Florian Feil

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.

α-Methyl-benzylcalcium complexes: syntheses, structures and reactivity

Abstracta-Methyl-benzylcalcium complexes were prepared analogue to a-Me 3 Si-benzylcalcium complexes for which procedures werereported earlier. The crystal structures of homoleptic bis(2-Me 2 N-a-Me-benzyl)calcium / (THF) 2 and heteroleptic (9-Me 3 Si-fluorenyl)(2-Me 2 N-a-Me-benzyl)calcium / (THF) were determined. For both compounds only one of the two diastereomerscrystallized. Barriers for inversion of the chiral benzylic carbon were estimated by variable temperature NMR spectroscopy. The a-methyl-benzylcalcium compounds are less stable and show a higher reactivity and faster initiation of styrene polymerization than theanalogue a-Me 3 Si-benzylcalcium complexes. Intramolecular C / H activation in a heteroleptic a-methyl-benzylcalcium complex wasobserved and the product, a calcium complex with a dianionic alkyl/fluorenyl ansa-ligand, was characterized by crystal structuredetermination.# 2003 Elsevier Science B.V. All rights reserved. Keywords: Calcium; Carbanion; Polystyrene; C / H activation

Single‐Particle and Ensemble Diffusivities—Test of Ergodicity

Diffusion is the irregular, omnipresent motion of the elementary constituents of matter. It is prerequisite for life quite in general and key to innumerable processes in nature and technology. After one and a half centuries of diffusion measurements with large ensembles of diffusing particles [1], the option of single-particle tracking (SPT) with single molecule sensitivity [2] has recently provided us with a totally new view of diffusion. With this in mind, a central problem of matter dynamics can now be addressed by direct experimental evidence – the proof of the ergodic theorem indicating that the average value of the squared displacement r2(t) of a diffusing particle during a time interval t, if taken over many subsequent time intervals (“time average”), agrees with the average taken over many different particles (“ensemble average”) during one and the same time interval t.

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.

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.