Publications

CCDC 926028: 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.

Oxidative Degradation of Small Cationic Vanadium Clusters by Molecular Oxygen:  On the Way from V<i>_n</i>⁺ (<i>n</i> = 2−5) to VO<i>_m</i>⁺ (<i>m</i> = 1, 2)

Ion-cyclotron resonance mass-spectrometric experiments are used to examine the reactions of small cationic vanadium clusters Vn+ and vanadium-oxide clusters VnOm+ (n ≤ 5, m ≤ 3) with molecular oxygen. Most of these reactions are very fast (k ≥ 3 × 10-10 cm3 molecule-1 s-1) and strongly exothermic. Oxidative degradation of the clusters (decreasing n) is generally more favored than oxygen-transfer resulting in VnOm+ cations (constant n). Consequently, the mononuclear oxide ions VO+ and VO2+ evolve as the major final products at the end of a reaction cascade. For V2+ and V3+, the complete network of elementary steps is explored by MS/MS experiments. Furthermore, some thermochemical brackets are derived, e.g., for the enthalpies of formation of the ions V2Om+ (m = 1−3): 920 kJ/mol ≤ ΔfH (V2O+) ≤ 1130 kJ/mol; 670 kJ/mol ≤ ΔfH (V2O2+) ≤ 880 kJ/mol, and 420 kJ/mol ≤ ΔfH (V2O3+) ≤ 630 kJ/mol.

CCDC 1951512: Experimental Crystal Structure Determination

Ion chemistry of the hexanuclear methoxo-oxovanadium cluster V6O7(OCH3)12

Probing the gas-phase structure of charge-tagged intermediates of a proline catalyzed aldol reaction – vibrational spectroscopy distinguishes oxazolidinone from enamine species

Charge-tagging enables the detection of reaction intermediates which are probed by IRMPD spectroscopy in combination with theory.

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

Auf frischer Tat ertappt: Das Engineering genetischer Reaktionspfade zusammen mit der HPLC/NMR-spektroskopischen Untersuchung sehr labiler Intermediate lieferte direkte Belege für den Aufbau von β,γ-Doppelbindungen während der Polyketidverlängerung zum Antibiotikum Bacillaen. Des Weiteren wurde das neuartige Kongener Bacillaen B (1) als schwierig nachzuweisendes wahres Endprodukt des Pfades in Bacillus amyloliquefaciens entdeckt. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

CCDC 684939: 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.

The blue-green eggs of dinosaurs: How fossil metabolites provide insights into the evolution of bird reproduction

Open-nesting birds use biological pigments in eggshell to camouflage their unhatched offspring, varying the colour to account for the nesting environment and location. The tetrapyrrolic pigments protoporphyrin (PP) and biliverdin (BV), which both participate in the haem metabolism, are responsible for the reddish brown of chicken eggs and the brilliant blue of robin and emu eggs. However, eggshell pigmentation correlates with the nest type in a wide range of avian species and suggests that coloured eggs are basal to the avian lineage, extending back to their non-avian dinosaur origins. Detecting preserved eggshell pigments could thus shed light on dinosaur nesting behaviour. Using HPLC separation coupled to ESI-Q-TOF mass spectrometry, we here provide the first record of the eggshell pigments PP and BV preserved in fossils from three different localities, in 66 million year-old oviraptorid eggshell ( Macroolithus yaotunensis ). These eggs were presumably laid in at least partially open nests by the oviraptorid Heyuannia huangi and camouflaged by an originally blue-greenish egg colouration. Such a blue-greenish eggshell pigmentation hints at increased paternal care in Heyuannia . Shell porosity measurements, preserved clutches and parental animals support an open nesting behaviour for oviraptorid dinosaurs. Furthermore, the detection of PP, together with supporting microscopic observations, represents the first evidence for cuticle preservation in fossil eggshell. Our study demonstrates that molecular biomarkers, such as preserved metabolites, can be used to trace the evolution of modern avian traits, and to provide insights into dinosaur reproductive biology and the preservation of endogenous organic matter in fossil vertebrates.

3D Au–Ag heterometallic supramolecular cage: Triplet capture by heavy atom effect

CCDC 2067865: 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.

Pederin-Type Pathways of Uncultivated Bacterial Symbionts: Analysis of <i>O</i>-Methyltransferases and Generation of a Biosynthetic Hybrid

The complex polyketide pederin is a potent antitumor agent isolated from Paederus spp. rove beetles. We have previously isolated a set of genes from a bacterial endosymbiont that are good candidates for pederin biosynthesis. To biochemically study this pathway, we expressed three methyltransferases from the putative pederin pathway and used the partially unmethylated analogue mycalamide A from the marine sponge Mycale hentscheli as test substrate. Analysis by high-resolution MS/MS and NMR revealed that PedO regiospecifically methylates the marine compound to generate the nonnatural hybrid compound 18-O-methylmycalamide A with increased cytotoxicity. To our knowledge, this is the first biochemical evidence that invertebrates can obtain defensive complex polyketides from bacterial symbionts.

Subcomponent Self‐Assembly of a Cyclic Tetranuclear Fe^II Helicate in a Highly Diastereoselective Self‐Sorting Manner

Abstract An enantiomerically pure diamine based on the 4,15‐difunctionalized [2.2]paracyclophane scaffold and 2‐formylpyridine self‐assemble into an optically pure cyclic metallosupramolecular Fe 4 L 6 helicate upon mixing with iron(II) ions in a diastereoselective subcomponent self‐assembly process. The cyclic assembly results from steric strain that prevents the formation of a smaller linear dinuclear triple‐stranded helicate, and hence, leads to the larger strain‐free assembly that fulfils the maximum occupancy rule. Interestingly, use of the racemic diamine also leads to a racemic mixture of the homochiral cyclic helicates as the major product in a highly diastereoselective narcissistic chiral self‐sorting manner given the fact that the assembly contains ten stereogenic elements, which can in principle give rise to 149 different diastereomers. The metallosupramolecular aggregates could be characterized by NMR, UV/Vis and CD spectroscopy, mass spectrometry, and X‐ray crystallography.

CCDC 1945938: Experimental Crystal Structure Determination

Dynamische Komplex‐zu‐Komplex‐Umwandlungen von heterobimetallischen Systemen und ihr Einfluss auf die Käfigstruktur oder den Spinzustand von Eisen(II)‐Ionen

Abstract Ein trigonal‐bipyramidaler und ein kubischer heterobimetallischer Käfig wurden mit Eisen(II)‐ und Palladium(II)‐Bausteinen gemäß dem Molecular‐Library‐Ansatz aus demselben einkernigen Metalloliganden aufgebaut. Das Ligandensystem wurde so entworfen, dass der Aufbau durch Subkomponenten‐Selbstorganisation möglich war. Dieser Ansatz ermöglicht es, sterische Spannung um die Eisen(II)‐Zentren in das System einzuführen, was deren paramagnetischen High‐Spin‐Zustand stabilisiert. Diese sterische Spannung wurde genutzt, um dynamische Komplex‐zu‐Komplex‐Umwandlungen mit dem Metalloliganden und den heterobimetallischen Systemen durchzuführen. So konnten durch den Einsatz weniger sperriger Subkomponenten alle Komplexe in ihre diamagnetischen Analoga umgewandelt werden. Dabei integrierten der Metalloligand und die Bipyramide den neuen Baustein bereitwilliger als der Würfel, wahrscheinlich weil die geometrische Struktur des sperrigeren Metalloliganden die Bildung des Würfels begünstigt. Außerdem gelang es, Strukturumwandlungen durch die Zugabe besser koordinierender Chelatliganden zu provozieren, wodurch die kubischen in bipyramidale Strukturen umgewandelt werden konnten.

Coordination of capsule assembly and cell wall biosynthesis in Staphylococcus aureus

Cleavage of Four Carbon−Carbon Bonds during Biosynthesis of the Griseorhodin A Spiroketal Pharmacophore

The rubromycins, such as gamma-rubromycin, heliquinomycin, and griseorhodin A, are a family of extensively modified aromatic polyketides that inhibit HIV reverse transcriptase and human telomerase. Telomerase inhibition crucially depends on the presence of a spiroketal moiety that is unique among aromatic polyketides. Biosynthetic incorporation of this pharmacophore into the rubromycins results in a dramatic distortion of the overall polyketide structure, but how this process is achieved by the cell has been obscure. To identify the enzymes involved in spiroketal construction, we generated 14 gene-deletion variants of the griseorhodin A biosynthetic gene cluster isolated from the tunicate-associated bacterium Streptomyces sp. JP95. Heterologous expression and metabolic analysis allowed for an assignment of most genes to various stages of griseorhodin tailoring and pharmacophore generation. The isolation of the novel advanced intermediate lenticulone, which exhibits cytotoxic, antibacterial, and elastase-inhibiting activity, provided direct evidence that the spiroketal is formed by cleavage of four carbon-carbon bonds in a pentangular polyketide precursor. This remarkable transformation is followed by an epoxidation catalyzed by an unusual cytochrome P450/NADPH:ubiquinone oxidoreductase pair that utilizes a saturated substrate. In addition, the absolute configuration of griseorhodin A was determined by quantum-chemical circular dichroism (CD) calculations in combination with experimental CD measurements.

A Versatile Toolbox for Variable DNA Functionalization at High Density

To broaden the applicability of chemically modified DNAs in nano- and biotechnology, material science, sensor development, and molecular recognition, strategies are required for introducing a large variety of different modifications into the same nucleic acid sequence at once. Here, we investigate the scope and limits for obtaining functionalized dsDNA by primer extension and PCR, using a broad variety of chemically modified deoxynucleotide triphosphates (dNTPs), DNA polymerases, and templates. All natural nucleobases in each strand were substituted with up to four different base-modified analogues. We studied the sequence dependence of enzymatic amplification to yield high-density functionalized DNA (fDNA) from modified dNTPs, and of fDNA templates, and found that GC-rich sequences are amplified with decreased efficiency as compared to AT-rich ones. There is also a strong dependence on the polymerase used. While family A polymerases generally performed poorly on "demanding" templates containing consecutive stretches of a particular base, family B polymerases were better suited for this purpose, in particular Pwo and Vent (exo-) DNA polymerase. A systematic analysis of fDNAs modified at increasing densities by CD spectroscopy revealed that single modified bases do not alter the overall B-type DNA structure, regardless of their chemical nature. A density of three modified bases induces conformational changes in the double helix, reflected by an inversion of the CD spectra. Our study provides a basis for establishing a generally applicable toolbox of enzymes, templates, and monomers for generating high-density functionalized DNAs for a broad range of applications.