University of Siegen
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Publication Access status: Open Access , Remote control of the synthesis of a [2]rotaxane and its shuttling via metal-ion translocation(2019); ; Remote control in an eight-component network commanded both the synthesis and shuttling of a [2]rotaxane via metal-ion translocation, the latter being easily monitored by distinct colorimetric and fluorimetric signals. Addition of zinc(II) ions to the red colored copper-ion relay station rapidly liberated copper(I) ions and afforded the corresponding zinc complex that was visualized by a bright sky blue fluorescence at 460 nm. In a mixture of all eight components of the network, the liberated copper(I) ions were translocated to a macrocycle that catalyzed formation of a rotaxane by a double-click reaction of acetylenic and diazide compounds. The shuttling frequency in the copper-loaded [2]rotaxane was determined to k298=30 kHz (ΔH≠=62.3±0.6 kJ mol−1, ΔS≠=50.1±5.1 J mol−1 K−1, ΔG≠298=47.4 kJ mol−1). Removal of zinc(II) ions from the mixture reversed the system back generating the metal-free rotaxane. Further alternate addition and removal of Zn2+ reversibly controlled the shuttling mode of the rotaxane in this eight-component network where the ion translocation status was monitored by the naked eye.Source Type:Article1 7 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , Influence of phenylethylammonium iodide as additive in the formamidinium tin iodide perovskite on interfacial characteristics and charge carrier dynamicsA combined electrical and time-resolved optical investigation of the perovskite formamidinium tin iodide (FASnI3) and its phenylethylammonium (PEA) derivative PEA0.08FA0.92SnI3, which recently achieved a power conversion efficiency of 9%, is presented to study the specifics of contact characteristics and charge carrier dynamics. Microstructured gold electrode arrays were used to investigate the charge transport across a metal-perovskite interface and through micrometers of the perovskite films. Symmetrical contact configuration enabled detailed polarization studies. Hysteresis in the current-voltage characteristics and a corresponding current-time behavior indicated limitations by charge transfer in the contacts. Hysteresis was less pronounced in PEA0.08FA0.92SnI3 compared with FASnI3. This is explained by a 2-dimensional interlayer at the contacts, which leads to decreased field-induced migration of ions at the contact. Carrier recombination in the bulk of FASnI3 films, however, was only slightly modified by the presence of PEA. Femtosecond broadband transient absorption experiments up to 1.5 ns provided rate constants for the Auger and bimolecular recombination processes in FASnI3 of k3 = 1 × 10−29 cm6 s−1 and k2 = 3.1 × 10−10 cm3 s−1, respectively. In PEA0.08FA0.92SnI3, no significant differences in k2 and an only slightly increased k3 = 2 × 10−29 cm6 s−1 were measured. In extension to previous photoluminescence studies, we found efficient cooling of hot carriers by coupling to optical phonons (τcop = 0.5 ps), which is even faster than in lead perovskites. The authors thank the Deutsche Forschungsgemeinschaft (DFG) for financial support (Nos. SCHL 340/21-3, OU 58/10-3, LE 926/11-3, and RTG 2204). We are also grateful to R. Kentsch for complementary steady-state absorption and PL measurements, M. Morgenroth for assistance during the transient absorption experiments, H. Hemmelmann for measuring XRD at grazing incidence, and ZfM/LaMa (JLU Gieβen) for support in SEM and photolithography.Source Type:Article4 11 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , Synthesis and characterization of methylammonium phosphates as crystalline approximants for anhydrous, low melting phosphate glasses(2019); ; ; Low-melting methylammonium phosphate glasses are synthesized from crystalline starting agents. To this end crystalline tris(methylammonium) cyclotriphosphate [CH3NH3]3P3O9, was synthesized by a novel and simple synthesis route from P4O10 and N-methylformamide. It, undergoes an irreversible phase transition to methylammonium catena-polyphosphate [CH3NH3]PO3. The crystal structure of the catena-polyphosphate was solved and refined from X-ray powder diffraction data by the Rietveld method using constraints obtained by solid-state 31P and 1H NMR spectroscopy. This compound crystallizes in a triclinic space group with a = 13.2236(9), b = 7.8924(6), c = 4.6553(2) Å, α = 91.068(4), β = 87.840(5) and γ = 106.550(3)°. Quantum chemical calculations confirm that the obtained structure lies at an energetic minimum. Finally the reaction of tris(methylammonium) cyclotriphosphate and P4O10 into methylammonium phosphate glass is presented. The synthesized, water-free phosphate glass shows a very low glass transition temperature Tg of 33 °C, which was verified by dynamic scanning calorimetry and NMR. The chain-like crystal structure of the high-temperature methylammoniumphosphate [CH3NH3]PO3 serves as an approximation for the short-range order of the glass.Source Type:Article2 6 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , Optimization and application of flowing atmospheric-pressure afterglow mass spectrometry for direct surface sampling and quantitative analysis(2019)Ambient desorption/ionization mass spectrometry (ADI-MS) has emerged as an important field for direct sample analysis since the mid-2000s, when desorption electrospray ionization (DESI) and direct analysis in real time (DART) were introduced. The main goal of ADI-MS is to minimize sample preparation procedures (e.g., solvent extraction) and to overcome the long analysis times, often encountered with chromatographic separations, by directly desorbing the target analytes from the sample surface. In the first part of this thesis, a brief summary and review will highlight the main achievements for the optimization of plasma-based ADI sources, which can be found in peer-reviewed journal articles. These ADI source optimization parameters are important to improve the methods sensitivity for fast analyte screening and direct surface analysis. Subsequently to this literature overview, own studies for the optimization of instrumental parameters for the flowing atmospheric-pressure afterglow (FAPA) source will be presented in a following chapter. In the second section of the thesis, DART-MS, FAPA-MS, and low-temperature plasma mass spectrometry (LTP-MS), are compared for the direct analysis of liquid-crystalline materials by MS. With this approach sample preparation is minimized for quick and cheap liquid crystal display (LCD) failure analysis. For DART-MS limits of detection (LODs, absolute amount) in the ng range and for LTP- and FAPA-MS LODs in the pg range are obtained. Additionally, mass-spectral imaging of LCDs by FAPA-MS and laser ablation halo-FAPA-MS (LA-h-FAPA-MS) will be presented. This instrumental setup enables the analysis of very low sample volumes inside an LCD and first experiments suggest an estimated spatial resolution of 1-2 mm and 0.6 mm for FAPA-MS and LA-h-FAPA-MS, respectively. Ultimately, these methods shall help to discriminate between different LCD components and to identify defects within an LCD by lateral profiling. Despite the versatile application possibilities for ADI-MS methods, these techniques are very sensitive to matrix effects. Thus, thin-layer chromatography (TLC) is used to quickly separate matrix components and reaction byproducts from the target analytes before spatial resolved and quantitative detection by FAPA-MS. Furthermore, different TLC stationary phases (e.g., normal phase, reversed phase, and cyano phase) as well as different particle sizes of the stationary phase are compared for best performance. Moreover, a validated TLC-FAPA-MS method is developed for quantification of 0.32 mg/mL caffeine in energy drinks via stable isotope dilution analysis. A second application involves the separation and individual detection of active agents in antimalarial preparations. Finally, FAPA-MS is applied for the analysis of a P4O10 in DMSO mixture, to elucidate the reaction mechanism between both compounds. With these measurements the presence of the important C2H5S+ intermediate product could be confirmed.Source Type:Doctoral Thesis5 9 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , POLYCHAR 18, World Forum on Advanced Polymeric Materials : synthesis, properties, characterisation ; April 7 - 10, 2010 in Siegen, Germany(2010)The international conference Polychar 18, World Forum on Advanced Polymeric Materials (Synthesis, Properties, Characterisation) took place from April 6th 2010 (short course on characterization) to April 9th 2010 (excursion April 10th) in Siegen. This annual meeting was devoted to the newest developments and results in the areas mentioned. Special attention was given among others to the topics of ionic liquids as medium for polymer synthesis and modification, biopolymer based materials, polymers and life sciences as well as modern characterization methods of macromolecular materials. All contributions presented at the conference are collected in the Book of Abstracts.Source Type:Conference Proceedings1 17 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , Single particle ICP-MS : capabilities of microsecond time resolution and coupling to capillary electrophoresis(2019)Single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) is a method that allows to obtain size, size distribution, and particle number concentration of nanoparticles (NPs) in suspensions only after few minutes of measurement. However, several challenges of commercially available SP-ICP-MS instruments currently exist that limit the analytical performance of the method. This thesis reports novel developments and improvements of SP-ICP-MS with the ultimate goal to be able to use it as a routine NP analysis method in the future. First, the state-of-the-art in SP-ICP-MS is reviewed on a step-by-step basis, from the sample introduction system to the detector. Applications of the method for the analysis of nanomaterials are critically discussed and current challenges are highlighted. Necessary improvements and directions for further developments are identified. Second, capillary electrophoresis (CE) is coupled to SP-ICP-MS and used for the first time with a data aquistion system (DAQ) that provides microsecond time resolution (5 µs dwell time, µsDAQ) for the separation and characterization of mixtures of Ag NPs. An online preconcentration approach is implemented to decrease the detection limits to the sub-microgram-per-liter range. In addition, it is demonstrated for the first time that the optimized CE-SP-ICP-MS method can be successfully used to separate NPs with similar sizes but different surface coatings. Each component in a complex mixture of 20 nm, 40 nm, 60 nm sized citrate-coated and 40 nm, 60 nm sized PVP-coated Ag NPs can be distinguished. Finally, a novel data processing algorithm for SP-ICP-MS with the µsDAQ is developed to extract NP signals from a continuous background signal. The method is based on Poisson statistics and allows to distinguish and quantify both NPs and dissolved elements. It is demonstrated that Ag NPs (20 nm – 100 nm) can be identified on a particle-by-particle level even in the presence of a significant concentration of ionic background (Ag+ up to 7.5 µg L-1, 107Ag+ up to 1 000 000 counts per second).Source Type:Doctoral Thesis2 9 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , Optimization and application of Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) for the detection of nanomaterials in tissue thin sections(2018)The increasing use of nanoparticle (NP)-containing products leads to an enhanced emis-sion of NP into the environment. The potential dangers associated with the exposition of organisms to these materials are barely investigated and the fate of the NP upon uptake into the body is not completely understood. One reason is the lack of suitable analytical techniques, which allow the sensitive detection of NP in tissue at high spatial resolution. Prerequisites for a reliable identification are high sensitivity, high mass resolution and high spatial resolution without the need for markers. Time-of-Flight secondary ion mass spectrometry (ToF-SIMS) is promising in this regard because it allows the simultaneous detection of atomic and molecular species from sur-faces without markers. However, its potential for the detection of NP in tissue has not yet been adequately explored. In the scope of this work, a suitable ToF-SIMS method is developed and optimised for the analysis of a variety of oxidic NP in lung tissue sec-tions. The suitability of ToF-SIMS for the successful detection of nanomaterials in bio-logical tissue is demonstrated by means of correlations and cross-validations of ToF-SIMS data with the results of reference techniques. In this thesis, rat lung tissue sections, containing different kinds of nanoparticles are analysed by ToF-SIMS and compared with reference techniques. Paramagnetic Fe2O3/SiO2 (core/shell) NP (primary particle size 10-20 nm; aggregate size 190 ± 20 nm) are detected by microscopic techniques (dark-field and bright-field microscopy) and ToF-SIMS colocalizing in the tissue sections. The NP are mostly attached to alveolar wall and only marginally internalized by cells. The colocalization of ToF-SIMS signal distributions for 56Fe+ and 28Si+ proves that the core/shell structure of the particles re-mains intact in the tissue. The phosphocholine head group (C5H15NPO4+) is colocalized with tissue (CH4N+) but not with the NP indicating that lipids do not adsorb onto NP under these conditions. The distribution of fluorescence-tagged SiO2 NP (25 nm) in rat lung tissue is revealed by fluorescence microscopy and ToF-SIMS. Extremely similar signal distributions for the fluorescence tag and ToF-SIMS signals (SiO3-) are obtained. Furthermore, the distribu-tions of protein (CN-) and phosphate-based signals (PO3-) can be related to the particle distribution. Rat lung tissue sections inhomogenously laden with CeO2 NP (10-200 nm) are subjected to successive analyses by first micro X-ray fluorescence (µ-XRF) and second ToF-SIMS. This approach allows a relatively fast screening of the complete section for ele-vated Ce levels at 25 µm lateral resolution, before selecting suitable regions-of-interest for high-resolution ToF-SIMS analysis at submicrometer lateral resolution (670 nm). Ce-related signal distributions (e.g. 140Ce+, 140CeO+, 140CeO2+) are detected along tissue-related signals (K2CN+) at a mass resolution of R = 4000. Besides pre-analyses, the µ-XRF also allows a coarse cross-validation of the ToF-SIMS signal distributions. ZrO2 NP (primary sizes of 9-10 nm) are mainly detected as agglomerates in phagocytic cells by both high-spatial resolution techniques, ToF-SIMS and ion beam microscopy (IBM). Both techniques detect ZrO2 related signals at high lateral resolutions (400-600 nm for ToF-SIMS and about 1000 nm for IBM). Only small quantities of NP are found in the lung epithelium. Besides the NP-related signals, S and P signal from IBM colocalize with PO+ and SO2+ from ToF-SIMS. The presence of S-, P- and Zr-related signals in both techniques enables a cross-validation of the results. Additionally, ToF-SIMS signals indicating the distribution of certain compounds such as phospholip-ids (C4H8N+, C6H12N+, C5H15NPO4+) and amino acids (K2CN+, C2H6N+, C3H8N+) are detected at mass resolutions of up to 9000. In summary, different oxidic nanoparticle types with sizes from 9 nm to more than 200 nm are directly detected by ToF-SIMS (without the need for markers) in rat lung tissue sections. The results are confirmed by independent techniques such as bright- and dark-field microscopy, µ-XRF and IBM. The presented ToF-SIMS analyses reveal the distribution of nanoparticles at high confidence and provide further elemental and mo-lecular information from the particle-surrounding matrix (e.g. amino acids or lipid resi-dues). Lateral resolutions of 400 nm and mass resolutions of up to 9000 with the ability to acquire organic and inorganic signals simultaneously across the whole mass-range are unique features highlighting the great potential of ToF-SIMS for the detection of nano-particles in tissue. These results serve as a basis for the analysis of the fate of the nano-particles in mammalian bodies for future nanotoxicology studies.Source Type:Doctoral Thesis1 6 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , Development and optimisation of mass spectrometric techniques for the analysis of antimalarial pharmaceuticals(2018)Antimalarials are drugs used against malaria, an infectious disease caused by a parasite that belongs to the genius plasmodium. Drug therapy to eradicate this disease is increasingly hindered by resistance of the parasite to drugs currently in use. The drug resistance has been partly attributed to the presence of drugs with wrong or low active pharmaceutical ingredients. Thus, there is an increasing need for analytical procedures to investigate the quality of antimalarial-based pharmaceuticals. Amongst the analytical techniques, the most used to date is high performance liquid chromatography (HPLC) in the reversed-phase (RP) mode coupled to mass spectrometry (MS). However, RP-HPLC is characterised by a relatively long analysis time and a consumption of a large amount of organic solvents. In a quest to develop a fast and efficient analytical method, different mass spectrometric-based techniques are developed and optimised in this thesis. In the first section, high-temperature HPLC mass spectrometry (HT-HPLC-MS)-based technique tailored for the analysis of antimalarials is developed and optimised. HPLC at high temperature permits faster separation compared to standard conditions with a reduction in chemical waste, better chromatographic selectivity and an enhanced desolvation in the MS ionisation source. Prior to HT-HPLC-MS method development, a HT-HPLC heating system was optimised for best performance and successfully coupled to a triple quadrupole mass spectrometer via electrospray ionisation (ESI) and atmospheric pressure chemical ionisation (APCI) sources. Because of the antimalarial properties of Cinchona alkaloids, a HT-HPLC-MS method with an XBridge C18 column and ESI source was developed and optimised for their analysis. The optimised method permits the separation and detection of the four major chiral alkaloids: cinchonine, cinchonidine, quinine, and quinidine and their dihydro-derivatives: dihydrocinchonine, dihydrocinchonidine, dihydroquinine, and dihydroquinidine with reduction in analysis time and organic solvents, better chromatographic selectivity and enhanced MS ionisation efficiency. Limits of detection (LOD) in the µg L-1 range were obtained. The method was shown to be suitable in the separation and detection of Cinchona alkaloids present in a commercial sample. Also, because of the antimalarial properties of artemisinin (ART) and some of its derivatives (artesunate (AS), dihydroartemisinin (DHA), and artemether (AM)), another HT-HPLC-MS strategy with a zirconia-polybutadiene (ZrO2-PBD) column, was developed and optimised for their analysis. After optimisation, DHA, ART, and AM were detected as their ammonium adducts ([M + NH4]+) at m/z 302, 300, and 316, while AS was detected as a characteristic fragment ion at m/z 272. From evaluation of ESI and APCI sources during HT-HPLC-MS analysis, best detection sensitivity for ART and derivatives is obtained with ESI compared to APCI. LODs in the µg mL-1 range were obtained with HT-HPLC-ESI-MS. The optimised HT-HPLC-ESI-MS and HT-HPLC-ESI-MS/MS method were successfully applied in the screening of AM in commercial Coartem drug tablets. In the second section, direct MS-based methods, which use minimal sample preparation procedures and relatively small sample amounts were developed and optimised for fast screening of antimalarials. In the first part of this section, a time-of-flight secondary ion mass spectrometry (ToF-SIMS) method was optimised to screen for Cinchona alkaloids including quinine (Qn). ToF-SIMS analysis of Qn provided significant fingerprint SIMS fragments, which were later used in the fast qualitative screening of Qn and related compounds in small amounts of Cinchona bark and extract. The results demonstrate for the first time the ability of ToF-SIMS to perform direct analysis and fast qualitative screening (less than 10 minutes analysis time) of Cinchona alkaloids. In the second part of this section, an analytical method involving low-temperature plasma ambient desorption/ionisation mass spectrometry (LTP-ADI-MS) was developed and optimised for rapid qualitative screening of active antimalarial pharmaceutical ingredients. The method was shown to be capable of detecting the active ingredient in antimalarial drug tablets (Coartem and Malarone) as their protonated molecular ions and other characteristic ions in less than three minutes and with minimal sample preparation. Characteristic fragment ions of target molecules were used for structural identification even in the presence of a tablet matrix.Source Type:Doctoral Thesis3 10 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , Synthesis and characterization of novel photocrosslinkable poly(2-oxazoline)-based hydrogel systems for the application as biosensor matrix(2018)The main work of this thesis is focused on the synthesis and characterization of novel photocrosslinkable and thermoresponsive hydrogel systems for the application as biosensor matrix. Poly(2-oxazoline)s are very attractive polymers for this application, as they exhibit a lower critical solution temperature (LCST) in aqueous media, with the possibility of tuning this LCST by copolymerization of monomers with different hydrophobic side chains. For this purpose, an optimized synthesis route of a novel benzophenone-2-oxazoline-based photocrosslinker (BPOxa) photocrosslinker was developed and this monomer was copolymerized with various 2-alkyl-2-oxazolines (2-ethyl-, 2-n-propyl- and 2-isopropyl-2-oxazoline), to study the impact on the cloud point of the resulting thermoresponsive BPOxa copolymer systems. Here it was found that the large hydrophobic benzophenone moieties cause a significant decrease of the cloud point temperature compared to the corresponding 2-alkyl-2-oxazoline homopolymers. Poly(2-oxazoline)-based hydrogel layers were fabricated from these polymers by photocrosslinking with UV light at wavelength of 365 nm. The fabricated layers were characterized by surface plasmon resonance and optical waveguide mode spectroscopy (SPR/OWS) with respect to their swelling properties in aqueous media, showing that an increasing irradiation dose leads to a decrease in swelling ratio as a direct consequence of the higher crosslinking density in the respective hydrogel network. In addition, phase transition temperature and swelling ratio were studied for polymer networks of varying monomer composition, which was found to correlate to their cloud point in aqueous media. Another major application target of this thesis is the development of a multifunctional sensor matrix in SPR-based biosensors. For this purpose, an azido-2-oxazoline derivative (AzOxa) was developed, which can serve as a post-modification unit for the incorporation of analyte-specific ligands or as a conjugation site for antifouling motives to improve protein binding resistance of the polymer network. First, the impact of the novel azido-2-oxazoline comonomer on the cloud point of poly(2-ethyl-2-oxazoline) and poly(2-isopropyl-2-oxazoline) derivatives was studied. A linear decrease of the cloud point temperature for an increasing AzOxa content was found, which is contrary to the expected trend for increased polarity of polymers with higher amounts of the more polar azide group (compared to plain alkyl substituents), but apparently, a higher tendency for chain aggregation is introduced with the N3 groups. Additionally, different alkyne-modified antifouling motives (e.g. sulfo- and carboxybetains, oligoethylene glycol and oligoethylene glycol-sulfobetaine) were developed and incorporated into the AzOxa copolymer backbone by copper(I) catalyzed azide-alkyne cycloaddition reaction (CuAAC). The conjugated hydrogels were characterized by SPR/OWS, with respect to their swelling behavior in aqueous solution. It was found that the swelling ratio (SR) of the prepared hydrogel layers is strongly influenced by the nature of the alkyne conjugate, as the SR increases from the non-modified polymer to the oligoethylene glycol and the zwitterionic systems. The results are explained by the increasing hydrophilic character of the modified polymers in correlation to their cloud point in aqueous media. In addition, this work includes the synthesis and characterization of photocrosslinkable and thermoresponsive poly(N-isopropylacrylamide)-based and photocrosslinkable dextran-based hydrogel systems (in analogy to previous publications). Resulting applications are highlighted by the joint publications that emerged from the collaboration with Jakub Dostalek and Wolfgang Knoll in the context of the Austrian Institute of Technology (AIT) partner group.Source Type:Doctoral Thesis2 8 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , Untersuchungen zur Berufsorientierung als Baustein eines relevanten Chemieunterrichts im Vergleich zwischen Mittel- und Oberstufe sowie Darstellung des Chem-Trucking-Projekts als daraus abgeleitete Interventionsmaßnahme für den Chemieunterricht(2017)Because of the bad image of science and a relating threatening skills shortage, many institutions demand an increased implementation of career orientation in science education for example by using more authentic learning environments and public-private-partnerships between schools and industry. Furthermore, students need to recognize the relevance of science for their everyday life. In their relevance model Stuckey, Hofstein, Mamlok-Naaman und Eilks (2013) point out the vocational dimension as one of three dimensions of relevance of science education. Based on these considerations, the status quo of vocational orientation in chemical education and factors influencing students’ expectations concerning their professional orientation - especially in the field of chemistry - were evaluated. In spring 2015, 1113 students from the eigth and eleventh grade of various types of schools in the region of Siegen in Germany were sur-veyed. Through factor analysis and multiple linear regression, a model for each grade was developed, in which the students’ vocational orientation is described in relation to self-concept, self-to-prototype-matching and image of school chemistry lessons and chemistry in general. The results of the survey and the reported big influence of the image of chemistry lessons and the prototype of chemists on chemistry-related career orientation were taken into consideration to develop an intervention project. The so called Chem-Trucking-Project consists of a mobile environmental lab, that allows students to perform chemical analyses on site, based on real and authentic problems. To evaluate the project, a small sample of the project participants were given a self-developed questionnaire. First results indicate a positive influence on a chemistry-oriented career orientation.Source Type:Doctoral Thesis3 6
