Oleg Borodin

Publication date: 17 April 2020

Source: Tetrahedron, Volume 76, Issue 16

Author(s): Chencong Xu, Tao Li, Pingkai Jiang, Yong Jian Zhang

Nature Communications, Published online: 18 March 2020; doi:10.1038/s41467-020-15190-3

Solid‐state light emission is very promising in view of potential applications. Scientific approaches to the realization of chiral emissive materials are indeed growing exponentially. The properties of the nanostructures discussed are related both to the way in which luminescence is generated upon aggregation (aggregation‐induced emission) and the way in which it is detected (circularly polarized emission).

Abstract

Chirality is becoming increasingly important in the design of organic materials with functional properties, when bulk anisotropy is needed. In the past decades, a plethora of chiral organic materials have been studied and developed. Nanostructures have brought substantial advancement to the realization of organic‐molecule‐based devices, and the possibilities for solid‐state light emission are very promising in view of potential applications. Scientific approaches to the realization of chiral emissive materials are indeed growing exponentially. The chiral nanostructures discussed are related both to the way in which luminescence is generated and the way in which it is detected. As to the former, the focus will be on organic chromophores with aggregation‐induced emission properties, so that emission is present, or at least largely amplified, when the molecules are in the aggregated state. As to the latter, the focus will be on the ability and a quantitative comparison of organic nanostructures capable of circularly polarized emission.

The activation of organic substrates by photoredox catalysis is now commonplace in organic synthesis. The review focusses on new strategies that combine photoredox activation with hydrogen evolution reactions that utilize cobaloxime catalysts. These processes allow the synthesis of a wide variety of organic compounds with minimal production of waste.

The development of efficient, mild, economical, and low‐waste processes is a cornerstone of sustainable chemistry. One such synthetic strategy that exemplifies these characteristics is the use of catalytic dehydrogenation in small‐molecule functionalization. This has been achieved in recent history through the use of photoredox catalysis in conjunction with cobaloximes, a class of catalysts that are capable of proton reduction. This has allowed for a variety of bond formations to be achieved with few to no stoichiometric additives while often producing hydrogen gas as the sole stoichiometric by‐product. Herein, select advancements made in this area of sustainable chemistry and catalysis are detailed and the mechanistic insights this body of work has provided thus far are evaluated. As such, this review aims to aid in the further development and study of synthetic strategies involving photoredox‐promoted hydrogen evolution.

Staying balanced: In this Science Voices article, Prof. Steven Townsend addresses strategies for obtaining a healthy start in academic careers and the provides a personal insight on assessing priorities and obtaining work–life integration as an independent researcher.

Beside sensing and delivery, another peculiar property arising from confinement in discrete molecular hosts comes from the possibility to have in close proximity, and in defined position, two different molecules (hetero co‐encapsulation). This phenomenon can be tuned considering steric and electronic properties of the guests. In this work, a study on the parameters affecting homo and hetero co‐encapsulation processes within a supramolecular cage is reported. In particular, different benzoate guests were bound within a supramolecular cage containing two metal binding sites and the experimental binding thermodynamics measured. Unexpectedly, from competition experiments we observed that the maximum concentration of hetero co‐encapsulation is achieved if a weakly binding guest is used to partially displace a strongly binding guest.

Quick as a F⁻lash: The use of Lewis acidic, water‐compatible phosphonium boranes is introduced for the quick and selective transport of F⁻ across biological membrane mimics.

Abstract

With the view of developing selective transmembrane anion transporters, a series of phosphonium boranes of general formula [p‐RPh₂P(C₆H₄)BMes₂]⁺ have been synthesized and evaluated. The results demonstrate that variation of the R group appended to the phosphorus atom informs the lipophilicity of these compounds, their Lewis acidity, as well as their transport activity. Anion transport experiments in POPC‐based large unilamellar vesicles show that these main‐group cations are highly selective for the fluoride anion, which is transported more than 20 times faster than the chloride anion. Finally, this work shows that the anion transport properties of these compounds are extremely sensitive to the steric crowding about the boron atom, pointing to the crucial involvement of the Group 13 element as the anion binding site.

Hydrogen bonds and salt bridges enable the length‐controlled generation of discrete tubular structures from rim‐differentiated and peralkylamino‐substituted pillar[5]arenes. The speed of guest molecule exchange in the tubes depends on the tube length.

Abstract

Supramolecular chemistry in confined spaces constructed from macrocyclic molecules has attracted much attention because it can utilize the specific binding properties of macrocyclic cavities. Herein we report the preparation of length‐controlled discrete tubular structures by homo‐/co‐assembly of rim‐differentiated and peralkylamino‐substituted pillar[5]arenes via hydrogen bonds and salt bridges. By dimerization and trimerization, the expanded tubes show a fivefold helical structure and stepwise binding, respectively. We found that the exchange speed of guest molecules in the tubes could be controlled by varying the tube length.

Nature, Published online: 13 March 2020; doi:10.1038/d41586-020-00739-5

Amide synthesis: An approach to the dynamic formation of amides is described. This method uses the reversible reaction between imines and acyl chlorides, occurs at ambient conditions, and does not require catalysts. Moreover, coupling this reaction with hydrolysis can be used to achieve the overall formation of robust products, and can be applied to the controlled assembly of various amide‐based materials (see scheme).

Abstract

Dynamic covalent chemistry has rapidly become an important approach to access supramolecular structures. While the products generated in these reactions are held together by covalent bonds, the reversible nature of the transformations can limit the utility of many these systems in creating robust materials. We describe herein a method to form stable and commonly employed amide bonds by exploiting the reversible coupling of imines and acyl chlorides. The reaction employs easily accessible reagents, is dynamic under ambient conditions, without catalysts, and can be trapped with simple hydrolysis. This offers an approach to create broad families of amide products under thermodynamic control, including the selective formation of amide macrocycles or polymers.

Nature Reviews Chemistry, Published online: 06 March 2020; doi:10.1038/s41570-020-0168-1

More the merrier: Multistationarity has rarely been demonstrated before. In this work, it is obtained when two template/product molecules are formed in two replication cycles while competing for a single common resource molecule. Since the T ₁ and T ₂ replication cycles are coupled, multiple steady states are obtained as a function of their coordinated activity.

Abstract

Systems Chemistry generates platforms for studying the emergence of function in networks operating far from equilibrium. In this area, we have previously used experiments and simulations towards characterization and manipulation of small peptide‐based networks, driven by reversible self‐replication processes, that exhibit bistability. We now show how coupling two such networks, each exhibiting bistability, yields new dynamic systems that reach multiple (up to four) steady states. Furthermore, we demonstrate how such multistationarity, rarely analyzed before, can be systematically programmed and tuned. Our results suggest that the key to mimic biological complexification lies not only in the applied network size, the number of molecules involved, or even in the emergence of elaborate structures, but also in the network nature and topology.

Design on a small scale ! Molecular self‐assembly in solution, with rational molecular design and under kinetic control, has achieved supramolecular nanosheets with controlled area and aspect ratio.

Abstract

Recent developments in kinetically controlled supramolecular polymerization permit control of the size (i.e., length and area) of self‐assembled nanostructures. However, control of molecular self‐assembly at a level comparable with organic synthetic chemistry and the achievement of structural complexity at a hierarchy larger than the molecular level remain challenging. This study focuses on controlling the aspect ratio of supramolecular nanosheets. A systematic understanding of the relationship between the monomer structure and the self‐assembly energy landscape has derived a new monomer capable of forming supramolecular nanosheets. With this monomer in hand, the aspect ratio of a supramolecular nanosheet is demonstrated that it can be controlled by modulating intermolecular interactions in two dimensions.

Cage tetracationic blue box molecules are bridged by supramolecular ball joints constituted by iodide anions to form a novel type of ordered porous networks. These new materials, named permutable organized frameworks (POFs), retain the limited directionality of microscopic BB⋅⋅⋅iodide interactions at the material level, where it manifests in terms of angular freedom in the mutual disposition of constituent species, leading to 3D networks with superior flexibility (see figure).

Abstract

XOFs‐type materials (X=M, C, S, that is, metal–organic frameworks, covalent organic frameworks and supramolecular organic frameworks, respectively) share a common unifying feature: mutual spatial orientation of constituting components is strictly directional and unchanging by design. Herein, we illustrate an alternate design for porous architectures, as rigid joints constituted by coordinative (MOFs), covalent (COFs), or hydrogen‐donor/acceptor (SOFs) bonds, are replaced by supramolecular ball joints, which confer unprecedented flexibility, especially angular, to porous networks. The obtained frameworks remain highly organized but are also permutable: lacking a forced convergence towards an immutable minimum energy structure, these systems remain able to adjust depending on external conditions. Results of POF (permutable organized framework) synthesis is a family of structures rather than a single pre‐determined three‐dimensional arrangement, as we demonstrate with an illustrative set of 5 XRD structures.

Nature Chemistry, Published online: 09 March 2020; doi:10.1038/s41557-020-0426-3

Communications Chemistry, Published online: 09 March 2020; doi:10.1038/s42004-020-0277-2

Communications Chemistry, Published online: 06 March 2020; doi:10.1038/s42004-020-0278-1

Materials for electrochemistry : Metal–organic framework and covalent organic framework nanosheets represent one promising kind of power materials for electrochemical. Synthesis strategies, tailored material properties and different electrochemical performances are prominent features of supercapacitors, batteries, OER and HER. Metal–organic framework and covalent organic framework nanosheets comprehensively summarized and evaluations are given in this Review.

Abstract

Metal–organic framework (MOF) and covalent organic framework (COF) nanosheets are a new type of two‐dimensional (2D) materials with unique design principles and various synthesis methods. They are considered ideal electrochemical devices due to the ultrathin thickness, easily tunable molecular structure, large porosity and other unique properties. There are two common methods to synthesize 2D MOF/COF nanosheets: bottom‐up and top‐down. The top‐down strategy mainly includes ultrasonic assisted exfoliation, electrochemical exfoliation and mechanical exfoliation. Another strategy mainly includes interface synthesis, modulation synthesis, surfactant‐assisted synthesis. In this Review, the development of ultrathin 2D nanosheets in the field of electrochemistry (supercapacitors, batteries, oxygen reduction, and hydrogen evolution) is introduced, and their unique dimensional advantages are highlighted.

Photoregulatory azobenzene diamide‐based transporters are reported. The anionophores exhibited efficient chloride transport with quick photoresponse time. A carrier‐mediated chloride‐anion antiport mechanism was confirmed, and the supramolecular interactions involved in chloride recognition within the sandwich complex were revealed from theoretical studies.

Abstract

There has been a tremendous evolution for artificial ion transport systems, especially gated synthetic systems, which closely mimic their natural congeners. Herein, we demonstrate a trans‐azobenzene‐based photoregulatory anionophoric system that transports chloride by forming a sandwich dimeric complex. Further studies confirmed a carrier‐mediated chloride‐anion antiport mechanism, and the supramolecular interactions involved in chloride recognition within the sandwich complex were revealed from theoretical studies. Reversible trans–cis photoisomerization of the azobenzene was achieved without any significant contribution from the thermal cis →trans isomerization at room temperature. Photoregulatory transport activity across the lipid bilayer membrane inferred an outstanding off‐on response of the azobenzene photoswitch.

Angle‐strained alkyne‐containing π‐conjugated macrocycles are attractive compounds both in functional materials chemistry and biochemistry. K. Miki and K. Ohe examine the recent advances in angle‐strained alkyne‐containing π‐conjugated macrocycles, highlighting their synthetic methods, the bond angles of alkynes, and their functions in their review on https://doi.org/10.1002/chem.201904114page 2529 ff.

Imaging beam‐sensitive materials by electron microscopy is of fundamental significance for materials science but remains a great challenge. This article provides a comprehensive review of the essential advances in electron microscopic techniques toward the dose‐efficient imaging of beam‐sensitive materials. These advances have led to significant materials science discoveries through the elucidation of crystal and local structures.

Abstract

Electron microscopy allows the extraction of multidimensional spatiotemporally correlated structural information of diverse materials down to atomic resolution, which is essential for figuring out their structure–property relationships. Unfortunately, the high‐energy electrons that carry this important information can cause damage by modulating the structures of the materials. This has become a significant problem concerning the recent boost in materials science applications of a wide range of beam‐sensitive materials, including metal–organic frameworks, covalent–organic frameworks, organic–inorganic hybrid materials, 2D materials, and zeolites. To this end, developing electron microscopy techniques that minimize the electron beam damage for the extraction of intrinsic structural information turns out to be a compelling but challenging need. This article provides a comprehensive review on the revolutionary strategies toward the electron microscopic imaging of beam‐sensitive materials and associated materials science discoveries, based on the principles of electron–matter interaction and mechanisms of electron beam damage. Finally, perspectives and future trends in this field are put forward.

Fluorogens with aggregation‐induced emission (AIEgens) have stimulated the development of AIE molecular probes and AIE nanoparticle probes for various biomedical applications. This Review reveals how the AIE probes have evolved with the development of new multifunctional AIEgens, and how new strategies have been developed to overcome the limitations of traditional AIE probes for more translational applications.

Abstract

The concept of aggregation‐induced emission (AIE) has opened new opportunities in many research fields. Motivated by the unique feature of AIE fluorogens (AIEgens), during the past decade, many AIE molecular probes and AIE nanoparticle (NP) probes have been developed for sensing, imaging and theranostic applications with excellent performance outperforming conventional fluorescent probes. This Review summarizes the latest advancement of AIE molecular probes and AIE NP probes and their emerging biomedical applications. Special focus is to reveal how the AIE probes are evolved with the development of new multifunctional AIEgens, and how new strategies have been developed to overcome the limitations of traditional AIE probes for more translational applications via fluorescence imaging, photoacoustic imaging and image‐guided photodynamic/photothermal therapy. The outlook discusses the challenges and future opportunities for AIEgens to advance the biomedical field.

Nature, Published online: 03 March 2020; doi:10.1038/d41586-020-00631-2

Geometry dictated : Introduction of arylethynyl moieties to the pyrrole α‐ and β‐positions of dipyrrolyldiketone BF₂ complexes as anion‐responsive π‐electronic molecules was investigated. Arylethynyl‐substituted derivatives formed assemblies in the solid state and mesophases in the form of ion pairs of the anion complexes and a counter cation. The geometries of the constituent anion complexes affected the packing modes of solid‐state and dimension‐controlled assemblies.

Abstract

The introduction of arylethynyl moieties at the pyrrole α‐ and β‐positions of dipyrrolyldiketone BF₂ complexes as anion‐responsive π‐electronic molecules was investigated. The arylethynyl‐substituted derivatives formed a variety of anion complexes with planar [1+1]‐ and interlocked [2+1]‐type structures in solution and in the solid state. The derivatives with long alkyl chains in the introduced arylethynyl groups also formed mesophases in the form of ion pairs of the anion complexes and a counter cation. The geometries of the constituent anion complexes affected the packing modes of the dimension‐controlled assemblies.

Nature, Published online: 26 February 2020; doi:10.1038/d41586-020-00565-9

Atomic force microscopy (AFM) with molecule-functionalized tips has emerged as the primary experimental technique for probing the atomic structure of organic molecules on surfaces. Most experiments have been limited to nearly planar aromatic molecules due to difficulties with interpretation of highly distorted AFM images originating from nonplanar molecules. Here, we develop a deep learning infrastructure that matches a set of AFM images with a unique descriptor characterizing the molecular configuration, allowing us to predict the molecular structure directly. We apply this methodology to resolve several distinct adsorption configurations of 1S-camphor on Cu(111) based on low-temperature AFM measurements. This approach will open the door to applying high-resolution AFM to a large variety of systems, for which routine atomic and chemical structural resolution on the level of individual objects/molecules would be a major breakthrough.