Oleg Borodin

In supramolecular materials, molecular building blocks are held together by non‐covalent interactions. These materials typically exist in equilibrium with their environment. Living biological materials exist out of equilibrium. They require constant dissipation of energy to be sustained. Here, we show the crucial differences between equilibrium and dissipative supramolecular materials. We focus on one unique property of the emerging materials: their tunable lifetime. With recent examples, we show the principles involved and how we can apply these materials in the future.

Abstract

Supramolecular materials are materials in which molecular building blocks are held together by non‐covalent interactions. These materials exist in equilibrium with their environment. In contrast, most biological materials exist out of equilibrium. They require constant dissipation of energy and consumption of nutrients to be sustained. As a result of their non‐equilibrium nature, biological materials have superior properties compared to their in‐equilibrium counterparts. These properties include spatial and temporal control over their presence, the ability to self‐heal and even the ability to self‐replicate. Inspired by biology, researchers have developed analogs of such dissipative supramolecular materials. This Focus Review introduces the crucial differences between in‐equilibrium and dissipative supramolecular materials. We focus on one unique property of the emerging materials: their tunable lifetime. With recent examples, we show the principles involved and how these materials can be applied in the future.

By using GEST‐NMR (guest exchange saturation transfer NMR), the authors demonstrate the quantitative evaluation of dynamic exchange rates (represented by a drum) between an anion and a series of synthetic receptors of the Bambusuril family (represented by a bamboo plant). The ability to amplify undetectable NMR signals of a low population of the complex reveals unprecedent anion–receptor interactions in water. More information can be found in the Communication by V. Šindelář, A. Bar‐Shir et al. on https://doi.org/10.1002/chem.201805973page 1687.

Fishing for iodide: Through the integration of a novel tetra‐iodotriazole halogen bonding motif into a family of interlocked host structures, strong halide binding and a high degree of iodide anion selectivity is achieved in aqueous‐organic solvent media.

Abstract

Whilst the exploitation of interlocked host frameworks for anion recognition is widely established, examples incorporating halogen bond donor groups are still relatively rare. Through the integration of a novel tetra(iodotriazole)‐pyridinium motif into macrocycle and axle components, a family of halogen bonding catenane and rotaxanes are constructed for anion recognition studies in a competitive aqueous‐organic solvent mixture. Importantly, the degree of anion selectivity displayed is dictated by the topological nature and charged state of the respective interlocked host cavity. All the interlocked hosts exhibit iodide anion selectivity over other halides and sulfate, with the level of discrimination being the greatest with the mono‐cationic rotaxane. Arising from greater electrostatic interactions working in tandem with halogen bonding and hydrogen bonding, the di‐cationic rotaxane displays stronger anion association at the expense of a relatively lower degree of iodide selectivity.

How to explore chemical space using algorithms and automation

How to explore chemical space using algorithms and automation, Published online: 15 January 2019; doi:10.1038/s41570-018-0066-y

Automation can help in performing routine tasks quickly and consistently. Algorithms facilitate the searching of current knowledge. Combining the two could lead to a chemically intelligent approach to the discovery of not only new molecules but also novel and unpredictable reactivity.

It has long been an aspirational goal to create artificial structures that allow fast permeation of water but reject even the smallest hydrated ions, replicating the feat achieved by nature in protein channels (e.g., aquaporins). Despite recent progress in creating nanoscale pores and capillaries, these structures still remain distinctly larger than protein channels. We report capillaries made by effectively extracting one atomic plane from bulk crystals, which leaves a two-dimensional slit of a few angstroms in height. Water moves through these capillaries with little resistance, whereas no permeation could be detected even for such small ions as Na⁺ and Cl^–. Only protons (H⁺) can diffuse through monolayer water inside the capillaries. These observations improve our understanding of molecular transport at the atomic scale.

Quantum dot activated indium gallium nitride on silicon as photoanode for solar hydrogen generation

Quantum dot activated indium gallium nitride on silicon as photoanode for solar hydrogen generation, Published online: 09 January 2019; doi:10.1038/s42004-018-0105-0

Nitride based photoelectrodes are promising candidates for photoelectrochemical water splitting and hydrogen generation but suffer from quick degradation. Here the authors show indium gallium nitride activated by InN quantum dots on silicon which can be used as stable photoanode for efficient water splitting.

Six project-management tips for your PhD

Six project-management tips for your PhD, Published online: 04 January 2019; doi:10.1038/d41586-018-07860-6

Use strategies from the private sector to better manage your graduate project.

Allosteric receptor: Two flexible covalent cages showed an on/off encapsulation mechanism triggered by significant conformational changes upon silver(I) coordination to the peripheral binding sites. In addition, the X‐ray structures of the silver(I)‐bound receptor and of the one with pyrazine as the guest molecule confirmed the large cavity size of the receptor.

Abstract

The allosteric control of the receptor properties of two flexible covalent cages is reported. These receptors consist of two zinc(II) porphyrins connected by four linkers of two different sizes, each incorporating two 1,2,3‐triazolyl ligands. Silver(I) ions act as effectors, responsible for an on/off encapsulation mechanism of neutral guest molecules. Binding silver(I) ions to the triazoles opens the cages and triggers the coordination of pyrazine or the encapsulation of N,N′‐dibutyl‐1,4,5,8‐naphthalene diimide. The X‐ray structure of the silver(I)‐complexed receptor with short connectors is reported, revealing the hollow structure with a cavity well‐defined by two eclipsed porphyrins. Rather unexpectedly, the crystallographic structure of this receptor with pyrazine as a guest molecule showed that the cavity is occupied by two pyrazines, each binding to the zinc(II) porphyrin in a monotopic fashion.

A tris‐urea unit was combined with CTV moiety, leading to a heteroditopic hemicryptophane capable of binding ion pairs efficiently and selectively.

Abstract

The synthesis of a hemicryptophane cage combining a CTV unit with a C₃ symmetrical moiety bearing three urea functions is reported. This host was found to bind anions with higher binding constants than other previously reported hemicryptophanes. Due to its heteroditopic character this cage proved to be an efficient ion‐pair receptor. The best cooperativity effect was observed for the tetramethylammonium bromide (TMABr) salt, which was confirmed and rationalized by DFT calculations.

MOPping up light: Metal–organic polyhedra (MOPs) are promising candidates for many potential applications, but have not previously been reported to act as photocatalysts for hydrogen production. For the first time, a molecular tetrahedron, as a representative zirconium‐based MOP, is demonstrated to act as a photocatalyst with fairly high catalytic activity for hydrogen production (see figure).

Abstract

Metal–organic polyhedra (MOPs) are promising candidates for many potential applications; however, their use as photocatalysts for hydrogen production has yet to be developed. Herein, the photocatalytic performance of a water‐stable Zr‐MOP, ZrT‐1‐NH₂, was evaluated, for the first time, through photocatalytic hydrogen evolution under visible‐light irradiation. ZrT‐1‐NH₂ shows clearly enhanced photocatalytic activity (510.42 μmol g⁻¹ h⁻¹) for hydrogen production, in comparison with that of other homogeneous crystalline materials. If platinum nanoparticles were introduced into the photocatalytic system, the hydrogen production efficiency of ZrT‐1‐NH₂ could be further improved. For ZrT‐1‐NH₂, the conspicuous improvement in photocatalysis can be attributed to efficient electron–hole separation, targeted electron transfer, and excellent recombination suppression. Furthermore, ZrT‐1‐NH₂ shows excellent stability during photocatalytic hydrogen evolution over five continuous runs. This work illustrates that MOP‐based photocatalysts hold promise for broad applications in the domain of clean energy.

Air-stable phosphorus-doped molybdenum nitride for enhanced elctrocatalytic hydrogen evolution

Air-stable phosphorus-doped molybdenum nitride for enhanced elctrocatalytic hydrogen evolution, Published online: 12 December 2018; doi:10.1038/s42004-018-0097-9

Molybdenum-based electrocatalysts are widely investigated as water splitting catalysts but they suffer from low efficiency due to surface oxidation. Here the authors report the synthesis of air-stable molybdenum nitride which displays enhanced hydrogen evolution activity.

Publication date: 19 December 2018

Source: Tetrahedron Letters, Volume 59, Issue 51

Author(s): Min-Sung Ko, Adil S. Aslam, Dong-Gyu Cho

Publication date: 10 January 2019

Source: Tetrahedron Letters, Volume 60, Issue 2

Author(s): Huimin Fu, Bangtun Zhao, Weimin Zhu

3D printing for chemical, pharmaceutical and biological applications

3D printing for chemical, pharmaceutical and biological applications, Published online: 21 November 2018; doi:10.1038/s41570-018-0058-y

3D printing is becoming a mainstream technology with considerable increase in access to affordable desktop printers. However, specific design principles and material considerations need to be weighed when printing functional devices that integrate catalytic and/or analytical functionalities, as well as when printing common laboratory hardware.

How biologists are creating life-like cells from scratch

How biologists are creating life-like cells from scratch, Published online: 07 November 2018; doi:10.1038/d41586-018-07289-x

Built from the bottom up, synthetic cells and other creations are starting to come together and could soon test the boundaries of life.

Autumn is here, and for most of us, it’s a time of beauty as the leaves cascade through an array of hues before pirouetting down from the trees. If you have to travel by train, however, you might tire of ‘leaves on the line’ being the supposed cause of train delays. It turns out to […]

An off and on relationship: In strongly acidic aqueous solutions, the oxime bond is dynamic and allows both a catenane and a macrocycle to self‐assemble in relatively high yields. The dynamic nature of oxime linkage could be turned OFF almost fully in neutral conditions, making the self‐assembled catenane kinetically inert in both solid state and solution at elevated temperatures or during chromatography and counteranion exchange.

Abstract

Oxime, whose dynamic nature was reported to be switchable between ON/OFF by tuning the acidity, is employed in a novel type of dynamic covalent approach that is amenable to use in water for self‐assembly of purely organic molecules with complex topology. In strongly acidic conditions, the dynamic nature of oxime is turned ON, allowing occurrence of error‐checking and therefore a catenane and a macrocycle self‐assembled in high yields. In neutral conditions, oxime ceases to be dynamic, which helps to trap the self‐assembled products even when the driving forces of their formation are removed. We envision that this switchable behaviour might help, at least partially, to resolve a commonly encountered drawback of dynamic covalent chemistry, namely that the intrinsic stability of the self‐assembled products containing dynamic bonds, such as imine or hydrazone, are often jeopardized by their reversible nature.

Oscillations, travelling fronts and patterns in a supramolecular system

Oscillations, travelling fronts and patterns in a supramolecular system, Published online: 15 October 2018; doi:10.1038/s41565-018-0270-4

A perylene diimide derivative shows nonlinear chemical dynamics when chemically fuelled in a semi-batch reactor.

Complexity from small molecules

Complexity from small molecules, Published online: 15 October 2018; doi:10.1038/s41565-018-0283-z

Chemical oscillations emerge during the chemically fuelled self-assembly of a perylene diimide derivative as a result of simple feedback mechanisms.