(Eta3-phenylallyl)(phosphanyloxazoline)palladium complexes: X-ray crystallographic studies,NMR investigations,and Ab initio/DFT calculations

All possible (eta(3)-allyl)palladium complexes (1-4) of the ligand (4S)-[2-(2'-diphenylphosphanyl)phenyl]-4,5-dihydro-4-(2-propyl)-oxazole (L 1) and eta(3)-allyl ligands with one to three phenyl substituents at the terminal allylic centers were synthesized and characterized by X-ray crystal structure analysis and, with respect to allylic isomers, by NMR investigations. Equilibrium geometries, electronic structures, and relative energies of isomeric complexes were computed by restricted Hartree-Fock (RHF) and density functional theory (DFT) calculations; experimentally determined isomer ratios could be reproduced. The results allowed important conclusions to be drawn regarding the mechanism of Pd-catalyzed asymmetric allylic substitutions.     

The diazo route to 2-vinylcyclopropylidenes

2-Vinylcyclopropylidene(2),3-methyl-2-vinylcyclopropylidenes(79,81)and2-(1-propenyl)cyclopropylidenes (95,97) were generated from the corresponding nitrosoureas in methanol at room temperature. The diazo route is initiated by the formation of 2-vinylcyclopropanediazonium ions (e.g.43) which do not undergo 1,3-carbon shifts. No cyclopentenyl products were found in weakly basic methanol where the diazonium ions prevail. Ring opening of the diazonium ions gives pentadienyl cations and products derived therefrom. Delocalisation of the pentadienyl cations was demonstrated by the distribution of deuterium and methyl labels. In the presence of strong base, 1-diazo-2-vinylcyclopropanes (e.g.48) arise by deprotonation of the diazonium ions. Rearrangement of 48 was excluded by independent generation of the potential product, 4-diazocyclopentene (103). Substantial quantities of 3-methoxycyclopentene (108) were obtained from 103, but not from 48. The 2-vinylcyclopropylidenes 2,79 and 95, arising by loss of nitrogen from the corresponding diazo compounds, undergo allene formation and Skattebøl rearrangement competitively. Cis-oriented methyl groups at either C-2(81) or C-2'(97) prevent the Skattebøl rearrangement. The cyclopentenylidenes 3 and 83 yield 4-methoxycyclopentenes (52,86) in excess over cyclopentadiens (4,84). In the presence of methyl vinyl ether, cycloaddition of 3 and electrophilic addition of 3-cyclopentenyl cation (51) occurred in a 1:14 ratio. Stereospecific formation of 52 indicates protonation of a ‘foiled carbene’ (3a) to give a bishomocyclopropenyl ion (51a). Our studies confirm that the various routes to 2-vinylcyclopropylidenes converge at the carbene stage.     

Giant dielectric constant response of the composites in ternary system CuO-TiO2-CaO

The subsolidus phase relations of the ternary system CuO-TiO₂-CaO sintered at 950 °C in air have been determined by powder X-ray diffraction method. Only one ternary compound CaCu₃Ti₄O₁₂ was found in this system. From room-temperature dielectric property mapping at 10 kHz, a giant dielectric constant (ε_r>10⁴) was observed for most of the ceramic composites in the CuO-rich region and in the region along the CaO-CuO binary line. The composites in the CaCu₃Ti₄O₁₂-rich region were found to give a comparable giant dielectric constant when sintered at 1050 °C. The particular microstructure of larger grains with predominant phase surrounded by smaller grains with the secondary phases was found in such composites with a high dielectric constant. The relations between structures and dielectric properties were investigated. An internal barrier layer capacitance effect is the most probable mechanism to explain this particular dielectric behavior.     

Fast Detection Allows Analysis of the Electronic Structure of Metalloprotein by X-ray Emission Spectroscopy at Room Temperature

The paradigm of "detection-before-destruction" was tested for a metalloprotein complex exposed at room temperature to the high x-ray flux typical of third generation synchrotron sources. Following the progression of the x-ray induced damage by Mn Kβ x-ray emission spectroscopy, we demonstrated the feasibility of collecting room temperature data on the electronic structure of native Photosystem II, a trans-membrane metalloprotein complex containing a Mn(4)Ca cluster. The determined non-damaging observation timeframe (about 100 milliseconds using continuous monochromatic beam, deposited dose 1*10(7) photons/μm(2) or 1.3*10(4) Gy, and 66 microseconds in pulsed mode using pink beam, deposited dose 4*10(7) photons/μm(2) or 4.2*10(4) Gy) is sufficient for the analysis of this protein's electron dynamics and catalytic mechanism at room temperature. Reported time frames are expected to be representative for other metalloproteins. The described instrumentation, based on the short working distance dispersive spectrometer, and experimental methodology is broadly applicable to time-resolved x-ray emission analysis at synchrotron and x-ray free-electron laser light sources.     

Coating of titanium implant materials with thin polymeric films for binding the signaling protein BMP2

A fast and simple approach for immobilization using copolymers as interlayers is reported. The synthesized copolymers form stable self-assembled layers on implant materials like, e.g., titanium in a simple coating/drying/washing sequence and have functional groups which can bind proteins from an aqueous solution. The copolymer films have been characterized via ellipsometry and contact angle measurements and were tested for biocompatibility. An immunoassay was used to determine the amount of BMP2 and demonstrated an approximately 10-fold increase as compared to previously used self-assembled monolayers. A BMP2-responsive cell line with luciferase detection was used to determine the biological activity of the bound signaling protein.     

Click‐Tag and Amine‐Tag: Chemical Tag Approaches for Efficient Protein Labeling In Vitro and on Live Cells using the Naturally Split Npu DnaE Intein

Protein labeling with synthetic moieties remains in many cases a technically challenging or unresolved task. Two new and simple concepts are presented. In both approaches, a very short tag of only a few amino acids is prepared with the desired chemical modification and, in a second step, it is transferred to the protein of interest by protein trans‐splicing. For the amine‐tag, a recombinant intein fragment free of lysine residues was generated such that the amine group of the N terminus could be selectively modified with regular amine‐reactive reagents. Thus, standard bioconjugation procedures without any chemical synthesis could be applied without modification of lysines in the protein of interest. For the click‐tag, protein trans‐splicing was combined with unnatural amino acid mutagenesis and subsequent bioorthogonal side chain modification, as demonstrated for click chemistry using p‐azidophenylalanine. By the two‐step strategy, exposure of the protein of interest to the copper catalyst was avoided.     

One-dimensional exciton diffusion in perylene bisimide aggregates

The dynamics and mobility of excitons in J-aggregates of perylene bisimides are investigated by transient absorption spectroscopy with a time resolution of 50 fs. The transient spectra are compatible with an exciton delocalization length of two monomers and indicate that vibrational and configurational relaxation processes are not relevant for the spectroscopic properties of the aggregates. Increasing the pump pulse energy and in that way the initial exciton density results in an accelerated signal decay and pronounced exciton-exciton annihilation dynamics. Modeling the data by assuming a diffusive exciton motion reveals that the excitons cannot migrate freely in all three directions of space but their mobility is restricted to one dimension. The observed anisotropy supports this picture and points against direct Fo?rster-transfer-mediated annihilation between the excitons. A diffusion constant of 1.29 nm(2)/ps is deduced from the fitting procedure that corresponds to a maximal exciton diffusion length of 96 nm for the measured exciton lifetime of 3.6 ns. The findings indicate that J-aggregates of perylene bisimides are promising building blocks to facilitate directed energy transport in optoelectronic organic devices or artificial light-harvesting systems.