Organometallic catalysis: some contributions to organic synthesis

In the present paper some general aspects of metal complex catalysis and its applications for oxyfunctionalization of various olefins, including naturally occurring ones, via selective oxidation, hydroformylation and alkoxycarbonylation are discussed.

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.

Catalisadores contendo carbenos n-heterocíclicos como ligantes: propriedades, sínteses, aplicações e comparação com outros ligantes

N-heterocyclic carbenes (NHCs) have become of considerable importance in modern organometallic chemistry and homogeneous catalysis. There are several advantages in the use NHCs over their phosphorus analogues, which explains the enormous development of NHC ligands in the field of organometallic catalysis in the past few years. In this article, we present an overview of the importance of the catalysts containing NHC ligands, their synthesis, some pertinent synthetic applications, and a brief comparison with other catalysts.

Antileishmanial action of organometallic complexes of Pt(II) and Rh(I)

The three organometallic complexes [(Cis-PtII (DDH) (2,5-Dihidroxibenzensulfonic)2, RhI (CO)2 Cl(2-Aminobenzothiazole) and RhI (CO)2 Cl(5-Cl-2-Methilbenzothiazole)] used in this study had been previously found to have a high in vitro activity against promastigote and amastigote like forms of Leishmania donovani. Here, the cytotoxic effect of these new organometallic complexes on the J-774 macrophages were studied. Only the RhI(CO)2 Cl (2-Aminobenzothiazole) complex induced substantial toxicity in the cells. Also, we assayed the effect of this complex on the parasite's biosynthesis of macromolecules. The RhI(CO)2Cl (5-Cl-2-Methylbenzothiazole) complex inhibited DNA, RNA, and protein synthesis. On the other hand, the two other compounds tested did not inhibit the incorporation of radioactive precursors. Finally important ultrastructural alterations in the parasites treated with the two non-cytotoxic complexes were observed.

Antiplasmodial activity of iron(II) and ruthenium(II) organometallic complexes against Plasmodium falciparum blood parasites

This work reports the in vitro activity against Plasmodium falciparumblood forms (W2 clone, chloroquine-resistant) of tamoxifen-based compounds and their ferrocenyl (ferrocifens) and ruthenocenyl (ruthenocifens) derivatives, as well as their cytotoxicity against HepG2 human hepatoma cells. Surprisingly with these series, results indicate that the biological activity of ruthenocifens is better than that of ferrocifens and other tamoxifen-like compounds. The synthesis of a new metal-based compound is also described. It was shown, for the first time, that ruthenocifens are good antiplasmodial prototypes. Further studies will be conducted aiming at a better understanding of their mechanism of action and at obtaining new compounds with better therapeutic profile.

Vanadium-modified molecular sieves: preparation, characterization and catalysis

Vanadium-containing molecular sieves are redox catalysts and are good candidates as substitutes for oxide-supported V2O5 in a number of reactions. These materials have the advantage of presenting better dispersion of vanadium species, as well as shape-selective properties and controllable acidities. They may be prepared by one-pot synthesis or by post-synthesis methods and a number of techniques such as diffuse reflectance UV-visible spectroscopy, 51V nuclear magnetic resonance and electron paramagnetic resonance, to name but a few, have been used to characterize these materials. In this review, methods of preparation of vanadium-modified molecular sieves, their characterization and applications in catalysis are discussed.

Glicólise do poli(3-hidroxibutirato) por via enzimática

Poly(3-hydroxybutyrate), PHB, is a polymer with broad potential applications because of its biodegradability and biocompatibility. However, its high crystallinity is a limiting factor for many applications. To overcome this drawback, one strategy currently employed involves the reduction of the molecular weight of PHB with the concomitant formation of end-functionalized chains, such as those obtained via glycolysis. The glycolysis of PHB can be catalyzed by acid, base, or organometallic compounds. However, to our knowledge, there are no reports regarding PHB glycolysis catalyzed enzymatically. Among the major types of enzymes used in biocatalysis, the lipases stand out because they have the ability to catalyze reactions in both aqueous and organic media. Thus, in this study, we performed the enzymatic glycolysis of PHB using the lipase Amano PS (Pseudomonas cepacia) with ethane-1,2-diol (ethylene glycol) as the functionalizing agent. The results indicated that the glycolysis was successful and afforded hydroxyl-terminated oligomeric PHB polyols. Nuclear magnetic resonance spectra of the products showed characteristic signals for the terminal hydroxyl groups of the polyols, while thermogravimetric and differential scanning calorimetry analyses confirmed an increase in the thermal stability and a decrease in the crystallinity of the polyols compared with the starting PHB polymer, which were both attributed to the reduction in the molecular weight due to glycolysis.

Nonconventional amide bond formation catalysis: programming enzyme specificity with substrate mimetics

This article reports on the design and characteristics of substrate mimetics in protease-catalyzed reactions. Firstly, the basis of protease-catalyzed peptide synthesis and the general advantages of substrate mimetics over common acyl donor components are described. The binding behavior of these artificial substrates and the mechanism of catalysis are further discussed on the basis of hydrolysis, acyl transfer, protein-ligand docking, and molecular dynamics studies on the trypsin model. The general validity of the substrate mimetic concept is illustrated by the expansion of this strategy to trypsin-like, glutamic acid-specific, and hydrophobic amino acid-specific proteases. Finally, opportunities for the combination of the substrate mimetic strategy with the chemical solid-phase peptide synthesis and the use of substrate mimetics for non-peptide organic amide synthesis are presented.

Chemical transformations of neolignans

Neolignans, generated by oxydative dimerization of propenylphenol and/or allylphenol, undergo further modifying steps. These biosynthetic reactions, confirmed in vitro, include Cope, retro-Claisen and Claisen rearrangements. Additionally acid catalysis effects convertions of bicyclo [3.2.1] octanoid neolignans into hydrobenzofuranoid neolignans, or inversely of hydrobenzofuranoid neolignans into bicyclo [3.2.1] octanoid neolignans, of hydrobenzofuranoid neolignans into futoenone type neolignans, of tetrahydrofuran neolignans into aryltetralin neolignans, as well as modifications by Friedel - Crafts reactions and the transformation of aryltetralin neolignans into arylindanones by pinacoline - pinacolone type rearrangement.

The use of polyvinyl alcohol glutaraldehyde as solid-phase in ELISA for plague

Discs of polyvinyl alcohol cross-linked with glutaraldehyde were synthesized under acid catalysis (H2SO4). Then, the antigen F1 purified from Yersinia pestis was covalently linked to this modified polymer. Afterwards, an enzyme-linked immunosorbent assay (ELISA) was established for the diagnosis of plague in rabbit and human. The best conditions for the method were achieved by using 1.3 ¼g of F1 prepared in 0.067 M phosphate buffer, pH 7.2, containing 1 M NaCl (PBS); anti-IgG peroxidase conjugate diluted 6,000 times and as a blocking agent 3% w/v skim milk in PBS. The titration of positive rabbit serum according to this procedure detected antibody concentrations up to 1:12,800 times. The present method, the conventional ELISA and passive haemagglutination assay are compared.

Genesis of the sombric horizon in ultisols (red argisols) in southern Santa Catarina, Brazil

Dark subsurface horizons, with properties similar to the sombric horizon characterized by the USA Soil Taxonomy, are frequent in Southern Brazil. The genesis of this horizon is controversial and poorly understood. This study aimed to describe the occurrence of sombric-like horizons in Ultisols in the South of Santa Catarina State, at low altitudes, and suggest possible processes of humus transference, accumulation and persistence in these horizons. Physical, chemical and mineralogical properties of four Ultisols were evaluated; three were sampled in a toposequence, and another representative one in an isolated profile (RSP). The dark subsurface horizons coincide with the AB and BA transitional genetic horizons; they are acid, low in base saturation, and have a similar clay mineralogy in all horizons. Very high amounts of Fe and Al extracted by ammonium oxalate and sodium pyrophosphate solution as well as maximum Al extracted by CuCl2 solution were observed in these dark subsurface horizons, indicating a possible migration of these elements in the form of organometallic complexes. The contents of Al plus ½ Fe extracted from the RSP soil horizons with ammonium oxalate indicated spodic materials in the sombric-like horizon, although the soil morphology was not compatible with Spodosols. Maximum contents of fine clay were also found in the sombric-like horizon, suggesting Fe and Al migration as clay-humic substances. However, the hypothesis that sombric-like horizons in these soils are a relict feature of a grass paleovegetation, different from the current dense seasonal forest, should not be discarded but investigated in further studies.

Ressonância magnética nuclear de platina-195 em compostos organometálicos

A brief review of 195Pt NMR is presented, focusing organometallic compounds. This article gives initially basic information of NMR processes involving 195Pt nucleus. It is followed by a discussion of the factors which affect the chemical shifts and coupling constants. Finally, some aspects of 195Pt NMR of solids are commented.

Reações de Etanol com CO/H2 na Presença do Sistema Catalítico Ru(acac)3/I-

The hydrocarbonylation reaction of ethanol with a CO/H2 mixture assisted by Ru(acac)3/iodide was investigated. Bronsted and Lewis acids and iodides salt were used as homogeneous promoters. The etherification reaction was the main reaction under typical acidic conditions of the catalytic system. When a hydrocarbon solvent (toluene) was added to the initial reaction, the alcohol conversion and the carbonylation products were increased. The catalytic activity of the Bronsted acids (conv. EtOH = 71-92%) was higher than that of the Lewis acids promoters (conv. EtOH = 65-85%). The salt present the lower catalytic activity among the promoters used. The long time reaction carried out with ethanol showed an increase of the product selectivity of the homologation and carbonylation reactions while the etherification reaction selectivity decreased. The recycled ether led to 60-65% ethanol conversion to C5 and C6 products. The main catalytic species are H+[Ru(CO)3I3]-, [HRu3(CO)11]- and [HRu(CO)4]-. The first one is active in the carbonylation and homologation reactions of alcohols while the two others take part only in the homologation reaction.

Membranas Inorgânicas e reatores catalíticos

Membrane reactors are reviewed with emphasis in their applications in catalysis field. The basic principles of these systems are presented as well as a historical development. The several kinds of catalytic membranes and their preparations are discussed including the problems, needs and challenges to be solved in order to use these reactors in commercial processes. Some applications of inorganic membrane reactors are also shown. It was concluded that these systems have a great potential for improving yield and selectivity of high temperature catalytic reactions. However, it is still an imerging technology with a need for a lot of fundamental research; several challenges should be overcome for the successful commercial application of these systems.

Reações intramoleculares como modelos não miméticos de catálise enzimática

This review gives a critical idea on the importance of intramolecular reactions as models for enzymatic catalysis. Intramolecular lactonizations, ester and amide hydrolysis studies result in theories which try to explain the difference between intermolecular, intramolecular and enzyme reactions and rationalize the enhancement promoted by these biological catalyst.