha and beta-glucosidases, and the currently available drugs capable to inhibit these enzymes.

Coordenadas cartesianas moleculares a partir da geometria dos modos normais de vibração

A simple method to obtain molecular Cartesian coordinates as a function of vibrational normal modes is presented in this work. The method does not require the definition of special matrices, like the F and G of Wilson, neither of group theory. The Eckart's conditions together with the diagonalization of kinetic and potential energy are the only required expressions. This makes the present approach appropriate to be used as a preliminary study for more advanced concepts concerning vibrational analysis. Examples are given for diatomic and triatomic molecules.

Um estudo teórico de propriedades moleculares em complexos de hidrogênio trimoleculares C2H4···2HF, C2H2···2HF e C3h6···2HF

We present a theoretical study of molecular properties in C2H4···2HF, C2H2···2HF and C3H6···2HF trimolecular hydrogen-bonded complexes. From B3LYP/6-311++G(d,p) calculations, the most important structural deformations are related to the C=C (C2H4), C≡C (C2H2), C-C (C3H6) and HF bond lengths. According to the Bader's atoms in molecules and CHELPG calculations, it was identified a tertiary interaction between the fluorine atom of the second hydrofluoric acid molecule and hydrogen atoms of the ethylene and acetylene within the C2H4···2HF and C2H2···2HF complexes, respectively. Additionally, the evaluation of the infrared spectrum characterized the new vibrational modes and bathochromic effect of the HF molecules.

Comparação entre métodos compostos no cálculo de afinidades por próton e elétron em sistemas moleculares

The CBS-4M, CBS-QB3, G2, G2(MP2), G3 and G3(MP2) model chemistry methods have been used to calculate proton and electron affinities for a set of molecular and atomic systems. Agreement with the experimental value for these electronic properties is quite good considering the uncertainty in the experimental data. A comparison among the six theories using statistical analysis (average value, standard deviation and root-mean-square) showed a better performance of CBS-QB3 to obtain these properties.

Efeitos da incorporação de peneiras moleculares 3A, 4A, 5A e 13X em membranas compósitas de quitosana/poli(vinil álcool)

The composite membranes prepared via incorporation of 12.5% of molecular sieves 3A, 4A, 5A and 13X into chitosan/poly(vinyl alcohol) (1:1). The composite membranes were immersed in the cross-linker sulfuric acid in order to acquire high proton conductivity for applications in electrolytes in PEMCF and DMF. The influence of the molecular sieves on the structural, optical, thermal, mechanical, morphologic and protonic conductivity properties and water/methanol swelling degree of membranes were investigated.

Compostos magnéticos moleculares: o desenvolvimento de novos materiais magnéticos nanoestruturados

The development of new magnetic materials has attracted attention of researchers of different areas. In the last decades, a distinguished class of materials emerged in magnetism, in which the magnetic moment is delocalized over molecules. By varying the synthetic conditions it is possible to obtain a large variety of structures and properties using the same starting molecules. These materials have a great scientific appeal due to the possibility of presenting not only magnetic, but also optical or electrical transport properties. In this review we will present an overview of some molecular magnetic compounds, in particular molecular nanomagnets.

Validação computacional de métodos compostos no estudo de propriedades moleculares

Composite methods using ONIOM and different basis sets have been used to calculate proton and electron affinities for a set of alcohols at QCISD(T)/6-311++G(2df,p) level of theory. The study was carried out considering HF, MP2 and DFT (25 exchange correlation functional) methods. The calculation performed at ONIOM2(QCISD(T)/6-311++G(2df,p):HF/6-31G(d))//ONIOM2(O3LYP/6-31G(d):HF/6-31G(d)) resulted in the smallest average absolute deviation for AP and AE, 4,75 kJ/mol e 0,43 eV, respectively.

Iodeto de potássio suportado em peneiras moleculares mesoporosas (SBA-15 e MCM-41) como catalisador básico para síntese de biodiesel

Iodide potassium incorporated on mesoporous molecular sieves (SBA-15 and MCM-41) was used as heterogeneous catalysts in the transesterification of sunflower oil under different conditions of reaction time and ratio catalyst/oil (w/w). The results have showed that the system supported in SBA-15 has been more active than the supported in MCM-41, promoting a conversion to methyl esters of 84.98%.

Bases moleculares da ação anti-inflamatória dos ácidos oleanólico e ursólico sobre as isoformas da ciclo-oxigenase por docking e dinâmica molecular

The triterpenoids oleanolic (OA) and ursolic (UA) acids show non-selective antiinflamatory activity in vitro for cyclooxygenase (COX) isoforms. 3D conformations of OA and UA, with three possible orientations (1, 1' and 2) in the active site of isoforms COX, obtained by docking, were submitted to molecular dynamics. The results show that orientation 2 of the OA in COX-2 is more favorable because orientation 1 moved away from the active site. The carboxylate group of OA interact by hydrogen bonds with Ser353 and with Phe357 and Leu359, mediated by water, while hydroxyl in C-3 interact by hydrogen bond, mediated by water, with Tyr385.