Structural and chemical evolution of Au-silica core-shell nanoparticles during 20 keV helium ion irradiation: a comparison between experiment and simulation

Au-silica core–shell nanoparticles have been irradiated with 20 keV He⁺ ions up to a maximum fluence of 4.7 × 10¹⁷ ions/cm². The nanoscale structural and crystallographic evolution induced by He⁺ ion irradiation was followed at various stages using Transmission Electron Microscopy (TEM). During irradiation satellite Au clusters are formed around the main Au core, which remained crystalline even after the maximum He⁺ ion fluence. The spherical silica shell deformed into a hemisphere due to He⁺ ion irradiation. Three dimensional Monte-Carlo simulations, based on the binary collision approximation, have been performed on stacked infinite layers and an individual particle. The stacked layers results show that the He⁺ beam interacts with most of the nanoparticle and Au migrates in the direction of beam incidence agreeing with experimental findings. The individual particle results match the experiment in terms of the volume which is sputtered away however additional mechanisms, not included in the simulations, are present in the experiment during the satellite formation and silica shell deformation. These results show the ability for 20 keV He⁺ ions to be used for the modification of nanostructures. Furthermore, these results contribute to a quantitative understanding of the dynamic evolution of materials observed using microscopy techniques based on He⁺ ions.

IUPAC Collaborative Trial Study of a Method To Detect Genetically Modified Soy Beans and Maize in Dried Powder

This paper presents results of a collaborative trial study (IUPAC project No. 650/93/97) involving 29 laboratories in 13 countries applying a method for detecting genetically modified organisms (GMOs) in food. The method is based on using the polymerase chain reaction to determine the 35S promoter and the NOS terminator for detection of GMOs. Reference materials were produced that were derived from genetically modified soy beans and maize. Correct identification of samples containing 2% GMOs is achievable for both soy beans and maize. For samples containing 0.5% genetically modified soy beans, analysis of the 35S promoter resulted also in a 100% correct classification. However, 3 false-negative results (out of 105 samples analyzed) were reported for analysis of the NOS terminator, which is due to the lower sensitivity of this method. Because of the bigger genomic DNA of maize, the probability of encountering false-negative results for samples containing 0.5% GMOs is greater for maize than for soy beans. For blank samples (0% GMO), only 2 false-positive results for soy beans and one for maize were reported. These results appeared as very weak signals and were most probably due to contamination of laboratory equipment.

High-resolution high-sensitivity elemental imaging by secondary ion mass spectrometry: from traditional 2D and 3D imaging to correlative microscopy

Secondary ion mass spectrometry (SIMS) constitutes an extremely sensitive technique for imaging surfaces in 2D and 3D. Apart from its excellent sensitivity and high lateral resolution (50 nm on state-of-the-art SIMS instruments), advantages of SIMS include high dynamic range and the ability to differentiate between isotopes. This paper first reviews the underlying principles of SIMS as well as the performance and applications of 2D and 3D SIMS elemental imaging. The prospects for further improving the capabilities of SIMS imaging are discussed. The lateral resolution in SIMS imaging when using the microprobe mode is limited by (i) the ion probe size, which is dependent on the brightness of the primary ion source, the quality of the optics of the primary ion column and the electric fields in the near sample region used to extract secondary ions; (ii) the sensitivity of the analysis as a reasonable secondary ion signal, which must be detected from very tiny voxel sizes and thus from a very limited number of sputtered atoms; and (iii) the physical dimensions of the collision cascade determining the origin of the sputtered ions with respect to the impact site of the incident primary ion probe. One interesting prospect is the use of SIMS-based correlative microscopy. In this approach SIMS is combined with various high-resolution microscopy techniques, so that elemental/chemical information at the highest sensitivity can be obtained with SIMS, while excellent spatial resolution is provided by overlaying the SIMS images with high-resolution images obtained by these microscopy techniques. Examples of this approach are given by presenting in situ combinations of SIMS with transmission electron microscopy (TEM), helium ion microscopy (HIM) and scanning probe microscopy (SPM).

Identification of a novel moth sex pheromone inEriocrania cicatricella (Zett.) (Lepidoptera: Eriocraniidae) and its phylogenetic implications

Extracts from different body parts of adult femaleEriocrania cicatricella (Zett.) were tested for electrophysiological activity on conspecific male antennae. Extracts from the Vth abdominal segment, containing a pair of exocrine glands, elicited the largest electroantennographic response when compared to extracts of other body parts. Female extracts were analyzed by gas chromatography with simultaneous flame ionization and electroantennographic detection (EAD). The EAD active peaks were identified as (Z)-4-hepten-2-one, (2R)-heptane-2-ol, and (2R)-(Z)-4-hepten-2-ol by coinjection on a gas chromatography and by comparison of mass spectra with those of synthetic standards. In field tests, a blend of these three pheromone components was highly attractive to conspecific males, and a subtractive assay confirmed that the unsaturated alcohol is the major pheromone component, whereas no definite behavioral activity could be assigned to the ketone or the saturated alcohol. A bait containing the two alcohols withS-configuration was attractive to maleE. sparrmannella (Bosc), whereas no males ofE. cicatricella were found in these traps. The sex pheromone compounds inE. cicatricella are chemically similar to pheromones reported in Trichoptera and they are produced in homologous glands.

Novel type of sex pheromone structure identified fromStigmella malella (Stainton) (Lepidoptera: Nepticulidae)

Short-chain unsaturated chiral methyl carbinols are identified as a new class of lepidopteran pheromone components. The natural female-produced pheromone of the banded apple pigmyStigmella malella (=Nepticula malella) (Stainton) (Lepidoptera: Nepticulidae) was identified to be a mixture of (S)-(E)-6,8-nonadien-2-ol and (S)-(Z)-6,8-nonadien-2-ol. For monitoring traps, a 10:3E:Z blend at 100-1000 µg is recommended. It is suggested that pheromones with similar structures may be specific to Nepticulidae and other related microlepidopteran families.

Pheromone specificity inEriocrania semipurpurella (Stephens) andE. sangii (Wood) (Lepidoptera: Eriocraniidae) based on chirality of semiochemicals

The fifth abdominal segment of femaleEriocrania semipurpurella (Stephens) andE. sangii (Wood) contains a pair of exocrine glands. Hexane extracts of this segment were prepared from both species and analyzed by gas chromatography with simultaneous flame ionization and electroantennographic detection (EAD). For both species, the EAD active peaks were identified as nonan-2-one, (Z)-6-nonen-2-one, and (Z)-6-nonen-2-ol by means of mass spectrometry and comparison of retention indices with those of synthetic standards. Enantiomeric separation of chiral alcohols from the female extracts was achieved by gas chromatographic analysis on a cyclodextrin column. InE. semipurpurella, a mixture of (2S,6Z)-nonen-2-ol and (2R,6Z)-nonen-2-ol (2: I) was found, whereas inE. sangii (2S,6Z)-nonen-2-ol was the predominant enantiomer and only traces of theR enantiomer were indicated by the antennal response. In field tests, a blend of the three compounds was not attractive to conspecific males. A subtractive assay showed that the alcohol in various enantiomeric mixtures was the only attractive compound, whereas addition of (Z)-6-nonen-2-one to the alcohol completely inhibited the attraction of both species. A trapping experiment including a wide range of ratios between theR andS enantiomers showed that baits containing 95-100% of theS enantiomer were attractive to maleE. sangii, whereas males ofE. semipurpurella were attracted to all tested ratios of the enantiomers. However, the response profiles of maleE. semipurpurella differed between populations from southern Sweden, south Finland, and the Kola Peninsula in Russia. In south Sweden males were maximally attracted to a racemic mixture of the alcohols. At the Kola PeninsulaE. semipurpurella was attracted to baits containing 95-100% of theR enantiomer. In south Finland all tested ratios between 0 and 100%R enantiomer trappedE. semipurpurella, but the trap catches appeared to be bimodally distributed with peaks around 15 and 70%R enantiomer. The trapping results suggest the existence of pheromone races or sibling species among the specimens identified asE. semipurpurella.

Identification and synthesis of new bicyclic acetals from the mountain pine beetle, Dendroctonus ponderosae Hopkins (Col.: Scol.)

Head-space volatiles obtained from male mountain pine beetles, Dendroctonus ponderosae, were analyzed by coupled GC-MS and chiral gas chromatography. 5-Ethyl-7-methyl-6,8-dioxabicyclo[3.2.1]octane (6) was found as a new naturally occurring isomer of brevicomin (1). In addition, several stereoisomers of 7-ethyl-5-methyl-6,8-dioxabicyclo[3.2.1]octan-2-ol (11) and 1-(5-methyl-6,8-dioxabicyclo[3.2.1]octyl)ethanol (12) could be identified. Relative and absolute configurations of the compounds were determined by unambiguous syntheses, which are described.

Pheromonal Production of and Response to Optically Active Epoxydienes in Some Geometrid Moths (Lepidoptera: Geometridae)

In pheromone extracts of calling female Chiasma clathrata L. (Lepidoptera: Geometridae), a defoliator pest of alfalfa, (Z,Z,Z)-3,6,9-heptadecatriene and (Z,Z)-6,9-cis-3,4-epoxyheptadecadiene was identified. Chiral gas chromatography using a modified cyclodextrin and synthetic reference samples proved the natural epoxide to show (3R, 4S)-configuration. In field trapping tests, only the pure (3R, 4S)-enantiom er of the epoxide attracted males. The addition of the triene component was synergistic. Males of the sympatric species Tephrina arenacearia Hbn. (Lepidoptera: Geometridae) were caught only in traps with baits containing the (3S, 4R)-enantiomer [together with a previously described minor component, (Z,Z)-3,9-cis- 6,7-epoxyheptadecadiene]. In trapping tests conducted in a different biotope, Abraxas grossulariata L. (Lepidoptera: Geometridae) males were attracted by the (3S, 4R)-enantiomer, whereas the (3R, 4S)-enantiomer attracted a close relative, Abraxas sylvata Scop. (Lepidoptera: Geometridae). The present results suggest that one of the key mechanisms responsible for pheromone specificity among both the two alfalfa geometrids and the two A braxas species in their respective biotops, may be the use of different enantiomers of the same polyenederived epoxide as a sex pheromone component. It is probable that this discrimination mechanism is widespread among moth species utilizing epoxide pheromone components

Luminol-enhanced chemiluminescence by Listeria monocytogenes: a test for rapid assessment of antimicrobial agents

Listeria monocytogenes produces chemiluminescence in brain heart infusion broth at 37 degrees C in the presence of carbonate ions and acetaldehyde. This phenomenon can be enhanced by the use of luminol rather than acetaldehyde. Furthermore, there is direct relationship between the extent of growth and the level of luminescence which culminates at the end of the exponential growth. This property was used to study the susceptibility of this bacterium to two antiseptics, cetrimonium bromide and chlorhexidine, and to two antibiotics, ampicillin and chloramphenicol. Inhibition of chemiluminescence was proportional to the antimicrobial agents' concentrations and was complete at their minimal inhibitory concentrations.

Pharmacokinetic profile of metaclazepam (Talis), a new 1.4-benzodiazepine. Influence of different dosage regimens on the pharmacokinetic profile of metaclazepam and its main metabolite under steady-state conditions

The pharmacokinetic parameters of the new 1.4-benzodiazepine metaclazepam (Talis) were investigated. In particular, the question of whether the drug and/or its main metabolite accumulates in the body under steady-state conditions was studied. Two dosage regimens were compared by a randomized two-way crossover design: a once-a-day dosing (15 mg metaclazepam in the evening, = A) versus a twice-a-day dosing (5 mg in the morning plus 10 mg in the evening, = B) over ten days in twelve healthy male volunteers. Plasma levels of metaclazepam and its major biotransformation product, N-desmethylmetaclazepam, were determined. Comparing the treatments, significant differences were found for Cmax, but not for AUC-3 and Tmax. These results are also valid for the comparison of days 1 and 10 of each treatment. Higher Cmax values for dosage regimen A were found but Tmax and Cl/F remained stable in both treatments taking into account that 12 hours after the first medication, another dosing took place in treatment B. Eight hours after application, plasma levels were markedly low, Cmax values after single-dosing were nearly twice as high as after multiple dosing. Therefore based on these pharmacokinetic findings, a second dosing seems to be necessary; the clinical relevance needs further investigation. It has been reported, in fact, that it is in general very difficult to demonstrate a correlation between blood levels and therapeutic effects for 1.4-benzodiazepines (1,2).

Comparison of the pharmacokinetic profile of metaclazepam in old and young volunteers

A single-centre, open, Phase I-study comparison of the pharmacokinetics of a single dose of metaclazepam 10 mg, a new 1,4-benzodiazepine has been done in 10 older and 20 younger volunteers. No important age-related effect was found on the kinetics of metaclazepam or its N-desmethyl derivative, the principal metabolite in man.