Transitions Between Lanthanum Cuprates: Crystal Structures of T′, Orthorhombic,and K2NiF4‐type La2CuO4

Through low‐temperature synthesis in CsOH flux, lanthanum cuprate La₂CuO₄ can be obtained in a metastable form, the so‐called T′ modification (tetragonal, I4/mmm, no. 139, a = 400.95(2) pm, c = 1254.08(7) pm). When heated, this T′ phase transforms into a K₂NiF₄‐type modification, whose crystal structure was now refined from X‐ray powder data (tetragonal, I4/mmm, no. 139, a = 383.29(3) pm, c = 1331.3(2) pm at T = 1073 K). The well‐known orthorhombic phase (s.g. Cmce, no. 64, a = 536.14(3) pm, b = 1315.53(8) pm, c = 540.20(3) pm) – usually obtained via conventional solid state synthesis – was observed to form upon cooling from the K₂NiF₄‐type modification. High‐temperature powder diffractometry allowed crystal structure refinements for all of the three phases.     

Advances in mass spectrometry-based post-column bioaffinity profiling of mixtures

In the screening of complex mixtures, for example combinatorial libraries, natural extracts, and metabolic incubations, different approaches are used for integrated bioaffinity screening. Four major strategies can be used for screening of bioactive mixtures for protein targets—pre-column and post-column off-line, at-line, and on-line strategies. The focus of this review is on recent developments in post-column on-line screening, and the role of mass spectrometry (MS) in these systems. On-line screening systems integrate separation sciences, mass spectrometry, and biochemical methodology, enabling screening for active compounds in complex mixtures. There are three main variants of on-line MS based bioassays: the mass spectrometer is used for ligand identification only; the mass spectrometer is used for both ligand identification and bioassay readout; or MS detection is conducted in parallel with at-line microfractionation with off-line bioaffinity analysis. On the basis of the different fields of application of on-line screening, the principles are explained and their usefulness in the different fields of drug research is critically evaluated. Furthermore, off-line screening is discussed briefly with the on-line and at-line approaches.     

On-line electrochemistry–bioaffinity screening with parallel HR-LC-MS for the generation and characterization of modified p38α kinase inhibitors

In this study, an integrated approach is developed for the formation, identification and biological characterization of electrochemical conversion products of p38α mitogen-activated protein kinase inhibitors. This work demonstrates the hyphenation of an electrochemical reaction cell with a continuous-flow bioaffinity assay and parallel LC-HR-MS. Competition of the formed products with a tracer (SKF-86002) that shows fluorescence enhancement in the orthosteric binding site of the p38α kinase is the readout for bioaffinity. Parallel HR-MSⁿ experiments provided information on the identity of binders and non-binders. Finally, the data produced with this on-line system were compared to electrochemical conversion products generated off-line. The electrochemical conversion of 1-{6-chloro-5-[(2R,5S)-4-(4-fluorobenzyl)-2,5-dimethylpiperazine-1-carbonyl]-3aH-indol-3-yl}-2-morpholinoethane-1,2-dione resulted in eight products, three of which showed bioaffinity in the continuous-flow p38α bioaffinity assay used. Electrochemical conversion of BIRB796 resulted, amongst others, in the formation of the reactive quinoneimine structure and its corresponding hydroquinone. Both products were detected in the p38α bioaffinity assay, which indicates binding to the p38α kinase.     

Photoinduced electron transfer between metal-coordinated cyclodextrin assemblies and viologens

Two novel tris(bipyridine)ruthenium(II) complexes bearing two and six beta-cyclodextrin binding sites on their ligands have been synthesised and characterised. Complex 1, bearing two cyclodextrins, adopts a conformation in aqueous solution where parts of the aromatic ligands are self-included into the cyclodextrin moieties. This results in a loss of symmetry of the complex and gives rise to a much more complicated 1H NMR spectrum than expected. Photophysical studies indicate that the appended cyclodextrins protect the luminescent ruthenium core from quenching by oxygen, which results in longer excited state lifetimes and higher emission quantum yields compared with the reference compound, the unsubstituted ruthenium tris(bipyridine). Inclusion of suitable guests such as dialkyl-viologens leads to a quenching of the luminescence of the central unit. In these supramolecular donor-acceptor dyads an efficient photoinduced electron transfer from the excited ruthenium moiety (the donor) to the viologen unit (the acceptor) is observed. The alkyl chain length of the acceptor plays an important role on the binding properties; when it exceeds a certain limit the binding becomes strong enough for electron transfer to occur. Interestingly, a viologen with only one long alkyl tail instead of two shows no efficient quenching; this indicates that cooperative interactions between two cyclodextrins binding one viologen are essential to raise the binding constant of the supramolecular dyad.     

Size Effects at Corners of Anisotropic Material Discontinuities

Reinforcement patches of composite laminates often possess corners due to design and manufacturing necessities. Hence, the patches reconstitute the demanded effective strength or stiffness in the region considered but at their boundaries also constitute a source for stress localizations. The complex potential method is a means for the investigation of such stress localizations. With the help of appropriate complex potentials the mechanical in-plane fields around the reinforcement corner can be expressed as series representations. A first analysis step is to obtain the exponents and corresponding modes which cause singular behavior of the membrane forces. Then, the determination of appropriately defined generalized membrane force intensity factors is used to show whether and how the singularity exponents are in effect. On this basis it is possible to deduce what impact a specific loading condition or the reinforcement corner's material combination and geometry have on the character of the singularity. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

On the Complexity of Equalizing Inequalities

We study two approaches to replace a finite mathematical programming problem with inequality constraints by a problem that contains only equality constraints. The first approach lifts the feasible set into a high-dimensional space by the introduction of quadratic slack variables. We show that then not only the number of critical points but also the topological complexity of the feasible set grow exponentially. On the other hand, the second approach bases on an interior point technique and lifts an approximation of the feasible set into a space with only one additional dimension. Here only Karush–Kuhn–Tucker points with respect to the positive and negative objective function in the original problem give rise to critical points of the smoothed problem, so that the number of critical points as well as the topological complexity can at most double.