SciCombinator

Discover the most talked about and latest scientific content & concepts.

Journal: Angewandte Chemie (International ed. in English)

226

During the beer brewing process, bitter tasting cis and trans iso-α-acids are generated from the precursor α-acids found in hops. The absolute configurations of the α-acid (-)-humulone and several of its derivatives have now been elucidated by X-ray crystallography, thus resolving decades of confusion over the humulone isomerization mechanism.

Concepts: X-ray, X-ray crystallography, Brewing, Beer, Hops, Brewery

31

Silicon analogues of the most prominent carbon nanostructures, namely, hollow spheroidals such as C60 and the fullerene family, have been unknown to date. Herein we show that discrete Si20 dodecahedra, stabilized by an endohedral guest and valence saturation, are accessible in preparative yields through a chloride-induced disproportionation reaction of hexachlorodisilane in the presence of tri(n-butyl)amine. X-ray crystallography revealed that each silicon dodecahedron contains an endohedral chloride ion that imparts a net negative charge. Eight chloro substituents and twelve trichlorosilyl groups are attached to the surface of each cluster in a strictly regioregular arrangement, a thermodynamically preferred substitution pattern according to quantum-chemical assessment. Our results demonstrate that the wet-chemical self-assembly of a complex, monodisperse Si nanostructure is possible under mild conditions starting from simple Si2 building blocks.

Concepts: Electron, Electric charge, Carbon, Sodium chloride, Ion, X-ray crystallography, Chlorine, Chloride

30

Messenger RNA (mRNA) represents a promising class of nucleic acid drugs. Although numerous carriers have been developed for mRNA delivery, the inefficient mRNA expression inside cells remains a major challenge. Inspired by the dependence of mRNA on 3'-terminal polyadenosine nucleotides (poly A) and poly A binding proteins (PABPs) for optimal expression, we complexed synthetic mRNA containing a poly A tail with PABPs in a stoichiometric manner and stabilized the ribonucleoproteins (RNPs) with a family of polypeptides bearing different arrangements of cationic side groups. We found that the molecular structure of these polypeptides modulates the degree of PABP-mediated enhancement of mRNA expression. This strategy elicits an up to 20-fold increase in mRNA expression in vitro and an approximately fourfold increase in mice. These findings suggest a set of new design principles for gene delivery by the synergistic co-assembly of mRNA with helper proteins.

Concepts: DNA, Protein, Cell nucleus, Gene expression, Transcription, RNA, Messenger RNA, Polyadenylation

30

Following his seminal work in 1953, Stanley Miller conducted an experiment in 1958 to study the polymerization of amino acids under simulated early Earth conditions. In the experiment, Miller sparked a gas mixture of CH4 , NH3 , and H2 O, while intermittently adding the plausible prebiotic condensing reagent cyanamide. For unknown reasons, an analysis of the samples was not reported. We analyzed the archived samples for amino acids, dipeptides, and diketopiperazines by liquid chromatography, ion mobility spectrometry, and mass spectrometry. A dozen amino acids, 10 glycine-containing dipeptides, and 3 glycine-containing diketopiperazines were detected. Miller’s experiment was repeated and similar polymerization products were observed. Aqueous heating experiments indicate that Strecker synthesis intermediates play a key role in facilitating polymerization. These results highlight the potential importance of condensing reagents in generating diversity within the prebiotic chemical inventory.

Concepts: Protein, Amino acid, Acid, Amine, Ammonia, Mass spectrometry, Hydrogen, Chemistry

29

Easy peasy: The title reaction employs N-formylsaccharin, which is an easily accessible crystalline compound, as an effective CO source. The reactions proceed with a small excess of the CO source at moderate temperatures and were successfully applied to a wide range of aryl bromides. DMF=N,N-dimethylformamide, dppb=1,4-bis-(diphenylphosphino)butane.

Concepts: Chemical reaction

29

A synthesis fit for a king: The total synthesis of (±)-kingianins A, D, and F has been achieved in ten steps. Key features include the gram-scale synthesis and partial reduction of a conjugated tetrayne to a (Z,Z,Z,Z)-tetraene, the domino 8π-6π electrocyclic ring closure of a (Z,Z,Z,Z)-tetraene, and the radical-cation-catalyzed formal Diels-Alder dimerization of functionalized bicyclo[4.2.0]octadiene precursors.

Concepts: Total synthesis, Paclitaxel total synthesis, Chemical synthesis, Vector space, Formal language

29

Confined to one cell: A method to detect and isolate single circulating melanoma cells (CMCs; see figure) has been produced by integrating a polymer-nanofiber-embedded nanovelcro cell-affinity assay with a laser microdissection (LMD) technique. This method is able to separate CMCs from normal white blood cells (WBCs) and sequence individual cells for a specific mutation related to cancer progression, allowing for more personalized cancer therapy.

Concepts: Immune system, White blood cell, DNA, Protein, Gene, Cell division, Leukemia, DNA replication

29

No transition metal needed: A calcium-catalyzed cycloisomerization yields highly substituted cyclopropanes with excellent diastereoselectivity (see scheme; Nu=nucleophile, Ts=p-toluenesulfonyl). The reaction is based on the equilibrium of a homoallenyl cation with its cyclopropane congener, which is known for gold-catalyzed reactions. According to mechanistic analysis the carbocation cascade is concerted asynchronous, and hence biomimetic.

Concepts: Cyclopropane

28

The first total synthesis of the dimeric berberine alkaloid ilicifoline (ilicifoline B) is reported. Its carbon skeleton is constructed from ferulic acid, veratrole, and methanol. The synthesis reported herein employs starting materials solely derived from wood. The natural product is thus constructed entirely from renewable resources. The same strategy is applied to a formal total synthesis of morphinan alkaloids. The use of wood-derived building blocks (xylochemicals) instead of the conventional petrochemicals represents a sustainable alternative to classical synthetic approaches.

Concepts: Oxygen, Alcohol, Total synthesis, Natural resource, Paclitaxel, Alkaloid, Natural products, Natural capital

28

We report a simple approach based on a chemical reduction method to synthesize aqueous inorganic ink comprised of hexagonal MnO2 nanosheets. The MnO2 ink exhibits long-term stability and continuous thin films can be formed on various substrates without using any binder. To obtain a flexible electrode for capacitive energy storage, the MnO2 ink was printed onto commercially available A4 paper pretreated with multiwalled carbon nanotubes. The electrode exhibited a maximum specific capacitance of 1035 F g(-1) (91.7 mF cm(-2) ). Paper-based symmetric and asymmetric capacitors were assembled, which gave a maximum specific energy density of 25.3 Wh kg(-1) and a power density of 81 kW kg(-1) . The device could maintain a 98.9 % capacitance retention over 10 000 cycles at 4 A g(-1) . The MnO2 ink could be a versatile candidate for large-scale production of flexible and printable electronic devices for energy storage and conversion.

Concepts: Energy, Fundamental physics concepts, Battery, Capacitor, Energy density, Manganese, Energy storage, Alkaline battery