Solvent‐free Liquid Crystals and Liquids from DNA

As DNA exhibits persistent structures with dimensions that exceed the range of their intermolecular forces, solid‐state DNA undergoes thermal degradation at elevated temperatures. Therefore, the realization of solvent‐free DNA fluids, including liquid crystals and liquids, still remains a significant challenge. To address this intriguing issue, we demonstrate that combining DNA with suitable cationic surfactants, followed by dehydration, can be a simple generic scheme for producing these solvent‐free DNA fluid systems. In the anhydrous smectic liquid crystalline phase, DNA sublayers are intercalated between aliphatic hydrocarbon sublayers. The lengths of the DNA and surfactant are found to be extremely important in tuning the physical properties of the fluids. Stable liquid‐crystalline and liquid phases are obtained in the ?20 °C to 200 °C temperature range without thermal degradation of the DNA. Thus, a new type of DNA‐based soft biomaterial has been achieved, which will promote the study and application of DNA in a much broader context.     

Light-Driven Catalyst-Free Access to Phthalazines: Entry to Antiviral Model Drugs by Merging Domino Reactions**

We report the development of a metal-free four-step one-pot synthetic strategy to access high-value functionalized phthalazines using o-methyl benzophenones as starting compounds. Combining a light-mediated enolization of o-methyl benzophenones/Diels-Alder reaction domino process with a subsequent deprotection/aromatization domino reaction in one-pot leads to sustainable and efficient organic synthesis. The tangible advantages, i. e., absence of catalysts or additives, utilization of commercially available and/or easily accessible substrates, mild reaction conditions, simplicity, and single work-up procedure, make this combined process highly appealing for the direct construction of various 1-aryl-phthalazines. Importantly, in vitro bioactivity evaluation of these newly prepared heterocyclic compounds demonstrated a strong antiviral efficacy against major human pathogens like HCMV and SARS-CoV-2.     

Structure and spectroscopic properties of the dimeric copper(I) N‐heterocyclic carbene complex [Cu2(CNCt‐Bu)2](PF6)2

In recent years, the use of copper N‐heterocyclic carbene (NHC) complexes has expanded to fields besides catalysis, namely medicinal chemistry and luminescence applications. In the latter case, multinuclear copper NHC compounds have attracted interest, however, the number of these complexes in the literature is still quite limited. Bis[μ‐1,3‐bis(3‐tert‐butylimidazolin‐2‐yliden‐1‐yl)pyridine]‐1κ⁴C²,N:N,C^2′;2κ⁴C²,N:N,C^2′‐dicopper(I) bis(hexafluoridophosphate), [Cu₂(C₁₉H₂₅N₅)₂](PF₆)₂, is a dimeric copper(I) complex bridged by two CNC, i.e. bis(N‐heterocyclic carbene)pyridine, ligands. Each Cu^I atom is almost linearly coordinated by two NHC ligands and interactions are observed between the pyridine N atoms and the metal centres, while no cuprophilic interactions were observed. Very strong absorption bands are evident in the UV–Vis spectrum at 236 and 274 nm, and an emission band is observed at 450 nm. The reported complex is a new example of a multinuclear copper NHC complex and a member of a compound class which has only rarely been reported.     

Structure and Biosynthesis of Crocagins: Polycyclic Posttranslationally Modified Ribosomal Peptides from Chondromyces crocatus

Secondary metabolome mining efforts in the myxobacterial multiproducer of natural products, Chondromyces crocatus Cm c5, resulted in the isolation and structure elucidation of crocagins, which are novel polycyclic peptides containing a tetrahydropyrrolo[2,3-b]indole core. The gene cluster was identified through an approach combining genome analysis, targeted gene inactivation in the producer, and in vitro experiments. Based on our findings, we developed a biosynthetic scheme for crocagin biosynthesis. These natural products are formed from the three C-terminal amino acids of a precursor peptide and thus belong to a novel class of ribosomally synthesized and post-translationally modified peptides (RiPPs). We demonstrate that crocagin A binds to the carbon storage regulator protein CsrA, thereby inhibiting the ability of CsrA to bind to its cognate RNA target.     

Microgels as drug carriers for sonopharmacology

The ultrasound-induced cleavage of covalent and non-covalent bonds to activate drugs (sonopharmacology) is a promising concept to gain control over the action of active pharmaceutical ingredients by an external trigger. Previously, linear polymer architectures bearing drug payloads were exploited for drug release by using the principles of polymer mechanochemistry. In this work, the carrier design is altered by the polymer topology to improve the ultrasound-triggered release of covalently anchored drugs from polymer scaffolds. We use microgels crosslinked by mechanoresponsive disulfides and copolymerized with Diels-Alder adducts of furylated payload molecules and acetylenedicarboxylate. Force-induced thiol formation induces a Michael-type addition liberating the payload from the microgels. The use of microgels significantly reduces sonication times compared to linear polymer chains and shields the cargo efficiently from non-triggered activation using ultrasound that produces inertial cavitation at a frequency of 20 kHz as model condition.     

Late-Stage Modification of Aminoglycoside Antibiotics Overcomes Bacterial Resistance Mediated by APH(3’) Kinases

The continuous emergence of antimicrobial resistance is causing a threat to patients infected by multidrug-resistant pathogens. In particular, the clinical use of aminoglycoside antibiotics, broad-spectrum antibacterials of last resort, is limited due to rising bacterial resistance. One of the major resistance mechanisms in Gram-positive and Gram-negative bacteria is phosphorylation of these amino sugars at the 3’-position by O-phosphotransferases [APH(3’)s]. Structural alteration of these antibiotics at the 3’-position would be an obvious strategy to tackle this resistance mechanism. However, the access to such derivatives requires cumbersome multi-step synthesis, which is not appealing for pharma industry in this low-return-on-investment market. To overcome this obstacle and combat bacterial resistance mediated by APH(3’)s, we introduce a novel regioselective modification of aminoglycosides in the 3’-position via palladium-catalyzed oxidation. To underline the effectiveness of our method for structural modification of aminoglycosides, we have developed two novel antibiotic candidates overcoming APH(3’)s-mediated resistance employing only four synthetic steps.     

Quasistatic thermal crack extension in the interfaces of bounded self-stressed multiphase compounds

The quasistatic growth of straight interface cracks in thermally loaded brittle multiphase solids consisting of two circular segments of brittle materials with different thermoelastic properties which are glued together at the interface with a special glass seal has been investigated. The resulting mixed boundary-value problems of the stationary plane thermoelasticity have been solved by applying the finite element method. Moreover, fracture mechanical data like crack surface displacements and strain energy release rates governing the propagation behavior of a quasistatic extending thermal interface crack have been calculated. The data obtained have been compared with the results of special cooling experiments in multiphase composite structures in which curved thermal cracks in one of the circular segments occur.     

Die temperatur- und druckinvariante Darstellung der Scherviskosität von geschmolzenem Polymethylmethacrylat

Zusammenfassung An Polymethylmethacrylaten mit zahlenmittleren Molekulargewichten zwischen 8000 und 145000 g/Mol wurde die Scherviskosität bei Temperaturen im Bereich von 130–190 °C und bei Drücken bis zu 1000 kp/cm² in Abhängigkeit vom Schergefälle gemessen. Trägt man die an ein und derselben Probe gemessenen relativen Viskositäten/ ₀ (₀ untere Newtonsche Viskosität) über ₀· doppeltlogarithmisch auf, so erhält man eine einzige temperatur- und druckinvariante Kurve (master curve). Mit sinkendem Molekulargewicht machen sich jedoch bei großen Abszissenwerten zunehmend Abweichungen von der Temperatur- und Druckinvarianz bemerkbar. Die an Proben mit verschiedenem Molekulargewicht ermittelten invarianten Kurven weisen Wendepunkte auf, die sich mit wachsendem Molekulargewicht immer mehr zu niedrigeren Werten von/ ₀ verlagern. Durch Verschieben in Abszissenrichtung kann man die Kurven bis zu ihren Wendepunkten miteinander zur Deckung bringen und erhält auf diese Weise einen begrenzten Bereich der Molekulargewichtsinvarianz.Die Temperatur- und Druckinvarianz läßt sich sowohl mit den vonPrandtl undEyring als auch mit den vonF. Bueche entwickelten Modellen für das Fließen von Hochpolymeren begründen. Aus der Temperatur- und Druckinvarianz folgt, daß der Temperatur- und der Druckkoeffizient der Viskosität mit zunehmendem Schergefälle in gleicher Weise abnehmen und ein Minimum durchlaufen, wie auch experimentell bestätigt wird.

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Summary The shear viscosity of polymethylmethacrylates (number average molecular weights from 8000 to 145000 g/mole) was measured in dependence of shear rate in the temperature range from 130–190 °C and with pressures up to 1000 kp/cm². If for one specimen ₀ ( ₀ lower Newtonian viscosity) is plotted over ₀· , both in logarithmic scales, one gets a curve, which is independent of temperature and pressure (master curve). With decreasing molecular weights increasing deviations from the master curve are found. The master curves found with specimens of different molecular weights have inflection points, which shift to lower values of ₀ with increasing molecular weight. By shifting of the whole curves in direction of the abscissa the parts until to the inflection point might be reduced to a single plot which is independent of molecular weight.The independence of temperature and pressure might be derived from the models developed by eitherPrandtl andEyring orF. Bueche for the flow in high polymers. From this follows that the temperature- and the pressure-coefficient of viscosity will similarly decrease with increasing shear rate until to a minimum, which was experimentally verified.

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Erweiterte Fassung eines auf der Jahrestagung der Deutschen Rheologen am 21. Mai 1968 in Berlin gehaltenen Vortrags.

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Herrn Dr.H. Kausch und Herrn Dipl.-Ing.H. Schönewald sind wir für wertvolle Diskussionen zu Dank verpflichtet. Der Arbeitsgemeinschaft industrieller Forschungsvereinigungen e.V. (AIP) danken wir für die finanzielle Unterstützung dieser Arbeit.