Fluorescence anisotropy using highly polarized emitting dyes confined inside BNNTs

Polarized fluorescence emission of nanoscale emitters has been extensively studied for applications such as bioimaging, displays, and optical communication. Extending the polarization properties in large assemblies of compact emitters is, however, challenging because of self-aggregation processes, which can induce depolarization effects, quenching, and cancellations of molecular dipoles. Here we use α-sexithiophene (6T) molecules confined inside boron nitride nanotubes (6T@BNNTs) to induce fluorescence anisotropy in a transparent host. The experiments first indicate that individual 6T@BNNTs exhibit a high polarization extinction ratio, up to 700, at room temperature. Using aberration-corrected HRTEM, we show that the fluorescence anisotropy is consistent with a general alignment of encapsulated 6T molecules along the nanotube axis. The molecular alignment is weakly influenced by the nanotube diameter, a phenomenon ascribed to stronger molecule-to-sidewall interactions compared to intermolecular interactions. By stretching a flexible thin film made of transparent polymers mixed with 6T@BNNTs, we induce a macroscopic fluorescence anisotropy within the film. This work demonstrates that the dyes@BNNT system can be used as an easy-to-handle platform to induce fluorescence anisotropy in photonic materials.

Patterns and drivers of genetic diversity and structure in the biological control parasitoid Habrobracon hebetor in Niger

When a promising natural enemy of a key pest exists locally, it is a common practice in biological control (BC) to rear and release it for supplementary control in the targeted agroecosystem even though significant knowledge gaps concerning pre/post release may still exist. Incorporating genetic information into BC research fills some of these gaps. Habrobracon hebetor, a parasitoid of many economically important moths that infest stored and field crops worldwide is commonly used, particularly against the millet head miner (MHM), a key pest of millet in Sahelian countries. To advance our knowledge on how H. hebetor that occurs naturally in open-field cropping systems and grain stores as well as being mass-produced and released for MHM control, performs in millet agroecosystems in Niger we evaluated its population genetics using two mitochondrial and 21 microsatellite markers. The field samples were genetically more diverse and displayed heterozygote excess. Very few field samples had faced significant recent demographic bottlenecks. The mating system (i.e. nonrandom mating with complementary sex determination) of this species may be the major driver of these findings rather than bottlenecks caused by the small number of individuals released and the scarcity of hosts during the longlasting dry season in Niger. H. hebetor population structure was represented by several small patches and genetically distinct individuals. Gene flow occurred at local and regional scales through human-mediated and natural short-distance dispersal. These findings highlight the importance of the mating system in the genetic diversity and structure of H. hebetor populations, and contribute to our understanding of its reported efficacy against MHM in pearl millet fields.

In vitro interaction and biocompatibility of titanate nanotubes with microglial cells

Titanate nanotubes (TiONts) are promising agents for biomedical applications. Microglial activation and associated oxidative burst are major challenges in drug delivery applications across the brain. Here, TiONts were designed for drug delivery systems by functionalizing them with (3-aminopropyl) triethoxysilane (APTES), their interactions and biocompatibility were studied in vitro using murine microglial BV-2 cells. TiONts-APTES exposure resulted in increased ROS production and transient mitochondrial hyperpolarization. However, there was no indication of microglial proliferation in BV-2 cells as suggested by cell cycle analysis and morphology evaluation. The endocytosis as well as passive diffusion mediated TiONts-APTES internalization were proved by transmission electron microscopy (TEM) with and without amiloride, an endocytosis inhibiting agent. In addition, the TiONts-APTES exhibited good biocompatibility on microglial BV-2 cells as revealed by the plasma membrane integrity, lysosmal membrane integrity, morphology and viability analysis.

The formation of the smallest fullerene-like carbon cages on metal surfaces

The nucleation and growth of carbon on catalytically active metal surfaces is one of the most important techniques to produce nanomaterials such as graphene or nanotubes. Here it is shown by in situ electron microscopy that fullerene-like spherical clusters with diameters down to 0.4 nm and thus much smaller than C60 grow in a polymerized state on Co, Fe, or Ru surfaces. The cages appear on the surface of metallic islands in contact with graphene under heating to at least 650 °C and successively cooling to less than 500 °C. The formation of the small cages is explained by the segregation of carbon on a supersaturated metal, driven by kinetics. First principles energy calculations show that the clusters polymerize and can be attached to defects in graphene. Under compression, the polymerized cages appear in a crystalline structure.

Identification of 21 polymorphic microsatellites in the African parasitoid wasp, Psyttalia lounsburyi (Silvestri) (Hymenoptera: Braconidae)

We have developed 21 dinucleotide repeat microsatellite loci from African populations of Psyttalia lounsburyi (Silvestri) (Hymenoptera: Braconidae), a parasitoid wasp of the olive fruit fly, as part of a study assessing the role of introgression/hybridization in the success of a biological control introduction. We proposed suitable conditions for polymerase chain reaction multiplexing. All 21 loci were polymorphic with two to 21 alleles per locus within the Kenyan and South African populations tested. Most of them were successfully amplified in two other Psyttalia species.

Eleven polymorphic microsatellite markers for Oedaleus decorus (Orthoptera, Acrididae), an endangered grasshopper in Central Europe

We isolated and characterized 11 microsatellite loci in the grasshopper Oedaleus decorus (Orthoptera: Acrididae), an endangered species in Central Europe. Polymorphism was studied from two populations, one out of two populations known from Switzerland (n = 20 individuals) and one site from south of France (n = 20). The number of alleles and the expected heterozygosity ranged from five to 12 and from 0.559 to 0.898, respectively, in the Swiss population, and from 14 to 23 and from 0.895 to 0.974, respectively, in the French population. These microsatellite markers are suitable for further conservation genetic studies of O. decorus.

Evidence of correlation between catalyst particles and the single-wall carbon nanotube diameter: a first step towards chirality control

Controlling the structure of single-wall carbon nanotubes during their synthesis by chemical vapor deposition remains a challenging issue. Here, using a specific synthesis protocol and ex situ transmission electron microscopy, we perform a statistical analysis of the structure of the tubes and of the catalyst particles from which they grow. We discriminate two nucleation modes, corresponding to different nanotube-particle junctions, that occur independently of the particle size. With the support of tight binding calculations, we show that a direct control of the nanotube diameter by the particle can only be achieved under growth conditions close to thermodynamic equilibrium.

Growth of Multi Walled CNX Nanotubes: The Role of Synthesis Methods

Multi walled nitrogen doped nanotubes were synthesized using two different methods. The growth mechanism and nitrogen concentration of the nanotubes synthesized by both methods are discussed and studied. The morphology and nitrogen concentration of the nanotubes are seen to strongly depend on the synthesis methods. The results are based on detailed high resolution transmission electron microscopy (HRTEM) data coupled with electron energy loss spectroscopy (EELS).

Ostwald ripening in nanoalloys: when thermodynamics drives a size-dependent particle composition

Ostwald ripening has been broadly studied because it plays a determinant role in the evolution of cluster size during both chemical and physical synthesis of nanoparticles. This thermoactivated process causes large particles to grow, drawing material from the smaller particles, which shrink. However, this phenomenon becomes more complex when considering the coarsening of metallic alloy clusters. The present experimental and theoretical investigations show that the relative composition of CoPt nanoparticles can be strongly modified during high temperature annealing and displays a size-dependent behavior. This compositional change originates from the higher evaporation rate of Co atoms from the nanoparticles. More importantly, this effect is expected in all alloy clusters containing species with different mobilities.

Permanent Genetic Resources added to the Molecular Ecology Resources Database 1 February 2010-31 March 2010

This article documents the addition of 228 microsatellite marker loci to the Molecular Ecology Resources Database. Loci were developed for the following species: Anser cygnoides, Apodemus flavicollis, Athene noctua, Cercis canadensis, Glis glis, Gubernatrix cristata, Haliotis tuberculata, Helianthus maximiliani, Laricobius nigrinus, Laricobius rubidus, Neoheligmonella granjoni, Nephrops norvegicus, Oenanthe javanica, Paramuricea clavata, Pyrrhura orcesi and Samanea saman. These loci were cross-tested on the following species: Apodemus sylvaticus, Laricobius laticollis and Laricobius osakensis (a proposed new species currently being described).

Many-body effects in electronic bandgaps of carbon nanotubes measured by scanning tunnelling spectroscopy

Single-walled carbon nanotubes provide an ideal system for studying the properties of one-dimensional (1D) materials, where strong electron-electron interactions are expected. Optical measurements have recently reported the existence of excitons in semiconducting nanotubes, revealing the importance of many-body effects. Surprisingly, pioneering electronic structure calculations and scanning tunnelling spectroscopy (STS) experiments report the same gap values as optical experiments. Here, an experimental STS study of the bandgap of single-walled semiconducting nanotubes, demonstrates a continuous transition from the gap reduced by the screening resulting from the metal substrate to the intrinsic gap dominated by many-body interactions. These results provide a deeper knowledge of many-body interactions in these 1D systems and a better understanding of their electronic properties, which is a prerequisite for any application of nanotubes in the ultimate device miniaturization for molecular electronics, or spintronics.

Size and shape effects on the order-disorder phase transition in CoPt nanoparticles

Chemically ordered bimetallic nanoparticles are promising candidates for magnetic-storage applications. However, the use of sub-10 nm nanomagnets requires further study of possible size effects on their physical properties. Here, the effects of size and morphology on the order-disorder phase transition temperature of CoPt nanoparticles (T(C)(NP)) have been investigated experimentally, using transmission electron microscopy, and theoretically, with canonical Monte Carlo simulations. For 2.4-3-nm particles, T(C)(NP) is found to be 325-175 degrees C lower than the bulk material transition temperature, consistent with our Monte Carlo simulations. Furthermore, we establish that T(C)(NP) is also sensitive to the shape of the nanoparticles, because only one dimension of the particle (that is, in-plane size or thickness) smaller than 3 nm is sufficient to induce a considerable depression of T(C)(NP). This work emphasizes the necessity of taking into account the three-dimensional morphology of nano-objects to understand and control their structural properties.

Thelytokous parthenogenesis, male clonality and genetic caste determination in the little fire ant: new evidence and insights from the lab

Previous studies indicate that some populations of the little fire ant, Wasmannia auropunctata, display an unusual reproduction system polymorphism. Although some populations have a classical haplodiploid reproduction system, in other populations queens are produced by thelytokous parthenogenesis, males are produced by a male clonality system and workers are produced sexually. An atypical genetic caste determination system was also suggested. However, these conclusions were indirectly inferred from genetic studies on field population samples. Here we set up experimental laboratory nests that allow the control of the parental relationships between individuals. The queens heading those nests originated from either putatively clonal or sexual populations. We characterized the male, queen and worker offspring they produced at 12 microsatellite loci. Our results unambiguously confirm the unique reproduction system polymorphism mentioned above and that male clonality is strictly associated with thelytokous parthenogenesis. We also observed direct evidence of the rare production of sexual gynes and arrhenotokous males in clonal populations. Finally, we obtained evidence of a genetic basis for caste determination. The evolutionary significance of the reproduction system polymorphism and genetic caste determination as well as future research opportunities are discussed.

Laser-based diagnostics applied to the study of BN nanotubes synthesis

The boron nitride nanotubes (BNNTs) synthesis, using CO2-laser vaporization of a BN target under nitrogen gas, is investigated by UV-laser induced fluorescence (LIF) of the vapor phase and UV-Rayleigh scattering (RS) of the gas-suspended nanoparticles. The LIF signal from B atoms is mainly detected in the 1.5 mm-thick region above the BN target. It originates from a boron-rich vapor region confined near the hot boron droplet formed at the target surface. Then, recombination between hot boron and N2 gas occurs through a fast condensation process as revealed by both the depletion of B atoms from the vapor phase and the RS signal arising from the grown BN nanoparticles. Fluorescence spectra exhibit a strong peak at 250 nm due to boron fluorescence and mainly to nanoparticles Rayleigh scattering. A narrow peak is observed at 210 nm and a broader peak at 189 nm. These bands are tentatively assigned to fluorescence or photoluminescence (PL) from gaseous or solid BN species respectively since both gas and solid phases coexist in the plume due to the rapid cooling process. Two very weak bands occur at 308 nm and 350 nm. They are related to PL of defects bands from BN nanostructures on the basis of ex situ PL spectra of h-BN crystallites and multi-wall BNNTs. Detection of oxygen impurities is shown feasible through LIF from BO radical which is detected just above the BN target evaporated under vacuum pressure (approximately 1 mbar). An optical diagnostic strategy is demonstrated from these first in situ observations during BNNTs synthesis.

Extending the analysis of EELS spectrum-imaging data, from elemental to bond mapping in complex nanostructures

Multiple least squares fitting has been employed for long time in elemental electron energy-loss spectroscopy (EELS) analysis, in particular in biology, but with the hypothesis of a rather stable shape for the used core-loss signals. In the present case, we explore its use for identifying the variations in the edges' fine structures in complex boron nitride samples and in particular for mapping the bonding types of boron in such samples. Details about this improved procedure applied to data acquired in the spectrum-imaging mode are reported here.

Spectroscopic study of nitrogen doping of multi-walled carbon nanotubes

Combined spatially resolved electron-energy loss spectroscopy (EELS) and high resolution near-edge X-ray absorption fine structure (NEXAFS) spectroscopy have been used to investigate the nitrogen doping of multi-walled carbon nanotubes (N-MWNT). EELS indicates that most of the tubes are nitrogen-doped. NEXAFS spectroscopy reveals pyridine-like and nitrile N structures. High resolution NEXAFS experiments show that the main nitrogen concentration originates from a high amount of molecular N2 encapsulated into only a small quantity of tubes.

Purification of single-walled boron nitride nanotubes and boron nitride cages

Continuous laser vaporization of a BN target under N2 atmosphere is up to now the unique route to single-walled boron nitride nanotubes (BN-SWNTs). Although grams of product can be obtained by this technique, the raw material contains in addition to the BN-SWNTs, different by-products made of boron and nitrogen. Since these materials are undesirable for the studying of the intrinsic properties of the nanotubes, we have undertaken a purification process using chemical and physical methods to separate the different components. We show here that most impurities can be removed by successive cycles of washing, sonication, and centrifugation. Furthermore, the two different types of boron nitride nanostructures i.e., BN-SWNTs and BN-cages can be isolated. Efficiency of the separation was monitored by transmission electron microscopy (TEM) at the different steps of the process. Finally, we envisage the further purification of the nanotubes-enriched fraction by functionalizing the nanotubes in a non covalent manner by specific polymers as for carbon nanotubes and BN multi-walled nanotubes.

Population genetic structure of two ecologically distinct multimammate rats: the commensal Mastomys natalensis and the wild Mastomys erythroleucus in southeastern Senegal

Using the same set of microsatellite markers, we compared the population genetic structure of two Mastomys species, one being exclusively commensal in southeastern Senegal, and the other being continuously distributed outside villages in this region. Both species were sampled in the same landscape context and at the same spatial scale. According to the expectations based on the degree of habitat patchiness (which is higher for commensal populations in this rural area), genetic diversity was lower and genetic differentiation was higher in commensal populations of Mastomys natalensis than in wild populations of Mastomys erythroleucus. Contrasting estimates of effective dispersal and current migration rates corroborates previous data on differences in social structure between the two species. Isolation-by-distance analyses showed that human-mediated dispersal is not a major factor explaining the pattern of genetic differentiation for M. natalensis, and that gene flow is high and random between M. erythroleucus populations at the spatial scale considered.

Genetic structure of black rat populations in a rural plague focus in Madagascar

The genetic structure of reservoir populations is a key characteristic in understanding the persistence of infectious diseases in natural systems. In the Highlands of Madagascar, where plague has persisted since 1920, the black rat, Rattus rattus (L., 1758), is the sole species acting as a reservoir of the disease. Ecological surveys have shown a clear correlation between the locations of the plague-persistence area in Madagascar (above 800 m elevation) and the distribution area of one endemic plague vector, the flea Synopsyllus fonquerniei , which is found exclusively on rats living outdoors. This clear habitat segregation has led to the suggestion that R. rattus populations in the central highlands are divided into indoor- and outdoor-dwelling populations. Using eight microsatellite markers, we analysed the genetic structure of R. rattus populations living within a human plague focus in relation to habitat and geographic distance. We found that habitat by itself was not a structuring factor, unlike geographic distance. Nevertheless, the significant genotypic differentiation of R. rattus populations that was found at a fine spatial scale might relate to differences in population dynamics between rats in indoor and outdoor habitats.

Raman spectroscopy of single-wall boron nitride nanotubes

Single-wall boron nitride nanotubes samples synthesized by laser vaporization of a hexagonal BN target under a nitrogen atmosphere are studied by UV and visible Raman spectroscopy. We show that resonant conditions are necessary for investigating phonon modes of BNNTs. Raman excitation in the UV (229 nm) provides preresonant conditions, allowing the identification of the A1 tangential mode at 1370 cm(-1). This is 5 cm(-1) higher than the E(2g) mode in bulk h-BN. Ab initio calculations show that the lower frequency of bulk h-BN with respect to large diameter nanotubes and the single sheet of h-BN is related to a softening of the sp2 bonds in the bulk due to interlayer interaction.

Spatial evolutions of Co and Ni atoms during single-walled carbon nanotubes formation: measurements and modeling

Spatial investigations of nickel and cobalt atoms and of C2 and C3 radicals are performed by laser induced fluorescence (LIF) in a continuous CO2 laser-vaporization reactor during the synthesis of single-walled carbon nanotubes. The chemical composition of the gas vaporized from bimetallic Ni/Co catalysts-carbon targets is determined using a chemical kinetic model. In this model, the evolution of Ni and Co atoms is driven by kinetics of condensation/evaporation process of pure metal clusters. Metal-carbon clusters are assumed to form from soot particles (C80) and 128-atom metal clusters. Spatial profiles of Ni and Co atoms obtained by LIF are compared with the calculations to validate the modeling and to adjust the input data. The value of the initial molar fraction of carbon-metal mixture diluted in helium is determined through a parametric study. Good agreement is found between the measured and the calculated evolution of Ni for a molar fraction of the helium diluent ranging from 10 to 15%. To fit the spatial profile of Co, the activation energy is adjusted in the evaporation rate, changing the cobalt dimer bond energy. The latter is found to be largely uncertain; and three values are tested: 167, 208, and 230 kJ x mol(-1). From comparison, the activation energy is found to be 208 kJ x mol(-1). However, the C2 LIF profiles show that the depletion of C2 is accelerated when cobalt is present. The observed Co evolutions suggest that small Co-C clusters are easier and/or faster to form compared to Ni-C clusters.

Electron energy loss spectroscopy measurement of the optical gaps on individual boron nitride single-walled and multiwalled nanotubes

Spatially resolved electron energy loss spectroscopy experiments have been performed in an electron microscope on several individual boron nitride (BN) single-, double-, and triple-walled nanotubes, whose diameters and number of shells have been carefully measured. In the low-loss region (from 2 to 50 eV) the spectra have been analyzed within the framework of the continuum dielectric theory, leading to the conclusion of a weak influence of out-of-plane contribution to the dielectric response of the tubes. The gap has been measured to be independent of the nanotubes geometry, and close to the in-plane gap value of hexagonal BN (5.8+/-0.2 eV).

Optical transitions in single-wall boron nitride nanotubes

Optical transitions in single-wall boron nitride nanotubes are investigated by means of optical absorption spectroscopy. Three absorption lines are observed. Two of them (at 4.45 and 5.5 eV) result from the quantification involved by the rolling up of the hexagonal boron nitride (h-BN) sheet. The nature of these lines is discussed, and two interpretations are proposed. A comparison with single-wall carbon nanotubes leads one to interpret these lines as transitions between pairs of van Hove singularities in the one-dimensional density of states of boron nitride single-wall nanotubes. But the confinement energy due to the rolling up of the h-BN sheet cannot explain a gap width of the boron nitride nanotubes below the h-BN gap. The low energy line is then attributed to the existence of a Frenkel exciton with a binding energy in the 1 eV range.

Nucleation and growth of single-walled nanotubes: the role of metallic catalysts

We present a review of experimental and theoretical results on the nucleation and growth of single-walled nanotubes, with particular emphasis on the growth of nanotube bundles emerging from catalyst particles obtained from evaporation-based elaboration techniques. General results are first discussed. Experiments strongly suggest a root-growth process in which carbon, dissolved at high temperatures in catalytic particles, segregates at the surface at lower temperatures to form tube embryos and finally nanotubes through a nucleation and growth process. A theoretical analysis of the reasons carbon does not always form graphene sheets to wrap the particles suggests analogies with other surface or interface instabilities, in particular, with those found in epitaxial growth. In the second part, detailed experimental results for nickel-rare earth metal catalysts are presented. By using various electron microscopy techniques, it is shown that carbon and the rare earth metal co-segregate at the surface of the particle and form carbide platelets, providing nucleation sites for nanotubes growing in directions perpendicular to the surface. A simple theoretical model is then presented in which the role of the rare earth metal is just to transfer electrons from metal to carbon. The graphene sheet is shown to become unstable; pentagons and heptagons are favored, which can explain the occurrence of local curvatures and of tube embryos. Finally, a brief discussion of some recent atomistic models is given.

In-situ optical analysis of the gas phase during the formation of carbon nanotubes

A reactor has been developed at ONERA to investigate the gas phase during carbon nanotube formation by laser-induced fluorescence (LIF), Laser-induced incandescence (LII), coherent anti-Stokes Raman Scattering (CARS), and emission spectroscopy. Continuous vaporization is achieved with a continuous wave CO2 laser. Optimized conditions are used for single-walled nanotube growth, that is, a graphite target doped with 2 atom % Ni and 2 atom % Co, helium as buffer gas at a flow rate of 50 ml/s, and a pressure of 300 hPa. Temperature profiles are measured by CARS on H2, and soot images are obtained by LII in the hot carbonaceous flow. LIF and spontaneous emission of the C2 radical and Ni and Co atoms are presented. Spectral investigations are conducted at 3100 and 3200 K to have an optimized pair of excitation/detection wavelengths. Spatial investigations of the relative concentrations in the hot carbonaceous flow are performed up to 3500 K. The concentrations are measured as a function of target temperature. Two regimes of vaporization are observed. Vaporization is slow up to 3350 K and becomes much faster above this temperature. The fast regime in the 3350-3500 K range corresponds to the observed spatial extent of the metal vapors region. At 3500 K, the C2 profiles obtained with and without catalysts are very different as a result of carbon coalescence as well as carbon dissolution into the metal nanoparticles when these are present in the gas phase. The shape of the C2 profile can be related to nanotube formation and growth at a target temperature of 3500 K.

Interactions between verapamil and neutral and acidic liposomes: effects of the ionic strength

Patients with cancer often develop major electrolyte disorders, which are aggravated by radiation therapy and chemotherapy and by the concomitant impairment of the renal function and the development of drug resistance. In addition, tumour cells have membranes with more negative charges than normal eukaryotic cells. This study was designed to test the hypothesis that the ability of the Ca(2+) blocker verapamil to mediate the reversal of multidrug resistance (MDR) by interacting with the membrane phospholipids may be correlated with the ionic strength and membrane surface potential in resistant tumours. The permeation properties of verapamil, which is the best-known MDR-modulator, were therefore studied by quantifying its ability to induce the leakage of carboxyfluorescein through unilamellar liposomes containing various mole fractions of phosphatidic acid (x(EPA)=0, 0.1 and 0.3), at four different ionic strengths (I=0.052, 0.124, 0.204 and 0.318 M). The dye leakage induced by verapamil varied greatly with I, depending on x(EPA). The permeation process was a co-operative one (1.3<Hill coefficient<3.5) and the permeation doses inducing 50% dye leakage (PD(50)) ranged between 0.2 and 1.8 mM. A highly significant multiple correlation was found to exist between the variations of log(1/PD(50)) with those of 1/ radical I and x(EPA) (dlog(1/PD(50))/d(1/ radical I)=0.15+/-0.01, dlog(1/PD(50))/dx(EPA)=2.07+/-0.08, y-intercept=2.46+/-0.03, P<0.000001). Kinetic studies on the permeation process showed that it involved two steps. The apparent rate constants of the slow and fast kinetic steps, which were driven by electrostatic and hydrophobic interactions, respectively, increased with the verapamil concentrations, depending on x(EPA). The results provide evidence that in resistant tumours (high negative membrane surface potential), the MDR reversal by verapamil might be enhanced by favourable drug-membrane interactions in patients with severe hypo-electrolytic (Na(+) and K(+)) disorders, whereas the MDR reversal might be reduced by unfavourable drug-membrane interactions in patients with severe hyper-electrolytic (Ca(2+), Na(+) and K(+)) disorders.

Synthesis of highly nitrogen-doped multi-walled carbon nanotubes

We present a new synthesis route for nitrogen doped carbon nanotubes (CNx) based on the aerosol method. Tubes with a record high concentration of nitrogen (approximately 20 atom%) have been synthesized, confirmed by electron energy loss spectroscopy (EELS). A strong correlation between the N/C ratio and morphology of the tubes is observed and discussed.

Field evaporation behaviour in the gamma phase in Ti-Al during analysis in the tomographic atom probe

A Ti-48 at% Al alloy has been successfully investigated, using atom probe field ion microscopy and transmission electron microscopy. After a specific heat treatment, this alloy has a (alpha2 + gamma) lamellar microstructure. Using the tomographic atom probe (TAP), it has been possible to image the stacking of superlattice planes of gamma and to identify titanium as the highest evaporation field element. In addition, the influence of analysis site on atom probe measurements has been estimated for this phase. A TAP analysis has also made it possible to observe an extremely thin step along a gamma/gamma interface at a near atomic scale.

Root-growth mechanism for single-wall carbon nanotubes

The catalytic growth of single-wall carbon nanotubes is investigated by high-resolution transmission electron microscopy. The similarities between the samples synthesized from different techniques suggest a common growth mechanism based on a vapor-liquid-solid model. Quantum-molecular-dynamics simulations support a root growth mechanism where carbon atoms are incorporated into the tube base by a diffusion-segregation process.

Left ventricular mechanical efficiency in hypertensive patients with and without increased myocardial mass and with normal pump function

Left ventricular hypertrophy (LVH) is a physiologic process of adaptation of the heart to mechanical load increase. Despite depression of left ventricular contractile performance, mechanical efficiency and ventriculoarterial coupling are preserved in hypertensive patients with LVH. To assess the differences between patients with and without LVH, left ventricular contractile performance and the ventriculoarterial coupling were compared in two groups of hypertensive patients with similar body surface area and arterial pressures, and normal pump function: 30 patients with LVH (group 1) and 23 without LVH (group 2). Left ventricular angiography coupled with simultaneous recording of pressures with a micromanometer were used to determine end-systolic stress-to-volume ratio (ESSVR), end-systolic elastance (Ees), effective arterial elastance (Ea), external work (EW), and pressure-volume area (PVA). Myocardial contractile performance, assessed by Ees normalized by myocardial mass and by ESSVR, was lower in group I than in group 2 (1.23 +/- 0.28 v 1.89 +/- 0.48 mm Hg/mL/100 g, and 3.85 +/- 0.99 v 5.13 +/- 0.56 g/cm2/mL, respectively, both P < .001). Ventriculoarterial coupling evaluated through Ea/Ees ratio, and mechanical efficiency evaluated through EW/PVA ratio, were similar in the two groups (0.53 +/- 0.08 v 0.51 +/- 0.05, and 0.78 +/- 0.03 v 0.80 +/- 0.02, respectively, NS). In conclusion, this study shows that ventriculoarterial coupling and mechanical efficiency are comparable in hypertensive patients with and without LVH. These results suggest that in hypertensive patients, the matching between left ventricular performance and arterial load and the energy transfer are preserved either through left ventricular hypertrophy with moderate depression of myocardial contractile performance or through enhancement of myocardial contractile performance in patients with normal left ventricular mass.

Genetic diversity of the honeybee in Africa: microsatellite and mitochondrial data

A total of 738 colonies from 64 localities along the African continent have been analysed using the DraI RFLP of the COI-COII mitochondrial region. Mitochondrial DNA of African honeybees appears to be composed of three highly divergent lineages. The African lineage previously reported (named A) is present in almost all the localities except those from north-eastern Africa. In this area, two newly described lineages (called O and Y), putatively originating from the Near East, are observed in high proportion. This suggests an important differentiation of Ethiopian and Egyptian honeybees from those of other African areas. The A lineage is also present in high proportion in populations from the Iberian Peninsula and Sicily. Furthermore, eight populations from Morocco, Guinea, Malawi and South Africa have been assayed with six microsatellite loci and compared to a set of eight additional populations from Europe and the Middle East. The African populations display higher genetic variability than European populations at all microsatellite loci studied thus far. This suggests that African populations have larger effective sizes than European ones. According to their microsatellite allele frequencies, the eight African populations cluster together, but are divided in two subgroups. These are the populations from Morocco and those from the other African countries. The populations from southern Europe show very low levels of 'Africanization' at nuclear microsatellite loci. Because nuclear and mitochondrial DNA often display discordant patterns of differentiation in the honeybee, the use of both kinds of markers is preferable when assessing the phylogeography of Apis mellifera and to determine the taxonomic status of the subspecies.

Designing multidrug-resistance modulators circumventing the reverse pH gradient in tumours

Multidrug-resistant tumours often exhibit a reverse pH gradient (acid outside), as they have an acid extracellular pH (pHe) and a neutral alkaline intracellular pH (pHi). This study was designed to test the hypothesis that the ability of lipophilic drugs to mediate multidrug resistance (MDR) reversal by interacting with the membrane phospholipids may be correlated with pH in resistant tumours. The permeation properties of five MDR modulators were therefore studied at 37 degrees C by quantifying their ability to induce the leakage of Sulfan blue through unilamellar anionic liposomes, over the range pH 6.5-7.7, and in the absence of any membrane potential (pHe = pHi). The dye leakage induced by two calcium blockers (diltiazem and verapamil) and two antiparasitic agents (thioacridine derivative and mepacrine) was found to significantly increase with the pH of the medium (P < 0.001), whereas that induced by a non-ionic detergent (Triton X-100) showed almost no pH-dependent variations. This process was a cooperative one (0.8 < Hill coefficient < 8.5) and the permeation doses inducing 50% dye leakage (PD50) ranged from 1.6 to 36.0 mM. The permeation ability of the MDR modulators (log(1/PD50)) significantly increased with their octanol-buffer distributions (logD) (slope = 0.35+/-0.06; y intercept = 1.65 +/- 0.14; P < 0.0001) and significantly decreased with their net electric charge (z) (slope = -0.48+/-0.07; y intercept = 2.85+/-0.08; P < 0.0001). A highly significant multiple correlation was found to exist between the variations of log(1/PD50) with those of logD and z (dlog(1/PD50)/dlogD = 0.21 +/- 0.05; dlog(1/PD50)/dz = -0.34+/-0.07; y intercept = 2.27+/-0.17; P < 0.000001). The results provide evidence that in resistant tumours (acid pHe and neutral alkaline pHi), the MDR reversal might be enhanced by favourable drug-membrane interactions if the modulators are designed in the form of highly lipophilic (logP approximately equals 4) mono-basic drugs with a near neutral pKa (pKa approximately equals 7-8).

Genetic diversity of the honeybee in Africa: microsatellite and mitochondrial data

A total of 738 colonies from 64 localities along the African continent have been analysed using the DraI RFLP of the COI-COII mitochondrial region. Mitochondrial DNA of African honeybees appears to be composed of three highly divergent lineages. The African lineage previously reported (named A) is present in almost all the localities except those from north-eastern Africa. In this area, two newly described lineages (called O and Y), putatively originating from the Near East, are observed in high proportion. This suggests an important differentiation of Ethiopian and Egyptian honeybees from those of other African areas. The A lineage is also present in high proportion in populations from the Iberian Peninsula and Sicily. Furthermore, eight populations from Morocco, Guinea, Malawi and South Africa have been assayed with six microsatellite loci and compared to a set of eight additional populations from Europe and the Middle East. The African populations display higher genetic variability than European populations at all microsatellite loci studied thus far. This suggests that African populations have larger effective sizes than European ones. According to their microsatellite allele frequencies, the eight African populations cluster together, but are divided in two subgroups. These are the populations from Morocco and those from the other African countries. The populations from southern Europe show very low levels of 'Africanization' at nuclear microsatellite loci. Because nuclear and mitochondrial DNA often display discordant patterns of differentiation in the honeybee, the use of both kinds of markers is preferable when assessing the phylogeography of Apis mellifera and to determine the taxonomic status of the subspecies.

Effects of acute and chronic hypertension on the labyrinthine barriers in rat

Hearing loss, vertigo, and tinnitus have been related to arterial hypertension. The aim of the present work was to study the permeability of the blood-perilymph and of the labyrinthine barrier, between endolymph and perilymph, to small molecules during chronic and acute hypertension. Experiments were performed in normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). Acute hypertension was induced by phenylephrine. Perilymph was sampled from the first turn of the scala vestibuli and the Na, K, urea, and radioactive concentrations ((14)C-urea and (3)H-mannitol) were measured. In another experimental set, the endocochlear potential was recorded from the basal turn of scala media, before and after phenylephrine injection. The composition of the perilymph and the kinetic constants for (14)C-urea and (3)H-mannitol were similar in WKY and SHR, and not modified after acute hypertension. In endolymph, the endocochlear potential in SHR (+80+/-2.7 mV, n=24) was lower (P<0.001) than in WKY (+98+/-1.5 mV, n=29). The endocochlear potential was decreased by 40 mV during acute hypertensive peak in seven out of 19 WKY but not in SHR rats (n=13). In conclusion, chronic or acute hypertension did not severely alter the permeability to small molecules of the blood-perilymph barrier. The relationship between the low endocochlear potential and hypertension in SHR remains to be evaluated. After acute hypertensive peak, the presence of vascular protective mechanisms in the cochlea could account for the stable endocochlear potential recorded in SHR and 60% of normotensive rats.

Thermal dependence of multidrug-resistant-modulator efficiency: a study in anionic liposomes

This study was designed to test the hypothesis that there exists a correlation between the ability of lipophilic drugs to mediate the reversal of multidrug-resistance (MDR) by interacting with the membrane phospholipids and the metabolic level in tissues. The permeation properties of five MDR-modulators were studied by quantifying their ability to induce the leakage of Sulphan blue through unilamellar liposomes, over the temperature range 27-42 degrees C. The dye leakage induced by a non-ionic detergent (Triton X-100), two calcium blockers (diltiazem and verapamil) and two antiparasitic agents (thioacridine derivative and mepacrine) was temperature-dependent. The permeation process was a co-operative one (1.1 < Hill coefficient < 7.5) and the permeation doses inducing 50% dye leakage (PD50) were 1.5 - 14.9 mM. The permeation ability of the MDR-modulators (log(1/PD50)) decreased significantly as the net electric charge (z) increased. The passive dye leakage (deltaG < 0) was found to be an endothermic process (deltaH > 0), favoured by an increase in the membrane disorder (deltaS > 0). The apparent enthalpy factor (deltaH50) associated with 50% dye leakage increased with the net electric charge of the compound, and this energetically non-favoured event was entirely offset by the concomitant increase in the entropy factor (deltaS50). The apparent permeation enthalpy (deltaH50) and entropy (deltaS50) showed the lowest values for Triton X-100 (deltaH50 = 7.1 +/- 0.53 kJ mol(-1), deltaS50 = 76.9 +/- 1.86 Jmol(-1) K(-1)), and the highest values for mepacrine (deltaH50 = 79.5 +/- 3.80 kJmol(-1), deltaS50 = 306.7 +/- 5-97 J mol(-1) K(-1)). When the temperature was increased from 27 to 42 degrees C, the apparent Gibbs free energy (deltaG50) of the dye leakage induced by Triton X-100 decreased by less than 10% of the initial value, and that induced by mepacrine decreased by nearly 40%. The results provide evidence that in tissues with high metabolic levels and therefore high temperatures, MDR-reversal is likely to be enhanced via favourable drug-membrane interactions controlled by the electric charge of the modulators.

Membrane permeation by multidrug-resistance-modulators and non-modulators: effects of hydrophobicity and electric charge

This study was designed to test the hypothesis that lipophilic cationic drugs with only roughly similar structures mediate the reversal of multidrug-resistance (MDR) by interacting with membrane phospholipids. The permeation properties of MDR-modulators and non-modulators were studied by quantifying their ability to induce the leakage of Sulphan blue through the membrane of negatively charged unilamellar liposomes. Of the 22 compounds under investigation, only those bearing a net positive electric charge per molecule (z) > or = 0.2 induced dye leakage. All these efficient drugs are well-known MDR-modulators: calcium-channel blockers (propranolol, verapamil, diltiazem and dipyridamole), calmodulin antagonists (clomipramine and thioridazine) and antiparasitic agents (mepacrine, thioacridine derivatives and quinine). The non-modulators tested, including antineoplastic agents and steroids, did not induce any membrane permeation. The permeation process was a co-operative one (1.1 < Hill coefficient < 4.1) and the permeation doses inducing 50% dye leakage (PD50) were 1.9-11.2 mM. The permeation ability of the MDR-modulators (log(1/PD50)) increased significantly with octanol-buffer distributions per unit net electric charge ((logD)/z). The results provide evidence that a complex interplay occurs between the electric charge and the lipophilicity of the MDR-modulators when a dye leakage is induced through model membranes, and probably also when the MDR is reversed in leukaemic cells.

[Left ventricular performance, ventriculo-arterial coupling and mechanical output in hypertensive patients with and without left ventricular hypertrophy]

Left ventricular hypertrophy (LVH) is a physiological process of adaptation of the heart to mechanical load increase. Despite depression of left ventricular (LV) contractile performance, work efficiency is preserved and ventriculoarterial coupling is almost normal in hypertensive patients with LVH. To assess the differences between patients with and without LVH, LV contractile performance, the ventriculoarterial coupling and mechanical efficiency were compared in 2 groups of hypertensive patients with similar body surface area and arterial pressures, 23 without LVH (group 1) and 30 with LVH (group 2) and compared to data of 20 normotensive subjects. Left ventricular angiography coupled with simultaneous recording of pressures with micromanometer were used to determine end-systolic stress-to-volume ratio (ESSVR), end-systolic elastance (Ees), effective arterial elastance (Ea), external work (EW) and pressure-volume area (PVA). Left ventricular contractile performance assessed by Ees/100 g myocardial mass and EESVR were lower in group 2 than in group 1 (1.23 +/- 0.28 vs 1.89 +/- 0.48 mmHg/mL/100 g and 6.22 +/- 1.07 vs 9.56 +/- 0.97 g/cm2/mL/m2, respectively, both p < 0.0001, control subjects: 1.47 +/- 0.41 and 6.97 +/- 1.22, respectively). Ventriculoarterial coupling evaluated through Ea/Ees ratio (0.51 +/- 0.05 in group 1 vs 0.53 +/- 0.08 in group 2, 0.49 +/- 0.09 in control subjects), and work efficiency evaluated through EW/PVA ratio (0.80 +/- 0.02 in group 1 vs 0.78 +/- 0.03 in group 2, 0.80 +/- 0.03 in control subjects), were similar in the 2 groups and were comparable to control subject values. In conclusion, this study shows that ventriculoarterial coupling and work efficiency are comparable in hypertensive patients with and without LVH. These results suggest that in patients without LVH the matching between left ventricle and arterial receptor is preserved through an enhancement of myocardial contractility which is energetically costly. Conversely, LVH seems to be a useful adaptation which minimizes the energetical cost of high pressure generation.

Halothane stimulates a Na+H+ antiporter involved in the regulation of intracellular pH in alveolar epithelial cells

Changes in intracellular pH (pHi) of alveolar type II (ATII) cells have been involved in the pathophysiology of pulmonary edema. ATII cells have evolved several ions transporters to regulate their pHi, including a Na+H+ antiporter. Because halothane alters the activity of ion transporters in various cells types, it may also affect the activity of this Na+H+ antiporter. This study was performed 1) to characterize a Na+H+ antiporter in a model of ATII cells and 2) to investigate the effect of halothane on the activity of this antiporter. ATII cells were obtained from primary rat ATII cells transfected with a mutant of simian virus SV40 large T antigen (SV40-T2), and their pHi was monitored using the pH-sensitive fluorescent probe 2'-7' (bis carboxyethyl)-5(6')-carboxyfluorescein. We demonstrated in vitro that 1) a Na+H+ antiporter (apparent Km 6.8 +/- 3.4 mM, Vmax 0.0105 +/- 0.0013 delta UpHi/s) regulates the pHi of SV40-T2 cells and 2) at clinically relevant concentrations (10(-3) to 10(-5) M) and for a short exposure duration (60 min), halothane enhances the activity of this antiporter. Because ATII cell acidification has been associated with alterations in the alveolar epithelial barrier, halothane-induced intracellular alkalinization might exhibit some protective effect in clinical situations, such as aspiration pneumonia.

IMPLICATIONS

In vitro, halothane induces an intracellular alkalinization of pneumocytes II via the activation of a Na+H+ antiporter. Because acidification of these cells has been associated with alterations in the alveolar epithelial barrier, halothane might exhibit some protective effect in clinical situations, such as aspiration pneumonia.