Encapsulation of luminescent homoleptic [Ru(dpp)3](2+)-type chromophores within an amphiphilic dendritic environment.

A new series of homoleptic metallodendrimers has been synthesized through ruthenium-metal complexation by dendritically modified bathophenanthroline ligands. The presence of hydrophilic oligo(ethylene glycol) groups on the surface of the monodisperse metal complexes enabled the solubilization of all of the fractal species in a wide range of solvents, including water. The specific properties of all of these compounds have been systematically investigated by using photophysical techniques as a function of the generation number. Accordingly, the encapsulation of the highly luminescent [Ru(dpp)(3)](2+)-type (dpp=4,7-diphenyl-1,10-phenanthroline) core unit within a dendritic microenvironment creates a powerful means to shield the center from dioxygen quenching. This shielding effect, as exerted on the phosphorescent ruthenium-derived center, is reflected by enhanced emission intensities and extended excited-state lifetimes that are close to the highest values reported so far, even in an air-equilibrated aqueous medium. Interestingly, when inspecting the largest dendritic assembly, that is, the third-generation assembly, significant drops in emission quantum yields and lifetimes are observed. This anomalous behavior has been attributed to the folding of the branches towards the luminescent core.

CH···O hydrogen bonds in "clicked" diketopiperazine-based amide rotaxanes.

Two amide [2]rotaxanes were synthesized in high yields using a novel N,N'-dipropargyl diketopiperazine axle centerpiece as the template to which the stoppers are attached through "click chemistry". (1)H and 2D NMR spectra provide evidence for two different H-bonding motifs, in one of which the triazole CH groups form C-H···O═C bonds with the wheel carbonyl O atoms. This motif can be controlled and switched reversibly by competitive anion binding.

Characterization of human chondrocytes exposed to simulated microgravity.

BACKGROUND: Tissue engineering is a strategy of cartilage regeneration, but scaffolds, required for 3D growth of chondrocytes, are still a problem. METHODS: Searching for possibilities to improve scaffold-free engineering of cartilage, we characterized human chondrocytes incubated on a random positioning machine (RPM) to simulate microgravity (microg). RESULTS: When cultured in simulated microg, human chondrocytes start forming 3D cell assemblies within 5 days. After 24h, we could not detect caspase-3, Fas, p53 or Bcl-2 proteins in these cells, Annexin V flow cytometry, however, revealed 18% of apoptotic chondrocytes in 1g cultures but only 10% on the RPM. Both rates of apoptosis were not changed, when vascular endothelial growth factor (VEGF) or basic fibroblast growth factor (bFGF) was added. 24 h, simulated microgravity also had significantly decreased collagen type I and X, but did not change collagen type IV and laminin, while collagen type II, chondroitin sulfate and aggrecan were elevated as compared with 1g controls. The production of collagen type II/X, chondroitin sulfate and aggrecan was modified, when external bFGF or VEGF had been applied. CONCLUSION: Chondrocytes exposed to simulated microg seem to change their extracellular matrix production behavior, while they rearrange their cytoskeletal proteins prior to forming 3D aggregates.

Highly dynamic motion of crown ethers along oligolysine peptide chains.

Molecular mobility has attracted considerable attention in supramolecular chemistry and biochemistry, but the simple question of whether a small molecule can move directly between different binding sites of a multitopic host without intermediate dissociation has not been addressed so far. To study such processes, we consider hydrogen/deuterium exchange experiments on a model system comprising complexes formed between 18-crown-6 and oligolysine peptides. Because direct binding-site hopping is indistinguishable in solution from a dissociation/reassociation mechanism, here we show that the high vacuum of a mass spectrometer offers a unique environment for probing such processes. The highly dynamic motion of crown ethers along oligolysine peptide chains proceeds mechanistically by a simultaneous transfer of the crown ether from its ammonium ion binding site to a nearby amino group together with a proton. Furthermore, the exchange experiments unambiguously reveal the zwitterionic structure of the 18-crown-6/oligolysine complexes, highlighting the versatility and potential of gas-phase experiments for investigating non-covalent interactions.

Integrative self-sorting: construction of a cascade-stoppered hetero[3]rotaxane.

In this Communication, a competing self-sorting system containing benzo-21-crown-7, dibenzo-24-crown-8 and two secondary ammonium salts is constructed, which is then modified to achieve a hetero[3]pseudorotaxane with a specific sequence of wheels. With these two systems, we successfully demonstrate the concept of integrative self-sorting, and their relation. Furthermore, based on this self-sorting scheme, a hetero[3]rotaxane with an efficient stopper cascade has been synthesized.