A Study of Cyanotetrazole Oxides and Derivatives thereof

In this work we report on the syntheses of energetic salts of cyanotetrazolate‐1‐ and ‐2‐oxides; this offers a unique ability to compare the effects of tetrazole 1‐ versus 2‐oxidation. 5‐Cyanotetrazolate‐2‐oxide can be synthesized by oxidation of the 5‐cyanotetrazolate anion with Oxone, while the corresponding 1‐oxide was synthesized by the rearrangement of azidoaminofurazan. Both chemical (multinuclear NMR, IR, and Raman spectroscopies, mass spectrometry, etc.) as well as explosive (impact, friction, and static sensitivities) properties are reported for these energetic salts. Calculated explosive performances using the EXPLO5 computer code are also reported. We furthermore detail the chemistry of these two anions, and their ability to form tetrazole‐carboxamides, dihydrotetrazines, and tetrazines. The ability to hydrolyze cyanotetrazole oxides to their amides was demonstrated by two copper complexes. Several crystal structures of these species are presented in addition to full chemical characterization. Finally, the unique 1,4,‐bis(2‐N‐oxidotetrazolate)‐1,2,4,5‐tetrazine anion was characterized as an energetic material as its ammonium salt.     

Regioselective Synthesis of Pyrazoles and Isoxazoles with Cyclopropanated Side‐Chain

Pyrazoles and isoxazoles with cyclopropanated side‐chain were prepared by cyclization of cyclopropanated 1,3,5‐tricarbonyl compounds with hydrazine and hydroxylamine, respectively. The regioselectivity is influenced by the reaction conditions.     

Molecular structure encodes nanoscale assemblies: understanding driving forces in electrostatic self-assembly

Supramolecular nanoparticles represent a key field in recent research as their synthesis through self-assembly is straightforward and they often can respond to external triggers. A fundamental understanding of structure-directing factors is highly desirable for a targeted structure design. This contribution demonstrates a quantitative relation between the size of supramolecular self-assembled nanoparticles and the free energy of association. Nanoparticles are prepared by electrostatic self-assembly of cationic polyelectrolyte dendrimers as model macroions and oppositely charged di- and trivalent organic dye molecules relying on the combination of electrostatic and π-π-interactions. A systematic set of sulfonate-group carrying azo-dyes was synthesized. Light scattering and ζ-potential measurements on the resulting nanoparticles yield hydrodynamic radii between 20 nm < R(H) < 50 nm and positive ζ-potential values indicating a positive particle charge. Studies on dye self-aggregation and dendrimer-dye association by isothermal titration calorimetry (ITC) and UV-vis spectroscopy allow for the correlation of the thermodynamic parameters of dendrimer-dye association with the size of the particles, showing that at least a free energy gain of ΔG ≈ - 32 kJ mol(-1) is necessary to induce dendrimer interconnection. Structural features of the azo dyes causing these to favor or prevent nanoparticle formation have been identified. The dye-dye-interaction was found to be the key factor in particle size control. A simple model yields a quantitative relation between the free energy and the particle sizes, allowing for predicting the latter based on thermodynamic measurements. Hence, a set of different molecular "building bricks" can be defined where the choice of building block determines the resulting assembly size.     

The Superacid HBr/AlBr3: Protonation of Benzene and Ordered Crystal Structure of [C6H7]+[Al2Br7]−

Crystalline and properly ordered protonated benzene as the [C₆H₇]⁺[Al₂Br₇]^??(C₆H₆) salt 1 are obtained by the combination of solid AlBr₃, benzene, and HBr gas. Compound 1 was characterized and verified by NMR, Raman and X‐Ray spectroscopy. This unexpected simple and straight forward access shows that HBr/AlBr₃ is an underestimated superacid that should be used more frequently.     

Selective Monitoring of the Enzymatic Activity of the Tumor Suppressor Fhit

Cancer is a leading cause of death worldwide. Functional inactivation of tumor suppressor proteins, mainly by mutations in the corresponding genes, is a key event in cancer development. The fragile histidine triade protein (Fhit) is a tumor suppressor that is frequently affected in different cancer types. Fhit possesses diadenosine triphosphate hydrolase activity, but although reduction of its enzymatic activity appears to be important for exerting its tumor suppressor function, the regulation of Fhit activity is poorly understood. Here, we introduce a novel fluorogenic probe that is suited to selectively analyze the enzymatic activity of Fhit in extracts derived from human cells. This novel method will allow in‐depth insight into the mechanisms involved in Fhit regulation in biologically relevant setups and, thus, into its role in the development of cancer.     

Asymmetric Synthesis of Spiropyrazolones by Sequential Organo‐ and Silver Catalysis

A stereoselective one‐pot synthesis of spiropyrazolones through an organocatalytic asymmetric Michael addition and a formal Conia‐ene reaction has been developed. Depending on the nitroalkene, the 5‐exo‐dig‐cyclization could be achieved by silver‐catalyzed alkyne activation or by oxidation of the intermediate enolate. The mechanistic pathways have been investigated using computational chemistry and mechanistic experiments.     

Vibrational Predissociation Spectra of C2N− and C3N−: Bending and Stretching Vibrations

We present infrared predissociation spectra of C₂N⁻(H₂) and C ₃N⁻(H₂) in the 300–1850 cm⁻¹ range. Measurements were performed using the FELion cryogenic ion trap end user station at the Free Electron Lasers for Infrared eXperiments (FELIX) laboratory. For C₂N⁻(H₂), we detected the CCN bending and CC−N stretching vibrations. For the C₃N⁻(H₂) system, we detected the CCN bending, the CC−CN stretching, and multiple overtones and/or combination bands. The assignment and interpretation of the presented experimental spectra is validated by calculations of anharmonic spectra within the vibrational configuration interaction (VCI) approach, based on potential energy surfaces calculated at explicitly correlated coupled cluster theory (CCSD(T)-F12/cc-pVTZ−F12). The H₂ tag acts as an innocent spectator, not significantly affecting the C_2,3N⁻ bending and stretching mode positions. The recorded infrared predissociation spectra can thus be used as a proxy for the vibrational spectra of the bare anions.     

5-Hydroxymethyl-, 5-Formyl- and 5-Carboxydeoxycytidines as Oxidative Lesions and Epigenetic Marks

The four non-canonical nucleotides in the human genome 5-methyl-, 5-hydroxymethyl-, 5-formyl- and 5-carboxydeoxycytidine (mdC, hmdC, fdC and cadC) form a second layer of epigenetic information that contributes to the regulation of gene expression. Formation of the oxidized nucleotides hmdC, fdC and cadC requires oxidation of mdC by ten-eleven translocation (Tet) enzymes that require oxygen, Fe(II) and α-ketoglutarate as cosubstrates. Although these oxidized forms of mdC are widespread in mammalian genomes, experimental evidence for their presence in fungi and plants is ambiguous. This vagueness is caused by the fact that these oxidized mdC derivatives are also formed as oxidative lesions, resulting in unclear basal levels that are likely to have no epigenetic function. Here, we report the xdC levels in the fungus Amanita muscaria in comparison to murine embryonic stem cells (mESCs), HEK cells and induced pluripotent stem cells (iPSCs), to obtain information about the basal levels of hmdC, fdC and cadC as DNA lesions in the genome.