Publications

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.

Abstract Suberin, a complex biopolymer, forms a water and gas insoluble barrier that protects the inner tissues of plants. It is abundant in tree bark, particularly in the cork oak Quercus suber . Anatomically, fossil bark has been described since the Devonian. However, its distinctive constituent suberin has not yet been reported from the fossil record. Here we present unambiguous chemical evidence for intact suberin from the outer layer of a middle Eocene monkeyhair tree from Geiseltal, eastern Germany. High-performance liquid chromatography coupled to electrospray ionization mass spectrometry (HPLC-ESI-MS) was employed to detect constituents of suberin in the outer layer of the fossil monkeyhair tree, which confirms previous morphological interpretation of this tissue as bark, and chemically differentiates this layer from the two tissues of the inner layer. Notably, this is the first study with compelling chemical evidence for suberin in fossil bark. Fluorescence microspectroscopy additionally supported the presence of suberin. Fossilization conditions in the Eocene Geiseltal deposit were likely mild, with low moisture and temperatures, contributing to the remarkable preservation of bark and inner laticifer mats of the monkeyhair trees growing there 45 million years ago.

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 gas-phase fragmentation behavior of self-assembled metallo-supramolecular rhombs based on an unusual chiral [2.2]paracyclophane bis(pyridine) ligand is studied by collision-induced dissociation mass spectrometry. The fragmentation patterns strongly depend on the charge state of the respective mass-selected aggregate. For the doubly charged ions, simple symmetric fragmentation is observed in full accordance with previous results reported for related metallo-supramolecular species. The triply charged species cleaves unsymmetrically which can be rationalized by a preferred formation of ions with low charge density. CID of the quadruply charged rhomb reveals a complex fragmentation. Besides ligand oxidation to the radical cation, facile cleavage of the central covalently bound part of the [2.2]paracyclophane ligand takes place which is even preferred over rupture of the weak dative pyridine-Pd bond.

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.

Abstract Reaction monitoring by electrospray (ESI) mass spectrometry (MS) is a valuable technique to investigate reaction mechanisms. It allows a glimpse into the reacting solution and the characterization of transient intermediates by tandem mass spectrometry. Herein we studied an intriguing gold(III)‐catalyzed synthesis of dicoumarins which includes a combination of hydroarylation and homocoupling steps. Reactants and products could be detected in positive mode. In negative mode, some species corroborating proposed transient intermediates could be detected by direct infusion ESI of reacting solutions. The ions were characterized by accurate mass determinations and gas‐phase fragmentation. Thus, indications for the nature and ligand sphere of reaction intermediates in the catalytic cycle could be collected.

Abstract Mass spectrometry has played a significant role in dendrimer chemistry, because it serves as an excellent analytical means to determine the purity and analyze the nature of defects even for higher generations. However, a mass spectrometer can also be used as a laboratory to study isolated dendrimer molecules in the gas phase or their host–guest complexes. Since the properties of molecules under environment‐free conditions are often quite different from those in solution, their gas‐phase chemistry provides valuable new insight into properties which cannot easily be studied in solution. This article summarizes some of our work on characterizing self‐assembling metallo‐supramolecular dendrimers, on analyzing ionization artifacts, on the differentiation between several, sometimes even isomeric defects through tandem MS experiments, and finally on the analysis of a surprisingly clear dendritic effect occurring in the fragmentation of dendritic host–guest complexes. Copyright © 2006 John Wiley & Sons, Ltd.

A little light release: Temporarily blocked ("caged") dG nucleosides that can be incorporated into oligodeoxynucleotides are presented (see figure). Their hydrogen-bond-recognition site is inaccessible in the inactive form; this prevents, for example, the formation of secondary structures. Light can trigger the release of the unmodified oligonucleotide and thus induce correct folding. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2268/2005/z500198_s.pdf or from the author. 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.

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.

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.

We report the synthesis and characterization of 12 new dinuclear gold(I) N-heterocyclic carbene (NHC) complexes and the corresponding imidazolium precursors. The focus lies in a systematic study of conformational changes and intra- and intermolecular gold-gold and π-π interactions of dinuclear gold(I) carbene complexes. Common to all members of the series of gold macrocycles are NHC ligands on the basis of imidazole with ethyl side chains and bromide as well as hexafluorophosphate counterions, respectively. The compounds vary in the length of a flexible alkyl linker between the NHC units. For the methylene and ethylene bridged macrocycles, a ring inversion movement can be observed by VT-NMR. In total, 11 molecular structures have been characterized by X-ray diffraction. Open ring conformations with intermolecular π-π and Au-Au interactions prevail, but a backfolded conformation with a short intramolecular Au-Au distance has been found for the ethylene-bridged species. The presence of Au-Au interactions could be proven by quantum chemical calculations.

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.

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.