No abstract

This work reports the novel results obtained from an in situ kinetic study, which was conducted via 1 H NMR, of the palmitic acid esterification reaction with deuterated methanol in the presence of organocatalysts: p-sulfonic acid calix[6]arene, p-hydroxybenzenesulfonic acid and p-toluenesulfonic acid. The kinetic order of reaction relative to the catalyst concentration and the main thermodynamic properties, such as the activation energy (ΔE), entropy variation (ΔS), enthalpy variation (ΔH) and Gibbs free energy variation (ΔG), were obtained. The results indicated that p-sulfonic acid calix[6]arene was the most active organocatalyst in esterification reactions, regardless of temperature or catalyst concentration employed. Additionally, by performing the reactions in the presence of increasing amounts of water, it was found that p-sulfonic acid calix[n]arenes are more tolerant to water than the other catalysts investigated.This result, when combined with the kinetic and thermodynamic measurements, may explain their highest catalytic activity.

Recebido em 20/11/12; aceito em 15/2/13; publicado na web em 24/5/13A bioassay-guided fractionation of culture filtrates of the fungus Alternaria euphorbiicola, a pathogen of the weed Euphorbia heterophylla, led to the isolation of anhydromevalonolactone (1), tyrosol (2), (R)-(-)-mevalonolactone (3), and cycloglycylproline (4). When tested on the punctured leaves of the host plant, these compounds produced bleached lesions with dark brown margins at concentrations as low as 80 µM. When tested on the leaves of other relevant weeds, only cycloglycylproline showed selective activity against E. heterophylla. This is the first report on the isolation of phytotoxins from A. euphorbiicola and on the phytotoxicity of anhydromevalonolactone, (R)-(-)-mevalonolactone, and cycloglycylproline.Keywords: fungi; phytotoxin; wild poinsettia. INTRODUCTIONSurveys for fungal pathogens of wild poinsettia in Brazil and their evaluation as potential mycoherbicides for the management of this weed were initiated in the late 1980s. Among the fungi collected and studied, preliminary results indicate that Alternaria euphorbiicola Simmons & Engelhard holds great promise for herbicidal control. This fungus was found to cause severe inflorescence necrosis, foliage blight, and stem canker on Euphorbia heterophylla L. 1 Euphorbia heterophylla (wild poinsettia) is regarded as a major weed in many tropical and subtropical countries, being responsible for substantial agricultural losses in important crops, particularly soybeans and corn. 2 During early investigation, when A. euphorbiicola was evaluated as a putative mycoherbicide, it was observed that the application of fungal spore suspensions on the host plant resulted in the production of widespread necrosis at time intervals ranging from few hours to 1-2 days after application. However, this was regarded as too short a period to allow for the occurrence of the whole process of spore germination, fungal penetration of tissues, colonization of plant organs, and development of symptoms due to plant infection. These observations led to the conjecture that A. euphorbiicola might produce phytotoxic metabolites capable of causing the first wave of damage to the host plant.It is well recognized that phytopathogenic fungi commonly produce toxins that may play a role in plant disease development, adversely affecting their infected hosts. 3,4 In this paper, we describe the isolation of anhydromevalonolactone (1), tyrosol (2), (R)-(-)-mevalonolactone (3), and cycloglycylproline (4) from A. euphorbiicola and their phytotoxic activity against the host plant wild poinsettia. EXPERIMENTAL Fungal strain, culture media, and growth conditionsAlternaria euphorbiicola was isolated from naturally infected E. heterophylla plants collected in Viçosa, Minas Gerais State, Brazil. The fungal species was identified by Prof. Robert Weingart Barreto, from the Department of Phytopathology, Universidade Federal de Viçosa (UFV), and stored at 5 °C in the culture collection Octávio de Almeida Drumond of UFV. The fungus was c...

The Iron Quadrangle has been one of the most important gold production regions in Brazil since the end of the seventeenth century. There, arsenic occurs in close association with sulfide-rich auriferous rocks. The most abundant sulfide minerals are pyrite and arsenopyrite, yet trace metal sulfides occur in subordinate phases as well. Historical mining activities have been responsible for the release of As and trace metals to both aquatic and terrestrial environments close to mining sites in the region. Therefore, this study was aimed to evaluate the distribution and mobility of As, Cd, Co, Cr, Cu, Ni, Pb, and Zn in streams in the southeast portion of the Iron Quadrangle between the municipalities of Ouro Preto and Mariana, the oldest Brazilian Au mining province. Total concentrations of some trace metals and arsenic in water were determined. The four-stage sequential extraction procedure proposed by the commission of the European Communities Bureau of Reference (BCR) was used to investigate the distribution of these elements in stream sediments. Arsenic concentration in water was > 10 μg L⁻¹ (maximum limit permitted by Brazilian environmental regulations for water destined for human consumption) at all sampling sites, varying between 36.7 and 68.3 μg L⁻¹. Sequential extraction in sediments showed high concentrations of As and trace metals associated with easily mobilized fractions.