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Item Open Access Entwicklung laserspektroskopischer Methoden zur Analyse der Verdunstungseigenschaften von Brennstofftropfen(Stuttgart : Deutsches Zentrum für Luft- und Raumfahrt, Institut für Verbrennungstechnik, 2021) Werner, Stefanie; Riedel, Uwe (Prof. Dr. rer. nat.)Die steigenden Emissionen des klimaschädlichen Treibhausgases CO2 durch die Verbrennung von fossilen, endlichen Energieträgern müssen möglichst schnell und nachhaltig reduziert werden. Ein vielversprechender Lösungsansatz zur Reduzierung der Schadstoffemissionen bei der Verbrennung liegt in dem Einsatz von alternativen und erneuerbaren Brennstoffen. Als Energieträger bieten sich auf Grund ihrer hohen Energiedichte vor allem flüssige Brennstoffe an. Diese werden typischerweise durch Druckzerstäubung in die Brennkammer eingebracht, verdunstet und dann mit dem Oxidationsmittel vermischt und verbrannt. Die Verdunstung der kleinen Brennstofftropfen des sogenannten Sprays ist von entscheidender Bedeutung für den Gesamtverbrennungsprozess in Verbrennungsmotoren und Gasturbinen. Im Allgemeinen bestimmt die Verdunstungsrate die Verbrennungsrate. Daher sind Modelle notwendig, die eine genaue Vorhersage der Brennstoffverdunstung ermöglichen. Zur Validierung dieser Modelle werden quantitative Messungen unter genau definierten Randbedingungen benötigt. Da die Prozesse in technischen Brennkammern sehr komplex sind, werden Experimente zur Tropfenverdunstung häufig mit linearen, monodispersen Tropfenketten durchgeführt, um die Kopplung zwischen den verschiedenen Effekten zu minimieren. Durch die geringe Größe der Tropfen (typischerweise wenige hundert Mikrometer oder weniger), erfordert die experimentelle Untersuchung eine hohe räumliche Auflösung. In dieser Arbeit wurden quantitative, laseroptische Messtechniken mit hoher räumlicher Auflösung zur experimentellen Untersuchung der Tropfenverdunstung an monodispersen Tropfenketten entwickelt. Mit den Messtechniken wurden Validierungsdaten für die Verdunstungseigenschaften von verschiedenen Brennstoffen bestimmt. Konzentrationsmessungen von verdunsteten Kohlenwasserstoffen wurden unter Verwendung von Infrarot-Laserabsorptionsspektroskopie und laserinduzierter Fluoreszenzspektroskopie (LIF) durchgeführt. Tropfenketten wurden mit einem Tropfenkettengenerator erzeugt, welcher vertikal in einem Strömungskanal installiert wurde. Die untersuchten Brennstoffe waren Cyclohexan, iso-Octan, n-Heptan, n-Pentan, 1-Butanol und Anisol. Der Strömungskanal wurde mit einer laminaren Luftströmung bei verschiedenen Temperaturen (313 K - 430 K) durchströmt. Da die untersuchten Tropfen einen Durchmesser in der Größenordnung von 120 bis 160 µm hatten und die Konzentrationsgradienten nahe der Tropfenoberfläche groß waren, war eine hohe räumliche Auflösung der Messtechniken erforderlich. Die Absorptionsmessungen wurden mit der Infrarotstrahlung eines HeNe-Lasers bei λ = 3,39 µm durchgeführt, um die CH-Streckschwingung der Kohlenwasserstoffe anzuregen. Die für die Quantifizierung der Brennstoffkonzentrationen benötigten Absorptionsquerschnitte wurden in einer beheizten Gaszelle für Temperaturen von 300 K - 773 K bestimmt. Die räumliche Auflösung im Strömungskanal betrug < 50 µm über eine Länge von 2 mm (Halbwertsbreite). Durch die Zylindersymmetrie und gute Stabilität der Tropfenketten konnten zeitliche Mittelungs- und Tomografieverfahren angewandt werden. Hierdurch konnten radiale Konzentrationsprofile an mehreren Positionen im Strömungskanal erhalten werden. Aus dem Anstieg der Dampfkonzentration an verschiedenen Messpositionen konnte die Verdunstungsrate bestimmt werden. Die Verdunstungsraten wurden in Abhängigkeit von der Mantelstromtemperatur (313 K - 430 K), der Tropfengeschwindigkeit (8 m/s - 23 m/s), der Tropfenerzeugungsfrequenz (12 kHz - 75 kHz) und dem Tropfenabstand (300 µm - 685 µm) gemessen. Im untersuchten Temperaturbereich steigt die Verdunstungsrate des Brennstoffs linear mit der Temperatur an. Die Reihenfolge der Brennstoffe in Bezug auf die Verdunstungsrate entspricht den Siedepunkten der einzelnen Brennstoffe. Da technische Brennstoffe häufig eine Mischung mehrerer Komponenten sind, ist die Untersuchung von Brennstoffgemischen von großem Interesse. Daher wurde ein Messverfahren entwickelt, um binäre Gemische zu untersuchen. Das Verfahren wurde verwendet, um eine Mischung aus Cyclohexan und Anisol zu untersuchen. Zwei Messtechniken - laserinduzierte Fluoreszenz (LIF) und Infrarot Absorptionsspektroskopie - wurden verwendet, um beide Spezies zu messen. Um λ = 3,39 µm ist der Absorptionsquerschnitt von Cyclohexan um etwa den Faktor 8 größer als von Anisol. Im untersuchten Fall war die Konzentration aufgrund des höheren Dampfdrucks ebenfalls deutlich größer. Daher konnte das Infrarot-Absorptionssignal praktisch ausschließlich Cyclohexan zugeordnet werden. Anisol hat bei Anregung bei λ = 266 nm eine sehr gute Fluoreszenzquantenausbeute, während Cyclohexan keine Fluoreszenz zeigt. LIF ermöglicht daher die Quantifizierung von Anisol (oder anderen Aromaten) ohne Interferenz durch Kohlenwasserstoffe. Es wurde ein Messverfahren entwickelt, welches Halationseffekte vermeidet, die typischerweise in planaren LIF-Experimenten an Tropfenketten auftreten. Kalibrationsmessungen, die im gleichen Strömungskanal durchgeführt wurden, ermöglichten die Quantifizierung der verdunsteten Anisolkonzentrationen. Die räumliche Auflösung betrug 80 µm. Ähnlich wie bei den Einzelkomponentenmessungen wurden Verdunstungsraten bestimmt. Wie aufgrund des niedrigeren Dampfdrucks zu erwarten, ist die Verdunstungsrate von Anisol niedriger als die von Cyclohexan. Die Verdunstungsrate von Cyclohexan in der binären Mischung stimmt gut mit den Einzelkomponentenmessungen überein. Das entwickelte Messverfahren ist sehr vielversprechend für weitere Untersuchungen an Mehrkomponentenmischungen. In dieser Arbeit konnte damit erstmals mit hoher räumlicher Auflösung die Verdunstung von Brennstoffkomponenten mittels Absorptionsspektroskopie in der Nähe von Brennstofftropfen untersucht werden. Zusätzlich wurden in Kombination mit laserinduzierter Fluoreszenzspektroskopie Messungen an binären Mischungen durchgeführt. Damit steht ein wertvoller Datensatz zur Validierung von numerischen Simulationen zur Verfügung.Item Open Access Enzymatic asymmetric dihydroxylation of alkenes(2016) Gally, Christine; Hauer, Bernhard (Prof. Dr.)The introduction of chirality into C=C double bonds is of special interest in organic synthesis. In particular, the catalytic asymmetric dihydroxylation (AD) of alkenes has attracted considerable attention due to the facile transformation of the chiral diol products into valuable derivatives. By chemical means, the metal-catalyzed AD of olefins provides both stereo- and regiospecific cis-diol moieties. Next to their toxicity, however, these metal catalysts can also lead to byproduct formation as a result of oxidative fission. In nature, Rieske non-heme iron oxygenases (ROs) represent promising biocatalysts for this reaction since they are the only enzymes known to catalyze the stereoselective formation of vicinal cis-diols in one step. ROs are key enzymes in the degradation of aromatic hydrocarbons and can target a wide variety of different arenes. Despite their broad substrate scope, limited data is available for the conversion of unnatural substrates by this class of enzymes. To explore their potential for alkene oxidation, three ROs were tested for the oxyfunctionalization of a set of structurally diverse olefins including linear and cyclic arene-substituted alkenes, cycloalkenes as well as several terpenes. Naphthalene- (NDO), benzene- (BDO) and cumene dioxygenases (CDO) from different Pseudomonas strains where selected as they are amongst the RO enzymes that have already been reported to catalyze the oxidation of a small number of olefins. The majority of compounds from the selected substrate panel could be converted by NDO, BDO or CDO and products were either isolated and identified by NMR analysis or using the authentic standards. Dependent on the substrate, allylic monohydroxylation was found in addition to the corresponding diol products, a reaction which is chemically still most reliably achieved by the use of SeO2 in stoichiometric amounts. However, having been evolved for the dihydroxylation of aromatic compounds, wild type ROs displayed low conversions (< 50%) and modest stereoselectivities (≤ 80% ee/de) for several of the tested olefins. To overcome these limitations, changes in the active site topology of RO catalysts were introduced. A single targeted point mutation that was identified based on sequence and structural comparisons with other members of the RO family proved to be sufficient to generate BDO and CDO variants displaying remarkable changes in regio- and stereoselectivity for various substrates. In particular biotransformations with CDO M232A gave excellent stereoselectivities (≥ 95% ee/de) and good activities (> 90%) also for linear alkenes, which have been reported to be challenging substrates for RO-catalyzed oxyfunctionalizations. Site-saturation mutagenesis at position 232 in CDO revealed a correlation between the steric demand of the amino acid side chain and its influence on regio- and/ or stereoselectivities for styrene and indene. While the wild type enzyme almost exclusively catalyzed the dihydroxylation of the aromatic ring, the regioselectivity was shifted with decreasing side chain size to the terminal vinyl group of styrene, yielding up to 96% of the alkene-1,2-diol. For cis-1,2-indandiol formation, enantiocomplementary enzymes could be generated, a fact further highlighting the importance of position 232 for the engineering of ROs. Moreover, site-saturation mutagenesis of additional residues in the substrate binding pocket of CDO (F278, I288, I336 and F378) identified further positions having an influence on selectivity and product formation for alkene oxidation. To proof the applicability of ROs for organic synthesis, semi-preparative scale biotransformations (70 mg) of selected substrates were performed with CDO M232A. Without further optimization of the reaction set-up, products were successfully isolated in > 30% yield. In addition, up-scaling of (R)-limonene hydroxylation to 4 L in a bioreactor with growing cells gave final isolated product titers of 0.4 g L-1 even though substrate volatility and product toxicity diminished the yield. In conclusion, these examples demonstrated that a single point mutation was sufficient to transform CDO wild type into an efficient catalyst, furthermore constituting the first example of the rational engineering of CDO and BDO enzymes for the oxyfunctionalization of a broad range of alkenes.Item Open Access Oleathydratase katalysierte stereoselektive Hydratisierungsreaktionen kurzkettiger Alkene(2025) Härterich, Natalie; Hauer, Bernhard (Prof. Dr.)Item Open Access Growth of oxide materials with Ruddlesden-Popper- and garnet-type structures via the optical float zone method: investigations of scintillation, optical, and magnetic properties, and post-growth modifications of single crystals via topochemical routes(2025) Yilmaz, Hasan; Clemens, Oliver (Prof. Dr.)With the continuous progress in materials science, the global market demand for high-performance functional materials, especially those with customized optical and magnetic properties, has increased significantly due to their critical role in next-generation technologies such as photonic devices, data storage systems, quantum computing, and biomedical applications. With this motivation, this dissertation is focused on the growth of high-quality oxide single crystals with Ruddlesden-Popper (RP) and garnet-type structures using the optical floating zone (OFZ) method and the detailed investigation of their scintillation, optical and magnetic properties. Furthermore, the use of chemical doping and post-growth topochemical modifications as strategies to modify material properties and stabilise metastable structures is also covered. With these approaches, we can classify this study into two parts: optical and magnetic properties. In the first part of this work, RP-type n = 1 LaSrGaO4 (LSGO) and Garnet-type Gd3In2Ga3O12 (GIGG) single crystals doped with different Rare Earths (RE) including Eu, Sm, Ho, Nd have been grown via OFZ method to investigate their luminescence, decay time kinetics and scintillation properties. To compare the scintillation behaviour, a well-known commercial scintillator, Gd2.98Ce0.02Al2Ga3O12 (0.02Ce:GAGG) single crystal, was synthesised and characterised using the same methods. This limits deviations in scintillation properties caused by different synthesis methods. Powder X-ray diffraction (XRD) and Single Crystal X-ray diffraction (SC-XRD) measurements together with Rietveld analysis confirmed phase purity and crystallinity, while Scanning Electron Microscopy (SEM-EDX) and backscatter electron imaging (BSE) confirmed the homogeneous distribution of the dopants. In addition to these analytical methods, Photoluminescence Spectroscopy (PL) and luminescence decay measurements have demonstrated that these RE-doped single crystals have strong emission, which is related to the low phonon energy of their host lattices. However, scintillation measurements under 137Cs gamma-ray point source excitation resulted in a limited gamma ray response. This response was significantly weaker than observed for the well-known commercial scintillator 0.02Ce:GAGG. Inefficient absorption of high-energy excitation or inadequate energy transfer to the activator ions in these materials are responsible for this relatively low scintillation performance. The second part of the thesis is focused on bilayer Ruddlesden-Popper nickelates. Single crystals of Sr3Ni2-xAlxO7-δ (SNAO) and its Y-substituted modification YᵧSr3-yNi2-xAlxO7-δ (YSNAO) have been grown by using strategically chemical substitutions and high oxygen pressure conditions to stabilize the RP phase. XRD and SC-XRD analysis confirmed the existence of the n = 2 RP-type structure by doping with Al, while thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS) indicated successful oxygen incorporation and corresponding changes in the Ni oxidation state. Magnetic susceptibility measurements (SQUID magnetometry) have demonstrated the antiferromagnetic ordering transitions in these doped nickelate single crystals, and transport measurements have shown enhanced electrical conductivity compared to the undoped parent compound. In addition, a topochemical fluorination process has been investigated as a post-growth modification for n = 1 RP-type La2NiO4+δ single crystals. Fluorine has been introduced into the crystal lattice at moderate temperatures using polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and CuF2 as fluorination reagent. PTFE has been found to be the most effective fluorinating agent, resulting in partially fluorinated La2NiO4+δ with a diffusion-limited penetration pattern. EDX and EDX-mapping analyses have demonstrated an inhomogeneous F distribution, indicating that fluorine incorporation is limited by diffusion kinetics. This inhomogeneity should be carefully considered in future structural and functional analyses as it may affect the accurate characterisation of intrinsic properties in fluorinated crystals. In summary, the results of this thesis demonstrate the flexibility of the optical floating zone technique for the growth of high-quality functional oxides and show how structural stability, and functional properties can be modified using specific chemical doping approaches. To optimise scintillation performance in novel garnet-type hosts and to improve the magnetic and electronic behaviour of RP-type nickelates, the combined approach of crystal growth and post-growth modification could provide an additional parameter for material modification.Item Open Access Polymer analogous reactions on redox-active and conjugated polymers for electronic applications(2021) Kuhlmann, Jochen; Ludwigs, Sabine (Prof. Dr.)Item Open Access Calculation of pure substance and mixture viscosities using PCP-SAFT and entropy scaling(Stuttgart : Universität Stuttgart, Institut für Technische Thermodynamik und Thermische Verfahrenstechnik, 2020) Lötgering-Lin, Oliver; Gross, Joachim (Prof. Dr.-Ing.)Item Open Access Biochemical characterization and identification of novel substrates of protein lysine methyltransferases(2019) Schuhmacher, Maren Kirstin; Jeltsch, Albert (Prof. Dr.)The methylation of lysine side chains is a prevalent post-translational modification (PTM) of proteins, which is introduced by protein lysine methyltransferases (PKMTs). Histone methylation can have different effects on chromatin structure, lysine methylation of non-histone proteins can regulate protein/protein interactions and protein stability. For most PKMTs currently not all methylation sites are known which limits our understanding of the regulatory role of these enzymes in cells. Therefore, it is an important research aim to gain more information about the substrate spectrum of PKMTs. The identification of the substrate specificity of a PKMT is a very important step on the way to identify new PKMT methylation sites. The focus of this study was the analysis of the substrate specificity of different PKMTs by SPOT peptide arrays and based on this on the identification and validation of possible new methylation substrates. The analysis of the substrate specificity of human SUV39H2 revealed significant differences to its human homolog SUV39H1, although both enzymes methylate the same histone substrate (H3K9). SUV39H2 is more stringent than the SUV39H1, which could be demonstrated by the lack of methylation of SUV39H1 non-histone targets by SUV39H2 and by the fact that it was not possible in this study to identify non-histone substrates for SUV39H2. Kinetic studies showed that SUV39H2 prefers the unmethylated H3K9 as substrate. Moreover, it was shown that the N324K mutation of SUV39H2 which leads to a genetic disease in Labrador retrievers causes a change in folding finally leading to the inactivation of the enzyme. It had been reported by another group that the histone variant H2AX is methylated by SUV39H2. However, the sequence of H2AX K134 does not fit to the substrate specificity profile of SUV39H2 determined in the present work. Follow-up in vitro peptide and protein methylation studies indeed showed that H2AX K134 is not methylated by SUV39H2. This indicates that H2AX methylation by SUV39H2 is most probably a wrong assignment of a substrate to a PKMT. Based on already available specificity data for the SUV39H1 PKMT, the SET8 protein was validated as novel substrate in cellular studies. SET8 is a PKMT itself and it could be shown in this thesis that methylation of SET8 at residue K210 by SUV39H1 stimulated the SET8 activity. In humans, there exist different PKMTs, which methylate H3K36. For example, NSD1, NSD2 and SETD2 which were investigated in this thesis. In literature, it was shown that the oncohistone mutation K36M inactivates NSD2 and SETD2. Steady-state methylation kinetics using a peptide substrate and a K36M peptide as inhibitor revealed that NSD1 is inhibited by this histone oncomutation as well. The steady-state inhibition parameters for all enzymes showed a better binding of the PKMTs to the inhibitor peptide than to the substrate, suggesting some mechanistic similarities in target peptide interaction. The SETD2 is a methyltransferase, which is able to introduce trimethylation of H3K36. During this thesis two substrate specificity motifs of SETD2 were determined using peptide array methylation experiments. Additionally, based on the substrate specificity investigations a super-substrate at peptide and protein level was determined. Furthermore, one novel substrate (FBN1) for SETD2 was discovered and validated. The Legionella pneumophila RomA PKMT was shown previously by our collaborators to methylate H3 at K14. Based on the specificity profile of RomA determined in this study it could be shown that this enzyme methylates seven additional human non-histone proteins. Collaborators tested the methylation of one of the non-histone targets (AROS) and could demonstrate its methylation during the infection of human cells with L. pneumophila. The role of these methylation events in the infection process must be studied in future experiments.Item Open Access Phase-space resolved decay rates of driven systems near the transition state(2020) Feldmaier, Matthias; Main, Jörg (Prof. Dr.)Die Bewegung einzelner Atome oder Moleküle bei chemischen Reaktionen lässt sich in vielen Fällen durch klassische Mechanik auf einer Born-Oppenheimer Potentialfläche beschreiben. Hierbei sind die Reaktanten oft durch eine Rang-1 Barriere von den Produkten getrennt. Eine solche Barriere ist durch einen instabilen Freiheitsgrad, die Reaktionskoordinate und eine gegebene Anzahl an stabilen Freiheitsgraden, die orthogonalen Moden, charakterisiert. Eine reagierende Trajektorie wird die Barriere meist in der Sattelregion, d. h. in einer direkten Umgebung des Sattels, überqueren. Diese Region fungiert als Flaschenhals für die Reaktion. Im Rahmen der Theorie der Übergangszustände (engl. transition state theory, TST) können Reaktionsraten über den Fluss reaktiver Trajektorien durch eine nur einmal durchstoßene Trennfläche (engl. dividing surface, DS) berechnet werden. Eine solche Trennfläche ist an der normal hyperbolischen invarianten Mannigfaltigkeit (NHIM) des Sattels verankert und trennt das System in Reaktanten und Produkte. Die NHIM ist dabei ein spezieller Unterraum des vollen Phasenraums und enthält Trajektorien, welche für alle Zeiten an die Sattelregion gebunden sind. Da diese Trajektorien somit weder zur Reaktanten- noch zur Produktseite gehören, bildet die NHIM einen Übergangszustand (engl. transition state, TS) der Reaktion. Für getriebene Systeme ist dieser zeitabhängig. In dieser Arbeit werden anhand eines zweidimensionalen, getriebenen Modellsystems mehrere Methoden zur Berechnung von NHIM und DS im Phasenraum vorgestellt. Basierend auf der Dynamik in einer direkten Umgebung der NHIM werden außerdem verschiedene Ansätze zur Berechnung des zugehörigen Zerfalls der Reaktantenpopulation nahe des TS diskutiert. Anschließend werden die vorgestellten Methoden auf ein realistischeres chemisches Modell angewandt, der getriebenen LiCN <-> LiNC Isomerisationsreaktion. Ein wichtiges Resultat hierbei ist, dass das externe Treiben dieses Systems einen großen Einfluss hat, sowohl auf die Dynamik von Trajektorien in der NHIM, als auch auf den zugehörigen Zerfall der Reaktantenpopulation nahe des TS.Item Open Access Development of a chemoenzymatic (-)-menthol synthesis(2018) Kreß, Nico; Hauer, Bernhard (Prof. Dr.)Biocatalysis is an emergent research area for the development of efficient and sustainable synthesis processes. A crucial milestone for the better applicability of biocatalysts thereby consists of the increasing knowledge of the adaptability of enzymes for distinct synthetic needs like the conversion of specific molecular structures with defined selectivity. In addition, it is equally important to demonstrate that such novel catalysts are combinable among themselves and with established non enzymatic catalysts to enable unexplored synthetic routes. Using the example of the chemoenzymatic synthesis of (-)-menthol from citral, this work therefore addresses the development and applicability of such evolved enzyme catalysts for the synthesis of an industrially relevant molecule. In this complementary synthetic route inspired from an existing industrial process, a mixture of citral isomers is reduced to citronellal using an R-selective ene reductase. In a subsequent Prins reaction, the selective cyclization of R-citronellal to (-)-isopulegol is achieved by the application of an engineered squalene hopene cyclase variant. The final reduction to (-)-menthol proceeds by hydrogenation on a palladium catalyst. Especially the first catalytic step enables an immediate synthetic advantage in comparison to the currently performed industrial process. So far, no catalyst is applied converting both isomers of citral R-selectively at the same time. Both isomers have to be separated under high energy expenditure by distillation prior to reduction. No enzymatic catalyst is described displaying this reactivity yet. As, however, the opposite enantioconvergent S-selective citral reduction by ene reductases is known, the development of an enzyme catalyst constituted an attractive solution for this limitation. Hence, a focus of the work laid on the inversion of the S-selectivity of the citral reduction by NCR ene reductase from Zymomonas mobilis by enzyme engineering. The studies started by characterization of the citral reduction by NCR wild type. Next to the determination of the course of the reaction over time, semi empiric quantum mechanics calculations on the oxidative half reaction of this conversion were carried out. The calculations suggest a so far undescribed catalytic role of an arginine at position 224 for a facilitated hydride transfer and a more complex proton shift involving water molecules in the reaction. The subsequently performed engineering comprised the identification of selectivity determining amino acid positions W66, Y177, I231 and F269 in the active site of the enzyme followed by their variation in an iterative combinatorial fashion. In order to enable the analysis of the multitude of generated enzyme variants, a whole cell screening was developed using chiral gas chromatography. Thereby, the triple variant W66A/I231R/F269V was created converting E/Z-citral in the whole system to R-citronellal with an enantiomeric excess of 89 %. It could be determined that a cell induced citral isomerization leads to increased enantioselectivity in comparison to using purified enzyme. Especially for the influence of the selectivity determining positions W66 and I231 an increased understanding of structure function relations was achieved during the course of semi rational enzyme evolution by the separated analysis of single citral isomers and by supportive in silico analyses like docking and molecular dynamics simulations. The subsequent integration of the established variant A419G/Y420C/G600A of the squalene hopene cyclase from Alicyclobacillus acidocaldarius is remarkable catalyzing the Prins cyclization to (-)-isopulegol with an enantiomeric excess of 99 % and a diastereoselectivity of 90 %. In this context, the enzyme’s underlying Brønsted acid chemistry could be evolved towards the in nature unknown Prins reaction reactivity. In this work it could be shown that enzyme catalysts acquired by such chemical inspection can be implemented in application oriented synthetic routes. In combination with the developed selective ene reductase, the bienzymatic cascade to (-)-isopulegol was successfully performed and characterized. For the final reduction to (-)-menthol an established heterogeneous catalyst like palladium on charcoal could be applied under hydrogen atmosphere. This demonstrates nicely that novel biocatalysts can be combined with approved synthetic processes. With the attained insights, highly valuable (-)-menthol was made accessible for the first time by a chemoenzymatic cascade using an isomeric mixture of citral on preparative scale with 7 % isolated yield. This work not only highlights different strategies for the development of novel biocatalysts, but also contributes to their possible synthetic applicability in the synthesis of industrially relevant molecules.Item Open Access Monodisperse highly ordered and polydisperse biobased solid foams(2018) Andrieux, Sébastien; Stubenrauch, Cosima (Prof. Dr.)The aim of this work was the synthesis of monodisperse highly ordered biobased polymer foams and a comparison with their polydisperse counterparts. We used the biobased and biodegradable polymer chitosan, which we cross-linked with genipin. The polymer foams were synthesised via foam templating, i.e. via a liquid foam whose continuous phase contains a polymer and can be solidified. In order to obtain monodisperse highly ordered polymer foams, one first has to generate monodisperse highly ordered liquid foam templates. We did so by using microfluidics, which allows to produce monodisperse liquid foams with bubble sizes from 200 µm to 800 µm and polydispersities below 5%. The monodisperse foams were collected outside of the microfluidic channels and left to self-order under the influence of gravity and confinement. We studied the kinetics of the cross-linking reaction to find the optimal storage conditions during cross-linking. Once cross-linked we freeze-dried the gelled foams to obtain solid chitosan foams. We compared the morphological properties of the solid foams with those of the liquid templates in order to test the efficiency of the developed templating route. We observed how modifying the cross-linking and drying conditions can strongly affect the morphology of the solid foams. The main issue was to maintain the key properties of the liquid foam template throughout the solidification process, namely the bubble size distribution, the structural order and the density. We then compared the synthesised monodisperse polymer foams with their polydisperse counterparts. Although easy foaming methods exist for the generation of polydisperse foams, they do not allow the control over the polydispersity. We thus used microfluidics to generate liquid chitosan foams with tunable polydispersities from below 5% up to 26%. Microfluidics allows to match the average bubble size and density of the polydisperse liquid chitosan foam with those of the monodisperse counterpart. After solidifying the liquid templates we obtained solid foams with controlled polydispersities and studied the in uence of the polydispersity on the mechanical properties. However, we observed that not the polydispersity but the foam density was the main parameter at play. Moreover, the solid chitosan foams had weak mechanical properties with elastic moduli below 100 kPa. To overcome this issue, we incorporated cellulose nanofibres to the original chitosan solution and followed the developed route for foam templating. We had to adapt the microfluidic parameters to account for the viscosity changes brought about by the nanofibres. However, we managed to produce monodisperse liquid foams having the same bubble size, i.e. ~300 µm, but different amounts of cellulose nanofibres. The cellulose content had a strong influence on the solid foam morphology in general and on the pore connectivity in particular.