164 publications from this institution
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.
Charge-stripping mass spectrometry and electronic structure calculations are combined to examine the energetics of the vanadium-containing dications VO2+, VOH2+, [HVOH]2+, and [V(OH2)]2+. Energy-resolved measurements, in conjunction with quantum-mechanical calculations, led to ionization energies (IE) of (VO+) = 16.6 +/- 0.3 eV and IE(VOH+) = 16.0 +/- 0.4 eV. Born-Haber cycles reveal that VO2+ and VOH2+ are both thermochemically stable dications with respect to their charge-separation asymptotes. Depending on the mode of ion generation, the [V,O,H2]+ monocations are formed as variable mixtures of the structural isomers [HVOH]+ and [V(OH2)]+. The measured IE([V,O,H2]+) = 13.7 +/- 0.3 eV is between the theoretical predictions for these isomers, indicating that mixtures of both isomers are sampled in the experiments. According to the theoretical results, [V(OH2)]2+ is also a thermochemically stable dication, whereas [HVOH]2+ is suggested to be metastable.
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.
Abstract In order to expand the repertoire of DNA sequences specifically interacting with transition metals, we report here the first examples of DNA sequences carrying mono‐ and bidentate phosphane ligands as well as P,N‐ligands. Aminoalkyl‐modified oligonucleotides have been reacted at predetermined internal sites with carboxylate derivatives of pyrphos, BINAP and phosphinooxazoline (PHOX) 2 b – d . Carbodiimide coupling in the presence of N ‐hydroxysuccinimide provided the DNA–ligand conjugates in 38–78 % yield. Phosphane‐containing oligonucleotides and their phosphane sulfide analogues were characterized by mass spectrometry (MALDI‐TOF and FT‐ICR‐ESI) and their stability after purification and isolation was systematically investigated. While DNA‐appended pyrphos ligand was quickly oxidized, BINAP and PHOX conjugates showed high stabilities, making them useful precursors for incorporation of transition metals into DNA.
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.
Plant stinging hairs have fascinated humans for time immemorial. True stinging hairs are highly specialized plant structures that are able to inject a physiologically active liquid into the skin and can be differentiated from irritant hairs (causing mechanical damage only). Stinging hairs can be classified into two basic types: Urtica-type stinging hairs with the classical “hypodermic syringe” mechanism expelling only liquid, and Tragia-type stinging hairs expelling a liquid together with a sharp crystal. In total, there are some 650 plant species with stinging hairs across five remotely related plant families (i.e., belonging to different plant orders). The family Urticaceae (order Rosales) includes a total of ca. 150 stinging representatives, amongst them the well-known stinging nettles (genus Urtica). There are also some 200 stinging species in Loasaceae (order Cornales), ca. 250 stinging species in Euphorbiaceae (order Malphigiales), a handful of species in Namaceae (order Boraginales), and one in Caricaceae (order Brassicales). Stinging hairs are commonly found on most aerial parts of the plants, especially the stem and leaves, but sometimes also on flowers and fruits. The ecological role of stinging hairs in plants seems to be essentially defense against mammalian herbivores, while they appear to be essentially inefficient against invertebrate pests. Stinging plants are therefore frequent pasture weeds across different taxa and geographical zones. Stinging hairs are usually combined with additional chemical and/or mechanical defenses in plants and are not a standalone mechanism. The physiological effects of stinging hairs on humans vary widely between stinging plants and range from a slight itch, skin rash (urticaria), and oedema to sharp pain and even serious neurological disorders such as neuropathy. Numerous studies have attempted to elucidate the chemical basis of the physiological effects. Since the middle of the 20th century, neurotransmitters (acetylcholine, histamine, serotonin) have been repeatedly detected in stinging hairs of Urticaceae, but recent analyses of Loasaceae stinging hair fluids revealed high variability in their composition and content of neurotransmitters. These substances can explain some of the physiological effects of stinging hairs, but fail to completely explain neuropathic effects, pointing to some yet unidentified neurotoxin. Inorganic ions (e.g., potassium) are detected in stinging hairs and could have synergistic effects. Very recently, ultrastable miniproteins dubbed “gympietides” have been reported from two species of Dendrocnide, arguably the most violently stinging plant. Gympietides are shown to be highly neurotoxic, providing a convincing explanation for Dendrocnide toxicity. For the roughly 648 remaining stinging plant species, similarly convincing data on toxicity are still lacking.
In situ formed Li/Cl phosphinidenoid complexes [Li(12-crown-4)][M(CO)5(ClPC5Me5)] 3a-c (M = Cr, Mo, W) reacted with cyclobutanone (4), cyclopentanone (5) and cyclohexanone (6) in Et2O to yield the first P-C5Me5 substituted C(3)-spirofused oxaphosphirane complexes 7a-c, 8a and 9a,a'. In the case of cyclopentanone and 1a the outcome of the reaction in THF was different: here the formation of 8a along with (anionic) phosphinoate complexes 14a and 15a was observed, the latter possess an unusual ring-opened oxaphosphirane and 2-cyclopentylidenecyclopentanone as co-ligands to the lithium cation. NMR, IR and MS data as well as single-crystal X-ray structures in the case of 7a-c, 8a, 9a and 15a are reported. DFT calculations on the parent 1-oxa-2-phosphaspiro[2.n]alkane pentacarbonylchromium(0) complexes 10 (a: n = 2; b: n = 3; c: n = 4; d: n = 5) revealed that both ring strain energies and G(r) values decrease significantly as the spiroring size increases. This is caused by an increase in the exocyclic α bond angle at the oxaphosphirane C(3) atom, hence decreasing the s-character of the corresponding orbitals involved in endocyclic bonds at C(3) and thus becoming better suited for accommodation of small ring angles.
