Insecticidal activity against Bemisia tabaci biotype B of peel essential oil of Citrus sinensis var. pear and Citrus aurantium cultivated in northeast Brazil

The fumigant action of peel essential oils of Citrus sinensis var. pear (pear orange = PO) and C. aurantium (bitter orange = BO) from the northeast of Brazil were evaluated against Bemisia tabaci biotype B and compared with eugenol as a positive control. The oil concentration in the PO at 8.5 microL/L of air caused 97% mortality, while the oil concentration of BO at 9.5 microL/L of air caused 99% mortality. However, the LC50 estimates for both oils (LC50 = 3.80 microL/L of air for PO and LC50 = 5.80 microL/L of air for BO) did not differ from each other, but they did when compared with eugenol (LC50 = 0.20 microL/L of air). Regarding their effects on oviposition, the Citrus oils showed concentration-response dependence, reducing the number of eggs as the concentration increased, which was not observed for eugenol. The minimum concentrations of the oils that caused a significant reduction in the egg lay were 3.5 and 7.0 microL/L of air for BO and PO, respectively. These results suggest that oils from PO and BO peels may be promising as models to develop new insecticides that might be applied into the integrated management of whiteflies.     

Shape resonances in slow electron scattering by aromatic molecules. I. Anthraquinone derivatives

A series of anthraquinone (C(14)O(2)H(8)) derivatives has been studied by means of electron capture negative ion mass spectrometry (ECNI-MS), photoelectron spectroscopy (PES), and AM1 quantum chemical calculations. Mean lifetimes of molecular negative ions M(-.) (MNI) have been measured. The mechanism of long-lived MNI formation in the epithermal energy region of incident electrons has been investigated. A simple model of a molecule (a spherical potential well with the repulsive centrifugal term) has been applied for the analysis of the energy dependence of cross sections at the first stage of the electron capture process. It has been shown that a temporary resonance of MNI at the energy approximately 0.5 eV corresponds to a shape resonance with lifetime 1-2.10(-13) s in the f-partial wave (l = 3) of the incident electron. The next resonant state of MNI at the energy approximately 1.7 eV has been associated with the electron excited Feshbach resonance (whose parent state is a triplet npi* transition). In all cases the initial electron state of the MNI relaxes into the ground state by means of a radiationless transition, and the final state of the MNI is a nuclear excited resonance with a lifetime measurable on the mass spectrometry timescale. Copyright 1999 John Wiley & Sons, Ltd.     

Green,lithium salt-free synthesis of 2-alkylated 1,4-benzenediols in hydroalcoholic media

Herein, we describe an efficient, green, and lithium salt-free synthesis of 2-substituted 1,4-benzenediol in water/ethanol as solvent and potassium carbonate as a base. Optimized reaction time, the required equivalent of base and the observed solvent effect are reported.     

Development of new polyolefin films with nanoclays for application in food packaging

Nanomaterials have been demonstrated to possess novel characteristics that can be applied in developing new packaging with better properties than packaging produced with micromaterials. Such developments include the production of packaging with improved barrier properties, which applied to the food industry will extend the shelf life of a food, thereby expanding its marketing potential. The present study entailed the optimization of experimental variables (pressure, temperature, processing time, feed position, etc.) involved in the elaboration of polypropylene and polyethylene films with nanoparticles, to obtain a film with good exfoliation, barrier and mechanical properties. SEM, TEM and XRD were also evaluated as tools for determining the degree of exfoliation of nanoparticles. Optimization of the technology involved in production of an exfoliated nanocompound is a complex process in which multiple variables and parameters are involved. The results of the study showed that the feed position of the nanoparticle in the double screw extruder is of vital importance in obtaining an exfoliated film. The maximum temperatures used in the extruder were 170 °C and 130 °C, for polypropylene and polyethylene respectively.     

New designs for MRI contrast agents

New designs for Magnetic Resonance Imaging contrast agents are presented. Essentially, they all are host–guest inclusion complexes between -cyclodextrins and polyazamacrocycles of gadolinium (III) ion. Substitutions have been made to the host to optimise the host–guest association. Molecular mechanics calculations have been performed, using the UFF force field for metals, to decide on the suitability of the substitutions, and to evaluate the host–guest energies of association. Interesting general conclusions have been obtained, concerning the improvement of Magnetic Resonance Imaging contrast agents; namely, a set of rational methodologies have been deduced to improve the association between the gadolinium (III) chelates and the cyclodextrins, and their efficiency is demonstrated with a large set of substituted complexes, opening new doors to increase the diagnostic capabilities of Magnetic Resonance Imaging.     

Synthesis of pure stereoisomers of benzo[b]thienyl dehydrophenylalanines by Suzuki cross-coupling. Preliminary studies of antimicrobial activity

Several benzo[b]thienyldehydrophenylalanines were synthesized from pure stereoisomers of the methyl ester of N-(tert-butoxycarbonyl)-β-bromodehydrophenylalanine as an extension of our previously reported method for the synthesis of dehydrotryptophan analogues to dehydrophenylalanine derivatives. The latter were obtained in high yields by N-deprotection and bromination of N,N-bis-(tert-butoxycarbonyl)-(Z)-dehydrophenylalanine using TFA and NBS. This was carried out in two steps or in a one pot procedure resulting in different E/Z ratios. These compounds were coupled under Suzuki cross-coupling conditions [Pd(PPh₃)₄, Na₂CO₃, DME/H₂O] with several boronic benzo[b]thienyl acids in good to high yields maintaining the stereochemistry of the starting materials. The best yields were obtained when the boronic acid was in position 7 of the benzo[b]thiophene and with the E isomer of the brominated dehydrophenylalanine. In some cases it was possible to increase the lower yields by changing the Pd source to PdCl₂(PPh₃)₂. A model dipeptide was prepared coupling a benzo[b]thienyldehydrophenylalanine with the methyl ester of alanine. Preliminary antimicrobial studies were performed with both isomers of one of the β, β-diaryldehydroalanines obtained. The results show that the compounds are selective and very active (very low MICs) against Gram positive bacteria (B. cereus and B. subtilis) the Z-isomer being more active. The compounds are also active against Candida albicans presenting similar MICs.     

Photoelectrochemical Properties of Sol-Gel Nb2O5 Films

Structural, optical, electro and photoelectrochemical properties of amorphous and crystalline sol-gel Nb₂O₅ coatings have been determined. The coatings are n-type semiconductor with indirect allowed transition and present an overall low quantum efficiency ( < 4%) for UV light to electric conversion. The photoconducting behavior of the coatings is discussed within the framework of the Gärtner and Södergren models. Improvement can be foreseen if Nb₂O₅ coatings can be made of 10–20 nm size nanoparticles.     

Low mass dimuon production in proton and ion induced interactions at the SPS

The low mass dimuon spectra collected in p-U collisions by the NA38 experiment significantly exceeds the total cross section expected from previous analysis, done by other experiments. The ‘excess’ events have a harder distribution than the muon pairs from and Dalitz decays, expected to dominate the mass window 0.4–0.65 GeV/. We conjecture that the excess events may be due to annihilations, negligible at low but made visible by the cut applied in the NA38 data. Taking this assumption to parametrise the p-U spectra, we proceed with the corresponding analysis of the S-Cu, S-U and Pb-Pb data, collected by the NA38 and NA50 experiments, comparing the measured low mass dimuon spectra with the ‘expected cocktail’. Received: 14 July 1999 / Revised version: 3 November 1999 / Published online: 27 January 2000     

Photon events with missing energy at \sqrt{s} =183 to 189 GeV

The production of single photons has been studied in the reaction at centre-of-mass energies of 183 GeV and 189 GeV. A previously published analysis of events with multi-photon final states accompanied by missing energy has been updated with 189 GeV data. The data were collected with the DELPHI detector and correspond to integrated luminosities of about 51 pb and 158 pb at the two energies. The number of light neutrino families is measured to be . The absence of an excess of events beyond that expected from Standard Model processes is used to set limits on new physics as described by supersymmetric and composite models. A limit on the gravitational scale is also determined. Received: 28 January 2000 / Revised version: 27 April 2000 / Published online: 26 July 2000