Infinite Gold Zig‐Zag Chains as Structural Motif in Ca3Au3In – A Ternary Ordered Variant of the Ni4B3 Type

New auride Ca₃Au₃In was synthesized from the elements in a sealed tantalum tube in a high‐frequency furnace. Ca₃Au₃In was investigated by X‐ray powder and single crystal diffraction: ordered Ni₄B₃ type, Pnma, a = 1664.1(6), b = 457.3(2), c = 895.0(3) pm, wR2 = 0.0488, 1361 F² values, and 44 variables. The three crystallographically independent boron positions of the Ni₄B₃ type are occupied by the gold atoms, while the four nickel sites are occupied by calcium and indium in an ordered manner. All gold atoms have trigonal prismatic coordination, i.e. Ca₆ prisms for Au1 and Au2 and Ca₄In₂ prisms for Au3. While the Au3 atoms are isolated, we observe Au1–Au1 and Au2–Au2 zig‐zag chains at Au–Au distances of 292 and 284 pm. These slabs resemble the CrB type structure of CaAu. Consequently Ca₃Au₃In can be considered as a ternary auride. Together the Au2, Au3 and indium atoms build up a three‐dimensional [Au₂In] polyanionic network (281–293 pm Au–In) in which the chains of Au1 centered trigonal prisms are embedded. The crystal chemical similarities with the structures of Ni₄B₃, CaAuIn, and CaAu are discussed.     

Binding sites of the viral RNA element TAR and of TAR mutants for various peptide ligands, probed with LILBID: A new laser mass spectrometry

A new laser-based mass spectrometry method, called laser induced liquid bead ion desorption (LILBID), was applied to investigate RNA:ligand interactions. As model system the HIV Tat:TAR transactivation complex and its binding behavior were analyzed. TARwt of HIV Type 1 and Type 2 and different artificial mutants were compared regarding their binding to Tat and different peptide ligands. Specific and nonspecific association to TAR was deduced, with the bulge being the well known specific binding site of TAR. In the case of triple arginine (RRR) as a nonspecific ligand, multiple electrostatic binding to TAR was found at higher concentration of RRR. This contrasted with the formation of only ternary complexes in competitive binding studies with TAR, Tat, and potential inhibitors. The fact that the stoichiometries of the complexes can be determined is a major advantage of MS methods over the widely applied fluorimetric methods. A quantitative evaluation of the spectra by a numeric model for ternary complex formation allows conclusions about the role and strength of the binding sites of the RNAs, the specificity and affinity of different ligands, the determination of apparent IC50 and KD values, and a comparison of the binding efficiencies of potential inhibitors.     

NMR chemical shifts of the rhodopsin chromophore in the dark state and in bathorhodopsin: a hybrid QM/MM molecular dynamics study

We investigate nuclear magnetic resonance (NMR) parameters of the rhodopsin chromophore in the dark state of the protein and in the early photointermediate bathorhodopsin via first-principles molecular dynamics simulations and NMR chemical shift calculations in a hybrid quantum/classical (QM/MM) framework. NMR parameters are particularly sensitive to structural properties and to the chemical environment, which allows us to address different questions about the retinal chromophore in situ. Our calculations show that both the 13C and the 1H NMR chemical shifts are rather insensitive to the protonation state of Glu181, an ionizable amino acid side chain located in the vicinity of the isomerizing 11-cis bond. Thus, other techniques should be better suited to establish its protonation state. The calculated chemical shifts for bathorhodopsin further support our previously published theoretical structure, which is in very good agreement with more recent X-ray data.     

Mono- and diprotonation of the superbasic bisguanidine 1,2-Bis(N,N,N',N'-tetramethylguanidino)benzene (btmgb) and Pt II and Pt IV complexes of chelating bisguanidines and guanidinates

New Pt complexes of chelating bisguanidines and guanidinate ligands were synthesized and characterized. 1,2-Bis(N,N,N',N'-tetramethylguanidino)benzene (btmgb) was used as a neutral chelating bisguanidine ligand, and 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidinate (hpp(-)) as a guanidinate ligand. The salts [btmgbH](+)[HOB(C(6)F(5))(3)](-) and [btmgbH(2)]Cl(2) and the complexes [(btmgb)PtCl(2)], [(btmgb)PtCl(dmso)](+)[PtCl(3)(dmso)](-), and [(btmgb)PtCl(dmso)](+)[Cl(-)] were synthesized and characterized. In the [btmgbH](+) cation the proton is bound to only one N atom. In the other complexes, both imine N atoms are coordinated to the Pt(II), thus adopting a eta(2)-coordinational mode. The hpp(-) anion, which usually prefers a bridging binding mode in dinuclear complexes, is eta(2)-coordinated in the Pt(IV) complex [(eta(2)-hpp)(hppH)PtCl(2){N(H)C(O)CH(3)}], which is formed (in low yield) by reaction between cis-[(hppH)(2)PtCl(2)] and H(2)O(2) in CH(3)CN.     

Determination of 13C/12C ratios of endogenous urinary steroids: method validation, reference population and application to doping control purposes

The application of a comprehensive gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS)-based method for stable carbon isotopes of endogenous urinary steroids is presented. The key element in sample preparation is the consecutive cleanup with high-performance liquid chromatography (HPLC) of underivatized and acetylated steroids, which allows the isolation of ten analytes (11beta-hydroxyandrosterone, 5alpha-androst-16-en-3beta-ol, pregnanediol, androsterone, etiocholanolone, testosterone, epitestosterone, 5alpha-androstane-3alpha,17beta-diol, 5beta-androstane-3alpha,17beta-diol and dehydroepiandrosterone) from a single urine specimen. These steroids are of particular importance to doping controls as they enable the sensitive and retrospective detection of steroid abuse by athletes.Depending on the biological background, the determination limit for all steroids ranges from 5 to 10 ng/mL for a 10 mL specimen. The method is validated by means of linear mixing models for each steroid, which covers repeatability and reproducibility. Specificity was further demonstrated by gas chromatography/mass spectrometry (GC/MS) for each analyte, and no influence of the sample preparation or the quantity of analyte on carbon isotope ratios was observed. In order to determine naturally occurring (13)C/(12)C ratios of all implemented steroids, a reference population of n = 61 subjects was measured to enable the calculation of reference limits for all relevant steroidal Delta values.     

The trapezoidal cylinder phase: a new mode of self-assembly in liquid-crystalline soft matter

A new rectangular columnar liquid crystalline phase with p2gg lattice is reported, which represents a polygonal cylinder array composed of cylinders with trapezoidal cross section. In these polygonal cylinders, one of the sides has a different length and is composed of a different material than the others. This tiling pattern was obtained in two series of T-shaped facial amphiphilic triblock molecules in which a rigid rod-like p-terphenyl core is substituted laterally by a polar and flexible oligoethylene glycol chain, terminated either by a hydrogen-bonding COOH group or by a Li carboxylate group, and having identical or different alkyl groups in the terminal positions. The trapezoidal cylinder phase provides an improved packing for relatively long and rigid alkyl chains at lower temperature and more space inside the polygonal cylinders than triangular cylinders. This combination of conformational and space-filling effects leads to different phase sequences. The trapezoidal cylinder phases pave the way to a new level of complexity in LC engineering and show the huge potential of the general concept of polyphilic tectons for the design of new complex soft matter structures.     

Rare earth metal-rich indides RE 4IrIn ( RE = Gd–Er), RE 4IrInO0.25 ( RE = Gd, Er), and RE 4 T In1– x Mg x ( RE = Y, Gd; T = Rh, Ir)

The rare earth-transition metal-indides RE ₄IrIn (RE = Gd–Er) and the solid solutions RE ₄ TIn_1–x Mg _x (RE = Y, Gd; T = Rh, Ir) were prepared by arc-melting of the elements and subsequent annealing. The rare earth sesquioxides were used as oxygen source for the suboxides RE ₄IrInO_0.25 (RE = Gd, Er). Single crystals of the indides were grown via slowly cooling of the samples and they were investigated via X-ray powder diffraction and single crystal diffractometer data: Gd₄RhIn type, F [`4]\bar 4 3m, a = 1372.3(6) pm for Gd₄IrIn, a = 1365.3(6) pm for Tb₄IrIn, a = 1356.7(4) pm for Dy₄IrIn, a = 1353.9(4) pm for Ho₄IrIn, a = 1344.1(4) pm for Er₄IrIn, a = 1370.3(5) pm for Y₄RhIn_0.54Mg_0.46, a = 1375.6(5) pm for Gd₄IrIn_0.55Mg_0.45, a = 1373.0(3) pm for Gd₄IrInO_0.25, and a = 1345.1(4) pm for Er₄IrInO_0.25. The rhodium and iridium atoms have a trigonal prismatic rare earth coordination. Condensation of the RhRE ₆ and IrRE ₆ prisms leads to three-dimensional networks which leave voids that are filled by regular In₄ or mixed In_4–x Mg _x tetrahedra. The indium (magnesium) atoms have twelve nearest neighbors (3In(Mg) + 9RE) in icosahedral coordination. The rare earth atoms build up a three-dimensional, adamantane-like network of condensed, edge and face-sharing octahedra. For Gd₄IrInO_0.25 and Er₄IrInO_0.25 the RE1₆ octahedra are filled with oxygen. The crystal chemical peculiarities of these rare earth rich compounds are discussed.     

Helical growth of semiconducting columnar dye assemblies based on chiral perylene bisimides

A perylene bisimide derivative bearing two phenyl substituents with chiral solubilizing alkyl chains at the imide N atoms has been synthesized, and its self-assembly properties in solution and condensed phase have been investigated. Temperature-dependent CD spectra revealed the coexistence of two different kinds of chiral aggregates, differing in size and handedness. The chiral side chains effect a higher order within the self-assemblies, resulting in an increased charge-carrier mobility in the columnar liquid crystalline mesophase. [structure: see text]     

Spider silk and amyloid fibrils: a structural comparison

Although spider silks have been studied for decades, the assembly properties of the underlying silk proteins have still not been unravelled. Previously, the detection of amyloid-like nanofibrils in the spider's silk gland suggested their involvement in the assembly process.Recombinantly produced spider silk also self-assembles into nanofibrils. In order to investigate the structural properties of such silk nanofibrils in more detail, they have been compared to amyloid-like fibrils to highlight structural similarities.