Synthese,Kristallstruktur und Konformation vontrans-[2.2](1,2)Ferrocenophan und seinen 1-Hydroxyderivaten

Starting from1-(dimethylaminomethyl)-2-iodo-ferrocene (3) [2.2](1,2)ferrocenophane (2) was prepared in an 8-step synthesis with 17% overall yield. Both from the oxoderivative12 and the ferrocenophane2 puretrans-isomers (12b and2b, resp.) were obtained; the former (12b) was reduced to a separable mixture ofexo andendo 1-hydroxy-ferrocenophanes13a andb, resp. (～ 3:7), the configurations of which were assigned by the LIS-method. X-ray crystal structure analysis of2b revealed a centrosymmetrical chair conformation. From¹H- and¹³C-NMR spectra both for2b and for the hydroxyderivatives13 a rigidexo-exo chair conformation was deduced.     

PdSCl,ein molekulares Palladium(II)-disulfidchlorid mit achtkernigen Pd8(S2)4Cl8−Komplexen und vierfach überbrückenden Disulfidgruppen

PdSCl, a Molecular Palladium(II) Disulfidechloride with Octanuclear Pd₈(S₂)₄Cl₈ Groups and with Tetra Metal-coordinated bridging Disulfide Groups Black crystals of PdSCl have been obtained by reaction of Pd with S₂Cl₂ in closed quartz ampoules at 200°C. The compound is to be formulated as a Palladium(II)-disulfidechloride consisting of Pd₈(S₂)₄Cl₈ molecules with approximately D_4h symmetry. In the octanuclear complexes Pd atoms form a cube, where bridging disulfide groups are found in front of 4 faces and μ₂?bridging Cl atoms on 8 edges. In the monoclinic crystal structure (a = 8.763(2) Å; b = 9.082(2) Å; c = 13.662(4) Å; β = 91.748(23)°; V = 1086.8 ų; Z = 16 PdSCl; Space gr. P2₁/n) the molecules form a cubic closed arrangement.     

Multireference calculations for ring inversion and double bond shifting in cyclooctatetraene

We present multireference calculations for the characterization of ring inversion and double bond shifting in cyclooctatetraene. The results show that it is necessary to treat the dynamical correlation very accurately to obtain correct values for the barrier heights. This can be done, for example, with multireference configuration interaction or with perturbation theory of third order. However, detailed analysis also shows that already a complete active space self‐consistent field treatment describes the processes surprisingly well. Thus, this method could be used as a computationally cheap method, for example, for dynamics simulations. © 2013 Wiley Periodicals, Inc.     

The method of increments—a wavefunction-based ab initio correlation method for solids

An overview of wavefunction-based correlation methods generalised for the application to solids is presented. Those methods based on a preceding Hartree–Fock treatment explicitly calculate the many-body wavefunction in contrast to the density-functional theory which relies on the ground-state density of the system. This review focus on the so-called method of increments where the correlation energy of the solid is expanded in terms of localised orbitals or of a group of localised orbitals. The method of increments is applied to a great variety of materials, from covalent semiconductors to ionic insulators, from large band-gap materials like diamond to the half-metal α$\alpha$-tin, from large molecules like fullerenes over polymers, graphite to three-dimensional solids. Rare-gas crystals where the binding is van der Waals like are treated as well as solid mercury, where the metallic binding is entirely due to correlation. Strongly correlated systems are examined and the correlation driven metal–insulator transition is described at an ab initio level.     

High-performance capillary electrophoresis using open tubes and gels

Summary This paper overviews several aspects of high performance capillary electrophoresis (HPCE), a promising new method of analytical and micropreparative separation of biochemically important samples. The basic migration equations of electrophoresis are first presented and the benefit of high fields for rapid analysis and high performance emphasized. Since power is generated with high voltages, Joule heating results and this heat must be dissipated. The use of capillary columns is shown to be important in efficient heat removal and in minimizing the temperature differences within the column. The various factors influencing band broadening are next described, and it is shown how plate counts close to 10⁶ can be achieved. Various results from our laboratory on open tube and gel columns are then presented to illustrate the potential of this method. Chiral resolution of dansylated amino acids using a chiral metal chelate micelle in open tube HPCE is shown. With the gel columns, the baseline separation of a 2-chain variant from methionine growth hormone (met-hGH) under non-denaturing conditions at fields close to 1000 V/cm is presented. Finally, the micropreparative purification of a 20-mer oligonucleotide using the gel column is described.     

Environment-Responsive Peptide Dimers Bind and Stabilize Double-Stranded RNA

Double-stranded RNAs (dsRNA) possess immense potential for biomedical applications. However, their therapeutic utility is limited by low stability and poor cellular uptake. Different strategies have been explored to enhance the stability of dsRNA, including the incorporation of modified nucleotides, and the use of diverse carrier systems. Nevertheless, these have not resulted in a broadly applicable approach thereby preventing the wide-spread application of dsRNA for therapeutic purposes. Herein, we report the design of dimeric stapled peptides based on the RNA-binding protein TAV2b. These dimers are obtained via disulfide formation and mimic the natural TAV2b assembly. They bind and stabilize dsRNA in the presence of serum, protecting it from degradation. In addition, peptide binding also promotes cellular uptake of dsRNA. Importantly, peptide dimers monomerize under reducing conditions which results in a loss of RNA binding. These findings highlight the potential of peptide-based RNA binders for the stabilization and protection of dsRNA, representing an appealing strategy towards the environment-triggered release of RNA. This can broaden the applicability of dsRNA, such as short interfering RNAs (siRNA), for therapeutic applications.     

A Mechanistic Perspective on Plastically Flexible Coordination Polymers

Mechanical flexibility in single crystals of covalently bound materials is a fascinating and poorly understood phenomenon. We present here the first example of a plastically flexible one‐dimensional (1D) coordination polymer. The compound [Zn(μ‐Cl)₂(3,5‐dichloropyridine)₂]_n is flexible over two crystallographic faces. Remarkably, the single crystal remains intact when bent to 180°. A combination of microscopy, diffraction, and spectroscopic studies have been used to probe the structural response of the crystal lattice to mechanical bending. Deformation of the covalent polymer chains does not appear to be responsible for the observed macroscopic bending. Instead, our results suggest that mechanical bending occurs by displacement of the coordination polymer chains. Based on experimental and theoretical evidence, we propose a new model for mechanical flexibility in 1D coordination polymers. Moreover, our calculations propose a cause of the different mechanical properties of this compound and a structurally similar elastic material.     

(E)‐5‐[Hydroxyimino(phenyl)methyl]‐1‐methyl‐3,4‐dihydro‐2H‐pyrrolium trifluoromethanesulfonate

The cation of the title compound, C₁₂H₁₅N₂O⁺·CF₃SO₃^?, exists as an E‐configured hydroxy­imino derivative conjugated with a nearly planar iminium system. The twist angle between the phenyl ring and the oxime group is 72.2 (2)°. An O—H?O hydrogen bond links the oxime group of the cation to the anion.