J.H.Z. dos Santos

Molecular survey of trichothecene genotypes of Fusarium graminearum species complex from barley in Southern Brazil

Fusarium head blight is a disease of primary concern to small-grain cereals of Brazil, including barley. Its main causal agent, Fusarium graminearum species complex (Fg complex)¸ is able to produce mycotoxins, especially deoxynivalenol (DON) and nivalenol (NIV), that usually contaminate grain. Strains that produce DON may also produce its acetylated derivatives: 3-acetyl-DON (3-ADON) and 15-acetyl-DON (15-ADON). Ninety two isolates were obtained from samplings of barley grain during three years (2007, 2008 and 2009) from several fields in both southern and northern production regions of Rio Grande do Sul state, Brazil. These isolates were examined for polymerase chain-reaction-based (PCR) trichothecene genotype based on the amplification of portions of Tri3 and Tri12. There was no effect of year or region on the proportion of trichothecene genotypes. Overall, 66% of the strains (61/92) were 15-ADON, 4.4% (4/92) were 3-ADON and 29.3% (27/92) were NIV. The overall NIV/DON ratio estimated (0.41) was five times higher than that found in previous studies with strains from wheat grown in the same region. Species identification of nine strains representing the trichothecene genotypes, based on comparisons of DNA sequences of portions of the PHO, RED and URA genes with sequences from curated reference isolates of Fusarium from GenBank, revealed that they belong to F. graminearum sensu stricto (four 15-ADON and one 3-ADON strain), F. meridionale (three NIV strains) and F. austroamericanum (one 3-ADON strain). These results add to the current regional knowledge of trichothecene genotypes and species within the Fg complex affecting barley in the region.

Determination of metals by total reflection X-ray fluorescence and evaluation of toxicity of a river impacted by coal mining in the south of Brazil

Metal (Fe, Mn, Zn, Ni, Cd, and Pb) concentrations in the region of Criciuma (Brazil), a region impacted by coal mining, were determined in water and sediments using total reflection X-ray fluorescence (TXRF) spectroscopy. Samples were collected from the Mãe Luzia River (south Brazil) at five different stations, from the source down to the river mouth (Ararangua estuary). Water and sediment toxicity were also evaluated using bioassays with Daphnia magna as the bioindicator. The metal present in the highest concentrations both in water (1.3-11 mg L(-1)) and in sediments (34-142 mg L(-1)) was iron. Results suggest an influence of coal mining on the aquatic receptors, showing a clear relationship between metal content (mostly Fe) and ecotoxicity.

Characterization of Zirconocene Catalysts and of Polyethylenes Produced Using Them

Our work of the last two years concerning the use of zirconocene catalysts in the production of polyethylene (PE) is reviewed. In earlier studies, using Cp 2 ZrCl 2 , the metal loading capacity of different commercial silicas, namely Grace 948, 952 and 956 was determined by Rutherford backscattering spectrometry (RBS). The adsorption isotherms of Al from methylaluminoxane (MAO) and trimethylaluminium (TMA) cocatalysts were determined using the 27 Al(p,γ) 28 Si nuclear reaction at 1.6 MeV. In the present work we could determine the Al/Si ratio with the simultaneous induction of nuclear reactions with 27 Al and 28 Si using protons of 1.7 MeV. After replacing Cp 2 ZrCl 2 by (nBuCp) 2 ZrCl 2 , an exhaustive search of activation, grafting and polymerization conditions (monitored by RBS, infrared spectroscopy, differential scanning calorimetry, and gel permeation chromatography) allowed us to set an optimized protocol that yielded polyethylene with thermal, molecular weight and composition characteristics typical of high-density PE.

Ethylene (co)polymerization with supported-metallocenes prepared by the sol–gel method

Four supported metallocenes prepared by the sol‐gel method were tested by ethylene homopolymerization and in ethylene/1-hexene copolymerization. The effects of Al/Zr ratio, polymerization temperature and cocatalysts were evaluated. Catalyst A2, produced by TEA and MAO treatments showed the highest activity (180 £ 10 3 kg PE/mol Zr h 21 ) among the tested systems at Al/Zra 1000. A2 showed thermal stability on polymerization performed at a temperature as high as 1208C. All the systems exhibited activity in the presence of common alkylaluminum (TMA, TEA, TIBA). Comonomer effect was observed in the copolymerization of ethylene with 1-hexene, where the comonomer incorporation is about 7 mol%. SAXS measurements of the employed xerogel suggested a weakly branched polymeric texture. Metal content in the resulting polymers showed extremely low levels of Zr. q 2001 Elsevier Science Ltd. All rights reserved.

Supported metallocenes using inorganic–organic hybrid xerogels

Abstract Four metallocene catalysts were prepared using two indenyl-containing aerogels as supports, treated under different conditions (triethylaluminum (TEA), methylaluminoxane (MAO) and butyllithium). The catalysts were characterized by complementary spectroscopic techniques: ultraviolet–visible spectroscopy (UV–Vis), X-ray photoelectronic spectroscopy (XPS), matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy (MALDI-TOF-MS), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). The highest metal content (1.32 mmol Zr/g-cat.) was achieved in the case of xerogel treated with TEA prior to metallocene synthesis. After MAO leaching, such content is reduced to 0.82 mmol-Zr/g-cat., exhibiting the highest activity in ethylene polymerization among the four developed catalysts. A relationship between catalyst activity and binding energy of Zr 3d 5/2 core level could be evidenced. The most active catalyst system showed a better Zr distribution, being the catalyst grain covered by aluminum cocatalyst. Depth profile monitoring by XPS measurements showed that, in fact, MAO leaches the zirconocene low binding energy species, being deposited in the uttermost surface of the grains.

Analysis and characterization of real catalysts using ion beam analysis

Abstract The aim of this work is to present the potentialities of IBA techniques in the characterization of catalytic precursors, real catalysts, supports and products of catalyzed reactions of industrial interest. RBS was used in the study of photochemical reactions of metal carbonyls with triphenylphosphine in the presence of alumina in order to follow the metal loadings on the alumina surface as a function of the irradiation time. In the characterization of Zr metallocene catalysts with Al based cocatalysts supported on silica, both RBS and NRA were used. The first technique allowed the determination of the adsorption isotherms of incorporated Zr SiO 2 ratios as a function of the initial ratios in the solutions, for different kinds of commercial silica powders. Using the 27Al(p,γ)28Si nuclear reaction, the Al SiO 2 incorporated ratios were obtained as a function of the initial ratios in the solutions of two different cocatalysts. IBA techniques were also used in the study of polymerization reactions and in the characterization of the polymers produced by reactions which used V based catalysts. From the RBS spectra the stoichiometry of the resulting polymers, their degree of contamination with the catalysts, as well as the metal catalyst distribution profile in industrially produced polymer pellets were determined. In the environmental protection field the synthesis steps of W, Pd and alumina based automobile exhaust converters were successfully followed by RBS. This technique was also very useful to determine the products of the thermal decomposition of bimetallic compounds derivative from diphenylphosphineferrocene (dppf). Finally, RBS played a key role in the confirmation of the stoichiometry of cationic nickel (II) complexes synthesized either chemically or electrochemically.

Sol–gel hybrid films based on organosilane and montmorillonite for corrosion inhibition of AA2024

The present work reports the production of films on AA2024-T3 composed of vinyltrimethoxysilane (VTMS)/tetraethylorthosilicate (TEOS) with incorporation of montmorillonite (sodium montmorillonite and montmorillonite modified with quaternary ammonium salt, abbreviated Na and 30B, respectively), generated by the sol-gel process. According to FT-IR analyses the incorporation of montmorillonite does not affect silica network. Electrochemical characterization was performed by electrochemical impedance spectroscopy measurement in 0.05 mol L(-1) NaCl solution. Results indicate that montmorillonite incorporation improves the corrosion protection compared to the non-modified system. Scanning electron microscopy micrographs reveal that high concentrations of montmorillonite provide agglomerations on the metallic surface, which is in detriment of the anticorrosive performance. The VTMS/TEOS/30B films with the lowest concentration (22 mg L(-1)) of embedded clay provide the highest corrosion protection.

Residual metal content in ethylene-propylene-diene monomers synthesized using vanadium- and zirconocene-based catalysts

Ethylene-propylene-diene monomer (EPDM) terpolymers were prepared using either vanadium (VOCl3/Al2Et3Cl3) or zirconocene (Et(Ind)2ZrCl2/MAO) catalyst systems. Residual metal contents in EPDM films were determined by Rutherford backscattering spectrometry. Metallocene catalyst systems exhibited a higher activity, producing EPDM with lower molecular weight and narrower molecular weight distribution. The highest activity guaranteed lower residual metal content (Zr/C = 10−5) than in the case of EPDM produced by VOCl3/Al2Et3Cl3 (V/C = 10−4). Subsequent steps of dissolution of the polymer and its reprecipitation were seen to reduce the metal contents in both metal systems. Concerning the cocatalyst retention, despite initial use of a very high amount of methylaluminoxane/metallocene (Al/Zr = 3000) in the reactor, only about 4% of this initial concentration remained in the polymer. On the other hand, in the case of vanadium-based catalyst, almost all Al present in the initial conditions (≃8.3) remained in the polymer. In both cases, the residual Al/M ratio was close to the value generally proposed for the generation/stabilization of the active species. In the case of vanadium systems, a test in the synthesis of ethylene propylene rubbers indicated that the absence of diene in the polymer structure leads to a reduction in the residual vanadium content, indicating that the diene double bond might be responsible for partially vanadium coordination.

A theoretical and experimental study about the effect of different organosilanes on immobilization of (nBuCp)2ZrCl2 on pre-treated SiO2

Abstract This work presents the results of theoretical and experimental characterization of supported ( n BuCp) 2 ZrCl 2 on organosilanes pre-treated SiO 2 . Several possibilities are analyzed and considered as an attempt to explain the observed zirconocene loadings, catalyst performance in ethylene polymerization and resulting polymer properties of these supported zirconocenes. The effect of silica pre-treatment with Ph 3 SiCl, Me 3 SiCl and Me 2 HSiCl on the immobilization of ( n BuCp) 2 ZrCl 2 was modeled. The main considered aspects were the role of the surface concentration of the organosilanes, the presence or absence of residual chlorine and the possibility of interactions between the organosilanes and the zirconocene. All these facts might afford different surface species at the impregnation step prior to the MAO activation during the polymerization reaction.

Fusarium species and fumonisins associated with maize kernels produced in Rio Grande do Sul State for the 2008/09 and 2009/10 growing seasons

Ear rots caused by Fusarium spp. are among the main fungal diseases that contribute to poor quality and the contamination of maize grains with mycotoxins. This study aimed to determine the visual incidence of fungal-damaged kernels (FDKs), the incidence of two main Gibberella (a teleomorph of Fusarium) complexes (G. fujikuroi and G. zeae) associated with maize using a seed health blotter test, and the fumonisin levels, using high performance liquid chromatography, in samples of maize grains grown across 23 municipalities during the 2008/09 and 2009/10 growing seasons. Additionally, 104 strains that were representative of all of the analysed samples were identified to species using PCR assays. The mean FDK was seven per cent, and only six of the samples had levels greater than six per cent. Fusarium spp. of the G. fujikuroi complex were present in 96% of the samples, and G. zeae was present in 18% of the samples (5/27). The mean incidence of G. fujikuroi was 58%, and the incidence of G. zeae varied from 2 to 6%. FB1 was found in 58.6%, FB2 in 37.9%, and both toxins in 37.9% of the samples. The FB1 and FB2 levels were below the quantification limits for 41.3% of the samples, and the mean FB1 levels (0.66 μg/g) were higher than the mean FB2 levels (0.42 μg/g). The PCR identification separated the 104 isolates into three of the G. fujikuroi complex: F. verticillioides (76%), F. subglutinans (4%) and F. proliferatum (2%); and G. zeae (anamorph = F. graminearum) (18%). Our results confirmed the dominance of F. verticillioides, similar to other regions of Brazil, but they differed due to the relatively higher incidence of F. graminearum. Total fumonisin levels were below the maximum limit determined by current Brazilian regulations.