Oleg Borodin

We describe a chemical robotic assistant equipped with a curiosity algorithm (CA) that can efficiently explore the states a complex chemical system can exhibit. The CA-robot is designed to explore formulations in an open-ended way with no explicit optimization target. By applying the CA-robot to the study of self-propelling multicomponent oil-in-water protocell droplets, we are able to observe an order of magnitude more variety in droplet behaviors than possible with a random parameter search and given the same budget. We demonstrate that the CA-robot enabled the observation of a sudden and highly specific response of droplets to slight temperature changes. Six modes of self-propelled droplet motion were identified and classified using a time-temperature phase diagram and probed using a variety of techniques including NMR. This work illustrates how CAs can make better use of a limited experimental budget and significantly increase the rate of unpredictable observations, leading to new discoveries with potential applications in formulation chemistry.

Taking shape: Cucurbit[7]uril‐threaded pseudorotaxanes containing two thiol groups at both termini polymerize by reversible disulfide bond formation into protofilament‐like linear poly‐pseudorotaxanes. These poly‐pseudorotaxanes associate laterally with each other in a self‐shape‐complementary manner to form multi‐stranded artificial microtubules.

Abstract

Hierarchical self‐assembly of building blocks over multiple length scales is ubiquitous in living organisms. Microtubules are one of the principal cellular components formed by hierarchical self‐assembly of nanometer‐sized tubulin heterodimers into protofilaments, which then associate to form micron‐length‐scale, multi‐stranded tubes. This peculiar biological process is now mimicked with a fully synthetic molecule, which forms a 1:1 host‐guest complex with cucurbit[7]uril as a globular building block, and then polymerizes into linear poly‐pseudorotaxanes that associate laterally with each other in a self‐shape‐complementary manner to form a tubular structure with a length over tens of micrometers. Molecular dynamic simulations suggest that the tubular assembly consists of eight poly‐pseudorotaxanes that wind together to form a 4.5 nm wide multi‐stranded tubule.

Locking‐in the conformation of supramolecular assemblies provides a new avenue to regulate the (opto)electronic properties of robust nanoscale objects. In the present contribution, we show that the covalent tethering of a perylene bisimide (PBI)‐derived supramolecular polymer with a molecular locker enables the formation of a locked superstructure equipped with emergent structure‐function relationships. Experiments that exploit variable‐temperature ground‐state electronic absorption spectroscopy unambiguously demonstrate that the excitonic coupling between nearest neighboring units in the tethered superstructure is preserved at a temperature (371 K) where the pristine, non‐covalent assembly exists exclusively in a molecularly dissolved state. A close examination of the solid‐state morphologies reveals that the locked superstructure engenders the formation of hierarchical 1D materials which are not achievable by unlocked assemblies. To complement these structural attributes, we further demonstrate that covalently tethering a supramolecular polymer built from PBI subunits enables the emergence of electronic properties not evidenced in non‐covalent assemblies. Using cyclic voltammetry experiments, the elucidation of the potentiometric properties of the locked superstructure reveals a 100‐mV stabilization of the conduction band energy when compared to that recorded for a non‐covalent assembly.

We report in this communication the synthesis, conformational structure, electrochemical property and non‐covalent anion binding of corona[5]arenes. A [3+2] fragment coupling reaction of 1,4‐bis((6‐chloro‐1,2,4,5‐tetrazin‐3‐yl)oxy)benzene and derivatives with HS‐C 6 H 4 ‐X‐C 6 H 4 ‐SH (X = S, CH 2 , CMe 2 and O) proceeded efficiently under mild conditions to produce a number of novel heteroatom and methylene bridged corona[3]arene[2]tetrazine macrocycles. Further selective oxidation of the sulfur atom between two phenylene rings afforded sulfoxide‐ and sulfone‐linked corona[5]arenes in good yields. All corona[5]arenes synthesized adopted similar 1,2,4‐alternate conformational structures forming pentagonal cavities. The cavity sizes and the electronic properties such as redox potentials, which were measured with CV and DPV, were regulated by the combination of bridging units. As electron‐deficient macrocycles, the acquired corona[3]arene[2]tetrazines acted as highly selective hosts to form complexes with the hydrogen‐bonded dimer of dihydrogen phosphate through cooperative anion‐π interactions.

X‐ray photoelectron spectroscopy (XPS) is an indispensable technique in modern materials science. A literature survey reveals that in the vast majority of cases an incorrect referencing of the binding energy scale is used, neglecting warnings that have been formulated from the early days of the technique. The purpose of this Viewpoint is to highlight the existing problems and suggest ways forward.

Abstract

X‐ray photoelectron spectroscopy (XPS) is an indispensable technique in modern materials science for the determination of chemical bonding as evidenced by more than 10 000 XPS papers published annually. A literature survey reveals that in the vast majority of cases an incorrect referencing of the binding energy scale is used, neglecting warnings that have been formulated from the early days of the technique. Consequences for the data reliability are disastrous and decades of XPS work require revisiting. The purpose of this Viewpoint is to highlight the existing problems, review the criticism and suggest ways forward.

The more the merrier: Phase separation triggers the stepwise oligomerization of two building blocks generating a library of dynamic species, leading to a structurally diverse, complex mixture of molecules. In contrast only two thermodynamically stable products are obtained with no phase separation.

Abstract

Chemical reactions occurring within liquid‐liquid phase separated systems drive numerous biological processes and have likely been involved in the emergence of first cellular compartments. Herein we report a reaction whose product distribution is drastically affected by the presence of a liquid‐liquid interface. Under phase separated conditions, the system produces a dynamic library of increasingly complex oligomeric structures. This reactivity is in sharp contrast to results under homogeneous conditions; when there is no phase separation only two thermodynamically stable products are formed. The reactivity observed using phase separated conditions stems from generating a dynamic out‐of‐equilibrium self‐assembling system. This work shows that relatively complex oligomeric products that would not be otherwise easily accessible can be made by biphasic out‐of‐equilibrium processes.

Controlling material properties with light is key for the development of optical technologies. In this context, molecular photoswitches have become powerful tools to induce structural changes, which can be translated and amplified to the macroscopic materials and device level. The implementation of photoswitches into a variety of materials, ranging from amorphous to crystalline, and their multifaceted operating principles are reviewed.

Abstract

Incorporating molecular photoswitches into various materials provides unique opportunities for controlling their properties and functions with high spatiotemporal resolution using remote optical stimuli. The great and largely still untapped potential of these photoresponsive systems has not yet been fully exploited due to the fundamental challenges in harnessing geometrical and electronic changes on the molecular level to modulate macroscopic and bulk material properties. Herein, progress made during the past decade in the field of photoswitchable materials is highlighted. After pointing to some general design principles, materials with an increasing order of the integrated photoswitchable units are discussed, spanning the range from amorphous settings over surfaces/interfaces and supramolecular ensembles, to liquid crystalline and crystalline phases. Finally, some potential future directions are pointed out in the conclusion. In view of the exciting recent achievements in the field, the future emergence and further development of light‐driven and optically programmable (inter)active materials and systems are eagerly anticipated.

Nature, Published online: 22 January 2020; doi:10.1038/d41586-019-03949-8

Signalling from the sympathetic nervous system of mice when subjected to stress leads to the depletion of a stem-cell population in their hair follicles. This discovery sheds light on why stress turns hair prematurely grey.

Chalcogen binding motifs: The synthesis of three new families of sulfur, selenium, and tellurium‐based chalcogen binding (ChB) motifs is reported. The stability of the chalcophene binding motifs has enabled the determination of the association constants for ChB halide anion binding in the polar aprotic solvent THF by ¹H, ⁷⁷Se, and ¹²⁵Te NMR experiments.

Abstract

The utilization of neutral receptors for the molecular recognition of anions based on chalcogen bonding (ChB) is an undeveloped area of host‐guest chemistry. In this manuscript, the synthesis of two new families of sulfur, selenium, and tellurium‐based ChB binding motifs are reported. The stability of the thiophene, selenophene, and tellurophene binding motifs has enabled the determination of the association constants for ChB halide anion binding in the polar aprotic solvent THF by ¹H, ⁷⁷Se, and ¹²⁵Te NMR experiments. Two different aromatic cores are used and one or two Ch‐binding motifs are incorporated with the purpose of encapsulating the anion, offering up to two concurrent chalcogen bonds. Theoretical calculations and NMR experiments reveal that, for S and Se receptors, hydrogen‐bonding interactions involving the acidic H atom adjacent to the chalcogen atom are energetically favored over the ChB interaction. However, for the tellurophene binding motif, the σ‐hole interaction is competitive and more favored than the hydrogen bond.

It takes two to tango: A rare example of substrate‐induced dimerization assembly of chiral macrocycle catalysts is presented. It enables a highly cooperative hydrogen‐bonding activation network for efficient and enantioselective transformation.

Abstract

An artificial system of substrate‐induced dimerization assembly of chiral macrocycle catalysts enables a highly cooperative hydrogen‐bonding activation network for efficient enantioselective transformation. These macrocycles contain two thiourea and two chiral diamine moieties and dimerize with sulfate to form a sandwich‐like assembly. The macrocycles then adopt an extended conformation and reciprocally complement the hydrogen‐bonding interaction sites. Inspired by the guest‐induced dynamic assembly, these macrocycles catalyze the decarboxylative Mannich reaction of cyclic aldimines containing a sulfamate heading group. The imine substrate can be activated toward nucleophilic attack of β‐ketoacid by a cooperative hydrogen‐bonding network enabled by sulfamate‐induced dimerization assembly of the macrocycle catalysts. Highly efficient (>95 % yield in most cases) and enantioselective (up to 97.5:2.5 er) transformation of a variety of substrates using only 5 mol % macrocycle was achieved.

Although coenzymes play key roles in biotic metabolism, they have not been in the focus as elements in protometabolism nor has their possible prebiotic generation been discussed in detail. This Review provides a conceptual view of the role of coenzymes with respect to known theories of protometabolism and their incorporation into the RNA world hypothesis.

Abstract

The evolution of coenzymes, or their impact on the origin of life, is fundamental for understanding our own existence. Having established reasonable hypotheses about the emergence of prebiotic chemical building blocks, which were probably created under palaeogeochemical conditions, and surmising that these smaller compounds must have become integrated to afford complex macromolecules such as RNA, the question of coenzyme origin and its relation to the evolution of functional biochemistry should gain new impetus. Many coenzymes have a simple chemical structure and are often nucleotide‐derived, which suggests that they may have coexisted with the emergence of RNA and may have played a pivotal role in early metabolism. Based on current theories of prebiotic evolution, which attempt to explain the emergence of privileged organic building blocks, this Review discusses plausible hypotheses on the prebiotic formation of key elements within selected extant coenzymes. In combination with prebiotic RNA, coenzymes may have dramatically broadened early protometabolic networks and the catalytic scope of RNA during the evolution of life.

Abstract

Ranging from 2D assemblies to peptide amphiphile‐based biomaterials, Prof. Samuel Stupp and his team have enriched the scientific community with many breakthroughs in the field of supramolecular self‐assembly. This Interview offers the unique possibility to share some highlights along his journey, providing also a glimpse to his vision of the future of supramolecular chemistry. Interdisciplinarity is an integral part of Prof. Stupp's research philosophy, and, using his own words, “it is the only way to understand the complex universe around us and help society along the way”. What a great guideline to us all!

Hydrogels are soft materials with a broad application area and a bright future as responsive materials. They contain a molecular network that can be made from crosslinked macromolecules, or small molecules that form a network through noncovalent interactions. These hydrogel classes outperform each other on properties such as reversibility, mechanical robustness, predictability, responsiveness, or adaptation.

Abstract

Hydrogels are fascinating soft materials with unique properties. Many biological systems are based on hydrogel‐like structures, underlining their versatility and relevance. The properties of hydrogels strongly depend on the structure of the building blocks they are composed of, as well as the nature of interactions between them in the network structure. Herein, gel networks made by supramolecular interactions are compared to covalent macromolecular networks, drawing conclusions about their performance and application as responsive materials.

An integrated molecular machine setup allows the transmission of potential energy from a motor unit onto a covalently connected, distant, and sterically strongly encumbered biaryl receiver. By action of the motor unit, single‐bond rotation of the receiver is strongly accelerated and forced to proceed unidirectionally.

Abstract

Light‐driven molecular motors possess immense potential as central driving units for future nanotechnology. Integration into larger molecular setups and transduction of their mechanical motions represents the current frontier of research. Herein we report on an integrated molecular machine setup allowing the transmission of potential energy from a motor unit onto a remote receiving entity. The setup consists of a motor unit connected covalently to a distant and sterically encumbered biaryl receiver. By action of the motor unit, single‐bond rotation of the receiver is strongly accelerated and forced to proceed unidirectionally. The transmitted potential energy is directly measured as the extent to which energy degeneration is lifted in the thermal atropisomerization of this biaryl. Energy degeneracy is reduced by more than 1.5 kcal mol⁻¹, and rate accelerations of several orders of magnitude in terms of the rate constants are achieved.

Nature, Published online: 10 January 2020; doi:10.1038/d41586-020-00029-0

But the scientific literature remains silent on lasagna.

Tactical combinations (TCs) are two-step reaction sequences that first, in a retrosynthetic direction, complexify the target structure but, by doing so, enable significant structural simplification in subsequent steps. TCs are often hard to identify, and only a few hundred have been cataloged to date. This work shows that computers can now discover TCs having no literature precedent systematically and in large numbers, in effect unlocking new and elegant synthetic approaches.

Revealing the contribution of - stacking interactions in supramolecular assembly is important for understanding the intrinsic nature of molecular assembly fundamentally. However, because they are much weaker than covalent bonds, - stacking interactions are usually ignored in the construction of porous materials. Obtaining stable porous materials that are only dependent on - stacking interactions, despite being very challenging, could address this concern. Here, we present a porous supramolecular framework (-1) stabilized only by intermolecular - stacking interactions. -1 shows good thermal and chemical stability not only in various organic solvents but also in aqueous solution in a broad pH range. Furthermore, featuring one-dimensional channels with dangling thiolate groups, -1 exhibits excellent Hg²⁺ removal performance, with adsorption capacity as high as 786.67 mg g^–1 and an adsorption ratio as high as 99.998%. In addition, -1 also shows high adsorption selectivity to Hg²⁺ in the presence of a series of interfering ions.