Neste artigo são apresentadas a síntese e a caracterização de dois compostos binucleares de ferro, os quais contêm uma ponte μ-oxo. Os compostos [(SO4)(L5)Fe(μ-O)Fe(L5)(SO4 )]•6H2O, 1, e [Cl(L5)Fe(μ-O)Fe(L5)Cl]Cl2• 2H2O, 2, foram obtidos nas reações entre 1-(bis-piridin-2-ilmetil-amino)-3-cloropropan-2-ol (L5) e os sais FeSO4•7H2 O e FeCl3•6H2 O, respectivamente. Os espectros eletrônicos dos complexos apresentam absorções somente na região do ultravioleta, sendo que a análise eletroquímica revelou que, após a formação da espécie FeIII FeII, a unidade binuclear do composto 1 é mais estável do que a do composto 2. Os ligantes monodentados (sulfato e cloreto) exercem influência sobre os parâmetros Mössbauer determinados para 1 e 2, particularmente sobre os desdobramentos de quadrupolo. Os compostos foram empregados como catalisadores em reações de oxidação do cicloexano, usando H2O2 e t-BuOOH como oxidantes em uma razão substrato:oxidante:catalisador de 1000:1000:1. Os resultados indicam que o composto 2 é um catalisador mais eficiente que o composto 1.

We report herein the synthesis and characterization of two dinuclear μ-oxo iron compounds obtained through the reactions of FeSO4•7H2 O and FeCl3•6H2 O with 1-(bis-pyridin-2-ylmethyl-amino)-3-chloropropan-2-ol (L5), which resulted in the compounds [(SO4)(L5)Fe(μ-O)Fe(L5)(SO4 )]•6H2O, 1, and [Cl(L5)Fe(μ-O)Fe(L5)Cl]Cl2• 2H2O, 2. The electronic spectra of both compounds show absorption bands only in the UV range. The electrochemical analysis showed that the dinuclear unit is more stable under reduction in compound 1 than in compound 2, while the Mössbauer spectroscopy revealed that the monodentate ligands (sulfate and chloride) have a significant influence on the Mössbauer parameters determined for 1 and 2, particularly on the quadrupole splitting values. Both compounds were studied as catalysts in reactions of cyclohexane oxidation, using H2O2 and t-BuOOH as oxidants, in a substrate:oxidant:catalyst ratio of 1000:1000:1. Cyclohexanol, cyclohexanone, cyclohexyl hydroperoxide, t-butyl cyclohexyl peroxide and adipic acid were formed during the process. The experiments revealed that compound 2 is, in general, more active than compound 1 in promoting cyclohexane oxidation.

A ferramenta de Gassman-Fentiman da demanda crescente de elétrons foi usada para identificar íons carbênios e íons carbônios. Contudo, devido ao seu entendimento ambíguo, ela foi pivô de uma disputa histórica. Nós aplicamos a metodologia da Teoria Quântica de Átomos em Moléculas - QTAIM - para caracterizar íons carbênios e íons carbônios de uma forma mais eficaz e mais fácil. Essa metodologia pode ser usada para avaliar se um carbocátion é clássico ou não. Além disso, é possível classificar um conjunto de íon carbônio na ordem de magnitude da deslocalização σ, ou π. Há poucas diferenças entre os resultados de nosso modelo baseado na QTAIM e da ferramenta de Gassman-Fentiman. Contudo, diferentemente da ferramenta de Gassman-Fentiman, os cátions 7-anisol-7-norbornenila e 2-anisol-2-norbornila são não-clássicos, embora sejam os menos íons não-clássicos em seus conjuntos correspondentes de cátions estudados.

The Gassman-Fentiman tool of increasing electron demand was used to identify carbonium and carbenium ions. Nonetheless, due to its ambiguous understanding, it was pivot of a historical dispute. We applied the Quantum Theory of Atoms in Molecules (QTAIM) metodology to characterize the carbonium and carbenium ions on an easier and more effective way. By comparing selected topological information of reference carbenium ions the QTAIM metodology can be used to evaluate whether a carbocation is classical or not. In addition, it is possible to rank a set of carbonium ions in order of their corresponding σ or π delocalization. There are few differences between our QTAIM-based model and Gassman-Fentiman tool. Unlike Gassman-Fentiman tool results, 7-anisyl-7-norbornenyl and 2-anisyl-2-norbornyl cations are non-classical, although they are the least nonclassical ions in their corresponding set of studied cations.

Different bacterial strains were screened to detect nitrilase and/or nitrile hidratase/amidase activities towards benzonitrile, to be used as biocatalyst to produce enantiomerically pure non-proteinogenic amino acids using amino nitriles as starting material. The best biocatalyst found was Pseudomonas aeruginosa 10145, which showed high enzyme activities. Whole cells were used as catalyst for the transformation of 2-phenyl-2-amino-acetonitrile for the corresponding D-phenylglycine. The percentage conversion was followed by chiral HPLC. After 1 hour reaction 18% of 2-phenyl-2-amino-acetonitrile was converted into D-phenylglycine with an enantiomeric excess of over 95%. When an inducer was added to the media, an increase in nitrile hydrolyzing activities was detected, hence leading to total conversion of (R)-2-phenyl-2-amino-acetonitrile to the corresponding amino acid in 30 min reaction. The isolated yield of the target product was 50% and its characterization was performed by polarimetry, chiral HPLC, IR-FT spectroscopy and GC-MS.

A estabilidade relativa do dicátion 1,3-desidro-5,7-adamantanediila é atribuída a sua aromaticidade tridimensional. Contudo, sua natureza eletrônica não é bem conhecida. A fim de entendê-la melhor, os di- e monocátions do adamantanodiil e alguns de seus análogos foram estudados utilizando a teoria de átomos e moléculas (AIM). Eles foram comparados com análogos de adamantano não-aromáticos. Os resultados de AIM indicam que a densidade eletrônica no centro da estrutura em gaiola e a média de todos os índices de deslocalização, envolvendo seus átomos cabeças-de-ponte são maiores em compostos aromáticos do que em não-aromáticos. A degenerescência energética dos átomos cabeça-de-ponte, a uniformidade e magnitude da carga compartilhada entre estes, distingue os dicátions 1,3-adamantila e 1,3-desidro-5,7-adamantanediila. Contudo, ambos são aromáticos, assim como o 1,3-desidro-5,7-diboroadamantano. O cátion 1,3-desidro-7-adamantila tem uma homoaromaticidade planar característica.

The relative stability of the 1,3-dehydro-5,7-adamantanediyl dication is ascribed to its tridimensional aromaticity. However, its electronic nature is not well known. In order to improve its understanding, dicationic and monocationic adamantanedyil species and some key analogues were studied by atoms in molecules (AIM) theory. They were compared to non-aromatic adamantane analogues. AIM results indicate that the density in center of the cage structure and the average of all delocalization indexes involving its bridged atoms are higher in aromatic than in non-aromatic compounds. Degeneracy in energy of the bridged atoms, uniformity and magnitude of their shared charge distinguish the dications 1,3-adamantyl and the 1,3-dehydro-5,7-adamantanediyl. However, both are aromatic as well as the 1,3-dehydro-5,7-diboroadamantane. The 1,3-dehydro-7-adamantyl cation has a characteristic planar homoaromaticity.

Em trabalhos anteriores em nosso laboratório, uma cepa de Pseudomonas aeruginosa demonstrou ter atividade enzimática na conversão de arilaminonitrilas em D-amino ácidos. Essa atividade enzimática aumentou por indução de modo a produzir D-fenilglicina enantiomericamente pura a partir de 2-fenil-2-aminoacetonitrila. No presente trabalho, as melhores condições para essa transformação são descritas. Para aumentar o uso potencial desse biocatalisador, células de Pseudomonas aeruginosa 10145 foram envolvidas em alginato em forma de pequenas esferas. Duas concentrações diferentes de alginato foram usadas nesse processo. A morfologia das pérolas foi analisada via microscopia eletrônica de varredura (MEV). As pérolas com altas porosidades, formadas com 1,5% de alginato de sódio conduziram às melhores conversões de 2-fenil-2-aminoacetonitrila em D-fenilglicina (20%, 3,0 horas de reação e excesso enantiomérico superior a 98%). Repetições em quatro bateladas consecutivas demonstraram a manutenção da atividade desse sistema catalítico.

In a preliminary work in our laboratory, a Pseudomonas aeruginosa strain was found to have enzymatic activity to convert arylaminonitriles into D-amino acids. This enzymatic activity was increased by induction to produce enantiomerically pure D-phenylglycine using 2-phenyl-2-aminoacetonitrile as starting material. In this work, the best conditions leading to this transformation are described. In order to increase the biocatalyst potential use, cells of Pseudomonas aeruginosa 10145 were entrapped in calcium alginate gel beads. Two different concentration of sodium alginate were used to immobilize these cells. Beads morphology was demonstrated by scanning electron microscopy (SEM). The beads with higher porosity, formed with 1.5% (m/v) of sodium alginate led to the best conversion of 2-phenyl-2-aminoacetonitrile into D-phenylglycine (20% of conversion, 3.0 h of reaction enantiomeric excess higher than 98%). Recycling was performed in four repeated batch reactions, which proved the biocatalyst activity maintenance.

A técnica de HPLC por troca de ligante foi utilizada para a separação de racematos de amino ácidos com cadeia lateral alifática. Para tanto, o seletor quiral escolhido foi o complexo de Cu(II) combinado com a L-fenilalananina. Os resultados mostram que o primeiro enanciômero a eluir foi a forma D, seguido da forma L. Segundo o conceito de interação de 3 pontos, foi proposto um mecanismo de reconhecimento quiral, no qual não há evidências de mudança de configuração após a formação dos complexos pseudo-homo e heteroquiral. Cálculos DFT-B3LYP para energia e espectro vibracional confirmaram a viabilidade deste mecanismo, pois mostram a que a configuração trans do complexo homoquiral é mais estável do que a forma cis.

Ligand exchange HPLC technique was applied to resolve chiral separation of aliphatic side chain aminoacid racemates. Chiral selector was copper L-phenylalaninate (II) and the results showed the elution of D enantiomer followed by L form. Considering the 3-point interaction concept, a mechanism of chiral recognition was proposed, in which no change of configuration would follow the formation of pseudo-homochiral and heterochiral complexes. To prove the reliability of this mechanism, the trans configuration of homochiral complex had to be more stable than the cis form, which was confirmed by DFT-B3LYP calculation in gas phase. The infrared frequencies were also calculated and the comparison with the subtracted and deconvoluted spectrum of the in-solution complex also pointed to the presence of the trans diasteroisomer.

A aromaticidade tem sido exaustivamente discutida e continua sendo um tema misterioso. Nesse trabalho é proposto um novo índice de aromaticidade chamado índice baseado na densidade-degenerescência-deslocalização ou, simplesmente, D3BIA, numa tentativa de lançar nova introspecção sobre esse tema. Esse índice é baseado na teoria de átomos em moléculas (AIM) e, de certa forma, é suportado pela teoria dos spins acoplandos (SC). A aromaticidade diminui com o número de heteroátomos na molécula aromática, pois a degenerescência diminui, e diminui com o aumento do tamanho do anel do composto aromático porque desfavorece a sobreposição dos estados monoeletrônicos. A relação entre planaridade do anel, sua densidade eletrônica e aromaticidade é também observada. A interação atrativa da ressonância de 6 elétrons pi no diânion ciclobutadieno compensa sua interação repulsiva carbono-carbono enquanto no seu parente dicatiônico a ressonância de 2 elétrons pi é insuficiente para contrabalancear sua interação repulsiva e adota uma estrutura não-plana.

Aromaticity has been exhaustedly discussed for several years and it remains as a misterious issue. In this work it is proposed a new index of aromaticity named density, degeneracy and delocalization-based index of aromaticity or simply D3BIA in an attempt to cast new insight and perspective over this theme. This index is based on AIM (atoms in molecules) theory and it is somewhat supported by SC (spin-coupled) theory. Aromaticity decreases as the number of heteroatoms in the aromatic molecule increases since degeneracy decreases and it decreases as the ring size of an aromatic compound increases because it disfavors overlap of single-electron states. The relation between planar structures, electron density and aromaticity is also observed. The attractive interaction of 6pi-electron resonance in cyclobutadiene dianion compensate its carbon-to-carbon repulsive interaction while in its dicationic parent the 2pi-electron resonance is insufficient to counterbalance its carbon-to-carbon repulsive interaction and it adopts a puckered structure.

Aromas and fragrances can be obtained through the microbial oxidation of monoterpenes. Many microorganisms can be used to carry out extremely specific conversions using substrates of low commercial value. However, for many species, these substrates are highly toxic, consequently inhibiting their metabolism. In this work, the conversion ability of Aspergillus niger IOC-3913 for terpenic compounds was examined. This species was preselected because of its high resistance to toxic monoterpenic substrates. Though it has been grown in media containing R-limonene (one of the cheapest monoterpenic hydrocarbons, which is widely available on the market), the species has not shown the ability to metabolize it, since biotransformation products were not detected in high resolution gas chromatography analyses. For this reason, other monoterpenes (alpha-pinene, beta-pinene and camphor) were used as substrates. These compounds were shown to be metabolized by the selected strain, producing oxidized compounds. Four reaction systems were used: a) biotransformation in a liquid medium with cells in growth b) with pre-grown cultures c) with cells immobilized in a synthetic polymer network and d) in a solid medium to which the substrate was added via the gas phase. The main biotransformation products were found in all the reaction systems, although the adoption of previously cultivated cells seemed to favor biotransformation. Cell immobilization seemed to be a feasible strategy for alleviating the toxic effect of the substrate. Through mass spectrometry it was possible to identify verbenone and alpha-terpineol as the biotransformation products of alpha-pinene and beta-pinene, respectively. The structures of the other oxidation products are described.

The compound R-(+)limonene is available and cheap than its oxidized products. Consequently, the selective oxidation of R(+)limonene has attracted attention as a promising process for the production of compounds with a higher market value, such as cis/trans-1,2-limoneneoxide, cis/trans-carveol and/or carvone. One of the these processes, described in the recent literature, is submission of R-(+)limonene to an oxidation reaction catalyzed by neutral or cationic Metal(Salen) complexes, in the presence of effective terminal oxidants such as NaOCl or PhIO. These reactions are commonly carried out in organic solvents (dichromethane, ethyl acetate, acetonitrile or acetone). Thus, the main objective of the present work was to study the effect of several factors (type of oxidant, catalyst, solvent and time) on reaction selectivity for the high-priced compounds referred to above. For this purposes, experimental statistical multivariate analysis was used in conjunction with a complete experimental design. From the results it was observed that for the three targeted products (1,2-limoneneoxide, carveol or carvone) some factors, including the nature of the terminal oxidant and the catalyst, were significant for product selectivity (with a confidence level of 95%). Therefore, this statistical analysis proved to be suitable for choosing of the best reaction conditions for a specific desired product.