Filling Single Wall Carbon Nanotubes with Metal Chloride and Metal Nanowires and Imaging with Scanning Transmission Electron Microscopy

Nanowires of magnetic metals (Ho, Gd) have been synthesized inside the hollow interior of single wall carbon nanotubes by the sealed-tube reaction. Amongst the d- and f-series metal chlorides investigated in this study, HoCl3 and GdCl3 fill the SWNTs to a significantly higher extent than FeCl2 and CoCl2. HoCl3 and GdCl3 nanowires have been transformed into the respective metal nanowires via the reduction of the chloride nanowires. The nanowires have been imaged using high-resolution transmission electron microscopy and scanning transmission electron microscopy (STEM). X-ray energy dispersive spectroscopy carried out in conjunction with STEM confirmed the presence of metal chloride and metal nanowires

The importance of forest structure for carbon fluxes of the Amazon rainforest

Precise descriptions of forest productivity, biomass, and structure are essential for understanding ecosystem responses to climatic and anthropogenic changes. However, relations between these components are complex, in particular for tropical forests. We developed an approach to simulate carbon dynamics in the Amazon rainforest including around 410 billion individual trees within 7.8 million km2. We integrated canopy height observations from space-borne LIDAR in order to quantify spatial variations in forest state and structure reflecting small-scale to large-scale natural and anthropogenic disturbances. Under current conditions, we identified the Amazon rainforest as a carbon sink, gaining 0.56 GtC per year. This carbon sink is driven by an estimated mean gross primary productivity (GPP) of 25.1 tC ha−1 a−1, and a mean woody aboveground net primary productivity (wANPP) of 4.2 tC ha−1 a−1. We found that successional states play an important role for the relations between productivity and biomass. Forests in early to intermediate successional states are the most productive, and woody above-ground carbon use efficiencies are non-linear. Simulated values can be compared to observed carbon fluxes at various spatial resolutions (>40 m). Notably, we found that our GPP corresponds to the values derived from MODIS. For NPP, spatial differences can be observed due to the consideration of forest successional states in our approach. We conclude that forest structure has a substantial impact on productivity and biomass. It is an essential factor that should be taken into account when estimating current carbon budgets or analyzing climate change scenarios for the Amazon rainforest

Tetrahalidocuprates(II)-structure and EPR spectroscopy. Part 1: Tetrabromidocuprates(II)

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Tetrahalidocuprates(II) show a high degree of structural flexibility. We present the results of crystallographic and electron paramagnetic resonance (EPR) spectroscopic analyses of four new tetrabromidocuprate(II) compounds and compare the results with previously reported data. The cations in the new compounds are the sterically demanding benzyltriphenylphosphonium, methyltriphenylphosphonium, tetraphenylphosphonium, and hexadecyltrimethylammonium ions; they were used to achieve a reasonable separation of the paramagnetic Cu(II) ions for EPR spectroscopy. X-Ray crystallography shows that in all four complexes the [CuBr4]2− units have a distorted tetrahedral coordination geometry which is in agreement with DFT calculations. The EPR hyperfine structure was not resolved. This is due to the exchange broadening resulting from still incomplete separation of the paramagnetic Cu(II) centres. Nevertheless, the principal values of the electron Zeemann tensor (gand g⊥) of the complexes could be determined. A correlation of structural (X-ray) parameters with the spin density at the copper centres (DFT) is well reflected in the EPR spectra of the bromidocuprates. This enables the correlation of X-ray and EPR parameters to predict the structure of tetrabromidocuprates in physical states other than the crystalline state. As a result, we provide a method to structurally characterize [CuBr4]2− in, for example, ionic liquids or in solution, which has important implications for e.g. catalysis or materials science

Effects of Silver Nanoparticles on Primary Mixed Neural Cell Cultures: Uptake, Oxidative Stress and Acute Calcium Responses

In the body, nanoparticles can be systemically distributed and then may affect secondary target organs, such as the central nervous system (CNS). Putative adverse effects on the CNS are rarely investigated to date. Here, we used a mixed primary cell model consisting mainly of neurons and astrocytes and a minor proportion of oligodendrocytes to analyze the effects of well-characterized 20 and 40 nm silver nanoparticles (SNP). Similar gold nanoparticles served as control and proved inert for all endpoints tested. SNP induced a strong size-dependent cytotoxicity. Additionally, in the low concentration range (up to 10 μg/ml of SNP), the further differentiated cultures were more sensitive to SNP treatment. For detailed studies, we used low/medium dose concentrations (up to 20 μg/ml) and found strong oxidative stress responses. Reactive oxygen species (ROS) were detected along with the formation of protein carbonyls and the induction of heme oxygenase-1. We observed an acute calcium response, which clearly preceded oxidative stress responses. ROS formation was reduced by antioxidants, whereas the calcium response could not be alleviated by antioxidants. Finally, we looked into the responses of neurons and astrocytes separately. Astrocytes were much more vulnerable to SNP treatment compared with neurons. Consistently, SNP were mainly taken up by astrocytes and not by neurons. Immunofluorescence studies of mixed cell cultures indicated stronger effects on astrocyte morphology. Altogether, we can demonstrate strong effects of SNP associated with calcium dysregulation and ROS formation in primary neural cells, which were detectable already at moderate dosage

Lianas in silico, ecological insights from a model of structural parasitism

Tropical forests are a critical component of the Earth system, storing half of the global forest carbon stocks and accounting for a third of terrestrial photosynthesis. Lianas are structural parasites that can substantially reduce the carbon sequestration capacity of these forests. Simulations of this peculiar growth form have only recently started and a single vegetation model included lianas so far. In this work we present a new liana implementation within the individual based model Formind. Initial tests indicate high structural realism both horizontal and vertical. In particular, we benchmarked the model against empirical observations of size distribution, mean liana cluster size and vertical leaf distribution for the Paracou site in French Guiana. Our model predicted a reduction of above-ground biomass between 10% for mature stands to 45% for secondary plots upon inclusion of lianas in the simulations. The reduced biomass was the result of a lower productivity due to a combination of lower tree photosynthesis and high liana respiration. We evaluated structural metrics (LAI, basal area, mean tree-height) and carbon fluxes (GPP, respiration) by comparing simulations with and without lianas. At the equilibrium, liana productivity was 1.9tC ha y or 23% of the total GPP and the forest carbon stocks were between 5% and 11% lower in simulations with lianas. We also highlight the main strengths and limitations of this new approach and propose new field measurements to further the understanding of liana ecology in a modelling framework

Ion and proton transport in aqueous/nonaqueous acidic ionic liquids for fuel-cell applications - insight from high-pressure dielectric studies

The use of acidic ionic liquids and solids as electrolytes in fuel cells is an emerging field due to their efficient proton conductivity and good thermal stability. Despite multiple reports describing conducting properties of acidic ILs, little is known on the chargetransport mechanism in the vicinity of liquid−glass transition and the structural factors governing the proton hopping. To address these issues, we studied two acidic imidazoliumbased ILs with the same cation, however, different anionsbulk tosylate vs small methanesulfonate. High-pressure dielectric studies of anhydrous and water-saturated materials performed in the close vicinity of Tg have revealed significant differences in the charge-transport mechanism in these two systems being undetectable at ambient conditions. Thereby, we demonstrated the effect of molecular architecture on proton hopping, being crucial in the potential electrochemical applications of acidic ILs

Anionic polymer brushes for biomimetic calcium phosphate mineralization : a surface with application potential in biomaterials

This article describes the synthesis of anionic polymer brushes and their mineralization with calcium phosphate. The brushes are based on poly(3-sulfopropyl methacrylate potassium salt) providing a highly charged polymer brush surface. Homogeneous brushes with reproducible thicknesses are obtained via surface-initiated atom transfer radical polymerization. Mineralization with doubly concentrated simulated body fluid yields polymer/inorganic hybrid films containing AB-Type carbonated hydroxyapatite (CHAP), a material resembling the inorganic component of bone. Moreover, growth experiments using Dictyostelium discoideum amoebae demonstrate that the mineral-free and the mineral-containing polymer brushes have a good biocompatibility suggesting their use as biocompatible surfaces in implantology or related fields

Recombinant DNA technology and click chemistry: a powerful combination for generating a hybrid elastin-like-statherin hydrogel to control calcium phosphate mineralization

Producción CientíficaUnderstanding the mechanisms responsible for generating different phases and morphologies of calcium phosphate by elastin-like recombinamers is supreme for bioengineering of advanced multifunctional materials. The generation of such multifunctional hybrid materials depends on the properties of their counterparts and the way in which they are assembled. The success of this assembly depends on the different approaches used, such as recombinant DNA technology and click chemistry. In the present work, an elastin-like recombinamer bearing lysine amino acids distributed along the recombinamer chain has been cross-linked via Huisgen [2 + 3] cycloaddition. The recombinamer contains the SNA15 peptide domains inspired by salivary statherin, a peptide epitope known to specifically bind to and nucleate calcium phosphate. The benefit of using click chemistry is that the hybrid elastin-like-statherin recombinamers cross-link without losing their fibrillar structure. Mineralization of the resulting hybrid elastin-like-statherin recombinamer hydrogels with calcium phosphate is described. Thus, two different hydroxyapatite morphologies (cauliflower- and plate-like) have been formed. Overall, this study shows that crosslinking elastin-like recombinamers leads to interesting matrix materials for the generation of calcium phosphate composites with potential applications as biomaterials.Ministerio de Economía, Industria y Competitividad (Project MAT2013- 42473-R and MAT2013-41723-R)Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA244U13, VA313U14 and GRS/516/A/10

Digitale Publikations- und Forschungsinfrastrukturen

Taubert NC. Digitale Publikations- und Forschungsinfrastrukturen. In: Simon D, Knie A, Hornbostel S, Zimmermann K, Springer NachschlageWissen, eds. Handbuch Wissenschaftspolitik. Wiesbaden: Springer Fachmedien; 2016: 1-18