Oleg Borodin

Nature, Published online: 06 January 2020; doi:10.1038/d41586-020-00013-8

Preparing for three races in three years at university showed Kathryn Wierenga parallels between running and PhD work.

Abstract

Prof. Takuzo Aida is one of the most visible materials chemists thanks to his many creative contributions to the broad field of supramolecular chemistry. Over the past two decades he has ingeniously utilized self‐assembly across scales and between various components to access a breathtaking variety of complex materials with fascinating properties. For example, the Aida Lab has pioneered conducting “bucky gel” by dispersing carbon nanotubes in ionic liquids as well as “aqua materials”, in which a tiny amount of additive renders water mechanically robust. From his personal insight he shares in this Interview, we can learn how his research evolved since his undergraduate studies. Moreover, he shares his vision on the importance of supramolecular polymers (Supra‐Plastics) to realize a sustainable society.

Rational design: The engineering of crystalline molecular solids through the simultaneous combination of distinctive non‐covalent interactions is an important field of research. Through rational design, chalcogenazolo pyridine scaffold modules were prepared here that can interact with suitable complementary molecular modules, undergoing formation of supramolecular polymers in the solid state.

Abstract

The engineering of crystalline molecular solids through the simultaneous combination of distinctive non‐covalent interactions is an important field of research, as it could allow chemist to prepare materials depicting multi‐responsive properties. It is in this context that, pushed by a will to expand the chemical space of chalcogen‐bonding interactions, a concept is put forward for which chalcogen‐ and halogen‐bonding interactions can be used simultaneously to engineer multicomponent co‐crystals. Through the rational design of crystallizable molecules, chalcogenazolo pyridine scaffold (CGP) modules were prepared that, bearing either a halogen‐bond acceptor or donor at the 2‐position, can interact with suitable complementary molecular modules undergoing formation of supramolecular polymers at the solid state. The recognition reliability of the CGP moiety to form chalcogen‐bonded dimers allows the formation of heteromolecular supramolecular polymers through halogen‐bonding interactions, as confirmed by single‐crystal X‐ray diffraction analysis.

Molecular gas station: This Minireview covers the state of the art of abiotic chemical fuels that have been used to trigger complete cycles of motion of molecular machines. Particular emphasis is placed on the operation mechanism of the machine/fuel systems.

Abstract

Natural molecular machines require a continuous fuel supply to perform motions and/or remain in a functional state. Consequently, the aim of developing artificial devices and materials with life‐type properties has motivated a growing interest in abiotic chemical fuels and in their supply modalities. Many artificial molecular machines have been developed in which the sequential addition of several chemical reagents allows the machine to perform complete cycles of motion. Only recently, examples of molecular machines whose cycles of motion are triggered by a single pulse of fuel have been reported. The latter systems are the object of this Minireview where the abiotic chemical fuels used so far to trigger the complete cycles of motion of molecular machines are described, with particular emphasis on the operation mechanism of the machine/fuel systems.

Spring fever: Supramolecular springs are defined as helical molecules or assemblies thereof in which the pitch can be modulated by external stimuli to achieve full control over the extension–contraction motion. In this Minireview, the structure–property relationships of supramolecular springs and spring‐like materials triggered by external stimuli are highlighted for potential future applications in responsive macroscopic devices.

Abstract

Molecular/supramolecular springs are artificial nanoscale objects possessing well‐defined structures and tunable physicochemical properties. Like a macroscopic spring, supramolecular springs are capable of switching their nanoscale conformation as a response to external stimuli by undergoing mechanical spring‐like motions. This dynamic action offers intriguing opportunities for engineering molecular nanomachines by translating the stimuli‐responsive nanoscopic motions into macroscopic work. These nanoscopic objects are reversible dynamic multifunctional architectures which can express a variety of novel properties and behave as adaptive nanoscopic systems. In this Minireview, we focus on the design and structure–property relationships of supramolecular springs and their (self‐)assembly as a prerequisite towards the generation of novel dynamic materials featuring controlled movements to be readily integrated into macroscopic devices for applications in sensing, robotics, and the internet of things.

Putting a twist on the electron: Enantioselective reactions can be induced by the electron spin, which is able to replace enantiopure reagents as the chiral bias. Three examples of enantioselective chemistry in electrochemical reactions resulting from electron‐spin polarization are presented. It is shown that the direction of the electron‐spin polarization defines the handedness of the enantioselectivity.

Abstract

We show that enantioselective reactions can be induced by the electron spin itself and that it is possible to replace a conventional enantiopure chemical reagent by spin‐polarized electrons that provide the chiral bias for enantioselective reactions. Three examples of enantioselective chemistry resulting from electron‐spin polarization are presented. One demonstrates the enantioselective association of a chiral molecule with an achiral self‐assembled monolayer film that is spin‐polarized, while the other two show that the chiral bias provided by the electron helicity can drive both reduction and oxidation in enantiospecific electrochemical reactions. In each case, the enantioselectivity does not result from enantiospecific interactions of the molecule with the ferromagnetic electrode but from the polarized spin that crosses the interface between the substrate and the molecule. Furthermore, the direction of the electron‐spin polarization defines the handedness of the enantioselectivity. This work demonstrates a new mechanism for realizing enantioselective chemistry.

Nature, Published online: 13 November 2019; doi:10.1038/d41586-019-03489-1

Anxiety and depression in graduate students is worsening. The health of the next generation of researchers needs systemic change to research cultures.

Nature, Published online: 12 November 2019; doi:10.1038/d41586-019-03371-0

The practice was probably used to improve the children’s chances of securing a university place.

During champagne cork popping, the CO₂/H₂O gas mixture initially under pressure in the bottleneck freely expands into ambient air and experiences adiabatic cooling. A comparison between the condensation phenomena accompanying cork popping from bottles stored at 20° and 30°C was made. The initial headspace-to-ambient-pressure ratio much exceeded the critical ratio needed for the gas mixture to reach Mach 1, thus forming under-expanded supersonic CO₂ freezing jets expelled from the throat of the bottlenecks. It was emphasized that, after adiabatic cooling and with a saturation ratio for gas-phase CO₂ about twice higher for the bottles stored at 30°C, dry ice CO₂ clusters grow bigger and reach the critical size needed to achieve the Mie scattering of light. Moreover, during the very first millisecond following cork popping, evanescent normal shock waves (or Mach disks) were unveiled in the jets, until the reservoir-to-ambient-pressure ratio goes below a critical ratio.

Twistacene self‐assembles forming two aggregates (AggI and AggII). In MCH, these two aggregates are very stable and it is possible to convert the former into the latter in a period of a month. In toluene, a consecutive pathway operates to yield the metastable aggregate AggI that is converted into AggII, the thermodynamically controlled aggregate, within a period of minutes or by the addition of seeds (see figure).

Abstract

The synthesis and self‐assembling features of twistacene 1 are reported. The supramolecular polymerization of 1 displays a consecutive pathway to afford slipped (AggI) and rotationally displaced (AggII) aggregates conditioned by the formation of intramolecularly H‐bonded pseudocycles. In methylcyclohexane, both AggI and AggII are highly stable and the interconversion of the kinetically controlled AggI into the thermodynamically controlled AggII takes several weeks to occur. The utilization of toluene as solvent changes the energetic level for both aggregates and favors a faster conversion of AggI into AggII within a period of minutes. This conversion can be accelerated by the addition of seeds. Furthermore, concentration dependent kinetic studies demonstrate the consecutive character of the supramolecular polymerization of 1.

Alkynes in ring systems: Angle‐strained alkynes show specific reactivity and properties. An overview of angle‐strained alkynes in π‐conjugated macrocycles is presented. Their synthetic methods and transformations, photophysical, and supramolecular properties, and bond angles are summarized.

Abstract

Angle‐strained alkyne‐containing π‐conjugated macrocycles are attractive compounds both in functional materials chemistry and biochemistry. Their interesting reactivity as well as photophysical and supramolecular properties have been revealed in the past three decades. This review highlights the recent advances in angle‐strained alkyne‐containing π‐conjugated macrocycles, especially their synthetic methods, the bond angles of alkynes (∠_sp at C≡C−C), and their functions. The theoretical and experimental research on cyclo[n]carbons and para‐cyclophynes consisting of ethynylenes and para‐phenylenes are mainly summarized. Related macrocycles bearing other linkers, such as ortho‐phenylenes, meta‐phenylenes, heteroaromatics, biphenyls, extended aromatics, are also overviewed. Bond angles of strained alkynes in π‐conjugated macrocycles, which are generable, detectable, and isolable, are summarized at the end of this review.

Conformationally flexible hexakis‐urea 1 is an allosteric receptor for anions; it recognizes chloride, bromide, and acetate in a 1:2 host–guest ratio in a positive allosteric manner. On the other hand, dihydrogen phosphate is recognized by 1 in a 1:3 host–guest ratio in a unique amphoteric allosteric manner (see figure).

Abstract

Conformationally flexible hexakis‐urea 1 was synthesized efficiently by condensing hexakis(aminomethyl)benzene with 4‐nitrophenyl‐(3,5‐di‐tert‐butylphenyl)carbamate. The hexakis‐urea 1 is unexpectedly soluble in organic solvents of low polarity due to intramolecular hydrogen bonding. The hexakis‐urea 1 recognizes chloride, bromide, and acetate in a 1:2 host‐guest ratio and in a positive allosteric manner in CDCl₃. The ability of 1 to recognize dihydrogen phosphate is a unique outcome, and the structure of the associated complex, which contains four dihydrogen phosphate ions, was clarified by single‐crystal X‐ray structural analysis. However, in solution, a complex with three dihydrogen phosphate ions was identified. The dihydrogen phosphate association in CDCl₃ proceeds in an amphoteric allosteric manner; in a positive allosteric manner (K ₁<K ₂) in the first step and a negative allosteric manner (K ₂>K ₃) in the subsequent step.

Nature, Published online: 18 September 2019; doi:10.1038/d41586-019-02711-4

A set of troubling charts shows how little progress nations have made toward limiting greenhouse-gas emissions.

Keep it moving: The self‐assembly of peptides into vesicles is coupled to a dynamic chemical reaction cycle. These vesicles emerge in response to fuel, and continuously remodel and decay when all fuel is depleted.

Abstract

Synthetic lipid membranes have served as important models for cellular membranes. However, these static membranes do not recapitulate the dynamic nature of the biological membranes which are frequently remodeled to support cellular function. An ideal membrane model would thus also display dynamic exchange of lipids. In this work, we achieve such a system by coupling the self‐assembly of peptides into membranes with a chemical reaction cycle. The reaction cycle activates and deactivates the peptides for self‐assembly at the expense of a chemical fuel. The resulting membranes are dynamically remodeled, and, over their 40 min lifetime, they emerge, grow, and are torn apart before they eventually decay.

Nature Chemistry, Published online: 16 September 2019; doi:10.1038/s41557-019-0322-x

The emergence of pristine RNA and DNA on the early Earth would have been hindered by a lack of specificity in their prebiotic syntheses. Now, it has been shown that chimeric sequences—with a mixture of RNA and DNA backbones—mediate the template-directed ligation of oligomers present in mixtures of nucleic acids, enabling the simultaneous appearance of RNA and DNA.

Hooked! An approach to prepare supramolecular polymers by hooking together sigmoidal monomers into 1D arrays of π‐stacked anthracene and acridine units is presented. It gives rise to micrometer‐sized fibrils that show pseudoconductivities, in line with other conducting materials.

Abstract

Supramolecular polymers show great potential in the development of new materials because of their inherent recyclability and their self‐healing and stimuli‐responsive properties. Supramolecular conductive polymers are generally obtained by the assembly of individual aromatic molecules into columnar arrays that provide an optimal channel for electronic transport. A new approach is reported to prepare supramolecular polymers by hooking together sigmoidal monomers into 1D arrays of π‐stacked anthracene and acridine units, which gives rise to micrometer‐sized fibrils that show pseudoconductivities in line with other conducting materials. This approach paves the way for the design of new supramolecular polymers constituted by acene derivatives with enhanced excitonic and electronic transporting properties.

Nature Communications, Published online: 09 September 2019; doi:10.1038/s41467-019-12150-4

Originally designed for measuring isotope abundances and elemental masses, mass spectrometry is becoming a mainstay across life sciences. As electrospray ionization of biomolecules turns 30 and the Orbitrap mass analyzer 20, we take this opportunity to highlight the role of both inventions in stirring mass spectrometry from physics into biology and discuss the advances and challenges that may impact the future applications of biomolecular mass spectrometry.

Nature Nanotechnology, Published online: 05 September 2019; doi:10.1038/s41565-019-0546-3

The trade-off between necessary scientific communication and the associated CO2 footprint asks for a thorough reconsideration of our travelling habits, new institutional travelling policies and for alternative approaches to interaction with colleagues and peers.

Cellular uptake: The introduction of halogen, particularly iodine, atoms to small molecules and proteins is emerging as a novel and promising strategy not only for studying membrane activity and cellular functions, but also for improving the delivery of therapeutic agents. The strong halogen‐bond forming ability of iodine atoms plays a crucial role in membrane transport (see scheme).

Abstract

The plasma membrane regulates the transport of molecules into the cell. Small hydrophobic molecules can diffuse directly across the lipid bilayer. However, larger molecules require specific transporters for their entry into the cell. Regulating the cellular entry of small molecules and proteins is a challenging task. The introduction of halogen, particularly iodine, to small molecules and proteins is emerging to be a promising strategy to improve the cellular uptake. Recent studies reveal that a simple substitution of hydrogen atom with iodine not only increases the cellular uptake, but also regulates the membrane transport. The strong halogen‐bond‐forming ability of iodine atoms plays a crucial role in the transport and the introduction of iodine may provide an efficient strategy for studying membrane activity and cellular functions and improving the delivery of therapeutic agents. This Concept article does not provide a comprehensive picture of membrane transport but highlights halogen‐substitution as a novel strategy for understanding and regulating the cell‐membrane traffic.

In recent years there have been great strides in artificial intelligence (AI), with games often serving as challenge problems, benchmarks, and milestones for progress. Poker has served for decades as such a challenge problem. Past successes in such benchmarks, including poker, have been limited to two-player games. However, poker in particular is traditionally played with more than two players. Multiplayer games present fundamental additional issues beyond those in two-player games, and multiplayer poker is a recognized AI milestone. In this paper we present Pluribus, an AI that we show is stronger than top human professionals in six-player no-limit Texas hold’em poker, the most popular form of poker played by humans.

Nature, Published online: 28 August 2019; doi:10.1038/d41586-019-02519-2

Electronic devices that are based on carbon nanotubes have the potential to be more energy efficient than their silicon counterparts, but have been restricted in functionality. This limitation has now been overcome.

Enlightening the blind spots: Newly established carbon‐ and nitrogen‐detection NMR experiments allow characterization of RNA structure and dynamics where traditional proton‐based techniques fail (see figure).

Abstract

Ribonucleic acid oligonucleotides (RNAs) play pivotal roles in cellular function (riboswitches), chemical biology applications (SELEX‐derived aptamers), cell biology and biomedical applications (transcriptomics). Furthermore, a growing number of RNA forms (long non‐coding RNAs, circular RNAs) but also RNA modifications are identified, showing the ever increasing functional diversity of RNAs. To describe and understand this functional diversity, structural studies of RNA are increasingly important. However, they are often more challenging than protein structural studies as RNAs are substantially more dynamic and their function is often linked to their structural transitions between alternative conformations. NMR is a prime technique to characterize these structural dynamics with atomic resolution. To extend the NMR size limitation and to characterize large RNAs and their complexes above 200 nucleotides, new NMR techniques have been developed. This Minireview reports on the development of NMR methods that utilize detection on low‐γ nuclei (heteronuclei like ¹³C or ¹⁵N with lower gyromagnetic ratio than ¹H) to obtain unique structural and dynamic information for large RNA molecules in solution. Experiments involve through‐bond correlations of nucleobases and the phosphodiester backbone of RNA for chemical shift assignment and make information on hydrogen bonding uniquely accessible. Previously unobservable NMR resonances of amino groups in RNA nucleobases are now detected in experiments involving conformational exchange‐resistant double‐quantum ¹H coherences, detected by ¹³C NMR spectroscopy. Furthermore, ¹³C and ¹⁵N chemical shifts provide valuable information on conformations. All the covered aspects point to the advantages of low‐γ nuclei detection experiments in RNA.