Release pathways of interferon α2a molecules from lipid twin screw extrudates revealed by single molecule fluorescence microscopy.

The pathways of interferon α2a release from a triglyceride based implant system were studied by single molecule fluorescence microscopy. The protein was labeled with a stable fluorescent dye ATTO647N, freeze-dried and embedded into the lipid matrix via twin-screw extrusion. The implant system consisted of a pore-forming agent (water soluble PEG 6000) and two types of triglycerides with different melting ranges which allowed the production of the implants at moderate temperatures and without the use of organic solvents. Single molecule microscopy and single particle tracking of labeled proteins contained in these implants revealed that two populations of diffusing proteins were present. Moreover, proteins were not only released via water-filled pores (created by dissolution of the pore-former), but surprisingly also through diffusion in a phase of molten lipid. Diffusion coefficients of IFNα 2a derived by tracking of individual protein molecules within the implant system were similar to diffusion coefficients obtained from control measurements in pure molten lipid and highly concentrated solutions of PEG 6000. In conclusion, tracking of individual protein molecules was successfully used to elucidate the release pathways of proteins from a relevant lipid based implant system.

Synchronous emission from nanometric silver particles through plasmonic coupling on silver nanowires.

We investigated silver nanowires using correlative wide-field fluorescence and transmission electron microscopy. In the wide-field fluorescence images, synchronous emission from different distinct positions along the silver nanowires was observed. The sites of emission were separated spatially by up to several micrometers. Nanowires emitting in such cooperative manner were then also investigated with a combination of transmission electron microscopy based techniques, such as high-resolution, bright-field imaging, electron diffraction, high-angle annular dark-field imaging, and energy-dispersive X-ray spectroscopy. In particular, analyzing the chemical composition of the emissive areas using energy-dispersive X-ray spectroscopy led to the model that the active emissive centers are small silver clusters generated photochemically and that individual clusters are coupled via surface plasmons of the nanowire.

Direct visualization of dye and oligonucleotide diffusion in silica filaments with collinear mesopores.

The diffusion dynamics of terrylene diimide (TDI) dye molecules and dye-labeled double-strand DNA were studied in micrometer long silica filaments containing collinear, oriented mesopores using single molecule fluorescence microscopy. TDI was used as a stable and hydrophobic probe molecule for single molecule structural analysis. We used template-free mesoporous silica filaments with 4 nm pore diameter and chemical functionalization with one or two types of trialkoxysilane groups to enhance the affinity between the host system and the guest molecules. Insights about the mesoporous structure as well as the translational and orientational diffusion dynamics of the guest molecules observed along micrometer long trajectories could be obtained. Additionally, the stability of DNA oligomers (15 base pairs, bp, about 5.3 nm long) within the mesopores was examined, showing no degradation of the oligonucleotide upon incorporation into the mesopores. Diffusion of both guest molecules could be controlled by exposure to vapors of water or chloroform; the latter both induced a reversible on-off control of the translational movement of the molecules.

Tautomerization of 2-nitroso-N-arylanilines by coordination as N,N'-chelate ligands to rhenium(I) complexes and the anticancer activity of newly synthesized oximine rhenium(I) complexes against human melanoma and leukemia cells in vitro.

The synthesis, structural characterization and biological activity of eight ortho-quinone(N-aryl)-oximine rhenium(I) complexes are described. The reaction of the halogenido complexes (CO)(5)ReX (X = Cl (4), Br (5)) with 2-nitroso-N-arylanilines {(C(6)H(3)ClNO)NH(C(6)H(4)R)} (R = p-Cl, p-Me, o-Cl, H) (3a-d) in tetrahydrofurane (THF) yields the complexes fac-(CO)(3)XRe{(C(6)H(3)ClNO)NH(C(6)H(4)R)} (6a-d, 7a-d) with the tautomerized ligand acting as a N,N'-chelate. The substitution of two carbonyl ligands leads to the formation of a nearly planar 5-membered metallacycle. During coordination the amino-proton is shifted to the oxygen of the nitroso group which can be observed in solution for 6 and 7 by (1)H NMR spectroscopy and in solid state by crystal structure analysis. After purification, all compounds have been fully characterized by their (1)H and (13)C NMR, IR, UV/visible (UV/Vis) and mass spectra. The X-ray structure analyses revealed a distorted octahedral coordination of the CO, X and N,N'-chelating ligands for all Re(I) complexes. Biological activity of four oximine rhenium(I) complexes was assessed in vitro in two highly aggressive cancer cell lines: human metastatic melanoma A375 and human chronic myelogenous leukemia K562. Chlorido complexes (6a and 6c) were more efficient than bromido compounds (7d and 7b) in inducing apoptotic cell death of both types of cancer cells. Melanoma cells were more susceptible to tested rhenium(I) complexes than leukemia cells. None of the ligands (3a-d) showed any significant anticancer activity.

Electronically coupled MM quadruply-bonded complexes (M = Mo or W) employing functionalized terephthalate bridges: toward molecular rheostats and switches.

Toluene solutions of M2(O2C(t)Bu)4 (M = Mo, W; 2 equiv) react with a range of functionalized terephthalic acids, HO2CArCO2H (Ar = C6H4, C6F4, C6Cl4, C6H2-2,5-Cl2, C6H2-2,5-(OH)2, C6H3-2-F), to give [(tBuCO2)3M2]2[mu-O2CArCO2]. These compounds show intense ML(bridge)CT absorptions in the visible region of the electronic spectrum, and the terephthalate bridge serves to electronically couple the two M2 units via interactions between the M2 delta and bridge pi orbitals. Electronic structure calculations reveal how the degree of electronic coupling is controlled by the dihedral angles between the terephthalate C6 ring and the two CO2 units and the degree of interaction between the M4 delta MOs and the LUMO of the bridge. Both of these factors are controlled by the aryl substituents, and collectively these determine the thermochromism displayed by these complexes in solution together with the physical properties of the oxidized radical cations as determined by electrochemical studies (CV, DPV), UV-vis-NIR and EPR spectroscopic methods.

"Alkaline-earth metals in a box": structures of solvent-separated ion pairs.

During our research on homoleptic organocalcium compounds, we found that fluorenylcalcium complexes show unusual solution behavior and precipitate from nonpolar solvents after addition of THF. Their solid-state structures reveal the unexpected rupture of both metal-carbanion bonds by the polar solvent THF. The crystal structures of five new Mg and Ca solvent-separated ion pairs are described. The compound [Ca(2+)(thf)(6)][Me(3)Si(fluorenyl(-))](2) is the first organometallic complex of a Group 2 element that crystallizes as a completely solvent-separated ion pair. The driving forces for its formation are: 1) the strong Ca-THF bond; 2) the stability of the free [Me(3)Si(fluorenyl)](-) ion; 3) encapsulation of [Ca(2+)(thf)(6)] in a "box", the walls of which consist of anionic fluorenyl ligands and benzene molecules; and 4) the presence of numerous (THF)C- H...pi interactions. The magnesium analogue [Mg(2+)(thf)(6)][Me(3)Si(fluorenyl(-))](2) is isostructural. Bis(7,9-diphenylcyclopenta[a]acenaphthadienyl)calcium also crystallizes as a completely solvent-separated ion pair and can likewise be described as a [Ca(2+)(thf)(6)] species in a box of delocalized anions and benzene molecules. In addition, the structures of two Ph(4)B(-) complexes of Mg and Ca are described. [Mg(2+)(thf)(6)][Ph(4)B(-)](2) crystallizes as a completely solvent-separated ion pair and also shows a solvated metal cation bonded via C-H.pi interactions in a cavity formed by Ph(4)B(-) ions. [(thf)(4)CaBr(+)][Ph(4)B(-)] has a structure in which one of the anionic ligands is still bonded to the Ca atom. Bridging bromide ligands result in the formation of the dimer [(thf)(4)CaBr(+)](2).

Novel Calcium Half-Sandwich Complexes for the Living and Stereoselective Polymerization of Styrene.

Tackling tacticity: The first well-defined heteroleptic benzylcalcium complex initiates the living polymerization of styrene. Chain-end control results in a polymer enriched in syndiotactic sequences. Stereo errors arise from fast inversion of the chiral carbanionic chain end. Increasing the styrene concentration accelerates the insertion and leads to a considerable reduction of the stereo errors.