Oleksandr

Astronomy: Earth's seven sisters

Nature 542, 7642 (2017). doi:10.1038/542421a

Authors: Ignas A. G. Snellen

Seven small planets whose surfaces could harbour liquid water have been spotted around a nearby dwarf star. If such a configuration is common in planetary systems, our Galaxy could be teeming with Earth-like planets. See Letter p.456

Nature Chemistry. doi:10.1038/nchem.2730

Authors: Hao Sun, Christopher P. Kabb, Yuqiong Dai, Megan R. Hill, Ion Ghiviriga, Abhijeet P. Bapat & Brent S. Sumerlin

Many properties of polymers are dictated by topology. However, the topology of a macromolecule is typically a static feature after synthesis. Now, an approach to dynamic and transformable macromolecular architecture has been developed. When triggered by an external stimulus, macromolecular topology can be triggered to transform via thermodynamic control.

Abstract

Producing metallic hydrogen has been a great challenge in condensed matter physics. Metallic hydrogen may be a room-temperature superconductor and metastable when the pressure is released and could have an important impact on energy and rocketry. We have studied solid molecular hydrogen under pressure at low temperatures. At a pressure of 495 gigapascals, hydrogen becomes metallic, with reflectivity as high as 0.91. We fit the reflectance using a Drude free-electron model to determine the plasma frequency of 32.5 ± 2.1 electron volts at a temperature of 5.5 kelvin, with a corresponding electron carrier density of 7.7 ± 1.1 × 1023 particles per cubic centimeter, which is consistent with theoretical estimates of the atomic density. The properties are those of an atomic metal. We have produced the Wigner-Huntington dissociative transition to atomic metallic hydrogen in the laboratory. Authors: Ranga P. Dias, Isaac F. Silvera

Stable colloids in molten inorganic salts

Nature 542, 7641 (2017). doi:10.1038/nature21041

Authors: Hao Zhang, Kinjal Dasbiswas, Nicholas B. Ludwig, Gang Han, Byeongdu Lee, Suri Vaikuntanathan & Dmitri V. Talapin

A colloidal solution is a homogeneous dispersion of particles or droplets of one phase (solute) in a second, typically liquid, phase (solvent). Colloids are ubiquitous in biological, chemical and technological processes, homogenizing highly dissimilar constituents. To stabilize a colloidal system against coalescence and aggregation, the surface of each solute particle is engineered to impose repulsive forces strong enough to overpower van der Waals attraction and keep the particles separated from each other. Electrostatic stabilization of charged solutes works well in solvents with high dielectric constants, such as water (dielectric constant of 80). In contrast, colloidal stabilization in solvents with low polarity, such as hexane (dielectric constant of about 2), can be achieved by decorating the surface of each particle of the solute with molecules (surfactants) containing flexible, brush-like chains. Here we report a class of colloidal systems in which solute particles (including metals, semiconductors and magnetic materials) form stable colloids in various molten inorganic salts. The stability of such colloids cannot be explained by traditional electrostatic and steric mechanisms. Screening of many solute–solvent combinations shows that colloidal stability can be traced to the strength of chemical bonding at the solute–solvent interface. Theoretical analysis and molecular dynamics modelling suggest that a layer of surface-bound solvent ions produces long-ranged charge-density oscillations in the molten salt around solute particles, preventing their aggregation. Colloids composed of inorganic particles in inorganic melts offer opportunities for introducing colloidal techniques to solid-state science and engineering applications.

Nature Chemistry. doi:10.1038/nchem.2723

Authors: Guoquan Liu, Marcel Levien, Niels Karschin, Giacomo Parigi, Claudio Luchinat & Marina Bennati

The analysis of complex (bio)molecules by NMR spectroscopy is often complicated by limitations in sensitivity. Now, it has been shown that 13C NMR signals are strongly enhanced in solution by resonant microwave irradiation of a nitroxide polarizer. This method exhibits up to 1,000-fold improvements in sensitivity, which stands to greatly improve the detail with which small molecules and metabolites can be studied.

Nature Nanotechnology. doi:10.1038/nnano.2016.305

Authors: Niko Pavliček, Anish Mistry, Zsolt Majzik, Nikolaj Moll, Gerhard Meyer, David J. Fox & Leo Gross

Triangulene, the smallest triplet-ground-state polybenzenoid (also known as Clar's hydrocarbon), has been an enigmatic molecule ever since its existence was first hypothesized. Despite containing an even number of carbons (22, in six fused benzene rings), it is not possible to draw Kekulé-style resonant structures for the whole molecule: any attempt results in two unpaired valence electrons. Synthesis and characterization of unsubstituted triangulene has not been achieved because of its extreme reactivity, although the addition of substituents has allowed the stabilization and synthesis of the triangulene core and verification of the triplet ground state via electron paramagnetic resonance measurements. Here we show the on-surface generation of unsubstituted triangulene that consists of six fused benzene rings. The tip of a combined scanning tunnelling and atomic force microscope (STM/AFM) was used to dehydrogenate precursor molecules. STM measurements in combination with density functional theory (DFT) calculations confirmed that triangulene keeps its free-molecule properties on the surface, whereas AFM measurements resolved its planar, threefold symmetric molecular structure. The unique topology of such non-Kekulé hydrocarbons results in open-shell π-conjugated graphene fragments that give rise to high-spin ground states, potentially useful in organic spintronic devices. Our generation method renders manifold experiments possible to investigate triangulene and related open-shell fragments at the single-molecule level.

Nicolas Chuard, Dr. Giulio Gasparini, Dr. Dimitri Moreau, Samuel Lörcher, Prof. Cornelia Palivan, Prof. Wolfgang Meier, Dr. Naomi Sakai and Prof. Stefan Matile

Giant Substrates, High Tension: Realized with liposomes and polymersomes, strain-promoted thiol-mediated cellular uptake of giant substrates is characterized by increasing activity with disulfide ring tension, inactivity of cationic charges and maleimides, inhibition by Ellman's reagent, self-activation in microdomains, and self-inhibition by micelle formation.

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Nature Chemistry. doi:10.1038/nchem.2712

Authors: Ryan Baumgartner, Hailin Fu, Ziyuan Song, Yao Lin & Jianjun Cheng

The secondary and tertiary structure of a protein has profound implications on function and catalysis. Now, both the secondary and tertiary structures of a synthetic polymer have been utilized to catalyse the polymerization of N-carboxyanhydrides. Both the folding of the resulting polypeptides into α-helices and their macromolecular organization dramatically enhance the polymerization rate.

Nature Chemistry. doi:10.1038/nchem.2716

Authors: Xiao Dong, Artem R. Oganov, Alexander F. Goncharov, Elissaios Stavrou, Sergey Lobanov, Gabriele Saleh, Guang-Rui Qian, Qiang Zhu, Carlo Gatti, Volker L. Deringer, Richard Dronskowski, Xiang-Feng Zhou, Vitali B. Prakapenka, Zuzana Konôpková, Ivan A. Popov, Alexander I. Boldyrev & Hui-Tian Wang

Helium is generally recognized as being chemically inert. A thermodynamically stable compound of helium and sodium, Na2He, has been predicted computationally and then synthesized at high pressure. It exists as an electride, where strongly localized electrons serve as anions located at the centre of Na8 cubes.

Trigger happy: Coassembly of carboxylate-substituted pillar[6]arenes and disulfide-linked benzimidazolium amphiphiles led to supramolecular vesicles that could be triggered by glutathione, pH, CO₂, Zn²⁺, and hexanediamine to release an encapsulated drug. The five stimuli are closely related to microenvironments of tumors and diseases of the human body. The microstructures of the supramolecular vesicles were also clearly elaborated.

[Communication]
Long Jiang, Xuan Huang, Dong Chen, Hua Yan, Xueyuan Li, Xuezhong Du
Angew. Chem. Int. Ed., January 31, 2017, DOI: 10.1002/anie.201611973. Read article

Nature Chemistry. doi:10.1038/nchem.2706

Authors: Nathalie Busschaert, Seong-Hyun Park, Kyung-Hwa Baek, Yoon Pyo Choi, Jinhong Park, Ethan N. W. Howe, Jennifer R. Hiscock, Louise E. Karagiannidis, Igor Marques, Vítor Félix, Wan Namkung, Jonathan L. Sessler, Philip A. Gale & Injae Shin

A squaramide-based anion transporter has now been shown to cause changes in the lysosomal pH leading to impairment of lysosomal enzyme activity and disruption of autophagic processes. The study provides the first experimental evidence that synthetic ion transporters can both disrupt autophagy and induce apoptosis.

Pentazole (HN5), an unstable molecular ring comprising five nitrogen atoms, has been of great interest to researchers for the better part of a century. We report the synthesis and characterization of the pentazolate anion stabilized in a (N5)6(H3O)3(NH4)4Cl salt. The anion was generated by direct cleavage of the C–N bond in a multisubstituted arylpentazole using m-chloroperbenzoic acid and ferrous bisglycinate. The structure was confirmed by single-crystal x-ray diffraction analysis, which highlighted stabilization of the cyclo-N5ˉ ring by chloride, ammonium, and hydronium. Thermal analysis indicated the stability of the salt below 117°C on the basis of thermogravimetry-measured onset decomposition temperature. Authors: Chong Zhang, Chengguo Sun, Bingcheng Hu, Chuanming Yu, Ming Lu

Guest of honor: Repeating guest units of polyesters were selectively encapsulated in a self-assembled capsule to produce supramolecular graft copolymers with an induced M-helical morphology. A unique chiral amplification was observed in the molecular recognition of the capsule, which is known as the majority-rules effect.

[Communication]
Yuta Tsunoda, Mei Takatsuka, Ryo Sekiya, Takeharu Haino
Angew. Chem. Int. Ed., January 25, 2017, DOI: 10.1002/anie.201611394. Read article

Current implant technology uses electrical signals at the electrode-neural interface. This rather invasive approach presents important issues in terms of performance, tolerability, and overall safety of the implants. Inducing light sensitivity in living organisms is an alternative method that provides groundbreaking opportunities in neuroscience. Optogenetics is a spectacular demonstration of this, yet is limited by the viral transfection of exogenous genetic material. We propose a nongenetic approach toward light control of biological functions in living animals. We show that nanoparticles based on poly(3-hexylthiophene) can be internalized in eyeless freshwater polyps and are fully biocompatible. Under light, the nanoparticles modify the light response of the animals, at two different levels: (i) they enhance the contraction events of the animal body, and (ii) they change the transcriptional activation of the opsin3-like gene. This suggests the establishment of a seamless and biomimetic interface between the living organism and the polymer nanoparticles that behave as light nanotransducers, coping with or amplifying the function of primitive photoreceptors.

Finding their partners: In multicomponent systems, colloids bearing molecular recognition units can self-sort in a social manner into their respective families. Additionally, the self-assemblies and their interactions are switchable using orthogonal triggers, such as light and redox chemistry.

[Communication]
Kang Han, Dennis Go, Thomas Tigges, Khosrow Rahimi, Alexander J. C. Kuehne, Andreas Walther
Angew. Chem. Int. Ed., January 18, 2017, DOI: 10.1002/anie.201612196. Read article

A tough aqua material for a tough application: The hybrid membrane's components self-assemble to synergistically enhance each other's structure and properties to result in a tough membrane that efficiently purifies water of heavy metals and organic molecules.

[Communication]
Erez Cohen, Haim Weissman, Eyal Shimoni, Ifat Kaplan-Ashiri, Kai Werle, Wendel Wohlleben, Boris Rybtchinski
Angew. Chem. Int. Ed., January 18, 2017, DOI: 10.1002/anie.201610288. Read article