@article{SchuergerEngel2023, author = {Sch{\"u}rger, Peter and Engel, Volker}, title = {Differential Shannon entropies characterizing electron-nuclear dynamics and correlation: momentum-space versus coordinate-space wave packet motion}, series = {Entropy}, volume = {25}, journal = {Entropy}, number = {7}, issn = {1099-4300}, doi = {10.3390/e25070970}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-362670}, year = {2023}, abstract = {We calculate differential Shannon entropies derived from time-dependent coordinate-space and momentum-space probability densities. This is performed for a prototype system of a coupled electron-nuclear motion. Two situations are considered, where one is a Born-Oppenheimer adiabatic dynamics, and the other is a diabatic motion involving strong non-adiabatic transitions. The information about coordinate- and momentum-space dynamics derived from the total and single-particle entropies is discussed and interpreted with the help of analytical models. From the entropies, we derive mutual information, which is a measure for the electron-nuclear correlation. In the adiabatic case, it is found that such correlations are manifested differently in coordinate- and momentum space. For the diabatic dynamics, we show that it is possible to decompose the entropies into state-specific contributions.}, language = {en} } @phdthesis{Matthaei2023, author = {Matthaei, Christian Tobias}, title = {Studying the Photodissociation of Chlorine-Containing Molecules with Velocity Map Imaging}, doi = {10.25972/OPUS-32740}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-327405}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2023}, abstract = {The first is via direct dissociation and the second likely involves a barrier slowing down dissociation. Chlorine-containing hydrocarbons pose a great risk for the environment and especially for the atmosphere. In this thesis I present the photodissociation dynamics of multiple chlorine-containing molecules. The method of velocity map imaging was utilized for gaining information on the kinetic energy distribution of the fragments generated in the photodissociation reactions. First, the photodissociation of benzoyl chloride after excitation to the S1, S2 and the S3 state between 279 nm and 237 nm was studied. This stable molecule was an ideal candidate for demonstrating a new ionization scheme for chlorine atoms. It was shown that benzoyl chloride dissociates statistically from the ground state. Afterwards, the results from experiments on the radicals trichloromethyl and dichlorocarbene are presented in the range of 230 to 250 nm. These radicals remain after the dissociation of carbon tetrachloride and have not been studied in detail because of their instability. Trichlormethyl dissociates via two paths: The loss of a chlorine atom to dichlorocarbene and by decaying to CCl and a chlorine molecule. The dissociation to dichlorocarbene involves a barrier. If the photon exciting the molecule has enough energy to surpass the barrier, which is the case starting at around 235 nm, trichlormethyl dissociates rapidly resulting in an anisotropic VMI. However, if the the excitation energy is lower, the dissociation takes longer than a rotational period and the anisotropy is lost.The path to CCl is a statistical dissociation. Dichlorocarbene dissociates to CCl and Cl via to separate channels. The first is via direct dissociation and the second likely involves a barrier slowing down dissociation.}, subject = {Photodissoziation}, language = {en} } @article{MuellerMetaMeidneretal.2023, author = {M{\"u}ller, Patrick and Meta, Mergim and Meidner, Jan Laurenz and Schwickert, Marvin and Meyr, Jessica and Schwickert, Kevin and Kersten, Christian and Zimmer, Collin and Hammerschmidt, Stefan Josef and Frey, Ariane and Lahu, Albin and de la Hoz-Rodr{\´i}guez, Sergio and Agost-Beltr{\´a}n, Laura and Rodr{\´i}guez, Santiago and Diemer, Kira and Neumann, Wilhelm and Gonz{\`a}lez, Florenci V. and Engels, Bernd and Schirmeister, Tanja}, title = {Investigation of the compatibility between warheads and peptidomimetic sequences of protease inhibitors — a comprehensive reactivity and selectivity study}, series = {International Journal of Molecular Sciences}, volume = {24}, journal = {International Journal of Molecular Sciences}, number = {8}, issn = {1422-0067}, doi = {10.3390/ijms24087226}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-313596}, year = {2023}, abstract = {Covalent peptidomimetic protease inhibitors have gained a lot of attention in drug development in recent years. They are designed to covalently bind the catalytically active amino acids through electrophilic groups called warheads. Covalent inhibition has an advantage in terms of pharmacodynamic properties but can also bear toxicity risks due to non-selective off-target protein binding. Therefore, the right combination of a reactive warhead with a well-suited peptidomimetic sequence is of great importance. Herein, the selectivities of well-known warheads combined with peptidomimetic sequences suited for five different proteases were investigated, highlighting the impact of both structure parts (warhead and peptidomimetic sequence) for affinity and selectivity. Molecular docking gave insights into the predicted binding modes of the inhibitors inside the binding pockets of the different enzymes. Moreover, the warheads were investigated by NMR and LC-MS reactivity assays against serine/threonine and cysteine nucleophile models, as well as by quantum mechanics simulations.}, language = {en} } @phdthesis{Gerlach2023, author = {Gerlach, Marius David}, title = {Spectroscopy of fulminic acid HCNO with VUV- and soft X-ray radiation}, doi = {10.25972/OPUS-32972}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-329722}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2023}, abstract = {Die Fulmins{\"a}ure HCNO wurde zum ersten Mal im Jahre 1800 synthetisiert und wurde seitdem immer wieder verwendet, um neue chemische Konzepte und Theorien zu entwickeln. Durch die erstmalige Entdeckung der Fulmins{\"a}ure im Weltall im Jahr 2009 ist die Fulmins{\"a}ure heutzutage vor allem im Bereich der Astrochemie interessant. In dieser Doktorarbeit haben wir die Interaktion von Fulmins{\"a}ure mit interstellar Strahlung, genauer mit VUV- sowie weicher R{\"o}ntgenstrahlung untersucht. In Zuge der Messung mit VUV-Strahlung konnten wir das Photoelektronenspektrum von HCNO mit hoher Aufl{\"o}sung aufnehmen und den Renner-Teller verzerrten Grundzustand des Kations mit Hilfe von Wellenpaketdynamiksimulationen beschreiben. Außerdem konnten wir den Mechanismus der dissoziativen Photoionisation bis zu einer Bindungsenergie von 15.3 eV aufkl{\"a}ren. Mit weicher R{\"o}ntgenstrahlung ist es m{\"o}glich die 1s Elektronen des HCNO zu ionisieren oder anzuregen. Der erzeugte Zustand zerf{\"a}llt anschließend durch einen Auger-Meitner Prozess, bei dem ein Auger-Elektron erzeugt wird. Im Zuge der Auger-Elektronenspektroskopie haben wir die kinetische Energie dieser Elektronen gemessen und konnten mittels quantenchemischer Rechnung die beobachten Signale analysieren. Wir untersuchten außerdem, wie das durch den Auger-Meitner Prozess erzeugte Ion zerf{\"a}llt. Hier konnten wir eine Selektivit{\"a}t des Zerfalls beobachten, je nachdem welches der 1s Elektronen im ersten Schritt angeregt oder ionisiert wurde. Diese Beobachtung konnten wir durch ein einfaches thermodynamisches Argument erkl{\"a}ren. Diese Arbeit gibt also ein vollst{\"a}ndiges Bild {\"u}ber die Interaktion von HCNO mit ionisierender Strahlung. Die erhaltenen Daten k{\"o}nnten f{\"u}r die Beschreibung von HCNO im interstellaren Raum Bedeutung haben.}, subject = {Chemie}, language = {en} } @phdthesis{Luettig2023, author = {L{\"u}ttig, Julian Konstantin}, title = {Coherent Higher-Order Spectroscopy: Investigating Multi-Exciton Interaction}, doi = {10.25972/OPUS-29318}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-293182}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2023}, abstract = {The goal of this thesis was the development and application of higher-order spectroscopic techniques. In contrast to ordinary pump-probe (PP) and two-dimensional (2D) spectroscopy, higher-order coherently detected spectroscopic methods measure a polarization that has an order of nonlinearity higher than three. The key idea of the techniques in this thesis is to isolate the higher-order signals from the lower-order signals either by their excitation frequency or by their excitation intensity dependence. Due to the increased number of interactions in higher-order spectroscopy, highly excited states can be probed. For excitonic systems such as aggregates and polymers, the fifth-order signal allows one to directly measure exciton-exciton annihilation (EEA). In polymers and aggregates, the exciton transport is not connected to a change of the absorption and can therefore not be investigated with conventional third-order techniques. In contrast, EEA can be used as a probe to study exciton diffusion in these isonergetic systems. As a part of this thesis, anisotropy in fifth-order 2D spectroscopy was investigated and was used to study geometric properties in polymers. In 2D spectroscopy, the multi-quantum signals are separated from each other by their spectral position along the excitation axis. This concept can be extended systematically to higher signals. Another approach to isolate multi-quantum signals in PP spectroscopy utilizes the excitation intensity. The PP signal is measured at specific excitation intensities and linear combinations of these measurements result in different signal contributions. However, these signals do not correspond to clean nonlinear signals because the higher-order signals contaminate the lower-order multi-quantum signals. In this thesis, a correction protocol was derived that uses the isolated multiquantum signals, both from 2D spectroscopy and from PP spectroscopy, to remove the contamination of higher-order signals resulting in clean nonlinear signals. Using the correction on the third-order signal allows one to obtain annihilation-free signals at high excitation intensities, i.e., with high signal-to-noise ratio. Isolation and correction in PP and 2D spectroscopy were directly compared by measuring the clean third-order signals of squaraine oligomers at high excitation intensities. Furthermore, higher-order PP spectroscopy was used to isolate up to the 13th nonlinear order of squaraine polymers. The demonstrated spectroscopic techniques represent general procedures to isolate clean signals in terms of perturbation theory. The technique of higher-order PP spectroscopy needs only small modifications of ordinary PP setups which opens the field of higher-order spectroscopy to the broad scientific community. The technique to obtain clean nonlinear signals allows one to systematically increase the number of interacting (quasi)particles in a system and to characterize their interaction energies and dynamics.}, subject = {Coherent Multidimensional Spectroscopy}, language = {en} } @article{AhmedOjhaHirschetal.2017, author = {Ahmed, Bilal and Ojha, Animesh K. and Hirsch, Florian and Fischer, Ingo and Patrice, Donfack and Materny, Arnulf}, title = {Tailoring of enhanced interfacial polarization in WO\(_3\) nanorods grown over reduced graphene oxide synthesized by a one-step hydrothermal method}, series = {RSC Advances}, volume = {7}, journal = {RSC Advances}, number = {23}, doi = {10.1039/c7ra00730b}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-181829}, pages = {13985-13996}, year = {2017}, abstract = {In the present report, well-defined WO3 nanorods (NRs) and a rGO-WO\(_3\) composite were successfully synthesized using a one-pot hydrothermal method. The crystal phase, structural morphology, shape, and size of the as-synthesized samples were studied using X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements. The optical properties of the synthesized samples were investigated by Raman, ultraviolet-visible (UV-Vis) and photoluminescence (PL) spectroscopy. Raman spectroscopy and TEM results validate the formation of WO\(_3\) (NRs) on the rGO sheet. The value of the dielectric constant (ε′) of WO3 NRs and rGO-WO\(_3\) composite is decreased with an increase in frequency. At low frequency (2.5 to 3.5 Hz), the value of ε′ for the rGO-WO3 composite is greater than that of pure WO\(_3\) NRs. This could be due to the fact that the induced charges follow the ac signal. However, at higher frequency (3.4 to 6.0), the value of ε′ for the rGO-WO\(_3\) composite is less compared to that of the pure WO3 NRs. The overall decrease in the value of ε′ could be due to the occurrence of a polarization process at the interface of the rGO sheet and WO3 NRs. Enhanced interfacial polarization in the rGO-WO\(_3\) composite is observed, which may be attributed to the presence of polar functional groups on the rGO sheet. These functional groups trap charge carriers at the interface, resulting in an enhancement of the interfacial polarization. The value of the dielectric modulus is also calculated to further confirm this enhancement. The values of the ac conductivity of the WO\(_3\) NRs and rGO-WO\(_3\) composite were calculated as a function of the frequency. The greater value of the ac conductivity in the rGO-WO\(_3\) composite compared to that of the WO\(_3\) NRs confirms the restoration of the sp:\(^{++}\) network during the in situ synthesis of the rGO-WO\(_3\) composite, which is well supported by the results obtained by Raman spectroscopy.}, language = {en} } @article{SchmidtFantuzziKlopfetal.2021, author = {Schmidt, Paul and Fantuzzi, Felipe and Klopf, Jonas and Schr{\"o}der, Niklas B. and Dewhurst, Rian D. and Braunschweig, Holger and Engel, Volker and Engels, Bernd}, title = {Twisting versus delocalization in CAAC- and NHC-stabilized boron-based biradicals: the roles of sterics and electronics}, series = {Chemistry - A European Journal}, volume = {27}, journal = {Chemistry - A European Journal}, number = {16}, doi = {10.1002/chem.202004619}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256636}, pages = {5160-5170}, year = {2021}, abstract = {Twisted boron-based biradicals featuring unsaturated C\(_2\)R\(_2\) (R=Et, Me) bridges and stabilization by cyclic (alkyl)(amino)carbenes (CAACs) were recently prepared. These species show remarkable geometrical and electronic differences with respect to their unbridged counterparts. Herein, a thorough computational investigation on the origin of their distinct electrostructural properties is performed. It is shown that steric effects are mostly responsible for the preference for twisted over planar structures. The ground-state multiplicity of the twisted structure is modulated by the σ framework of the bridge, and different R groups lead to distinct multiplicities. In line with the experimental data, a planar structure driven by delocalization effects is observed as global minimum for R=H. The synthetic elusiveness of C\(_2\)R\(_2\)-bridged systems featuring N-heterocyclic carbenes (NHCs) was also investigated. These results could contribute to the engineering of novel main group biradicals.}, language = {en} } @article{RoyTroesterFantuzzietal.2021, author = {Roy, Dipak Kumar and Tr{\"o}ster, Tobias and Fantuzzi, Felipe and Dewhurst, Rian D. and Lenczyk, Carsten and Radacki, Krzysztof and Pranckevicius, Conor and Engels, Bernd and Braunschweig, Holger}, title = {Isolation and Reactivity of an Antiaromatic s-Block Metal Compound}, series = {Angewandte Chemie International Edition}, volume = {60}, journal = {Angewandte Chemie International Edition}, number = {7}, doi = {10.1002/anie.202014557}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-224447}, pages = {3812 -- 3819}, year = {2021}, abstract = {The concepts of aromaticity and antiaromaticity have a long history, and countless demonstrations of these phenomena have been made with molecules based on elements from the p, d, and f blocks of the periodic table. In contrast, the limited oxidation-state flexibility of the s-block metals has long stood in the way of their participation in sophisticated π-bonding arrangements, and truly antiaromatic systems containing s-block metals are altogether absent or remain poorly defined. Using spectroscopic, structural, and computational techniques, we present herein the synthesis and authentication of a heterocyclic compound containing the alkaline earth metal beryllium that exhibits significant antiaromaticity, and detail its chemical reduction and Lewis-base-coordination chemistry.}, language = {en} } @article{DietschreitWagnerLeetal.2020, author = {Dietschreit, Johannes C. B. and Wagner, Annika and Le, T. Anh and Klein, Philipp and Schindelin, Hermann and Opatz, Till and Engels, Bernd and Hellmich, Ute A. and Ochsenfeld, Christian}, title = {Predicting \(^{19}\)F NMR Chemical Shifts: A Combined Computational and Experimental Study of a Trypanosomal Oxidoreductase-Inhibitor Complex}, series = {Angewandte Chemie International Edition}, volume = {59}, journal = {Angewandte Chemie International Edition}, number = {31}, doi = {10.1002/anie.202000539}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-214879}, pages = {12669 -- 12673}, year = {2020}, abstract = {The absence of fluorine from most biomolecules renders it an excellent probe for NMR spectroscopy to monitor inhibitor-protein interactions. However, predicting the binding mode of a fluorinated ligand from a chemical shift (or vice versa) has been challenging due to the high electron density of the fluorine atom. Nonetheless, reliable \(^{19}\)F chemical-shift predictions to deduce ligand-binding modes hold great potential for in silico drug design. Herein, we present a systematic QM/MM study to predict the \(^{19}\)F NMR chemical shifts of a covalently bound fluorinated inhibitor to the essential oxidoreductase tryparedoxin (Tpx) from African trypanosomes, the causative agent of African sleeping sickness. We include many protein-inhibitor conformations as well as monomeric and dimeric inhibitor-protein complexes, thus rendering it the largest computational study on chemical shifts of \(^{19}\)F nuclei in a biological context to date. Our predicted shifts agree well with those obtained experimentally and pave the way for future work in this area.}, language = {en} } @article{SchleierReuschLummeletal.2019, author = {Schleier, Domenik and Reusch, Engelbert and Lummel, Lisa and Hemberger, Patrick and Fischer, Ingo}, title = {Threshold photoelectron spectroscopy of IO and IOH}, series = {ChemPhysChem}, volume = {20}, journal = {ChemPhysChem}, number = {19}, doi = {10.1002/cphc.201900813}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-204751}, pages = {2413-2416}, year = {2019}, abstract = {Iodine oxides appear as reactive intermediates in atmospheric chemistry. Here, we investigate IO and HOI by mass-selective threshold photoelectron spectroscopy (ms-TPES), using synchrotron radiation. IO and HOI are generated by photolyzing iodine in the presence of ozone. For both molecules, accurate ionization energies are determined, 9.71±0.02 eV for IO and 9.79±0.02 eV for HOI. The strong spin-spin interaction in the 3Σ- ground state of IO+ leads to an energy splitting into the Ω=0 and Ω=±1 sublevels. Upon ionization, the I-O bond shortens significantly in both molecules; thus, a vibrational progression, assigned to the I-O stretch, is apparent in both spectra.}, language = {en} }