Reginaldo B. dos Santos

Antimicrobial activity and potential use of monoterpenes as tropical fruits preservatives.

Banana, mamao e abacaxi sao as frutas tropicais mais consumidas no mundo, sendo o Brasil um dos principais produtores. Os fungos Colletotrichum musae, Colletotrichum gloeosporioides e Fusarium subglutinans f.sp ananas sao os principais causadores de doencas e perdas em pos-colheita de frutas. A proposta deste estudo foi avaliar a eficacia de cinco monoterpenos em inibir o crescimento micelial e a germinacao dos conidios destes tres fitopatogenos. Os monoterpenos citral, citronelal, L-carvona, isopulegol e a-pineno foram diluidos em etanol a concentracao final de 0,2 a 1%. Todos os monoterpenos testados inibiram os tres fungos estudados de maneira dose-dependente. Citral foi o mais efetivo dos oleos testados e apresentou uma potente atividade fungicida em concentracoes acima de 0,5%. Mais ainda, avaliacao in vivo com estas frutas tropicais demonstrou a eficacia de citral como inibidor do crescimento fungico. Estes resultados indicam o uso em potencial de citral como um pesticida natural no controle das doencas em pos-colheita de frutas tropicais.Banana, papaya and pineapple are the most consumed tropical fruits in the world, being Brazil one of the main producers. Fungi Colletotrichum musae, Colletotrichum gloeosporioides and Fusarium subglutinans f.sp. ananas cause severe post harvest diseases and losses in fruits quality. The aim of this work was to evaluate the effectiveness of five monoterpenes to inhibit the mycelial growth and conidia germination of these three phytopathogens. The monoterpenes citral, citronellal, L-carvone, isopullegol and a-pinene were diluted in ethanol to final concentrations from 0.2 to 1%. All monoterpenes were found to inhibit the growth of the three studies fungi in a dose-dependent manner. Citral was the most effective of the oils tested and showed potent fungicidal activity at concentrations above 0.5%. Also, in vivo evaluation with these tropical fruits demonstrated the efficiency of citral to inhibit fungal growth. These results indicate the potential use of citral as a natural pesticide control of post-harvest fruit diseases.

A convenient deoxygenation of α,β-epoxy ketones to enones

Abstract A new and efficient methodology for the deoxygenation of α,β-epoxy ketones to enones has been developed, using aminoiminomethanesulfinic acid (thiourea dioxide) as the reducing agent under phase transfer conditions. The epoxides of mesityl oxide, isophorone, (−)-carvone, (+)-6-methyl-carvone, (+)-6-ethyl-carvone and (−)-myrtenal, were converted into their respectives enones in good to excellent yields.

NMR property calculations and experimental study of the 1,6-epoxycarvone and α-epoxypinene: a comparison of models

This work aims at using theoretical calculations of shielding tensors (σ) through different methods [gauge‐independent atomic orbital (GIAO), continuous set of gauge transformations (CSGT) and individual gauges for atoms in molecules (IGAIM)] and spin‐spin coupling constants J using GIAO method to compare these methods and to corroborate the data obtained with the assignment of all of 1H and 13C NMR signals and the relative stereochemistry of the 1,6‐epoxycarvone and the α‐epoxypinene. All the 1H and 13C NMR signals were assigned unequivocally. The stereochemistry for the epoxides is trans and the B3LYP theory level with CSGT and IGAIM methods is the best choice to evaluate theoretical chemical shifts for compounds studied. Copyright

Stereochemistry of cyclopentane derivatives from (2,3)J(CH) dependence on dihedral angle (theta H--C--C--X).

The 2, 3JCH dependence on dihedral angle (θ HCCX) for cyclopentane derivatives was investigated. We observed that the combined use of experimentally obtained 2, 3JCH values and the theoretically determined dihedral angles between the corresponding nuclei can be used to infer the relative stereochemistry of the ring substituents in cyclopentane derivatives. There is a good correlation between the magnitude of 3JCH and the dihedral angle between the hydrogen and the coupled carbon (R2 = 0.88). Copyright

1H and 13C NMR spectral data of bioactive cage-like polycyclic compounds

Bioactive cage‐like polycyclic compounds have attracted the attention of several research groups because of their unique appearance and their biological activities. Their structures were established on the basis of 1H NMR and 13C NMR spectroscopic data. The 1H and 13C signal assignments and most homonuclear hydrogen coupling constants were assigned by use of techniques such as 1D 1H and 13C NMR and 2D gCOSY, non‐edited gHSQC and gHMBC. The gNOESY experiments proved the endo‐stereochemistry. Copyright

Análise do teor e da qualidade dos lipídeos presentes em sementes de oleaginosas por rmn de baixo campo

To choose among the variety of oleaginous plants for biodiesel production, the oil content of several matrices was determined through different low-field 1H nuclear magnetic resonance (NMR) experiments with varied pulse sequences, namely single-pulse, spin-echo, CPMG, and CWFP. The experiments that involved the first three sequences showed high correlation with each other and with the solvent extraction method. The quality of the vegetable oils was also evaluated on the basis of the existing correlation between the T2 values of the oils and their properties, such as viscosity, iodine index, and cetane index. These analyses were performed using HCA and PCA chemometric tools. The results were sufficiently significant to allow separation of the oleaginous matrices according to their quality. Thus, the low-field 1H NMR technique was confirmed as an important tool to aid in the selection of oleaginous matrices for biodiesel production.

A New, Simple and Efficient Method of Steglich Esterification of Juglone with Long-Chain Fatty Acids: Synthesis of a New Class of Non-Polymeric Wax Deposition Inhibitors for Crude Oil

A esterificacao direta de naftoquinonas mostrou-se uma tarefa dificil. Metodologias mais comuns envolvem a aplicacao de cloretos de acila em piridina ou anidridos, entretanto, quando acidos de cadeia longa sao utilizados tais metodologias se mostram ineficientes devido aos baixos rendimentos obtidos. Apresentamos uma nova sintese de esteres de cadeia longa de juglona baseado na esterificacao de Steglich utilizando um acido de Lewis barato como cocatalisador. Rendimentos obtidos sao consideravelmente maiores do que os reportados previamente. Quimica computacional foi utilizada para avaliar os efeitos do CeCl3 como cocatalisador. Os compostos preparados foram testados como inibidores de deposicao de parafinas em petroleo. Ester palmitico da juglona foi capaz de reduzir 4 oC na temperatura de inicio de aparecimento de cristais (WAT) do oleo estudado, representando uma reducao de 1,5% m/m de parafinas normais precipitadas. Direct esterification on naphthoquinone presented itself as a hard task. Usual methodologies apply acyl chloride in pyridine or anhydrides but with long-chain esters this procedure proved to be ineffective because of the low yields obtained. We present a new synthesis of long-chain esters of juglone based on Steglich esterification using a cheap Lewis acid as cocatalyst. Yields obtained are considerably better than those found previously. Computational chemistry was used to evaluate the effects of CeCl 3 as cocatalyst. Prepared compounds were tested as wax deposition inhibitors in crude oil. Palmitic ester of juglone was able to lower 4 oC on the wax appearance temperature (WAT) of the studied oil, representing a reduction of precipitated normal paraffin of 1.5% m/m.

Unequivocal structural assignments of three cycloheptenoid intermediates for guaiane sesquiterpenes: an experimental and theoretical approach.

* Correspondence to: Valdemar Lacerda Jr., Departamento de Química, Centro de Ciências Exatas, Universidade Federal do Espírito Santo, Av. Fernando Ferrari 514, 29.075-910, Vitória, ES, Brazil. E-mail: valdemar.lacerda@ufes.br ** Correspondence to: Timothy J. Brocksom, Departamento de Química, Universidade Federal de São Carlos, 13.565-905, São Carlos, SP, Brazil. E-mail: brocksom@terra.com.br, www.lqbo.ufscar.br

Niobium(V) chloride as catalyst in Diels-Alder reaction of furan ring

According to the relevant literature, the Diels-Alder reaction of furan without a catalyst can last several weeks and shows a low yield due to the dienes low reactivity. The use of Lewis acid catalysts or high pressures is described as an effective method for improving the reaction yields. This paper describes our recent study on the use of niobium pentachloride as the catalyst in Diels-Alder reactions between furan and several reactive dienophiles, among which methyl acrylate showed good yields, especially at lower temperatures. Other dienophiles have shown lower yields because of problems such as byproduct formation and the high reversibility of the reaction.

Construção de uma célula de gás de baixo custo para análise no infravermelho

Infrared spectroscopy is a versatile technique used for qualitative and quantitative determination of all types of molecular species. As far as analysis of confined or flowing gases is concerned, different types of cell can be found in the market, but they are often very expensive. This study describes the construction of a very efficient gas cell with good reproducibility for qualitative infrared analysis of confined or flowing gases, using easily available and low-cost materials.