trans-Bis(triphenylphosphin)phthalocyaninato(2–)rhenium(II): Synthese,Eigenschaften und Kristallstruktur

trans -Bis(triphenylphosphine)phthalocyaninato(2–)rhenium(II): Synthesis, Properties, and Crystal Structure Dirheniumheptoxide reacts with phthalodinitrile in boiling 1-chloronaphthalene and subsequent reprecipitation of the green raw product from conc. sulfuric acid to yield an oxo-phthalocyaninate of rhenium, which is reduced by molten triphenylphosphine forming dark green trans-bis(triphenylphosphine)phthalocyaninato(2–)rhenium(II), ^trans[Re(PPh₃)₂pc^2–]. The latter crystallizes triclinic in the space group P 1 with the cell parameters as follows: a = 11.512(2) Å, b = 12.795(2) Å, c = 12.858(2) Å, α = 64.42(2)°, β = 79.45(2)°, γ = 72.74(1)°; V = 1628.1(5); Z = 1. Re is in the centre of the (N_p)₄ plane (N_p: N1, N3) and coordinates two triphenylphosphine ligands axially in trans position. The average Re–N_p and Re–P distances are 2.007(1) and 2.516(3) Å, respectively. Despite the many extra bands the typical B, Q and N regions of the pc^2– ligand are observed at ca. 16500, 28900/32900 and 35300 cm^–1. A weak band group at ca. 8900 cm^–1 is attributed to a trip-multiplet transition, another one at ca. 14500 cm^–1 to a P → Re charge transfer. The vibrational spectra are dominated by internal vibrations of the pc^2– ligand. The very weak intensity of the IR bands at 905 and 1327 cm^–1 are diagnostic of the presence of Re^II.     

The role of tangential diffusion in evaluating the performance of flamelet models

For non-premixed combustion, the steady laminar flamelet model (SLFM) and flamelet/progress variable approach (FPVA) are two popular methods for tabulating flamelet manifolds. Even if the two methods are used to tabulate and parameterize the same flamelet database, their results sometimes differ in the subsequent simulation. In this work, a novel perspective is provided to assess the performance of the SLFM and FPVA. Both approaches are compared with respect to their capabilities to capture tangential diffusion (TD) of the thermochemical state variables along iso-surfaces of mixture fraction. The relevance of TD effects is identified using generalized flamelet equations and regimes by comparing flamelet solutions with and without TD terms to a FTC (full transport and chemistry) solution of a well-known non-premixed coflow flame. It is found that TD effects can play an important role in entire mixture fraction space, even in the classical flamelet regime. This suggests that the ability to characterize TD effects is an important performance indicator for tabulation strategies. Thereafter, an a priori analysis is conducted comparing the results from the FPVA and SLFM (using the same flamelet database) with the FTC results. The results show that the FPVA is able to more accurately describe the thermochemical state and the flame structure than the SLFM. For a more detailed assessment of the two tabulation strategies, the TD terms reconstructed from the FPVA and SLFM are compared to those from the FTC results. It is found that the FPVA can capture a significant portion of TD effects, while the SLFM can hardly characterize TD effects. This particular capability allows the FPVA to describe chemistry-transport interaction and flame structure more accurately than the SLFM.     

钨离子团簇与N2分子的反应性

利用激光蒸发团簇源产生Wn团簇束,团簇束通过一个充有N2气体分 子的低压反应池,利用飞行时间质谱探测反应产物,在类单次碰撞条件下研究了W+10 -W+50和N2分子的反应性,在室温条件下测量了N2分子与W+n团簇反应的 反应几率。团簇尺寸在10～26原子的团簇与N2分子的反应几率与团簇尺寸有很强的相关性 ,对n=16,22,23的团簇具有比较高的反应性。W+n与N2分子的反应性与Wn与N 2分子的反应性显示出相似的规律性。     

Biosynthesis of a fluorescent protein with extreme pseudo-Stokes shift by introducing a genetically encoded non-natural amino acid outside the fluorophore

A novel kind of fluorescent protein relying on the intramolecular interplay between two different fluorophores, one of chemical origin and one of biological origin, was developed. The fluorescent non-natural amino acid l-(7-hydroxycoumarin-4-yl)ethylglycine was site-specifically incorporated into the recombinant enhanced cyan fluorescent protein (eCFP) at a permissible surface position ～20 ? away from the protein fluorophore using amber suppression in Escherichia coli with an engineered cognate Methanococcus jannaschii tRNA synthetase. The resulting eCFP(Cou) exhibited almost quantitative intramolecular Fo?rster resonance energy transfer (FRET) between its two fluorophores, showing brilliant cyan emission at 476 nm upon excitation in the near-UV at 365 nm (a wavelength easily accessible via conventional laboratory UV sources), in contrast to its natural counterpart. Thus, this fluorescent protein with unprecedented spectroscopic properties reveals an extreme apparent Stokes shift of ～110 nm between the absorption wavelength of the coumaryl group and the emission wavelength of eCFP.     

Palladium nanoparticles on modified cellulose as a novel catalyst for low temperature gas reactions

Cellulose - Palladium was incorporated into carboxymethylated cellulose fibers as a support, thereby becoming an efficient and stable catalyst for low temperature gas phase reaction. Thus, NO was...     

Proof complexity of propositional default logic

Default logic is one of the most popular and successful formalisms for non-monotonic reasoning. In 2002, Bonatti and Olivetti introduced several sequent calculi for credulous and skeptical reasoning in propositional default logic. In this paper we examine these calculi from a proof-complexity perspective. In particular, we show that the calculus for credulous reasoning obeys almost the same bounds on the proof size as Gentzen??s system LK. Hence proving lower bounds for credulous reasoning will be as hard as proving lower bounds for LK. On the other hand, we show an exponential lower bound to the proof size in Bonatti and Olivetti??s enhanced calculus for skeptical default reasoning.     

Capillary Pressures by Fluid Saturation Profile Measurements During Centrifuge Rotation

A novel centrifuge technique to obtain the capillary pressure curve by measuring the local fluid distribution in a spinning core is presented. The Nuclear Tracer Imaging Centrifuge (NTIC) method measures the fluid saturation profile along the length of the core to directly obtain the capillary pressure curve. The proposed method is superior to conventional centrifuge techniques because (1) the capillary pressure curve is obtained at one rotational speed, (2) core plugs are not removed from the spinning centrifuge for imaging, and (3) no mathematical solution is needed to calculate the capillary pressure curve. The literature states that the various mathematical solutions used in conventional centrifuge tests are the greatest source of error, not the uncertainty in the experimental data. By eliminating the dependence of such solutions, the NTIC represents an alternative to conventional centrifuge tests, and may be used to validate the various mathematical procedures applied in conventional centrifuge capillary pressure tests. NTIC may also confirm the applicability of other imaging techniques that rely on core plug removal for saturation imaging, by verifying if there is no fluid re-distribution at static conditions.     

Synthesis of Cyclic Peptides by Photochemical Decarboxylation of N‐Phthaloyl Peptides in Aqueous Solution

The synthesis of a variety of cyclic peptides from N‐phthaloyl‐protected di‐, tri‐, tetra‐, and pentapeptides with different aminocarboxylic acid tethers by photodecarboxylation – initiated by intramolecular electron transfer – has been explored in aqueous media. The progress and the chemoselectivity of the follow‐up processes after CO₂ extrusion were traced by the respective pH/time‐profiles, as well as by the overall change in pH after completion of the reaction. The competition between cyclization and simple oxidative decarboxylation depends on spacer length and geometry, H‐bonding interaction between the electron accepting phthalimide C?O groups and amide H‐atoms, as well as the geometric reorganization coupled with the radical combination step and the formation of the lactam rings. With progressing reaction, hydrolysis of the phthalimide chromophore becomes an increasingly important side reaction due to the constant increase in pH. The use of phosphate‐buffered aqueous media consequently improved the cyclization yields. The ground‐state interactions between amide groups and the terminal COO^? group with the imide C?O groups were studied for the model system [N‐(phthaloyl)glycyl]sarcosine ( 1 ) by NMR spectroscopy where the amide (E/Z)‐equilibrium depends on the presence of carboxylate vs. free carboxylic acid, demonstrating the role of H‐bonding and metal coordination.