RMN 2D: Detecção inversa e gradiente de campo na determinação estrutural de compostos orgânicos

A view of the general aspects involving the 2D NMR spectroscopy using inverse detection and field gradient techniques is presented through the analysis of a sesquiterpene.

Triterpenóides pentacíclicos de Mentha villosa: identificação estrutural e atribuição dos deslocamentos químicos dos átomos de hidrogênio e carbono

The structures of seven oleanene and ursene triterpenoids (1-7) isolated from aerial parts of Mentha villosa were identified. In addition, the complete ¹H and 13C resonance assignments of these triterpenoids were accomplished using 1D and 2D NMR spectroscopic experiments.

Caracterização textural e estrutural de V2O5/TiO2 obtidos via sol-gel: comparação entre secagem convencional e supercrítica

This work describes a modified sol-gel method for the preparation of V2O5/TiO2 catalysts. The samples have been characterized by N2 adsorption at 77K, x-ray diffractometry (XRD) and Fourier Transform Infrared (FT-IR). The surface area increases with the vanadia loading from 24 m² g-1, for pure TiO2, to 87 m² g-1 for 9wt.% of V2O5. The rutile form is predominant for pure TiO2 but became enriched with anatase phase when vanadia loading is increased. No crystalline V2O5 phase was observed in the catalysts diffractograms. Two species of surface vanadium observed by FT-IR spectroscopy a monomeric vanadyl and polymeric vanadates, the vanadyl/vanadate ratio remains practically constant.

Modelagem de proteínas por homologia

Modeling methods to derive 3D-structure of proteins have been recently developed. Protein homology-modeling, also known as comparative protein modeling, is nowadays the most accurate protein modeling method. This technique can produce useful models for about an order of magnitude more protein sequences than there have been structures determined by experiment in the same amount of time. All current protein homology-modeling methods consist of four sequential steps: fold assignment and template selection, template-target alignment, model building, and model evaluation. In this paper we discuss in some detail the protein-homology paradigm, its predictive power and its limitations.

Introdução a modelagem molecular de fármacos no curso experimental de química farmacêutica

Molecular Modeling is an important tool in drug design and it is very useful to predict biological activity from a library of compounds. A wide variety of computer programs and methods have been developed to visualize the tridimensional geometry and calculate physical properties of drugs. In this work, we describe a practical approach of molecular modeling as a powerful tool to study structure-activity relationships of drugs, including some antibacterials, hormones, cholinergic and adrenergic agents. At first, the students learn how to draw 3D structures and use them to perform conformational and molecular analysis. Thus, they compare drugs with similar pharmacological activity by superimposing one structure on the top of another and evaluate the geometry and physical properties.

Fixação de nitrogênio: estrutura, função e modelagem bioinorgânica das nitrogenases

Biological nitrogen fixation, catalyzed by nitrogenases, contributes about half of the nitrogen needed to global agriculture. For forty years synthetic chemists and theoreticians have tried to understand and model the structure and function of this important metalloenzyme. Ten years after the first report on the crystal structure of the MoFe protein, scientists still have not been able to synthesize a chemical equivalent of the FeMo cofactor nor the structure knowledge revealed the key to its catalytic activity. This paper with 104 references presents a review of the most relevant advances in chemical nitrogen fixation and their relation with the nitrogenases.

Análise estrutural de ciclodextrinas: um estudo comparativo entre métodos teóricos clássicos e quânticos

In the present work, we analyzed the accuracy of distinct theoretical methods to reproduce the solid state structures of cyclodextrins. The a, b and g-cyclodextrins (CD) were considered and also their hydrates with included water molecules: a-CD.2H2O, b-CD.10H2O and g-CD.12H2O. The geometries were fully optimized using Molecular Mechanics (MM2), semiempirical (AM1 and PM3) and ab initio (HF/3-21G) methods and quantitatively compared with experimental data from X ray diffraction. The results obtained from the classical MM2 method were in best agreement with the experiment. The semiempirical and ab initio structures were also in satisfactory accordance with the experimental data. In general, the PM3 method was found to be more suitable than the AM1 to describe the CD geometries, mainly when the intramolecular hydrogen bonds are considered.

Resina de Protium heptaphyllum: isolamento, caracterização estrutural e avaliação das propriedades térmicas

Three mixtures of triterpenes (maniladiol and breine; alpha and beta-amyrin; lupenone, alpha and beta-amyrinone) were isolated from Protium heptaphyllum March resin. The structural identification was based on NMR and mass spectrometry data. Lupenone, and alpha and beta-amyrinone were not reported before as constituents of this resin. The resin was submitted to methylation and acetylation reactions. The pure and derivatized resins and the mixtures (maniladiol and breine; alpha and beta-amyrin) were analyzed by TG and DSC. The TG curves revealed that the derivatization decreases the thermal stability of the resin. The DSC curves showed peaks that can be assigned to evaporation and phase transitions processes.

Estudo de modelagem molecular de complexos ferriprotoporfirina-IX e quinolinocarbinolaminas antimaláricas: proposta de um farmacóforo

Quinine and quinidine are well-known 4-quinolinecarbinolamines that exhibit antimalarial activity, but, in contrast, their epimers 9-epiquinine and 9-epiquinidine are almost inactive. Literature data are conflicting in describing the 4-quinolinecarbinolamine interaction mode with the molecular target, the ferriprotoporphyrin IX [Fe(III)PPIX]. In the present paper, a pharmacophore is proposed based on the binding of the non-aromatic nitrogen to the iron atom. The 4-quinolinecarbinolamine antimalarials were superimposed on the pharmacophore under consideration and complexes with Fe(III)PPIX were constructed. Conformational analyses of the complexes were performed applying the MM+ molecular mechanics method. The analysis of the complexes showed that the proposed ligand mode is possible although it does not explain the activity differences between epimers. A discussion of the structural aspects is also provided.

Elucidação estrutural de substâncias orgânicas com auxílio de computador: evoluções recentes

The development of new tools for chemoinformatics, allied to the use of different algorithms and computer programmes for structure elucidation of organic compounds, is growing fast worldwide. Massive efforts in research and development are currently being pursued both by academia and the so-called chemistry software development companies. The demystification of this environment provoked by the availability of software packages and a vast array of publications exert a positive impact on chemistry. In this work, an overview concerning the more classical approaches as well as new strategies on computer-based tools for structure elucidation of organic compounds is presented. Historical background is also taken into account since these techniques began to develop around four decades ago. Attention will be paid to companies which develop, distribute or commercialize software as well as web-based and open access tools which are currently available to chemists.

Utilização de modelagem numérica para o estudo da dispersão de poluentes emitidos pela usina termoelétrica Presidente Médici

The purpose of the present study is to evaluate the atmospheric behavior in the dispersion of the pollutants SO2, PM10 and NOx emitted by the President Medici power plant in Candiota, RS. The RAMS atmospheric model was applied and the simulations were conducted from april in 20 to 24, 2004. The concentrations of the pollutants simulated by RAMS were compared with the data measured at the air quality monitoring stations. The results showed significant influence of the emissions generated by the power plant on the concentration of the pollutants.

Síntese da hidroxiapatita e refinamento estrutural por difração de raios-x

A sample of hydroxyapatite was synthesized and its crystalline structure was analyzed by X-ray diffraction by means of the Rietveld method. Two functions were used to fit the peak profiles, modified Voigt (TCHZ) and Pearson VII. The occupational factors and lattice parameters obtained by both models show that the sample does not contain relevant cationic substitutions. The interatomic distances from Ca1 to oxygens O1, O2 and O3 were adequate for a pure hydroxyapatite without defect at site Ca1. Besides, the use of multiple lines in planes (300) and (002) associated with the model Pearson VII resulted in good agreement with the TCHZ model with respect to the size-strain effectswith an ellipsoidal shape of crystallites. In conclusion, the procedures adopted in the synthesis of hydroxyapatite produced a pure and crystalline material. The experimental results of transmission electron microscopy confirmed the predicted shape of crystals.

Síntese, avaliação biológica e modelagem molecular de arilfuranos como inibidores da enzima tripanotiona redutase

Trypanosoma cruzi is a protozoan parasite that causes a severe disease (Chagas'disease) in Central and South America. The currently available chemotherapeutic agents against this disease are still inadequate. The enzyme trypanothione reductase (TR) is considered a validated molecular target for the development of new drugs against this parasite. In this regard, a series of arylfurans based on 2,5-bis-(4-acetamidophenyl)furan was synthesized and tested for their in vitro inhibitory activity against TR. Molecular modeling studies of putative enzyme-inhibitor complexes revealed a possible mechanism of interaction. From synthesized compounds, a benzylaminofuran derivative was found to be more active than the lead compound.

Métodos simples de formação de monocristal de substância orgânica para estudo estrutural por difração de raios X

This work presents three operationally simple laboratory protocols for monocrystal growth of small-molecule organic compounds, which have been applied with success in the last ten years for the formation of single crystals for X-ray structural studies. In addition, five structure hints were formulated as general guidelines for selecting a small-molecule organic compound as a candidate for monocrystal growth: molecular weight >200 D, melting point >100 ºC, two or more aromatic rings in the structure, at least two sites for intermolecular hydrogen bond formation, and a halogen or other heavy atom in the structure.

Ocorrência e diversidade estrutural de metabólitos fúngicos com atividade antibiótica

Several reasons motivated the development of new generations of antibiotics, such as their high ability to develop resistance to virtually all kinds of anti-infective agents and the crescent market demand for new drugs to treat special demanding patients. After penicillin discovery, several antibiotics were developed from fungal metabolites, since antibacterial secondary metabolites consists on a fungal endogenous protective mechanism against natural competitors. The aim of this review is to present the structural diversity of antibacterial and antifungal metabolites produced by fungi, mentioning sources of fungal isolates, cultivation process and details on the scope of their antibiotic activity.