Die Kristall- und Molekülstruktur von Bis(trimethylsilyldiimin)

The crystal structure of bis(trimethylsilyl)diimine, (CH3)3Si-N=N-Si(CH3)3, has been determined from three-dimensional X-ray data collected on a Stoe two-circle diffractometer at -130°C (Mo K(alpha) radiation, 673 reflexions, R=0·067). The crystals are monoclinic, space group P2(1/c), with cell dimensions a=6·12 (2), b=10·788 (3), c=8·892 (3) Å, and ß=103·4 (1)°. There are only two molecules in the unit cell and, consequently, the crystal site symmetry must be 1¯ (Ci). For several reasons, however, the free molecule is to be expected to adopt the higher point symmetry 2/m (C2h). Important molecular dimensions are the very short N-N bond (1·17 Å), the unusual long Si-N bond (1·81 Å), and the Si-N-N angle of 120°, which indicate the exceptional position of this compound among the other known trans-X-N=N-X systems. It is shown that some geometrical details of the crystal and molecular structure result from the stereochemical activity of the nitrogen lone pair

Detecting Malicious Code by Model Checking

Abstract. The ease of compiling malicious code from source code in higher programming languages has increased the volatility of malicious programs: The first appearance of a new worm in the wild is usually followed by modified versions in quick succession. As demonstrated by Christodorescu and Jha, however, classical detection software relies on static patterns, and is easily outsmarted. In this paper, we present a flexible method to detect malicious code patterns in executables by model checking. While model checking was originally developed to verify the correctness of systems against specifications, we argue that it lends itself equally well to the specification of malicious code patterns. To this end, we introduce the specification language CTPL (Computation Tree Predicate Logic) which extends the well-known logic CTL, and describe an efficient model checking algorithm. Our practical experiments demonstrate that we are able to detect a large number of worm variants with a single specification. Key words: Model Checking, Malware Detection.

Group 14 metallated 6-amino-1-azafulvene dimers : evidence for a double intramolecular nitrogen-tin interaction

The structures of group 14 C-metalated 6-amino-1-azafulvene dimers have been investigated in solution and in the solid state by NMR spectroscopy. For one of these compounds, 5,10-bis(dimethylamino)-3,8-bis(trimethylstannyl)-5H,10H-dipyrrolo[1,2-a: 1\u27,2\u27-d]-pyrazine (2c), the molecular structure in the solid state has been determined by X-ray diffractometry. The two tin centers have a distorted-trigonal-bipyramidal co-ordination geometry with the more electronegative N ligand at a pseudoaxial position, resulting in one of the longest known Sn - N interactions: 3.101 (5) A°. Moreover, the temperature-dependent 13C CP-MAS NMR spectrum of this compound shows an appreciable narrowing of the Me3Sn signal between 296 and 333 K. By comparison with nonmetalated analogs or with isomer 5c, the nonreactivity of compound 2c toward hydrolytic decomposition into corresponding 5-(trimethylstannyl)-pyrrole-2-carbaldehyde (3c) may be the result of stabilization of the dimeric form 2c by a double Sn - N interaction. In silicon and germanium analogs (2a, 2b) the Si(Ge) - N interaction is weaker

An amplicon sequencing protocol for attacker identification from DNA traces left on artificial prey

1. Clay model studies are a popular tool to identify predator–prey interactions that are challenging to observe directly in the field. But despite its wide use, the meth-od's applicability is limited by its low taxonomic resolution. Attack marks on clay models are usually identified visually, which only allows classification into higher taxonomic levels of predators. Thus, the method is often biased, lacks proof and, above all, standardization.2. Here, we tested whether precise identification of attackers can be provided by amplification and sequencing of mitochondrial DNA left in bite marks on clay models. We validated our approach in a controlled laboratory study as well as in a field experiment using clay models of a common European amphibian, the European fire salamander Salamandra salamandra. DNA-based taxonomic assign-ments were additionally compared to visual assessments of bite marks.3. We show that trace DNA of attackers can be routinely isolated and sequenced from bite marks, providing accurate species-level classification. In contrast, visual identification alone yielded a high number of unassigned predator taxa. We also highlight the sensitivity of the method and show likely sources of contamination as well as probable cases of secondary and indirect predation.4. Our standardized approach for species-level attacker identification opens up new possibilities far beyond the standard use of clay models to date, including food web studies at unprecedented detail, invasive species monitoring as well as biodi-versity inventories

The bicoid mRNA localization factor Exuperantia is an RNA-binding pseudonuclease.

This is the author accepted manuscript.Final version available from Nature Research via the DOI in this record.Anterior patterning in Drosophila is mediated by the localization of bicoid (bcd) mRNA at the anterior pole of the oocyte. Exuperantia (Exu) is a putative exonuclease (EXO) associated with bcd and required for its localization. We present the crystal structure of Exu, which reveals a dimeric assembly with each monomer consisting of a 3'-5' EXO-like domain and a sterile alpha motif (SAM)-like domain. The catalytic site is degenerate and inactive. Instead, the EXO-like domain mediates dimerization and RNA binding. We show that Exu binds RNA directly in vitro, that the SAM-like domain is required for RNA binding activity and that Exu binds a structured element present in the bcd 3' untranslated region with high affinity. Through structure-guided mutagenesis, we show that Exu dimerization is essential for bcd localization. Our data demonstrate that Exu is a noncanonical RNA-binding protein with EXO-SAM-like domain architecture that interacts with its target RNA as a homodimer.This project received funding from the Max Planck Gesellschaft, the European Research Council under the European Union's Seventh Framework Programme (FP7/2007-2013), ERC grant agreement no. 310957 and the Deutsche Forschungsgemeinschaft (SFB860 to K.K. and H.U., and BO3588/2-1 to F.B.)