Molekulare Schalter für potentielle Weltraumanwendungen

Aufgrund der immer weiter voranschreitenden Miniaturisierung elektrischer Bauteile und der Limitierung Silicium-basierter Technologien ist die Suche nach neuen Materialien unausweichlich. Eine mögliche Alternative stellen hierbei molekulare Schalter auf Basis von Spin-Crossover-Verbindungen dar. Dabei handelt es sich um Materialien, welche durch äußere chemische oder physikalische Einwirkungen, beispielsweise elektromagnetische Strahlung oder Temperaturänderungen, ihre Eigenschaften verändern. Vielversprechende Materialien sind hierbei Koordinationsverbindungen mit FeIII-Zentren, welche reversibel zwischen einem sogenannten High-Spin- und Low-Spin-Zustand wechseln können. Dies geht unter anderem mit signifikanten Änderungen ihrer optischen und magnetischen Eigenschaften einher. Mögliche Anwendungsbereiche stellen hierbei die Sensorik oder die Datenspeicherung dar. Im Rahmen dieser Dissertation werden neue FeIII-Koordinationsverbindungen auf Basis von tetradentaten, pentadentaten und potentiell hexadentaten Liganden synthetisiert und charakterisiert. Die tetradentaten Verbindungen vom Salen-Typ werden mit unterschiedlichen monodentaten Liganden umgesetzt und auf potentielle Spin-Crossover-Eigenschaften untersucht. Dabei hat sich gezeigt, dass durch einen Ligandenaustausch mit Imidazol und Perchlorat als Gegenion neue molekulare Schalter erhalten werden. Bei den pentadentaten Verbindungen handelt es sich um FeIII-Komplexe mit einem Salpet-Liganden, welchen durch die Substitution mit einer pH-sensitiven Sulfonsäure-Gruppe neue, sensorische Eigenschaften hinzugefügt wurden. Dazu gehören unter anderem eine signifikante Farbänderung beim Kontakt mit Säuren oder Basen. Die letzte Gruppe bilden mit Methylpyridin- substituierte Salpet-Liganden. Das Ziel ist hier die Strukturaufklärung hinsichtlich der Koordinationssphäre des Metallzentrums. Dabei liegt das besondere Augenmerk auf der Bindung zwischen dem Eisen-Zentrum und der Methylpyridin-Gruppe. Die in dieser Arbeit vorgestellten Ergebnisse sollen neue Erkenntnisse für den Einsatz von molekularen Schaltern in sensorischen Anwendungen liefern.Due to the ever increasing demand for miniaturization of electrical components and the limitations of silicon-based technologies, the search for new materials is inevitable. Molecular switches based on spin crossover compounds represent a possible solution for these problems. Molecular switches are materials that change their properties through external chemical or physical stimuli, such as electromagnetic radiation or different temperatures. Promising materials are coordination compounds with iron(III) centres, which can reversibly switch between a so-called high spin and low spin state. This is accompanied by significant changes for example in their optical and magnetic properties. For this reason, such materials are promising candidates regarding sensor technology or data storage. In this thesis, new FeIII coordination compounds based on tetradentate, pentadentate and potentially hexadentate ligands are synthesized and characterised. The tetradentate Salen-type compounds are combined with different monodentate ligands and investigated for potential spin crossover properties. It could be shown that new molecular switches can be obtained by exchanging the monodentate ligands with imidazole and perchlorate as anion. The pentadentate compounds are FeIII complexes with Salpet ligands, to which new sensory properties, e. g. colour changes on contact with acids or bases, could be added by substitution with a pH-sensitive sulfonic acid group. The last part consists of methylpyridine-substituted Salpet ligands. The aim is to elucidate the structure with regard to the coordination sphere of the metal centre. Special attention is paid to the bonding between the iron centre and the methylpyridine group. The results presented in this thesis should provide new insights for the use of molecular switches in sensory applications

Structural, Magnetic, and Electrochemical Characterization of Iron(III) and Cobalt Complexes with Penta-N3O2-dentate Ligands

Six new mononuclear [FeIII(LBr,Cl)X]-complexes (LBr,Cl is the dianionic penta-N3O2-dentate Schiff base ligand N,N′-bis(2’-hydroxy-3-bromo-5-chlorobenzylidene)-1,6-diamino-3-azahexane; X: Cl−, N3−, NCO−, NCS−, NCSe−, CN−) were synthesized and their structures, magnetic and electrochemical properties studied. Structure analysis and magnetic measurements showed that [FeIII(LBr,Cl)CN] is in the low spin state and the other five complexes are in high spin states. Furthermore, the trinuclear mixed valent cobalt complex {[CoIII(LH,H)CN]2[CoII(1-methylimidazole)3(H2O)]} was prepared and its magnetic behavior studied. © 2021 The Authors. European Journal of Inorganic Chemistry published by Wiley-VCH Gmb

Impact of Hard Magnetic Nanocrystals on the Properties of Hardened Cement Paste

In this work, nano-sized hard magnetic gallium-substituted iron oxide crystals, wherein gallium is used to stabilize the metastable epsilon iron oxide phase, were added to cement-water suspensions at different ratios, which were subsequently hydrated for at least 28 days. It is shown that higher contents of such nanocrystals in the hardened cement paste introduce a magnetic moment, whereas the mechanical properties remain unchanged compared to non-blended hardened cement paste for a wide concentration range

Database resources of the National Center for Biotechnology Information

In addition to maintaining the GenBank® nucleic acid sequence database, the National Center for Biotechnology Information (NCBI) provides analysis and retrieval resources for the data in GenBank and other biological data made available through the NCBI web site. NCBI resources include Entrez, the Entrez Programming Utilities, MyNCBI, PubMed, PubMed Central, Entrez Gene, the NCBI Taxonomy Browser, BLAST, BLAST Link (BLink), Electronic PCR, OrfFinder, Spidey, Splign, Reference Sequence, UniGene, HomoloGene, ProtEST, dbMHC, dbSNP, Cancer Chromosomes, Entrez Genomes and related tools, the Map Viewer, Model Maker, Evidence Viewer, Trace Archive, Sequence Read Archive, Retroviral Genotyping Tools, HIV-1/Human Protein Interaction Database, Gene Expression Omnibus, Entrez Probe, GENSAT, Online Mendelian Inheritance in Man, Online Mendelian Inheritance in Animals, the Molecular Modeling Database, the Conserved Domain Database, the Conserved Domain Architecture Retrieval Tool, Biosystems, Peptidome, Protein Clusters and the PubChem suite of small molecule databases. Augmenting many of the web applications are custom implementations of the BLAST program optimized to search specialized data sets. All these resources can be accessed through the NCBI home page at www.ncbi.nlm.nih.gov

Contextualizing climate justice activism: knowledge, emotions, motivations, and actions among climate strikers in six cities

In August 2018, Swedish teenager Greta Thunberg started to strike from school on Fridays to protest against a lack of action on the climate crisis. Her actions sparked a historically large youth movement, leading to a series of school strikes across the world. Over the course of one week in September 2019, striking school children, students and other grassroots movements, such as Extinction Rebellion, called for everyone to participate in a global Climate Strike. This paper is based on comparative research with climate protesters in six cities: Brighton and London (United Kingdom), Montreal (Canada), New Haven and New York (USA), and Stavanger (Norway). Based on original interviews with 64 protesters, the study examines their knowledge, emotions, motivations, and actions in relation to climate change, including any lifestyle changes they have undertaken before or after their protests. Our findings show that protesters have varying degrees of knowledge about climate change, and have taken a range of actions in their own lives to address climate change. They also manifest a wide spectrum of emotions about climate change, and different motivations for taking part in climate strikes. These features are under-studied and dynamically evolving at the present conjuncture. On this basis, we call for expanded academic attention to human, emotional, epistemic, and seemingly mundane aspects of climate protests, their structural tendencies and relational expressions, and the implications for our ability to address underlying drivers

Transparent conductive three-layered composite films based on carbon nanotubes with improved mechanical stability

A layered composite coating material with favorable properties for application as a transparent conductor is presented. It is composed of layers of three nanoscopic materials, namely zinc oxide nanoparticles, single wall nanotubes, and graphene oxide nanosheets. The electrically conducting layer consists of single wall nanotubes (SWNTs). The layer of zinc oxide nanoparticles acts as a primer. It increases the adhesion and the stability of the films against mechanical stresses. The top layer of graphene oxide enhances the conductivity of such coatings. Such three-layer composite coatings show better conductivity (without compromising transparency) and improved mechanical stability compared to pure SWNT films. The processes used in the preparation of such coatings are easily scalable. Copyright © Materials Research Society 2014

Polymer Optical Waveguide Sensor Based on Fe-Amino-Triazole Complex Molecular Switches

We report on a polymer-waveguide-based temperature sensing system relying on switchable molecular complexes. The polymer waveguide cladding is fabricated using a maskless lithographic optical system and replicated onto polymer material (i.e., PMMA) using a hot embossing device. An iron-amino-triazole molecular complex material (i.e., [Fe(Htrz)2.85(NH2-trz)0.15](ClO4)2) is used to sense changes in ambient temperature. For this purpose, the core of the waveguide is filled with a mixture of core material (NOA68), and the molecular complex using doctor blading and UV curing is applied for solidification. The absorption spectrum of the molecular complex in the UV/VIS light range features two prominent absorption bands in the low-spin state. As temperature approaches room temperature, a spin-crossover transition occurs, and the molecular complex changes its color (i.e. spectral properties) from violet-pink to white. The measurement of the optical power transmitted through the waveguide as a function of temperature exhibits a memory effect with a hysteresis width of approx. 12 °C and sensitivity of 0.08 mW/°C. This enables optical rather than electronic temperature detection in environments where electromagnetic interference might influence the measurements