Technische Universität Dresden: Qucosa
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Near-Field Optical Spectroscopy of Molecular Aggregates
No full textThe self-assembly of molecules leads to the formation of molecular aggregates where the strong interaction between the transition dipole moments of the molecules result in delocalised excited states. The absorption spectra of the aggregates, obtained through optical spectroscopy, provide rich information about the electronic states of the aggregates. We theoretically study the absorption properties of the aggregates on a dielectric surfaces in a scanning near-field optical microscopy (s-SNOM) setup. In this setup, the aggregates are placed very close to a metallic tip and interact with the near-field radiation emanating from the tip’s apex. The incident field at the tip induces a Hertz dipole on the metallic tip, with the polarisation and direction of the incident field determining the direction of the tip-dipole. We focus on understanding the dependence of the near-field spectra of the aggregate on the orientation of the incident radiation. Using a simple method, we evaluate the absorption of the eigenstates of aggregates because of the near-field of the tip and we find that the spectra strongly depend on the tip-dipole directions. For a general aggregate, we show that the polarisation dependence can be understood in terms of three fundamental functions that depend only on the arrangements of the molecules in an aggregate and the separation between the tip and the molecules. We present position-dependent absorption for different examples of single molecules and important cases of one-dimensional and two-dimensional aggregates obtained for different positions of the tip above the molecular plane. Our study shows the near-field spectra for different polarizations provide direct access to the eigenstates of the aggregate. Furthermore, we implement a detailed method to account for the back coupling of molecules to the tip since the molecules are placed near to the tip. We validate the results of the simple method, while explicitly treating the interaction of the tip and the molecules with incident radiation. We further investigate the absorption properties of interesting two-dimensional aggregates composed of two sublattice geometries, where each molecule possesses complex transition dipole moment. The periodic aggregates have bulk energy bands with non-trivial topology, leading to the presence of a number of excitonic edge states in finite size aggregates, and in these edge states excitations are present only at the boundaries. In typical far-field spectroscopy, where the aggregates interact with homogeneous electromagnetic fields, the edge states absorb very little compared to the bulk states, making them difficult to detect. We show that the strongly varying field from the tip in an s-SNOM setup can not only excite these edge states but also reveal their signature through spatially resolved near-field spectra. We find that the absorption of each edge state is localized at the boundaries, with distinct patterns resulting from their complex-valued eigenstates. Our analysis enables the detection of the topological phases in molecular aggregates by using near-field optical spectroscopy
The role of stand structural complexity and canopy space occupation for shaping biodiversity-productivity relationships: insights from tree diversity experiments
No full textThe increasing deforestation incites climate change, and climate change threatens the carbon mitigation potential of forests. Mixed-species tree communities are often promoted to improve ecosystem functioning and meet human needs. However, there is still a lack of understanding of the extent and dynamics of the mechanisms underlying positive biodiversity-productivity relationships (BPRs). Using data from two tree biodiversity-ecosystem functioning experiments, I examined the effects of tree diversity and mycorrhizal associations on stand structural complexity and productivity (study 1, MyDiv experiment, Germany) and the effects of tree species richness and leaf functional traits on canopy space filling and productivity (study 2, Sardinilla experiment, Panama). In addition, following my 2nd study, I tried to estimate the relative canopy space filling (RCSF) in different delineated canopy spaces and identify the canopy space that best correlated to productivity in my 3rd study (study 3, Sardinilla experiment). Terrestrial laser scanning was used to precisely quantify the three-dimensional characteristics of the stands. Tree growth data were used to analyse aboveground stand productivity at both study sites.
The results of study 1 showed that tree species richness increased stand productivity by increasing stand structural complexity with high light interception through functional diversity of shade tolerance, while mycorrhizal associations had no significant effect. I found in study 2 that species identity effect plays a crucial role than richness effect in canopy space filling, where communities dominated by conservative resource use showed higher canopy space filling and higher canopy space filling led to higher stand productivity. In both studies, positive biodiversity effects on stand structural complexity (study 1) and canopy space filling with functional diversity of leaf traits (study 2) arose due to taxonomic diversity of tree communities contributing to overyielding. Following study 2, study 3 demonstrated that positive and significant RCSF-productivity relationships were robust, while the strength of the relationships varied across different canopy space definitions. Interestingly, excluding the uppermost part and including the lowest part of the canopy resulted in distinct variations in explained variance in productivity. Additionally, mixtures played a very important role in RCSF-productivity relationships compared to monocultures.
This thesis contributes to a better understanding of the mechanisms of how tree diversity effect and identity effect simultaneously shape the forest structures and contribute to the biomass allocation patterns of the forest. All in all, the insights from this thesis recommend enhancing functional and taxonomic diversity in the afforestation and reforestation projects, contributing structural diversity to increase biomass allocation in order to combat the current climatic challenge
Investigation of processing and structural properties of cathodic arc deposited carbon-based coatings for bipolar plates
No full textWith the urgent need for renewable energy and clean mobility solutions, polymer electrolyte membrane fuel cells (PEMFCs) are a crucial technology. The performance and durability of a PEMFC are heavily dependent on the metallic bipolar plate which requires a protective and conductive coating to prevent corrosion and provide high electrical conductivity.
The aim of this thesis is the development and investigation of carbon-based coatings deposited via cathodic arc evaporation on SS316L substrates to improve the electrochemical properties and electrical conductivity for metallic bipolar plates. Cathodic arc evaporation offers distinct advantages in terms of high deposition rate and elevated ionization enabling rapid processing and precise tuning of coating properties. This capability allows for the development of coatings with enhanced performance characteristics important for metallic bipolar plates.
First, metal ion sputtering (MIS) for surface preparation is studied. The process duration was varied from 0 to 60 min revealing that a 15-minute MIS duration beneficial for a high corrosion and low contact resistance. Following this, the impact of the chromium interlayer thickness is investigated, showing its role in enhancing corrosion resistance and further reducing ICR. Central to this thesis is the systematic variation of the process parameters for the carbon top layer deposition, including bias voltage, process temperature and pressure as well as deposition time. Here, the focus is on the individual impact of the process parameters on the microstructure and resulting properties. The results indicate that a graphitic structure is crucial for achieving suitable bipolar-plate related properties. Additionally, the optimal deposition time is established to achieve a sufficient thickness without compromising coating properties. Based on the results, a parameter combination of -600 V bias voltage, 200 °C process temperature, 0.1 Pa process pressure, and a deposition time of 2 x 60 s is preferred to further optimize the carbon-based coating.
In conclusion, the combination of optimized parameters leads to a significant improvement of the functionality of SS16L as bipolar plate material via a more efficient and fast deposition process
Alkoholdehydrogenasen für die asymmetrische Reduktion zyklischer Carbonylverbindungen
No full textZinkabhängige Alkoholdehydrogenasen (ADH) sind vielversprechende Biokatalysatoren für die Synthese chiraler Hydroxylverbindungen, da sie Carbonylfunktionen meist mit hoher Stereoselektivität reduzieren können. Ihre Selektivität und die Breite an akzeptierten Substraten machen die ADH der mittelkettigen Dehydrogenasen/ Reduktasen (MDR)- Überfamilie besonders interessant für eine industrielle Anwendung. Die Mehrheit der MDR ADH bevorzugen linear aliphatische und phenylsubstituierte Aldehyde und Ketone. Ihre Substratspezifität und Stereoselektivität resultieren aus zwei unterschiedlich großen hydrophoben Substratbindetaschen, die die Orientierung der Substituenten der Carbonylgruppe vom Substratmolekül im aktiven Zentrum steuern. Die MDR ADH aus Thauera aromatica (ThaADH) katalysiert dagegen bevorzugt die Reduktion sterisch anspruchsvoller alizyklischer Carbonylverbindungen wie die des α-Diketons 1,2-Cyclo-hexandion. Die strukturellen Gründe für die einzigartige Substratspezifität der ThaADH innerhalb der MDR-Überfamilie sind trotz erster Vermutungen noch kaum erforscht. Ziel dieser Arbeit war es daher, die strukturellen Ursachen für die Präferenz zyklischer Carbonylverbindungen aufzuklären und die Eignung des Enzyms für eine industrielle Anwendung zu bewerten.
Im Rahmen einer Expressionsoptimierung konnte zunächst die Menge an Biokatalysator verdoppelt und eine beachtliche Aktivitätssteigerung um das 21-Fache erreicht werden. Neben dem für ADH mesophilen Ursprungs typischen temperaturabhängigen Aktivitätsprofil zeigte die ThaADH maximale Reaktionsgeschwindigkeiten bei pH 6,5 (Reduktion) bzw. pH 9,0 (Oxidation). Ihre thermische und pH-abhängige Stabilität betreffend, erwies sich die ThaADH als außerordentlich robust im Vergleich zu verwandten ADH. Die ermittelten Halbwertszeiten von mehreren Tagen (z.B. t1/2, 24 °C= 17 Tage) können einen entscheidenden Vorteil für eine industrielle Anwendung darstellen. Gegenüber organischen Lösungsmitteln zeigte die ThaADH ebenfalls eine vergleichsweise hohe Stabilität. Mit bspw. DMSO und Ethylenglykol stehen verschiedene Additive für den Einsatz in ThaADH-katalysierten Prozessen zur Auswahl, um u.a. eine verbesserte Löslichkeit der meist hydrophoben Substrate zu erreichen und damit die Effizienz der Biokatalyse zu erhöhen. Bei 10 % (v/v) DMSO im Reaktionsansatz zeigte die ThaADH eine hohe Restaktivität von 92 %. Ihre Lösungsmitteltoleranz bewies die ThaADH auch im Zweiphasensystem.
Von besonderem Interesse war die Untersuchung der außergewöhnlichen Substratspezifität und der Stereoselektivität. Die ThaADH zeigte eine hohe Substratspezifität und bevorzugte alizyklische Carbonylverbindungen wie das α-Diketon 1,2-Cyclohexandion und α-halogenierte Cycloalkanone. Ein elektronenziehender Substituent in direkter Nachbarschaft zur reagierenden Carbonylfunktion scheint die Umsetzbarkeit der Carbonylverbindungen zu fördern. Aromatische Verbindungen wurden vom Biokatalysator dagegen nicht reduziert, einige linear aliphatische Diketone mit geringer Reaktionsgeschwindigkeit. Mit (S)-2-Hydroxy-cyclohexanon (ee: 75 %) als Hauptprodukt der 1,2-Cyclohexandion-Reduktion folgt die ThaADH der Prelog-Regel ebenso wie viele andere MDR ADH. Neben der (S) Stereoselektivität konnte auch eine (S)-Stereospezifität der ThaADH festgestellt werden.
Zur Untersuchung der Struktur-Funktionsbeziehungen der ThaADH wurde zunächst die Enzymstruktur in Kooperation mit Prof. Gideon Grogan (University of York) aufgeklärt. Der Vergleich mit der verwandten Carbonylreduktase aus Candida parapsilosis (CPCR2) mit der klassischen Substratpräferenz zeigte entscheidende Unterschiede in der Architektur der aktiven Zentren. Die ThaADH besitzt, entgegen des bei MDR ADH vorherrschenden Zwei-Substratbindetaschen-Modells, eine einzelne große Substratbindetasche, die die Präferenz für zyklische Carbonylverbindungen begünstigen zu scheint. Ursächlich hierfür ist das Fehlen einer sperrigen aromatischen Aminosäure mit Keilfunktion am Taschenboden. Die Modellierung verschiedener Substratmoleküle im aktiven Zentrum der ThaADH führte zur Identifizierung von 15 am Aufbau der Substratbindetasche beteiligten strukturellen Determinanten. Zu diesen zählen der Protonendonor T44 und die koordinierenden Reste des in einer nicht katalytisch aktiven Position vorliegenden katalytischen Zinks C42, H65 und E66. Im Rest W302 könnte wiederum die Ursache für die fehlende Umsetzung γ-substituierter Cycloalkanone liegen. Der Grad der Hydrophobizität der Substratbindetasche, beeinflusst durch Y48 und M113, spielt durch das veränderte Potenzial hydrophobe Wechselwirkungen auszubilden ebenfalls eine Rolle für die Substratspezifität.
Mit der ADH aus Deferrisoma camini (DecADH), Geobacter bemidjiensis (GebADH) und Thauera phenylacetica (ThpADH) wurden drei alternative ADH identifiziert und durch heterologe Genexpression in E. coli hergestellt, die eine nahezu identische Substratpräferenz für alizyklische Carbonylverbindungen wie die ThaADH aufweisen. Die ADH zeigten eine hohe strukturelle Ähnlichkeit im aktiven Zentrum, was auf eine hohe Konserviertheit schließen lässt. Mit der DecADH wurde des Weiteren eine thermostabile ADH identifiziert, die für den Einsatz in industriellen Prozessen von besonderem Interesse sein könnte.
In dieser Arbeit wurden somit mehrere strukturelle Determinanten für die außergewöhnliche Substratspezifität der ThaADH für alizyklische α-substituierte Carbonylverbindungen identifiziert. Die gewonnenen Erkenntnisse tragen zu einem besseren Verständnis der Struktur-Funktionsbeziehungen zinkabhängiger MDR ADH bei. Ihre einzigartige Substratpräferenz kombiniert mit vorteilhaften biochemischen Eigenschaften, verleiht der ThaADH und der thermostabilen DecADH ein hohes Potenzial für die chirale Synthese industriell wertvoller (Zwischen-)Produkte einer bisher nicht erschlossenen Substratklasse.Zinc-dependent alcohol dehydrogenases (ADH) are promising biocatalysts for the synthesis of chiral hydroxyl compounds, due to their frequent ability to reduce carbonyl groups with high stereoselectivity. Their selectivity and broad substrate range make ADH of the medium-chain dehydrogenase/reductase (MDR) superfamily particularly interesting for industrial applications. Most MDR ADH prefer linear aliphatic and phenyl-substituted aldehydes and ketones. Their substrate specificity and stereoselectivity result from two differently sized hydrophobic substrate-binding pockets that control the orientation of the substituents of the carbonyl group of the substrate molecule in the active site. However, the ADH from Thauera aromatica (ThaADH) preferentially catalyzes the reduction of sterically demanding alicyclic carbonyl compounds such as the α-diketone 1,2-cyclohexanedione. The structural reasons for the unique substrate specificity of ThaADH within the MDR superfamily remain largely unexplored, despite initial hypotheses. Therefore, the aim of this study was to elucidate the structural causes for the preference of cyclic carbonyl compounds and evaluate the enzyme's suitability for industrial applications.
Initially, in the course of an expression optimization, the amount of biocatalyst was doubled, and a considerable increase in activity by a factor of 21 was achieved. In addition to the typical temperature-dependent activity profile of ADH with a mesophilic origin, ThaADH showed maximum reaction velocities at pH 6.5 (reduction) and pH 9.0 (oxidation). In terms of thermal and pH stability, ThaADH proved to be exceptionally robust compared to related ADH. The determined half-lives of several days (e.g., t1/2, 24 °C = 17 days) could offer an outstanding advantage for industrial applications. The ThaADH also exhibited relatively high stability in the presence of organic solvents. For example, with DMSO and ethylene glycol, various additives are available for use in ThaADH-catalyzed processes to improve the solubility of the typically hydrophobic substrates and thereby enhance the efficiency of biocatalysis. At 10% (v/v) DMSO in the reaction mixture, ThaADH exhibited a high residual activity of 92%. ThaADH also demonstrated its solvent tolerance in a two-phase system.
Of particular interest was the investigation of the exceptional substrate specificity and stereoselectivity. ThaADH showed a high substrate specificity and favored alicyclic carbonyl compounds such as the α-diketone 1,2-cyclohexanedione and α-halogenated cycloalkanones. The presence of an electron-withdrawing substituent in close proximity to the reacting carbonyl group appears to promote the reducibility of the carbonyl compounds. In contrast, aromatic compounds were not reduced by the biocatalyst, while some linear aliphatic diketones were accepted with low reaction rates. With (S)-2-hydroxycyclohexanone (ee: 75 %) as the main product of the 1,2-cyclohexanedione reduction, ThaADH follows the Prelog rule as well as many other MDR ADH. In addition to the (S)-stereoselectivity, ThaADH was also found to be (S)-stereospecific.
To investigate the structure-function relationships of ThaADH, the enzyme structure was first solved in cooperation with Prof. Gideon Grogan (University of York). The comparison with the related carbonyl reductase from Candida parapsilosis (CPCR2), which exhibits the conventional substrate preference, revealed decisive differences in the architecture of the active site. Contrary to the two substrate binding pockets prevalent in MDR ADH, ThaADH has a single large substrate binding pocket that favors the preference for cyclic carbonyl compounds. This can be attributed to the absence of a bulky aromatic amino acid with a wedge-like function at the bottom of the pocket. The modeling of different substrate molecules in the active site of ThaADH led to the identification of 15 structural determinants defining the substrate binding pocket. These include the proton donor T44 and the coordinating residues of the active zinc in a non-catalytically active position C42, H65, and E66. The residue W302 could in turn be the reason for the lack of conversion of γ-substituted cycloalkanones. The degree of hydrophobicity of the substrate binding pocket, influenced by Y48 and M113, also plays a role in substrate specificity due to the altered potential to form hydrophobic interactions.
With the ADH from Deferrisoma camini (DecADH), Geobacter bemidjiensis (GebADH) and Thauera phenylacetica (ThpADH), three alternative ADHs were identified and produced by heterologous gene expression in E. coli, which show an almost identical substrate preference for alicyclic carbonyl compounds as ThaADH. The ADH showed a high structural similarity in the active site, suggesting a high degree of conservation. DecADH was also identified as a thermostable ADH that could be of particular interest for use in industrial processes.
Thus, several structural determinants for the exceptional substrate specificity of ThaADH for alicyclic α-substituted carbonyl compounds were identified in this work. The insights gained contribute to a better understanding of the structure-function relationships of zinc-dependent MDR ADH. The uniqueness in the substrate preference combined with favorable biochemical properties gives ThaADH and the thermostable DecADH a high potential for the chiral synthesis of industrially valuable intermediates and products of a previously unexplored substrate class
ESG 2025 – Relevanz, Herausforderungen und strategische Perspektiven in deutschen Unternehmen: Kurzbericht auf Basis einer Civey Studie
No full textAus Punkt 1:
Die Diskussion zu den Themen Umwelt (Environmental), Soziales (Social) und Unternehmensführung (Governance) (ESG) – hat sich in den letzten Jahren zunehmend polarisiert. Während einige Stimmen das Konzept als ideologisch motiviert ansehen, oder es als bloßes Marketinginstrument kritisieren, das zunehmend obsolet wird, zeigt die vorliegende Studie ein differenzierteres Bild. Befragt wurden zwischen dem 10.02. und 04.03.2025 rund 1.500 privatwirtschaftliche Entscheidungsträger:innen aus Unternehmen mit mindestens 50 Mitarbeitenden in Deutschland. Die Ergebnisse liefern Einblicke in die aktuelle Praxis und strategische Ausrichtung deutscher Unternehmen hinsichtlich ESG-relevanter Themen.:1. Hinführung und Studiendesign 2
2. ESG ist nicht tot – wird aber strategischer 2
3. Schutz von Demokratie und Minderheiten gewinnt an Bedeutung – Unternehmerische Positionierung wird aber ambivalent bewertet 3
4. Umweltziele dominieren, gesellschaftspolitische Themen polarisieren 5
5. Diversität und Inklusion wird kritisch gesehen 6
6. Deutschland agiert moderat im internationalen ESG-Vergleich 7
7. ESG ist immer noch ein Nischenthema in der Unternehmensstrategie 8
8. Themen mit Zukunft: Energie und Emissionsreduktion 9
9. Schlussbetrachtung und Implikationen für Wirtschaft und Forschung 9
10. Quellen und statistische Angaben 12
Autoren 1