Oleksandr

Slide! Helical foldamers are shown that can be used to design selective molecular recognition patterns of rod‐like guests and combine them with fine control of self‐assembly kinetics to promote directional sliding processes in which both the rod and the helix have a defined orientation.

Abstract

We have investigated the self‐assembly of a dissymmetrical aromatic oligoamide helix on linear amido‐carbamate rods. A dissymmetric sequence bearing two differentiated ends is able to wrap around dissymmetric dumbbell guest molecules. Structural and thermodynamic investigations allowed us to decipher the mode of binding of the helix that can bind specifically to the amide and carbamate groups of the rod. In parallel kinetic studies of threading and sliding of the helix along linear axles were also monitored by ¹H NMR. Results show that threading of a dissymmetrical host can be kinetically biased by the nature of the guest terminus allowing a preferential sense of sliding of the helix. The study presented below further demonstrates the valuable potential of foldaxanes to combine designed molecular recognition patterns with fine control of self‐assembly kinetics to conceive complex supramolecular events.

Bonded in solution: The thermodynamic properties of intramolecular hydrogen bond formation in solution is investigated for a series of molecules with variable separation of the donor and acceptor sites. Formation of the hydrogen bond is more likely in chloroform than in water and free energies show a constant‐offset behavior. Crowding of the solution only influences the kinetics, but not the thermodynamic equilibrium.

Abstract

The energetics of intramolecular recognition processes are governed by the balance of pre‐organization and flexibility, which is often difficult to measure and hard to predict. Using classical MD simulations, we predict and quantify the effective strength of intramolecular hydrogen bonds between donor and acceptor sites separated by a variable alkyl linker in several solvents and crowded solutions. The balance of entropic and enthalpic contributions poses a solvent‐dependent limit to the occurrence of intramolecular H‐bonding. Still, free energies show a constant offset among different solvents with, for example, a 13 kJ mol⁻¹ difference between water and chloroform. Molecular crowding shows little effect on the thermodynamic equilibrium, but induces variations on the H‐bond kinetics. The results are in quantitative agreement with experiments in chloroform and showcase a general strategy to investigate molecular interactions in different environments, extending the limits of current experiments towards the prospective prediction of H‐bond interactions in a variety of contexts.

Thermodynamically stable whilst kinetically labile coordination bonds lead to strong and tough self-healing polymers

Thermodynamically stable whilst kinetically labile coordination bonds lead to strong and tough self-healing polymers, Published online: 11 March 2019; doi:10.1038/s41467-019-09130-z

Tuning surface strain is a powerful strategy for tailoring the reactivity of metal catalysts. Traditionally, surface strain is imposed by external stress from a heterogeneous substrate, but the effect is often obscured by interfacial reconstructions and nanocatalyst geometries. Here, we report on a strategy to resolve these problems by exploiting intrinsic surface stresses in two-dimensional transition metal nanosheets. Density functional theory calculations indicate that attractive interactions between surface atoms lead to tensile surface stresses that exert a pressure on the order of 10⁵ atmospheres on the surface atoms and impart up to 10% compressive strain, with the exact magnitude inversely proportional to the nanosheet thickness. Atomic-level control of thickness thus enables generation and fine-tuning of intrinsic strain to optimize catalytic reactivity, which was confirmed experimentally on Pd(110) nanosheets for the oxygen reduction and hydrogen evolution reactions, with activity enhancements that were more than an order of magnitude greater than those of their nanoparticle counterparts.

We report DNA- and RNA-like systems built from eight nucleotide "letters" (hence the name "hachimoji") that form four orthogonal pairs. These synthetic systems meet the structural requirements needed to support Darwinian evolution, including a polyelectrolyte backbone, predictable thermodynamic stability, and stereoregular building blocks that fit a Schrödinger aperiodic crystal. Measured thermodynamic parameters predict the stability of hachimoji duplexes, allowing hachimoji DNA to increase the information density of natural terran DNA. Three crystal structures show that the synthetic building blocks do not perturb the aperiodic crystal seen in the DNA double helix. Hachimoji DNA was then transcribed to give hachimoji RNA in the form of a functioning fluorescent hachimoji aptamer. These results expand the scope of molecular structures that might support life, including life throughout the cosmos.

Thanks for the lift, mate! A molecular machine based on a rotaxane embedded in a lipid bilayer can carry potassium ions across the membrane by taking advantage of the stochastic shuttling motion of its macrocyclic ring.

Abstract

The controlled transport of molecular and ionic substrates across bilayer membranes is a fundamental task for the operation of living organisms. It is also a highly fascinating and demanding challenge for artificial molecular machines. The recent report of a synthetic transmembrane molecular shuttle that can transport potassium ions selectively down a gradient in a liposomal system makes a small but significant step towards this goal.

Acenes, which can be viewed as one‐dimensional graphene nanoribbons, are readily twisted out of planarity, resulting in a change in their electronic, optical and chiroptical properties. In a combined computational and experimental study, involving a series of tethered twisted acenes in their enantiopure form, the effect of the acene twist on their chiroptical properties has been studied. The key chiroptical properties of acenes consistently increase with increasing twist, rendering twisted acenes as excellent chiroptical materials. More information can be found in the Full Paper by O. Gidron and A. Bedi on https://doi.org/10.1002/chem.201805728page 3279.

Essential elements for high-impact scientific writing

Essential elements for high-impact scientific writing, Published online: 11 February 2019; doi:10.1038/d41586-019-00546-7

Extreme chemistry: experiments at the edge of the periodic table

Extreme chemistry: experiments at the edge of the periodic table, Published online: 30 January 2019; doi:10.1038/d41586-019-00285-9

Bonded in solution: The thermodynamic properties of intramolecular hydrogen bond formation in solution is investigated for a series of molecules with variable separation of the donor and acceptor sites. Formation of the hydrogen bond is more likely in chloroform than in water and free energies show a constant‐offset behavior. Crowding of the solution only influences the kinetics, but not the thermodynamic equilibrium.

Abstract

The energetics of intramolecular recognition processes are governed by the balance of pre‐organization and flexibility, which is often difficult to measure and hard to predict. Using classical MD simulations, we predict and quantify the effective strength of intramolecular hydrogen bonds between donor and acceptor sites separated by a variable alkyl linker in several solvents and crowded solutions. The balance of entropic and enthalpic contributions poses a solvent‐dependent limit to the occurrence of intramolecular H‐bonding. Still, free energies show a constant offset among different solvents with, for example, a 13 kJ mol⁻¹ difference between water and chloroform. Molecular crowding shows little effect on the thermodynamic equilibrium, but induces variations on the H‐bond kinetics. The results are in quantitative agreement with experiments in chloroform and showcase a general strategy to investigate molecular interactions in different environments, extending the limits of current experiments towards the prospective prediction of H‐bond interactions in a variety of contexts.

Bimolecular nucleophilic substitution (S_N2) plays a central role in organic chemistry. In the conventionally accepted mechanism, the nucleophile displaces a carbon-bound leaving group X, often a halogen, by attacking the carbon face opposite the C–X bond. A less common variant, the halogenophilic S_N2X reaction, involves initial nucleophilic attack of the X group from the front and as such is less sensitive to backside steric hindrance. Herein, we report an enantioconvergent substitution reaction of activated tertiary bromides by thiocarboxylates or azides that, on the basis of experimental and computational mechanistic studies, appears to proceed via the unusual S_N2X pathway. The proposed electrophilic intermediates, benzoylsulfenyl bromide and bromine azide, were independently synthesized and shown to be effective.

The effect of publishing peer review reports on referee behavior in five scholarly journals

The effect of publishing peer review reports on referee behavior in five scholarly journals, Published online: 18 January 2019; doi:10.1038/s41467-018-08250-2

Catalyst design in asymmetric reaction development has traditionally been driven by empiricism, wherein experimentalists attempt to qualitatively recognize structural patterns to improve selectivity. Machine learning algorithms and chemoinformatics can potentially accelerate this process by recognizing otherwise inscrutable patterns in large datasets. Herein we report a computationally guided workflow for chiral catalyst selection using chemoinformatics at every stage of development. Robust molecular descriptors that are agnostic to the catalyst scaffold allow for selection of a universal training set on the basis of steric and electronic properties. This set can be used to train machine learning methods to make highly accurate predictive models over a broad range of selectivity space. Using support vector machines and deep feed-forward neural networks, we demonstrate accurate predictive modeling in the chiral phosphoric acid–catalyzed thiol addition to N-acylimines.

Disk- and rod-shaped molecules are incompatible in coassembly, as the former tend to stack one-dimensionally whereas the latter tend to align in parallel. Because this type of incompatibility can be more pronounced in condensed phases, different-shaped molecules generally exclude one another. We report that supramolecular polymerization of a disk-shaped chiral monomer in nematic liquid crystals comprising rod-shaped molecules results in order-increasing mesophase transition into a single mesophase with a core-shell columnar geometry. This liquid crystalline material responds quickly to an applied electric field, resulting in unidirectional columnar ordering. Moreover, it can be modularly customized to be optoelectrically responsive simply by using a photoisomerizable rod-shaped module. The modular strategy allows for cooperative integration of different functions into elaborate dynamic architectures.

The rational synthesis of nanographenes and carbon nanoribbons directly on nonmetallic surfaces has been an elusive goal for a long time. We report that activation of the carbon (C)–fluorine (F) bond is a reliable and versatile tool enabling intramolecular aryl-aryl coupling directly on metal oxide surfaces. A challenging multistep transformation enabled by C–F bond activation led to a dominolike coupling that yielded tailored nanographenes directly on the rutile titania surface. Because of efficient regioselective zipping, we obtained the target nanographenes from flexible precursors. Fluorine positions in the precursor structure unambiguously dictated the running of the "zipping program," resulting in the rolling up of oligophenylene chains. The high efficiency of the hydrogen fluoride zipping makes our approach attractive for the rational synthesis of nanographenes and nanoribbons directly on insulating and semiconducting surfaces.

How to give a great scientific talk

How to give a great scientific talk, Published online: 19 December 2018; doi:10.1038/d41586-018-07780-5

A sticky situation: An unprecedented pure, dynamic, crystalline framework held together with weak “sticky fingers” van der Waals interactions has been developed. The fullerene‐based material exhibits a remarkable single‐crystal‐to‐single‐crystal hydrogenation reaction accompanied by a color change in the visible range.

Abstract

Engineering high‐recognition host–guest materials is a burgeoning area in basic and applied research. The challenge of exploring novel porous materials with advanced functionalities prompted us to develop dynamic crystalline structures promoted by soft interactions. The first example of a pure molecular dynamic crystalline framework is demonstrated, which is held together by means of weak “sticky fingers” van der Waals interactions. The presented organic‐fullerene‐based material exhibits a non‐porous dynamic crystalline structure capable of undergoing single‐crystal‐to‐single‐crystal reactions. Exposure to hydrazine vapors induces structural and chemical changes that manifest as toposelective hydrogenation of alternating rings on the surface of the [60]fullerene. Control experiments confirm that the same reaction does not occur when performed in solution. Easy‐to‐detect changes in the macroscopic properties of the sample suggest utility as molecular sensors or energy‐storage materials.

e^‐‐‐lucidation of structures: The microcrystal electron diffraction (MicroED) method promises to significantly accelerate the ability of synthetic chemists to gain structural information about small organic molecules and might be crucial for the acceleration of innovations across many fields.

Abstract

The development of new methods to analyze and determine molecular structures parallels the ability to accelerate synthetic research. For many decades, single‐crystal analysis by X‐ray diffraction (SXRD) has been the definitive tool for structural analysis at the atomic level; the drawback, however, is that a suitable single crystal of the analyte needs to be grown. The recent innovation of the crystalline sponge (CS) method allows the microanalysis of compounds simply soaked in a readily prepared CS crystal, thus circumventing the need to screen crystallization conditions while also using only a trace amount of the sample. In this context, electron diffraction for the structure determination of small molecules is discussed as potentially the next big development in this field.