Oleg Borodin

Many approaches to the origin of life focus on how the molecules found in biology might be made in the absence of biological processes, from the simplest plausible starting materials. Another approach could be to view the emergence of the chemistry of biology as process whereby the environment effectively directs...

Self‐assembled organic semiconducting nanostructures possessing tunable optical, electronic, and mechanical properties are ideal active components for the next generation of organic electronic devices. An overview of recent achievements in nano‐/microfabrication of supramolecular (opto) electronic devices by making use of unconventional technologies is presented, by highlighting the challenges and opportunity toward the emergence of a viable technology based on supramolecular nanostructures.

Abstract

The scientific effort toward achieving a full control over the correlation between structure and function in organic and polymer electronics has prompted the use of supramolecular interactions to drive the formation of highly ordered functional assemblies, which have been integrated into real devices. In the resulting field of supramolecular electronics, self‐assembly of organic semiconducting materials constitutes a powerful tool to generate low‐dimensional and crystalline functional architectures. These include 1D nanostructures (nanoribbons, nanotubes, and nanowires) and 2D molecular crystals with tuneable and unique optical, electronic, and mechanical properties. Optimizing the (opto)electronic properties of organic semiconducting materials is imperative to harness such supramolecular structures as active components for supramolecular electronics. However, their integration in real devices currently represents a significant challenge to the advancement of (opto)electronics. Here, an overview of the unconventional nanofabrication techniques and device configurations to enable supramolecular electronics to become a real technology is provided. A particular focus is put on how single and multiple supramolecular fibers and gels as well as supramolecularly engineered 2D materials can be integrated into novel vertical or horizontal junctions to realize flexible and high‐density multifunctional transistors, photodetectors, and memristors, exhibiting a set of new properties and excelling in their performances.

The influence that the insertion method (post‐insertion vs. pre‐insertion) of “two‐wall” and “four‐wall” aryl‐extended calix[4]pyrrole carriers into liposomal membranes exerts on their chloride transport properties using the HPTS assay is described. The pre‐insertion method allowed a more accurate and reliable comparison of the transport activities of these carriers, being greater for the “four‐wall” carrier.

Abstract

We disclose the results of our investigations on the influence that the insertion method of aryl‐extended calix[4]pyrrole into liposomal membranes exerts on their properties as anion carriers. We use the standard HPTS assay to assess the transport properties of the carriers. We show that the post‐insertion of the carrier, as DMSO solution, assigns better transport activities to the “two‐wall” α,α‐aryl‐extended calix[4]pyrrole 1 compared to the “four‐wall” α,α,α,α‐counterpart 2. Notably, opposite results were obtained when the carriers were pre‐inserted into the liposomal membranes. We assign this difference to an improved incorporation of carrier 2 into the membrane when delivered by the pre‐insertion method. On the other hand, carrier 1 shows comparable levels of transport independently of the method used for its incorporation. Thus, an accurate comparison of the chloride transport activities featured by these two carriers demands their pre‐incorporation in the liposomal membranes. In contrast, using the lucigenin assay with the pre‐insertion method both carriers displayed similar transport efficiencies.

Competition leading to partnership: Study of aromatic bis‐urea derivatives in DMSO reveals their unexpectedly high acidity (pK _a≈14). Consequently, partial proton transfer occurs in their reaction with basic anions (AcO⁻ and H₂PO₄ ⁻). This process was quantitatively accounted for in the course of anion binding studies. Reliable stability constants of anion complexes (1:1 and 1:2, receptor/anion) were determined. Factors defining the anion binding properties of the studied ligand series are discussed.

Abstract

A series of aromatic bis‐urea derivatives was prepared and their proton dissociation, as well as anion binding properties in DMSO were investigated. To this end, UV/Vis and ¹H NMR spectroscopies and computational methods were employed. The synthesized molecules differed in the relative position of the urea moieties (ortho‐ and meta‐derivatives) and in the functional groups (−H, −CH₃, −OCH₃, −NO₂) in the para‐position of the pendant phenyl groups. Remarkably high acidities of the compounds (logK ₁ ^H≈14), were ascribed primarily to the stabilizing effect of the aromatic subunits. Quantum chemical calculations corroborated the conclusions drawn from experimental data and provided information from the structural point of view. Knowledge regarding protonation properties proved to be essential for reliable quantitative determination of anion binding affinities. Studied receptors were selective for acetate and dihydrogen phosphate among several anions. Formation of their complexes of 1:1 and 1:2 (ligand/anion) stoichiometries was quantitatively characterized. Proton transfer was taken into account in the course of data analysis, which was especially important in the case of AcO⁻. ortho‐Receptors were proven to be more efficient acetate binders, achieving coordination with all four NH groups. The meta‐analogues preferred dihydrogen phosphate, which acted as both hydrogen bond donor and acceptor. Cooperative binding was detected in the case of 1:2 H₂PO₄ ⁻ complexes, which was assigned to formation of interanionic hydrogen bonds.

The supramolecular polymerization of an acid‐sensitive pyridyl‐based ligand (L1) bearing a photoresponsive azobenzene moiety has been elucidated via mechanistic studies. Addition of trifluoroacetic acid (TFA) leads to the transformation of the anti‐parallel H‐bonded fibers of L1 in MCH into superhelical braid‐like fibers stabilized by H‐bonding of parallel‐stacked monomer units. Interestingly, L1‐dimers held together by unconventional pyridine‐TFA N···H···O bridges represent the main structural elements of the assembly. UV light irradiation causes a strain‐driven disassembly and subsequent aggregate reconstruction that ultimately leads to short fibers. Our results have enabled us to understand the mechanism of mutual influence of acid and light stimuli on supramolecular polymerization processes, thus opening up new possibilities to design advanced stimuli‐triggered supramolecular systems.

The balance between hydrogen bonding and hydrophobic interactions dictates nanofiber obtained by self‐assembly of many low molecular weight gelators. In here, we demonstrate that thermal history can be used as a simple route of controlling structure and function in supramolecular gels. Using a model aromatic peptide amphiphile, Fmoc‐tyrosyl‐leucine and a combination of fluorescence, FTIR, CD and NMR spectroscopy, we show that the balance of these interactions can be adjusted by varying thermal history followed by supramolecular locking in the gel state. Depending on the thermal history that the gelators are exposed to, three regimes can be identified regarding the balance between H‐bonding and aromatic stacking interactions, resulting in different modes of supramolecular packing. Consequently, non‐equilibrium gels can be obtained with customizable properties, including supramolecular chirality, gel stiffness and proteolytic stability, highlighting the possibility of obtaining a range of supramolecular architectures from a single molecular structure.

New additions to the family: Insights into the reductive functionalization of fullerenes and its application for preparing highly sophisticated fullerene architectures including an unprecedented 1,4‐cycloadduct are presented. Investigations on the exohedral reactivity of fullerenides and the scope of different electrophiles as addition partners leading to a series of fullerene adducts and cycloadducts involving either 1,2‐ or 1,4‐addition patterns are reported.

Abstract

A systematic screening study of the exohedral reactivity of the reduced fullerenes (fullerenides) C₆₀ ²⁻ and C₆₀ ^⋅− is reported. These doubly and singly negatively charged carbon cages were prepared by two‐fold reduction of C₆₀ with potassium, leading to K₂C₆₀, or by in situ monoreduction with the radical anion of benzonitrile PhCN^⋅−, respectively. Several series of electrophiles, including geminal and distant dihalides, benzyl bromides, and diazonium compounds, were employed as addition partners. In general, the investigated bromides proved to be the most suitable reaction partners. A series of fullerene adducts and cycloadducts involving either 1,2‐ or 1,4‐addition patterns, depending on the precise architecture and the steric demand of the addends, were synthesized and fully characterized. Some of the reaction products are unprecedented and inaccessible forms of neutral C₆₀. The fullerenide chemistry presented here closely resembles related reactions of graphenides and carbon nanotubides, which are the most powerful methods for the functionalization of these macromolecular forms of synthetic carbon allotropes (SCAs). Activation of C₆₀ by negative charging represents a little explored concept of fullerene chemistry, providing both new insights of fullerene reactivity itself and new types of exohedral derivatives.

The modulation of higher‐order behaviour in model protocell communities was investigated. Enzyme‐loaded silica colloidosomes are spontaneously engulfed by magnetic Pickering emulsion (MPE) droplets containing complementary enzyme substrates to initiate a range of processes within the host–guest protocells.

Abstract

Collective behaviour in mixed populations of synthetic protocells is an unexplored area of bottom‐up synthetic biology. The dynamics of a model protocell community is exploited to modulate the function and higher‐order behaviour of mixed populations of bioinorganic protocells in response to a process of artificial phagocytosis. Enzyme‐loaded silica colloidosomes are spontaneously engulfed by magnetic Pickering emulsion (MPE) droplets containing complementary enzyme substrates to initiate a range of processes within the host/guest protocells. Specifically, catalase, lipase, or alkaline phosphatase‐filled colloidosomes are used to trigger phagocytosis‐induced buoyancy, membrane reconstruction, or hydrogelation, respectively, within the MPE droplets. The results highlight the potential for exploiting surface‐contact interactions between different membrane‐bounded droplets to transfer and co‐locate discrete chemical packages (artificial organelles) in communities of synthetic protocells.

Hydrogen electrocatalysts are essential in electrochemical transformation reactions. Understanding the hydrogen reaction kinetics and mechanisms is critical for catalyst design and development. A detailed description of hydrogen evolution and oxidation reaction (HER/HOR) kinetics and mechanisms, and a brief summary about the recent development of hydrogen electrocatalysts and recent advances in understanding the origin of pH‐dependent HER/HOR are presented.

Abstract

Electrochemical energy storage and conversion through hydrogen is essential for a clean and sustainable energy system. Highly efficient hydrogen electrocatalysts play a key role in the electrochemical transformation reactions. A comprehensive understanding of the hydrogen reaction kinetics and mechanisms is critical for the catalyst design and development. Especially pH‐dependent hydrogen evolution and oxidation reaction (HER/HOR) kinetics receives increasing interest, and understanding its origin adds new knowledge to fundamental hydrogen electrocatalysis. Here, a detailed description of kinetic analysis and reaction mechanisms for HER/HOR, and a brief summary about recent development of highly efficient and cost‐effective hydrogen electrocatalysts are presented. Lastly, recent advances in the fundamental understanding of pH‐dependent hydrogen electrocatalysis are discussed.

A metal phosphonate‐derived strategy is designed for constructing P‐doped carbon‐confined cobalt phosphides (Co‐P@PC) by converting a 1D Co‐based phosphonate without extra P‐containing agent. The Co‐P@PC exhibits excellent electrocatalytic activity (1.60 V cell voltage at the current density of 10 mA cm⁻²) and durability for water splitting, benefiting from the synergistic effect between the active cobalt phosphides and P‐doped carbon matrix.

Abstract

The development of low‐cost and highly efficient electrocatalysts via an eco‐friendly synthetic method is of great significance for future renewable energy storage and conversion systems. Herein, cobalt phosphides confined in porous P‐doped carbon materials (Co‐P@PC) are fabricated by calcinating the cobalt‐phosphonate complex formed between 1‐hydroxyethylidenediphosphonic acid and Co(NO₃)₂ in alkaline solution. The P‐containing ligand in the complex acts as the carbon source as well as in situ phosphorizing agent for the formation of cobalt phosphides and doping P element into carbon material upon calcination. The Co‐P@PC exhibits high activity for all‐pH hydrogen evolution reaction (overpotentials of 72, 85, and 76 mV in acidic, neutral, and alkaline solutions at the current density of 10 mA cm⁻²) and oxygen evolution reaction in alkaline solution (an overpotential of 280 mV at the current density of 10 mA cm⁻²). The alkaline electrolyzer assembled from the Co‐P@PC electrodes delivers the current density of 10 mA cm⁻² at the voltage of 1.60 V with a durability of 60 h. The excellent activity and long‐term stability of the Co‐P@PC derives from the synergistic effect between the active cobalt phosphides and the porous P‐doped carbon matrix.

Crowned: The films of large π‐extended molecular crowns and their supramolecular complexes with fullerenes, which served as the active layer, generated photocurrents under light irradiation. These molecular crowns bearing curved nanographenes as the sidewalls were synthesized in gram‐scale quantities. Their photophysical properties were investigated by steady‐state and time‐resolved fluorescence spectroscopy.

Abstract

This study presents synthesis and characterizations of two novel curved nanographenes that strongly bind with fullerene C₆₀ to form photoconductive heterojunctions. Films of the self‐assembled curved nanographene/fullerene complexes, which served as the photoconductive layer, generated a significant photocurrent under light irradiation. Gram‐scale quantities of these curved nanographenes (TCR and HCR) as the “crown” sidewalls can be incorporated into a carbon nanoring to form molecular crowns, and the molecular structure of C₆₀@TCR is determined by single‐crystal X‐ray diffraction. The UV/Vis absorption and emission spectra, and theoretical studies revealed their unique structural features and photophysical properties. Time‐resolved spectroscopic results clearly suggest fast photoinduced electron transfer process in the supramolecular heterojunctions.

Janus‐faced amino alcohols: The fate of the most ancient oligonucleotide sequences born in a strongly acidic prebiotic broth could be decided by a delicate balance between covalent and non‐covalent binding of amino‐alcohols.

Abstract

Alkylation of RNA oligonucleotides by the amino alcohols 2‐amino‐2‐hydroxymethyl‐propane‐1,3‐diol (commonly known as Tris‐base) and 2‐amino‐2‐methyl‐1‐propanol has been observed in strongly acidic environments. The reaction occurs according to a carbocationic mechanism and is time‐, temperature‐, concentration‐ and, strictly, pH‐dependent. Our results suggest that amino alcohols present in the prebiotic mix could not only alter the chemical composition of the oligonucleotides formed on dry land under hydrothermal conditions, but, more importantly, they could protect the first informational polymers from degradation.

Shear-induced assembly of a transient yet highly stretchable hydrogel based on pseudopolyrotaxanes

Shear-induced assembly of a transient yet highly stretchable hydrogel based on pseudopolyrotaxanes, Published online: 01 April 2019; doi:10.1038/s41557-019-0235-8

Synthetic dissipative systems, formed by out-of-equilibrium self-assembly processes, can mimic some of the properties of biological systems, but often show poor mechanical performance. Now, a shear-induced transient hydrogel has been prepared that is also highly stretchable. The system is based on coordination interactions between Cu(ii) centres and the pendant carboxylate groups of a pseudopolyrotaxane.

Borocarbonitrides, (B_xC_yN_z) as a metal‐free electrocatalyst, exhibit superior activity in hydrogen generation. Carbon‐rich B_xC_yN_z contains more pyridinic and pyrollic nitrogens and a greater percentage of BC bonds with low proportion of BN domains and thus shows efficiency in the hydrogen evolution reaction by enhancing its conductivity. Excess of N substitution increases the electron population in the conduction bands to facilitate electrocatalysis.

Abstract

Hydrogen generation by water splitting is clearly a predominant and essential strategy to tackle the problems related to renewable energy. In this context, the discovery of proper catalysts for electrochemical and photochemical water splitting assumes great importance. There is also a serious intent to eliminate platinum and other noble metal catalysts. To replace Pt by a non‐metallic catalyst with desirable characteristics is a challenge. Borocarbonitrides, (B_xC_yN_z) which constitutes a new class of 2D material, offer great promise as non‐metallic catalysts because of the easy tunability of bandgap, surface area, and other electronic properties with variation in composition. Recently, B_xC_yN_z composites with excellent electrochemical and photochemical hydrogen generation activities have been found, especially noteworthy being the observation that B_xC_yN_z with a carbon‐rich composition or its nanocomposites with MoS₂ come close to Pt in electrocatalytic properties, showing equally good photochemical activity.

Chloride carriers as cotransporters for organic ion pairs: Calix[6]arene tris(thio)ureas, bearing a cavity that can accommodate primary ammonium ions, can perform the cotransport of PrNH₃Cl across a lipid bilayer, as well as Cl⁻/NO₃ ⁻ antiport. The advantage of the cavity is highlighted by comparing calixarenes to receptors without a cavity, and by attempting to transport bulkier alkylammonium ions, which cannot be complexed in the cavity.

Abstract

Given the biological importance of organic cations, the facilitated transport of organic ion pairs could find many applications. Calix[6]arene tris(thio)ureas, which possess a cavity that can accommodate primary ammonium ions, can not only act as carriers for Cl⁻/NO₃ ⁻ antiport but can also perform the cotransport of PrNH₃Cl. Transport was monitored by fluorescence spectroscopy and the presence of the different species inside the vesicles was characterized by ¹H and ³⁵Cl NMR experiments involving shift reagents. The cotransport of PrNH₃Cl was also observed by receptors deprived of a cavity, but the presence of the cavity conveys an advantage, as the cotransport by calix[6]arenes was observed to be more efficient than the Cl⁻/NO₃ ⁻ antiport, which is not the case with receptors without a cavity. The role played by the cavity was further highlighted by the disappearance of this advantage when using a bulky ammonium ion, which cannot be complexed within the cavity.

A top trap: Two topologically distinct supramolecular polymers, circular and helically folded nanofibers, were formed from highly polymerizable azobenzene‐functionalized supramolecular rosettes. The nanorings exhibited higher resistance toward UV‐induced deformation over open‐ended supramolecular polymers, but opened up and formed elongated supramolecular polymers in more polar media (see picture), thus functioning as a topological kinetic trap.

Abstract

Topological features of one‐dimensional macromolecular chains govern the properties and functionality of natural and synthetic polymers. To address this issue in supramolecular polymers, we synthesized two topologically distinct supramolecular polymers with intrinsic curvature, circular and helically folded nanofibers, from azobenzene‐functionalized supramolecular rosettes. When a mixture of circular and helically folded nanofibers was exposed to UV light, selective unfolding of the latter open‐ended supramolecular polymers was observed as a result of the curvature‐impairing internal force produced by the trans‐to‐cis photoisomerization of the azobenzene. This distinct sensitivity suggests that the topological features of supramolecular polymers define their mechanical stability. Furthermore, the exposure of circular supramolecular polymers in more polar media to UV irradiation resulted in ring opening followed by chain elongation, thus demonstrating that the circular supramolecular polymer can function as a topological kinetic trap.

Reaction dynamics: As molecular systems are in constant motion, it is essential to get more information on their dynamics, including formation of new bonds, stereomutations, or molecular recognition. Exchange NMR techniques help to elucidate both bond‐breaking and non‐bond‐breaking events in solution and the solid phase.

Abstract

Detailed mechanistic information is crucial to our understanding of reaction pathways and selectivity. Dynamic exchange NMR techniques, in particular 2D exchange spectroscopy (EXSY) and its modifications, provide indispensable intricate information on the mechanisms of organic and inorganic reactions and other phenomena, for example, the dynamics of interfacial processes. In this Review, key results from exchange NMR studies of small molecules over the last few decades are systemised and discussed. After a brief introduction to the theory, the key types of dynamic processes are identified and fundamental examples given of intra‐ and intermolecular reactions, which, in turn, could involve, or not, bond‐making and bond‐breaking events. Following that logic, internal molecular rotation, intramolecular stereomutation and molecular recognition will first be considered because they do not typically involve bond breaking. Then, rearrangements, substitution‐type reactions, cyclisations, additions and other processes affecting chemical bonds will be discussed. Finally, interfacial molecular dynamics and unexpected combinations of different types of fluxional processes will also be highlighted. How exchange NMR spectroscopy helps to identify conformational changes, coordination and molecular recognition processes as well as quantify reaction energy barriers and extract detailed mechanistic information by using reaction rate theory in conjunction with computational techniques will be shown.

Soft materials: The important role of solvents in manipulating the chirality of self‐assembled systems is discussed in this Concept article. Molecular self‐assembly in specific solvents might undergo the chirality transfer, exhibiting a chiral induction effect (see scheme).

Abstract

Supramolecular self‐assembly stands for the spontaneous aggregation of small organic compounds or polymers into ordered structures at any scale. When being induced by inherent molecular chiral centers or ambient asymmetric factors, asymmetric spatial arrangement between building units shall occur, which is defined as supramolecular chirality. Except for molecular design, utilizing external stimulus factors to tune supramolecular chirality is a promising approach. In this Concept article, we particularly discuss the important role of solvents in manipulating the chirality of self‐assembled systems. The impact of solvents on the chirality is generally based on three properties of solvents, i.e., chirality, polarity, and active coassembly with building blocks. Molecular self‐assembly in chiral solvents could undergo the chirality transfer, exhibiting a chiral induction effect. Solvent polarity often determines intermolecular orientation. As a consequence, those building blocks with both polar and apolar segments might change their chirality depending on the solvent polarity. We elaborate the active participation of solvent molecules into ordered structures together with building blocks, where solvents and building blocks exhibit a coassembly manner. By specific treatments such as heating and cooling, solvents could be released or re‐entrapped, allowing a smart control over supramolecular chirality. The solvent effect in manipulating two‐dimensional chiral self‐assemblies is then discussed. The perspective and future development in this research field are presented at last.

Stuck like glue: Non‐enzymatic ligation of 5′‐phosphorimidazolide RNAs programmed by short splint (“guide”) RNAs allows assembly of an active RNA polymerase ribozyme from RNA oligomer fragments no longer than 30 nucleotides in a “single pot” reaction.

Abstract

Central to the “RNA world” hypothesis of the origin of life is the emergence of an RNA catalyst capable of RNA replication. However, possible replicase ribozymes are quite complex and were likely predated by simpler non‐enzymatic replication reactions. The templated polymerisation of phosphorimidazolide (Imp) activated ribonucleotides currently appears as the most tractable route to both generate and replicate short RNA oligomer pools from which a replicase could emerge. Herein we demonstrate the rapid assembly of complex ribozymes from such Imp‐activated RNA fragment pools. Specifically, we show assembly of a newly selected minimal RNA polymerase ribozyme variant (150 nt) by RNA templated ligation of 5’‐2‐methylimidazole‐activated RNA oligomers <30 nucleotides long. Our results provide support for the possibility that complex RNA structures could have emerged from pools of activated RNA oligomers and outlines a path for the transition from non‐enzymatic/chemical to enzymatic RNA replication.

Swap around: Non‐covalent attractive forces in pseudopeptidic building blocks are used to guide the product distribution in a dynamic library towards topologically more complex compounds that are in principle unexpected. The interactions are highly dependent on molecular architecture and media, meaning that effective recognition can be altered by minimal structural or environmental changes.

Abstract

Molecular recognition is essential in many chemical and biological processes. Studying the behavior of pseudopeptides using dynamic covalent chemistry allows the exploration of a wide range of structural components and molecular interactions with minimal synthetic effort. Herein, we describe how non‐covalent attractive forces in pseudopeptidic building blocks can successfully guide the product distribution in a dynamic library towards topologically more complex compounds that are in principle not expected. The interactions described herein are highly dependent on molecular architecture and media so effective recognition can be altered by just minimal structural or environmental changes. Thus, the chemical and constitutional information contained in the respective building blocks is decoded and expressed through dynamic covalent and non‐covalent bonds in the assembly of either a single macrostructure or an ensemble of components with larger structural diversity. The understanding of supramolecular forces responsible for the component assembly in minimalistic systems can help to comprehend more complex bio‐related processes such as protein folding or protein−protein interactions.

Pore-forming small molecules offer a promising way to tackle cystic fibrosis

Pore-forming small molecules offer a promising way to tackle cystic fibrosis, Published online: 13 March 2019; doi:10.1038/d41586-019-00781-y

In cystic fibrosis, ion-transport abnormalities cause problems in many organs. A small molecule that forms cell-membrane pores allowing ion transport shows therapeutic promise in human cells and a model of the disease.