Publications by authors named "Geibel C"

The unconventional superconductor CeRh_{2}As_{2} (critical temperature T_{c}≈0.4  K) displays an exceptionally rare magnetic-field-induced transition between two distinct superconducting (SC) phases, proposed to be states of even and odd parity of the SC order parameter, which are enabled by a locally noncentrosymmetric structure. The superconductivity is preceded by a phase transition of unknown origin at T_{0}=0.

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Feature-based molecular networking (FBMN) is a popular analysis approach for liquid chromatography-tandem mass spectrometry-based non-targeted metabolomics data. While processing liquid chromatography-tandem mass spectrometry data through FBMN is fairly streamlined, downstream data handling and statistical interrogation are often a key bottleneck. Especially users new to statistical analysis struggle to effectively handle and analyze complex data matrices.

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Untargeted tandem mass spectrometry (MS/MS) has become a high-throughput method to measure small molecules in complex samples. One key goal is the transformation of these MS/MS spectra into chemical structures. Computational techniques such as MS/MS library search have enabled the reidentification of known compounds.

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Covering: 1995 to 2023Advances in bioanalytical methods, particularly mass spectrometry, have provided valuable molecular insights into the mechanisms of life. Non-targeted metabolomics aims to detect and (relatively) quantify all observable small molecules present in a biological system. By comparing small molecule abundances between different conditions or timepoints in a biological system, researchers can generate new hypotheses and begin to understand causes of observed phenotypes.

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The ATM kinase is a promising target in cancer treatment as an important regulator of the cellular response to DNA double-strand breaks. In this work, we present a new class of specific benzimidazole-based ATM inhibitors with picomolar potency against the isolated enzyme and favorable selectivity within relative PIKK and PI3K kinases. We could identify two promising inhibitor subgroups with significantly different physicochemical properties, which we developed simultaneously.

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Recently, a superconducting (SC) transition from low-field (LF) to high-field (HF) SC states was reported in CeRh_{2}As_{2}, indicating the existence of multiple SC states. It has been theoretically noted that the existence of two Ce sites in the unit cell, the so-called sublattice degrees of freedom owing to the local inversion symmetry breaking at the Ce sites, can lead to the appearance of multiple SC phases even under an interaction inducing spin-singlet superconductivity. CeRh_{2}As_{2} is considered as the first example of multiple SC phases owing to this sublattice degree of freedom.

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The nature of the antiferromagnetic order in the heavy fermion metal YbRh_{2}Si_{2}, its quantum criticality, and superconductivity, which appears at low mK temperatures, remain open questions. We report measurements of the heat capacity over the wide temperature range 180  μK-80  mK, using current sensing noise thermometry. In zero magnetic field we observe a remarkably sharp heat capacity anomaly at 1.

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This work reports on targeted UHPLC-tandem mass spectrometry methods for the chiral separation of anteiso-methyl branched fatty acids (aiFAs). The methods involve precolumn derivatization with 1-naphthylamine and chiral separation on Chiralpak IG-U. anteiso-Methyl branched fatty acids with up to eight carbons can be separated.

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The present work reports on a novel stable-bonded amino silica stationary phase obtained by crosslinking of surface aminopropyl moieties using triglycidyl isocyanurate. The obtained cross-linked amido-amino network silica material exhibited superior hydrolytic stability compared to classical 3-aminopropyl phases and showed, inter alia, excellent separation of nine therapeutically effective sulfonamides in hydrophilic interaction/weak anion exchange chromatography elution mode. Additionally, the separation of carbohydrates was investigated under classical hydrophilic interaction chromatography conditions as well proving the suitability of the novel phase for such applications.

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The present work systematically investigates the chemical microheterogeneity as part of the optimization of a single-step surface bonding chemistry of 3-mercaptopropylsilatrane (MPS) on mesoporous silica gel in comparison to the state-of-the-art silane chemistry with 3-mercaptopropyltrimethoxysilane (MPTMS). MPS functionalization turns out to be a favourable chemistry for the further use in thiol-ene click reactions such as the immobilization of chiral selectors, herein tert-butylcarbamoylquinine (tBuCQN), for the synthesis of chiral stationary phases (CSPs). MPS has higher reactivity than MPTMS and prefers the formation of trifunctional siloxane bondings unlike MPTMS which favours difunctional siloxane bonds to silica, as investigated by solid-state cross-polarization/magic angle spinning (CP/MAS) NMR (Si and C nuclei).

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The ATM kinase is a key molecule regulating DNA damage response and can be targeted resulting in efficient radio- or chemosensitization. Due to the enormous size of this protein and the associated difficulties in obtaining high-quality crystal structures, we sought to develop an accurate in silico model to identify new targeting possibilities. We identified a urea group as the most beneficial chemical anchor point, which could undergo multiple interactions in the aspartate-rich hydrophobic region I of the atypical ATM kinase domain.

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A chemical reinvestigation of the Indonesian strain sp. SHP 22-7 led to the isolation of three new pyrimidine nucleosides, along with six known analogues and zincphyrin. The structures of the new compounds (, , ) were elucidated by employing spectroscopic techniques (NMR, MS, CD, and IR) as well as enantioselective analyses of methyl branched side chain configurations.

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Spatial inversion symmetry in crystal structures is closely related to the superconducting (SC) and magnetic properties of materials. Recently, several theoretical proposals that predict various interesting phenomena caused by the breaking of the local inversion symmetry have been presented. However, experimental validation has not yet progressed owing to the lack of model materials.

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Branched-chain fatty acids (BCFAs) are mostly saturated fatty acids with one or more methyl, seldom ethyl, branches in the alkyl chain. They are derived from branched-chain amino acids, ruminant-derived food, or biosynthetic side products of acetyl-CoA carboxylase. They possess iso- (branching at penultimate carbon) and anteiso-fatty acid structure (branching at antepenultimate carbon) or are branched at any other position of the carbon chain.

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Given the clinical potential of poly(ADP-ribose) polymerases (PARP) imaging for the detection and stratification of various cancers, the development of novel PARP imaging probes with improved pharmacological profiles over established PARP imaging agents is warranted. Here, we present a novel F-labeled PARP radiotracer based on the clinically superior PARP inhibitor talazoparib. An automated radiosynthesis of [F]talazoparib (RCY: 13 ± 3.

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In this work, we present a unique, robust and fully automated analytical platform technology for the enantioselective amino acid analysis using a multiple heart cutting RPLC-enantio/stereoselective HPLC-ESI-QTOF-MS method. This 2D-LC method allows the full enantioselective separation of 20 proteinogenic AAs plus 5 isobaric analogues, namely allo-Threonine (aThr), homoserine (Hse), allo-isoleucine (aIle), tert-Leucine (Tle) and Norleucine (Nle), after pre-column derivatization with 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate (AQC; AccQ). This N-terminal AA-derivatization method introduces on the one hand beneficial chromatographic properties for D RP-LC (stronger retention) and D chiral separation (better chiral recognition), and on the other hand favorable detection properties with its chromophoric, fluorophoric, and easily ionizable quinoline mass tag.

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Materials with multiple superconducting phases are rare. Here, we report the discovery of two-phase unconventional superconductivity in CeRhAs Using thermodynamic probes, we establish that the superconducting critical field of its high-field phase is as high as 14 tesla, even though the transition temperature is only 0.26 kelvin.

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The present work systematically investigates a new strategy for the functionalization of silica gel using alkyl silatrane chemistry instead of alkylsilanes for synthesis of chromatographic stationary phases. In this work, silica was chemically modified for further functionalization by a thiol-ene click reaction. Thus, 3-mercaptopropylsilatrane (MPS) was used which is capable to form self-assembled monolayers (SAM) on top of silanol surfaces in a controlled manner as previously shown for silicon wafers.

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In small molecule binding, water is not a passive bystander but rather takes an active role in the binding site, which may be decisive for the potency of the inhibitor. Here, by addressing a high-energy water, we improved the IC value of our co-crystallized glycogen synthase kinase-3β (GSK-3β) inhibitor by nearly two orders of magnitude. Surprisingly, our results demonstrate that this high-energy water was not displaced by our potent inhibitor ()-3-(3-((7-ethynyl-9-pyrimido[4,5-]indol-4-yl)(methyl)amino)piperidin-1-yl)propanenitrile (-, IC value of 6 nM).

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The present work reports on the preparation of polythiol-functionalized silica particles by thermally and photo-initiated radical addition reactions using poly(3-mercaptopropyl)methylsiloxane (PMPMS) as sulfhydryl group-rich surface modification reagent. Prior to surface modification with PMPMS, the silica was vinylized with vinyl trimethoxysilane. Finally, the usefulness of the thiolated silica particles was demonstrated by their further modification for various HPLC applications such as argentation chromatography and chiral separations.

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In the iron-pnictide material CeFeAsO not only the Fe moments, but also the local 4f moments of the Ce order antiferromagnetically at low temperatures. We elucidate on the peculiar role of the Ce on the emergence of superconductivity. While application of pressure suppresses the iron SDW ordering temperature monotonously up to 4 GPa, the Ce-4f magnetism is stabilized until both types of magnetic orders disappear abruptly and a narrow SC dome develops.

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Glycogen synthase kinase-3β (GSK-3β) is a potential target in the field of Alzheimer's disease drug discovery. We recently reported a new class of 9-pyrimido[4,5-]indole-based GSK-3β inhibitors, of which 3-(3-((7-chloro-9-pyrimido[4,5-]indol-4-yl)(methyl)amino)piperidin-1-yl)propanenitrile () demonstrated promising inhibitory potency. However, this compound underwent rapid degradation by human liver microsomes.

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The magnetocrystalline anisotropy of GdRhSi is examined in detail via the electron spin resonance (ESR) of its well-localised Gd moments. Below T = 107 K, long range magnetic order sets in with ferromagnetic layers in the (aa)-plane stacked antiferromagnetically along the c-axis of the tetragonal structure. Interestingly, the easy-plane anisotropy allows for the observation of antiferromagnetic resonance at X- and Q-band microwave frequencies.

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This work reports procedures for the immobilization of vinyl ligands on silica particles by UV-initiated thiol-ene radical addition reaction (photo-click immobilization). tert‑Butylcarbamoyl quinine was the functional ligand (ene component) for the synthesis of chiral stationary phases. Two distinct surface chemistries were evaluated.

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Zwitterionic chiral ion-exchange selectors (ZWIX) obtained by conjugation of quinine and 2-aminocyclohexanesulfonic acid via a carbamate bond were immobilized on three different silica particle types, viz. 120 Å 3 μm fully porous particles (FPP), 200 Å 3 μm FPP and 160 Å 2.7 μm superficially porous particles (SPP).

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