Publications

An Octanuclear Metallosupramolecular Cage Designed To Exhibit Spin‐Crossover Behavior

Abstract By employing the subcomponent self‐assembly approach utilizing 5,10,15,20‐tetrakis(4‐aminophenyl)porphyrin or its zinc(II) complex, 1 H ‐4‐imidazolecarbaldehyde, and either zinc(II) or iron(II) salts, we were able to prepare O‐symmetric cages having a confined volume of ca. 1300 Å 3 . The use of iron(II) salts yielded coordination cages in the high‐spin state at room temperature, manifesting spin‐crossover in solution at low temperatures, whereas corresponding zinc(II) salts led to the corresponding diamagnetic analogues. The new cages were characterized by synchrotron X‐ray crystallography, high‐resolution mass spectrometry, and NMR, Mössbauer, IR, and UV/Vis spectroscopy. The cage structures and UV/Vis spectra were independently confirmed by state‐of‐the‐art DFT calculations. A remarkably high‐spin‐stabilizing effect through encapsulation of C 70 was observed. The spin‐transition temperature T 1/2 is lowered by 20 K in the host–guest complex.

CCDC 1520090: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Evaluation of the QCxMS2 method for the calculation of collision-induced-dissociation spectra via automated reaction network exploration

Collision-induced dissociation mass spectrometry (CID-MS) is an important tool in analytical chemistry for the structural elucidation of unknown compounds. The theoretical prediction of CID spectra plays a critical role in supporting and accelerating this process. To this end, we adapt the recently developed QCxMS2 program originally designed for the calculation of electron ionization (EI) spectra to enable the computation of CID-MS. To account for the fragmentation conditions characteristic of CID within the automated reaction network discovery approach of QCxMS2 we adapted the internal energy distribution to match the experimental conditions. This distribution can be adjusted via a single parameter to approximate various activation settings, thereby eliminating the need for explicit simulations of the collisional process. We evaluate our approach on a test set of 13 organic molecules with diverse functional groups, compiled specifically for this study. All reference spectra were recorded consistently under the same measurement conditions, including both CID and higher-energy collisional dissociation (HCD) modes. Overall, QCxMS2 achieves good average entropy similarity scores (ESS) of 0.687 for the HCD spectra and 0.773 for the CID spectra. The direct comparison to experimental data demonstrates that the QCxMS2 approach, even without explicit modeling of collisions, is generally capable of computing both CID and HCD spectra with reasonable accuracy and robustness. This highlights its potential as a valuable tool for integration into structure elucidation workflows in analytical mass spectrometry.

Electron capture dissociation of a self-assembled tetranuclear metallosupramolecular complex in the gas phase

CCDC 1411729: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

CCDC 1411726: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Gas‐Phase Dehydrogenation of Methanol with Mononuclear Vanadium‐Oxide Cations

Abstract The reactions of methanol with mass‐selected V + , VOH + , VO + , and VO 2 + cations are studied by Fourier‐transform ion‐cyclotron resonance (FT‐ICR) mass spectrometry in order to investigate the influence of the formal oxidation state of the metal on the reactivity of vanadium–oxide compounds. Interestingly, the most reactive species is the low‐valent hydroxide cation VOH + , for which a formal condensation reaction prevails to afford VOCH 3 + . In contrast, atomic V + is oxidized and the high‐valent dioxide cation VO 2 + is reduced by methanol. The dehydrogenation of methanol mediated by VO + does not involve any change of the metal's oxidation state. For the latter reaction, the experimental results are complemented by a theoretical investigation by using density functional theory.

Mass spectrometric evidence for catenanes and rotaxanes from negative-ESI FT-ICR tandem-MS-experiments

The Final Steps of Bacillaene Biosynthesis in <i>Bacillus amyloliquefaciens</i> FZB42: Direct Evidence for β,γ Dehydration by a <i>trans</i>‐Acyltransferase Polyketide Synthase

Caught in the act: Genetic pathway engineering in conjunction with HPLC–NMR spectroscopy of highly labile intermediates provided direct evidence for the installation of β,γ double bonds during polyketide elongation to form the antibiotic bacillaene. The novel congener bacillaene B (1) was also discovered as an elusive true end product of the pathway in Bacillus amyloliquefaciens.

Self-assembly of metallosupramolecular rhombi from chiral concave 9,9’-spirobifluorene-derived bis(pyridine) ligands

Two new 9,9’-spirobifluorene-based bis(4-pyridines) were synthesised in enantiopure and one also in racemic form. These ligands act as concave templates and form metallosupramolecular [(dppp) 2 M 2 L 2 ] rhombi with cis -protected [(dppp)Pd] 2+ and [(dppp)Pt] 2+ ions. The self-assembly process of the racemic ligand preferably occurs in a narcissistic self-recognising manner. Hence, a mixture of all three possible stereoisomers [(dppp) 2 M 2 {( R )-L} 2 ](OTf) 4 , [(dppp) 2 M 2 {( S )-L} 2 ](OTf) 4 , and [(dppp) 2 M 2 {( R )-L}{( S )-L}](OTf) 4 was obtained in an approximate 1.5:1.5:1 ratio which corresponds to an amplification of the homochiral assemblies by a factor of approximately three as evidenced by NMR spectroscopy and mass spectrometry. The racemic homochiral assemblies could also be characterised by single crystal X-ray diffraction.

A Family of Heterobimetallic Cubes Shows Spin‐Crossover Behaviour Near Room Temperature

Abstract Using 4‐(4′‐pyridyl)aniline as a simple organic building block in combination with three different aldehyde components together with metal(II) salts gave three different Fe 8 Pt 6 ‐cubes and their corresponding Zn 8 Pt 6 analogues by employing the subcomponent self‐assembly approach. Whereas the use of zinc(II) salts gave rise to diamagnetic cages, iron(II) salts yielded metallosupramolecular cages that show spin‐crossover behaviour in solution. The spin‐transition temperature T 1/2 depends on the incorporated aldehyde component, giving a construction kit for the deliberate synthesis of spin‐crossover compounds with tailored transition properties. Incorporation of 4‐thiazolecarbaldehyde or N ‐methyl‐2‐imidazole‐carbaldehyde yielded cages that undergo spin‐crossover around room temperature whereas the cage obtained using 1 H ‐4‐imidazolecarbaldehyde shows a spin‐transition at low temperatures. Three new structures were characterized by synchrotron X‐ray diffraction and all structures were characterized by mass spectrometry, NMR and UV/Vis spectroscopy.

Enantiomerically Pure Trinuclear Helicates via Diastereoselective Self-Assembly and Characterization of Their Redox Chemistry

A tris(bipyridine) ligand 1 with two BINOL (BINOL = 2,2'-dihydroxy-1,1'-binaphthyl) groups has been prepared in two enantiomerically pure forms. This ligand undergoes completely diastereoselective self-assembly into D2-symmeteric double-stranded trinuclear helicates upon coordination to copper(I) and silver(I) ions and to D3-symmetric triple-stranded trinuclear helicates upon coordination to copper(II), zinc(II), and iron(II) ions as demonstrated by mass spectrometry, NMR and CD spectroscopy in combination with quantum chemical calculations and X-ray diffraction analysis. According to the calculations, the single diastereomers that are formed during the self-assembly process are strongly preferred compared to the next stable diastereomers. Due to this strong preference, the self-assembly of the helicates from racemic 1 proceeds in a completely narcissistic self-sorting manner with an extraordinary high degree of self-sorting that proves the power and reliability of this approach to achieve high-fidelity diastereoselective self-assembly via chiral self-sorting to get access to stereochemically well-defined nanoscaled objects. Furthermore, mass spectrometric methods including electron capture dissociation MS(n) experiments could be used to elucidate the redox behavior of the copper helicates.

CCDC 911128: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

CCDC 699742: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Molecular Taphonomy of Heme: Chemical Degradation of Hemin under Presumed Fossilization Conditions

The metalloporphyrin heme acts as the oxygen-complexing prosthetic group of hemoglobin in blood. Heme has been noted to survive for many millions of years in fossils. Here we investigate its stability and degra-dation under various conditions expected to occur during fossilization. Oxidative, reductive, aerobic, and anaerobic conditions were studied at neutral and alkaline pH values. Elevated temperatures were applied to accelerate degradation. High-performance liquid chromatography coupled to tandem mass spectrome-try (HPLC-MS/MS) identified four main degradation products. The vinyl residues are oxidized to formyl and further to carboxylate groups. In the presence of air or H2O2, cleavage of the tetrapyrrole ring occurs, and hematinic acid is formed. The highest stability of heme was observed under anaerobic reductive condi-tions (half-life 9.5 days), while the lowest stability was found in the presence of H2O2 (half-life 1 min). We confirmed that the iron cation plays a crucial role in degradation, since protoporphyrin IX, lacking iron, re-mained significantly more stable. Under anaerobic, reductive conditions, the above-mentioned degradation products were not observed, suggesting a different degradation pathway. To our knowledge, this is the first molecular taphonomy study on heme, which will be useful for understanding its fate during fossiliza-tion.

CCDC 754718: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Competitive Hydrogen‐Atom Abstraction versus Oxygen‐Atom and Electron Transfers in Gas‐Phase Reactions of [X₄O₁₀]^.+ (X=P, V) with C₂H₄

Why so different? The comparison of the reaction of "bare" [P4O10](·+) and [V4O10](·+) with ethene by mass-spectrometric and computational studies permits insight into mechanistic aspects of the competition between C-H bond activation and oxygen-atom and electron transfers. Whereas [P4O10](·+) reacts by homolytic C-H bond cleavage and electron transfer, the isostructural [V4O10](·+) shows only oxygen-atom transfer (see picture).

How useful is mass spectrometry for the characterization of dendrimers?