Solid state NMR and computational studies on cyclopentadienyl lithium.

Lithiumcyclopentadienide, previously identified to be an endless polymer in the ligand-free solid state, was investigated by C- and Li-CP/MAS NMR spectra, and by B3LYP-GIAO theoretical calculations. By spectra simulation, the axially symmetric C-shift tensor components were identified to be δ = δ = 151.5 ppm, δ = 15.

Deeper Insight into the Six-Step Domino Reaction of Aldehydes with Malononitrile and Evaluation of Antiviral and Antimalarial Activities of the Obtained Bicyclic Products.

The straightforward and efficient synthesis of complex aza- and carbobicyclic compounds, which are of importance for medicinal chemistry, is a challenge for modern chemical methodology. An unprecedented metal-free six-step domino reaction of aldehydes with malononitrile was presented in our previous study to provide, in a single operation, these bicyclic nitrogen-containing molecules. Presented here is a deeper investigation of this atom-economical domino process by extending the scope of aldehydes, performing post-modifications of domino products, applying bifunctional organocatalysts and comprehensive NMR studies of selected domino products.

Production of the Cytotoxic Cardenolide Glucoevatromonoside by Semisynthesis and Biotransformation of Evatromonoside by a Digitalis lanata Cell Culture.

Recent studies demonstrate that cardiac glycosides, known to inhibit Na/K-ATPase in humans, have increased susceptibility to cancer cells that can be used in tumor therapy. One of the most promising candidates identified so far is glucoevatromonoside, which can be isolated from the endangered species ssp. .

Generation of Complex Azabicycles and Carbobicycles from Two Simple Compounds in a Single Operation through a Metal-Free Six-Step Domino Reaction.

Aza- and carbobicyclic compounds possess favorable pharmaceutical properties, but they are difficult to access. Herein, we demonstrate an unprecedented organocatalytic two component six-step chemodivergent domino reaction, which provides a straightforward, sustainable and atom economical route to difficult-to-access complex bicyclic architectures: azabicycles and carbobicycles, whose ratios can be controlled by the applied electrophiles and catalysts. Detailed NMR and X-ray studies on the structures and relative stereochemistry of selected compounds are presented.

Synthesis and Atropisomerism of Cascaded Tetraphenylporphyrin-[60]Fullerene Hybrids.

Flexible, linked dendritic tetraphenylporphyrin (TPP)-fullerene hybrids were synthesized. They were designed to gain insight into and mimic the primary events in the natural photosynthetic reaction center. These multiporphyrin moieties are based on a light-harvesting concept.

Preparation of candidate reference materials for the determination of phosphorus containing flame retardants in styrene-based polymers.

Candidate reference materials (RM) for the analysis of phosphorus-based flame retardants in styrene-based polymers were prepared using a self-made mini-extruder. Due to legal requirements of the current restriction for the use of certain hazardous substances in electrical and electronic equipment, focus now is placed on phosphorus-based flame retardants instead of the brominated kind. Newly developed analytical methods for the first-mentioned substances also require RMs similar to industrial samples for validation and verification purposes.

Carbon nanodots: toward a comprehensive understanding of their photoluminescence.

We report the characterization of carbon nanodots (CNDs) synthesized under mild and controlled conditions, that is, in a microwave reactor. The CNDs thus synthesized exhibit homogeneous and narrowly dispersed optical properties. They are thus well suited as a testbed for studies of the photophysics of carbon-based nanoscopic emitters.

Fused perylene-phthalocyanine macrocycles: a new family of NIR-dyes with pronounced basicity.

The synthesis and characterization of a new type of chromophore, namely PePc consisting of a central phthalocyanine core and four fused perylene-bisimide (PBI) units is described for the first time. The entire architecture represents a highly extended conjugated heterocyclic π-system with C4h symmetry. In order to guarantee pronounced solubility in organic solvents the corresponding PBI units were bay-functionalized with tert-butylphenoxy substituents.

Optically active tetra-tert-butyl-P(5)-deltacyclene epimers: preparation, spectroscopy, dynamic equilibriums, H/D exchange, and transition-metal complex chemistry.

On the basis of isolated diastereomeric triorganylstannyl-P5 -deltacyclenes 7' and 7'', almost pure enantiomers of their destannylation products 8' and 8'' are now available. These stereochemically inert cage chiral species contain a configurationally labile P1H1 group that defines two epimers 8 a and 8 b of each of the enantiomers, which are connected by a rapid equilibrium. Mirror-symmetric circular dichroism (CD) spectra of the enantiomeric cages are compatible with the identification of epimers.

Sulfur species in graphene oxide.

The structure of graphene oxide (GO) is of crucial importance for its chemical functionalization. However, the sulfur content present in GO prepared by Hummers' method has only been addressed by a few authors so far. It has been reported that hydrolysis of sulfur species takes place and that stable sulfonic groups are present in graphite oxide.

On the way to graphane-pronounced fluorescence of polyhydrogenated graphene.

Chemistry meets graphane: a Birch-type reaction using frozen water as a gentle proton source causes the exfoliation of graphite and formation of hydrogenated graphene with electronically decoupled π-nanodomains. This highly functionalized graphene displays pronounced fluorescence.

Microenvironment engineering in ortho- and para-dendronized metalloporphyrin-fullerene conjugates involving a trans-2-bisaddition pattern.

A new series of dendronized metalloporphyrin-fullerene conjugates as photosynthetic reaction center mimics was developed in a highly regioselective fashion through tether-controlled synthesis. The microenvironment around the porphyrin core is dependent on the spatial substitution pattern and the nature and generation number of the dendrons, which was proven by cyclic voltammetry.

No shot in the dark: myxozoans chemically detect fresh fish.

This work reports the discovery of an hitherto unknown chemical recognition trait enabling a parasitic life cycle in aquatic habitats. We believe this is the first record of a natural, host-derived chemical molecule identified as a recognition cue for the phylum Myxozoa. The actinospores of these parasites attach to fish hosts via polar filaments that are extruded upon mechanical stimulation after preceding recognition of a chemical trigger contained in surface mucus.

Dendronizing and metalating trans-2 C60 tetraaryl porphyrins--a versatile approach toward water-soluble donor-acceptor conjugates.

We have realized for the first time a series of truly water-soluble and tightly coupled porphyrin/C(60) electron-donor-acceptor conjugates in which the charge separation and charge recombination dynamics are controlled by modifying the nature of the dendrimer and/or the choice of the central metal atom.

Head-to-tail interactions in tyrosine/benzophenone dyads in the ground and the excited state: NMR and laser flash photolysis studies.

The formation of head-to-tail contacts in de novo synthesized benzophenone/tyrosine dyads, bp logical sum Tyr, was probed in the ground and excited triplet state by NMR techniques and laser flash photolysis, respectively. The high affinity of triplet-excited ketones towards phenols was used to trace the geometric demands for high reactivity in the excited state. A retardation effect on the rates with increasing hydrogen-bond-acceptor ability of the solvent is correlated with ground-state masking of the phenol.

Solvent dependent reactivity: solvent activation vs. solvent coordination in alkylphosphane iron complexes.

The pyridine-derived tetrapodal tetraphosphane C5H3N[CMe(CH2PMe2)2]2 is susceptible to selective protonolysis of a phosphorus-carbon bond in the presence of iron(II) salts. Water produces dimethylphosphinic acid, Me2POH, and protonates the anionic remainder of the tetraphosphane. The resulting iron(II) complexes and (tetrafluoroborate and perchlorate salts, respectively) contain the residual chelate ligand in which a methyl group, derived from the ligand skeleton, is in agostic interaction with the metal centre, and in which Me2POH, unavailable in the free state owing to rapid tautomerisation, is metal-coordinated and thus stabilised.

The formation of endo-complexes between calixarenes and amines--a reinvestigation.

The formation of an endo-complex between p-allylcalix[4]arene and t-butylamine was described by Gutsche in 1985. However, for a comparable system, it has been shown using NOE methods that the amine does not reside inside the calix. Instead, an exo-calix complex is formed.

Ligand cleavage put into reverse: P--C bond breaking and remaking in an alkylphosphane iron complex.

Complex formation between FeX(2)6 H(2)O (X=BF(4) or ClO(4)) and the pyridine-derived tetrapodal tetraphosphane C(5)H(3)N[CMe(CH(2)PMe(2))(2)](2) (1) in methanol proceeds with solvent-induced cleavage of one PMe(2) group. Depending on the reaction temperature and the nature of the counterion, iron(II) is coordinated, in distorted square-pyramidal fashion, by the anionic remainder of the chelating ligand, C(5)H(3)N[CMe(CH(2)PMe(2))(2)][CMe(CH(2)PMe(2))(CH(2) (-))] (NP(3)C(-) donor set: X=BF(4), -50 degrees C: 2; X=ClO(4), RT: 4) or its protonated form C(5)H(3)N[CMe(CH(2)PMe(2))(2)][CMe(CH(2)PMe(2))(CH(3))], in which the methyl group is in agostic interaction with the metal centre (X=BF(4), RT: 3; X=ClO(4), +50 degrees C: 5). A monodentate phosphinite ligand Me(2)POMe, formed from the cleaved PMe(2) group and methanol, completes the coordination octahedron in both cases.

Synthesis, structure, and dynamics of six-membered metallacoronands and metallodendrimers of iron and indium.

In the reaction of the N-substituted diethanolamines (H(2)L(1-3)) (1-3) with calcium hydride followed by addition of iron(III) or indium(III) chloride, the iron wheels [Fe(6)Cl(6)(L(1))(6)] (4) and [Fe(6)Cl(6)(L(2))(6)] (6) or indium wheels [In(6)Cl(6)(L(1))(6)] (5), [In(6)Cl(6)(L(2))(6)] (8) and [In(6)Cl(6)(L(3))(6)] (9) were formed in excellent yields. Exchange of the chloride ions of 6 by thiocyanate ions afforded [Fe(6)(SCN)(6)(L(2))(6)] (7). Whereas the structures of 4, 5 and 7 were determined unequivocally by single-crystal X-ray analyses, complexes 8 and 9 were characterised by NMR spectroscopy.

Enantiomerisation of tetrahedral homochiral [M4L6] clusters: synchronised four Bailar twists and six atropenantiomerisation processes monitored by temperature-dependent dynamic 1H NMR spectroscopy.

Temperature-dependent 1H NMR studies prove homochiral, racemic [([symbol: see text])/([symbol: see text])]-((NH4)4[symbol: see text] [Mg4(L1)6]) (1) to be kinetically stable on the NMR timescale. Due to steric reasons, rotation around the central C-C single bond in (L1)2- is blocked, which prevents 1 from enantiomerisation. Most interestingly, however, the 1H NMR spectrum of racemic 2a reveals dynamic temperature dependence.