03 Fakultät Chemie
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Item Open Access Specific DNMT3C flanking sequence preferences facilitate methylation of young murine retrotransposons(2024) Dossmann, Leonie; Emperle, Max; Dukatz, Michael; de Mendoza, Alex; Bashtrykov, Pavel; Jeltsch, AlbertThe DNA methyltransferase DNMT3C appeared as a duplication of the DNMT3B gene in muroids and is required for silencing of young retrotransposons in the male germline. Using specialized assay systems, we investigate the flanking sequence preferences of DNMT3C and observe characteristic preferences for cytosine at the -2 and -1 flank that are unique among DNMT3 enzymes. We identify two amino acids in the catalytic domain of DNMT3C (C543 and V547) that are responsible for the DNMT3C-specific flanking sequence preferences and evolutionary conserved in muroids. Reanalysis of published data shows that DNMT3C flanking preferences are consistent with genome-wide methylation patterns in mouse ES cells only expressing DNMT3C. Strikingly, we show that CpG sites with the preferred flanking sequences of DNMT3C are enriched in murine retrotransposons that were previously identified as DNMT3C targets. Finally, we demonstrate experimentally that DNMT3C has elevated methylation activity on substrates derived from these biological targets. Our data show that DNMT3C flanking sequence preferences match the sequences of young murine retrotransposons which facilitates their methylation. By this, our data provide mechanistic insights into the molecular co-evolution of repeat elements and (epi)genetic defense systems dedicated to maintain genomic stability in mammals.Item Open Access Redox-acid/base phase diagrams as an entry to computational redox chemistry(2024) Becker, Patrick M.; Heinze, Katja; Sarkar, Biprajit; Kästner, JohannesThe rapid depletion of fossil fuels and the change from conventional energy supply to so‐called sustainable and renewable energy sources have led to a renaissance of electrochemical, photochemical, and photoelectrochemical methods for chemical synthesis. While drastic experimental improvements have been realized in recent years, systematic computational studies of these types of reactions are, however, rather limited caused by a lack of suitable representations. Herein we present a generalized method to investigate and analyze a chemical system with respect to its redox‐ and acid/base‐properties based on Gibbs free‐energy differences. We represent the results in a clear manner by means of redox-acid/base phase diagrams. Motivated by computational needs, the presented method is a direct link between experimentally measurable values and Gibbs free‐energy profiles, connecting experiment and simulation. Thus, it serves as an entry to systematic computational studies of reactions, which involve a combination of electron transfers and acid/base‐chemical reaction steps, because it enables the representation of both thermodynamic and kinetic properties. The presented method is applied to four exemplary systems: Phenol, dicobaltocenium amine as a proton‐coupled electron transfer (PCET) reactant, and two porphyrin Ni II catalysts for the electrocatalytic hydrogen evolution reaction (HER).Item Open Access Understanding the temperature-induced decomposition of commercial nickel-cobalt-aluminum oxide (LiNi0.8Co0.15Al0.05O2) electrodes(2025) Hölderle, Tobias; Baran, Volodymyr; Schökel, Alexander; Westphal, Lea; Stelzer, Robert U.; Niewa, Rainer; Müller‐Buschbaum, Peter; Senyshyn, AnatoliyThis study addresses the thermal degradation and structural stability of the NCA (nickel-cobalt-aluminum oxide) cathode materials under varying states of charge (SOC)/delithiation and temperature. Using simultaneous thermogravimetric and differential thermal analysis and high‐resolution X‐ray diffraction, the sequential evolution from a layered NaCrS2‐type structure to spinel phases (M3O4‐type and LiM2O4‐type) and finally to a rock salt phase is characterized. Degradation involves cation migration, oxygen release, and lattice instabilities, influenced by SOC/lithium content. Fully lithiated NCA (SOC 0%) exhibits superior thermal stability with a single‐step transition, whereas partially delithiated NCA exhibits a multistep transformation process involving spinel intermediates. These findings highlight the complex interplay between energy density and thermal safety, offering guidance for designing NCA cathodes with optimized performance, safety, and stability for high‐energy lithium‐ion batteries.Item Open Access The impact of donor‐orientation on the emission properties of chlorinated trityl radicals(2025) Arnold, Mona E.; Toews, Robert; Schneider, Lars; Schmid, Jonas; Putra, Miftahussurur Hamidi; Busch, Michael; Groß, Axel; Deschler, Felix; Köhn, Andreas; Kuehne, Alexander J. C.Chlorinated trityl radicals functionalized with electron‐donating groups are promising red‐emitting materials for optoelectronic and spintronic applications, overcoming the spin‐statistical limit of conventional emitters. Donor functionalization induces charge transfer character, enhancing photoluminescence quantum yield, which depends on the donor strength and its orientation. However, donor‐functionalized tris(trichlorophenyl)methyl radicals often show lower quantum yield than their perchlorinated derivatives, likely due to weaker donor‐acceptor electronic coupling and enhanced non‐radiative decay. A novel trityl derivative is presented with two additional chlorines that restrict the orientation of the donor to a nearly perpendicular arrangement toward the trityl plane, minimizing vibronic coupling and non‐radiative losses. Spectroscopic and computational studies reveal that this steric constraint improves the photoluminescence quantum yield compared to the tris(trichlorophenyl)methyl analogs. These findings highlight the potential of donor‐acceptor decoupling to enable efficient, redshifted emission, offering a design strategy for high‐performance radical emitters.Item Open Access Accelerating ab initio melting property calculations with machine learning : application to the high entropy alloy TaVCrW(2024) Zhu, Li-Fang; Körmann, Fritz; Chen, Qing; Selleby, Malin; Neugebauer, Jörg; Grabowski, BlazejMelting properties are critical for designing novel materials, especially for discovering high-performance, high-melting refractory materials. Experimental measurements of these properties are extremely challenging due to their high melting temperatures. Complementary theoretical predictions are, therefore, indispensable. One of the most accurate approaches for this purpose is the ab initio free-energy approach based on density functional theory (DFT). However, it generally involves expensive thermodynamic integration using ab initio molecular dynamic simulations. The high computational cost makes high-throughput calculations infeasible. Here, we propose a highly efficient DFT-based method aided by a specially designed machine learning potential. As the machine learning potential can closely reproduce the ab initio phase-space distribution, even for multi-component alloys, the costly thermodynamic integration can be fully substituted with more efficient free energy perturbation calculations. The method achieves overall savings of computational resources by 80% compared to current alternatives. We apply the method to the high-entropy alloy TaVCrW and calculate its melting properties, including the melting temperature, entropy and enthalpy of fusion, and volume change at the melting point. Additionally, the heat capacities of solid and liquid TaVCrW are calculated. The results agree reasonably with the CALPHAD extrapolated values.Item Open Access The role of spacer length in macrocyclization reactions under confinement(2024) Nandeshwar, Muneshwar; Weisser, Kilian; Ziegler, Felix; Frey, Wolfgang; Buchmeiser, Michael R.We studied the influence of the distance of olefin metathesis catalysts from the inner surface of a mesoporous support on macrocyclization and Z‐selectivity under confinement. For these purposes, the cationic molybdenum imido alkylidene N‐heterocyclic carbene (NHC) catalysts [Mo(N‐(2‐tBu‐C6H4)(1‐mesityl‐3‐(3‐trimethoxysilylprop‐1‐yl)‐imidazol‐2‐ylidene)(CHCMe2Ph)(MeCN)Br+ B(ArF)4-] Mo2, [Mo(N‐(2‐tBu‐C6H4)(1‐mesityl‐3‐(3‐trimethoxysilylprop‐1‐yl)‐imidazol‐2‐ylidene)(CHCMe2Ph)(MeCN)OTf+ B(ArF)4-] Mo3, [Mo(N‐(2,6‐Me2‐C6H3)(1‐mesityl‐3‐(3‐trimethoxysilylprop‐1‐yl)‐imidazol‐2‐ylidene)(CHCMe2Ph)(MeCN)Br+ B(ArF)4-] Mo5, and [Mo(N‐(2,6‐iPr2‐C6H3)(1‐mesityl‐3‐(3‐trimethoxysilylprop‐1‐yl)‐imidazol‐2‐ylidene)(CHCMe2Ph)(MeCN)+Br B(ArF)4-] Mo7 (B(ArF)4 = tetrakis[3,5‐bis(trifluoromethyl)phenyl]borate), all containing a trimethoxysilylpropyl tether, were selectively immobilized inside the mesopores of SBA‐15. Under confinement, both macro(mono)cyclization (MMC) and Z‐selectivity were higher than in solution but lower than with catalysts directly bound to the surface of the mesoporous supports. These findings are in agreement with existing theoretical models on substrate and product distribution in mesopores, which suggest that the highest substrate concentration is found at the pore wall and that it increases with decreasing pore diameter.Item Open Access Synthesis, reactivity, and mechanistic investigations of molybdenum carbene complexes in olefin metathesis and related chemistry(2026) Kundu, Koushani; Buchmeiser, Michael R. (Prof. Dr.)Item Open Access Two of a kind : the cerium(III) oxidomolybdates(VI) Ce2Mo3O12 and Ce4Mo7O27(2025) Knies, Benjamin; Strobel, Sabine; Hartenbach, IngoAlthough primarily received as by‐products, the title compounds can be synthesized directly by the admixture of CeO2, Ce, and MoO3, with the latter used as reactant and fluxing agent in flux‐mediated solid‐state syntheses at 850 °C for 7 days. Both cerium molybdates crystallize in space group C2/c with a = 1692.12(3), b = 1184.26(3), c = 1598.66(3) pm, and β = 108.4940(10)° (Z = 12) for Ce2Mo3O12 and a = 4609.00(12), b = 747.700(10), c = 1432.71(4) pm, and β = 101.023(2)° (Z = 8) for Ce4Mo7O27. The crystal structure of Ce2Mo3O12 comprises three crystallographically distinguishable Ce3+ cations with coordination numbers of 8 in shapes of trigonal dodecahedra. The five different Mo6+ cations are situated in the centers of noncondensed [MoO4]2- tetrahedra, and the overall arrangement of the mentioned building blocks is derived from the scheelite type. In the structure of Ce4Mo7O27, four crystallographically different Ce3+ cations with coordination numbers of 8 and 9 are found, as well as five non‐condensed [MoO4]2- tetrahedra and one pyroanionic [Mo2O7]2- unit.Item Open Access Applying isothermal titration calorimetry and saturation transfer difference-NMR to study the mode of interaction of flavan-3-ols with α‑amylase to understand their impact on starch hydrolysis(2025) Claasen, Birgit; Xiong, Mengyao; Mayer, Pia S.; Sogl, Greta; Buchweitz, MariaFor flavan-3-ols, significant effects to prevent the development of diabetes mellitus are postulated. Inter alia , this is attributed to inhibitory effects on the intestinal α-amylase, in particular for high-molecular-weight procyanidins. In order to gain a deeper insight into the mode of interaction and the resulting α-amylase inhibition, the interaction between the monomers (+)-catechin (CAT) and (-)-epicatechin (EC), the dimers procyanidin (PC) B1 and PC B2, and the trimer PC C1 and their inhibition of porcine pancreatic α-amylase were investigated. Weak interactions were determined by isothermal titration calorimetry (ITC), with no clear difference between monomers and dimers and even no observable interaction with PC C1. Data from saturation transfer difference (STD)-NMR experiments supported these results with respect to reversible interactions. The detailed NMR signal assignments revealed that the formation of rotamers is solvent-dependent, which might explain the differences in the interaction strength between both diastereomers. The results for interaction were in contrast to the accumulating inhibitory strength with an increasing degree of polymerization when monitoring hydrolysis of the natural substrate starch in a novel continuous approach by ITC. By combining the data from the interaction and inhibition studies, we propose that protein aggregation occurs in the presence of flavan-3-ol oligomers, which are responsible for the inhibitory effects. This rather irreversible interaction is not susceptible to detection by ITC and STD-NMR and was also not observable by CD spectroscopy.Item Open Access Theoretical understanding of molecular magnetic properties : mono- and dinuclear single-molecule magnets based on cobalt(2026) Netz, Julia; Köhn, Andreas (Prof. Dr.)In this thesis, we explore various single-ion and single-molecule magnets from a theoretical perspective, employing a range of computational methods to investigate their magnetic behavior. Our primary focus is the mononuclear system [Co(bmsab)2], which we analyze using PNO-CASPT2 and embedded ic-MRCC theory. This complex has an unsually strong zero-field splitting with an energy differnce of 253 cm-1 between the two lowest Kramers doublets. To gain deeper insight into the interplay between its electronic states, we utilize two different spin Hamiltonian models, the second only also takes the second quartet state into account. We are able to identify experimental magnetic-field dependent signals and attribute them to specific state transitions. We then take a brief detour to assess the accuracy and efficiency of different approximations to the full two-electron spin-orbit coupling operator, particularly comparing mean-field approaches with alternative methods across a set of transition metal complexes. We visualize the spin-orbit matrix and compare the results of the various methods and therefore were able to show that the mean-field methods introduce errors of up to 40 cm-1 for some matrix elements, which could potentially heavily influence the prediction of magnetic properties. We propose the use of a one-center approach instead of using a mean-field when computing transition metal complexes. Following this, we examine the exchange-coupled dinuclear cobalt complex [Co(bmsab)]2(μ-tmsab)]. Using PNO-CASPT2 in combination with advanced spin Hamiltonian models, we elucidate the emergence of its spin ladder structure and provide a detailed explanation for the observed significant zero-field splitting. Here we are able to present the importance of the inclusion of the second quartet in the spin Hamiltonian model to explain the spin-ladder structure as well as the prediction of the energy levels. Additionally, we interpret the experimental spectra by identifying key transitions between excited states.