Oleg Borodin

Cycloparaphenylenes and their complexes in the gas phase : A straightforward method—(MA)LDI—is introduced to characterize CPPs and their host–guest complexes either with another ring size or with different fullerenes. The method enables the detection of thus far unknown complexes. Fragmentation experiments and DFT calculations provide insight into geometries, binding and fragmentation energies as well as charge location of CPP host–guest complexes.

Abstract

[n ]Cycloparaphenylenes ([n ]CPPs) with n =5, 8, 10 and 12 and their noncovalent ring‐in‐ring and [m ]fullerene‐in‐ring complexes with m =60, 70 and 84 have been studied by direct and matrix‐assisted laser desorption ionization ((MA)LDI) and density‐functional theory (DFT). LDI is introduced as a straightforward approach for the sensitive analysis of CPPs, free from unwanted decomposition and without the need of a matrix. The ring‐in‐ring system of [[10]CPP⊃[5]CPP]^+. was studied in positive‐ion MALDI. Fragmentation and DFT indicate that the positive charge is exclusively located on the inner ring, while in [[10]CPP⊃C₆₀]^+. it is located solely on the outer nanohoop. Positive‐ion MALDI is introduced as a new sensitive method for analysis of CPP⊃fullerene complexes, enabling the detection of novel complexes [[12]CPP⊃C_{60, 70 and 84}]^+. and [[10]CPP⊃C₈₄]^+.. Selective binding can be observed when mixing one fullerene with two CPPs or vice versa, reflecting ideal size requirements for efficient complex formation. Geometries, binding and fragmentation energies of CPP⊃fullerene complexes from DFT calculations explain the observed fragmentation behavior.

Green biosynthetic hydrogen: Approaches to engineer artificial hydrogen‐evolution catalysts are discussed in this review. These bioinorganic hybrids are based on the redesign of various natural proteins and the assemblies of molecular catalysts with polypeptide scaffolds. Important design considerations in the first coordination sphere and remote interactions around the active site in tuning the physical, catalytic, and mechanistic properties of these artificial biohybrids are also covered.

Abstract

Hydrogen is a clean and sustainable form of fuel that can minimize our heavy dependence on fossil fuels as the primary energy source. The need of finding greener ways to generate H₂ gas has ignited interest in the research community to synthesize catalysts that can produce H₂ by the reduction of H⁺. The natural H₂ producing enzymes hydrogenases have served as an inspiration to produce catalytic metal centers akin to these native enzymes. In this article we describe recent advances in the design of a unique class of artificial hydrogen evolving catalysts that combine the features of the active site metal(s) surrounded by a polypeptide component. The examples of these biosynthetic catalysts discussed here include i) assemblies of synthetic cofactors with native proteins; ii) peptide‐appended synthetic complexes; iii) substitution of native cofactors with non‐native cofactors; iv) metal substitution from rubredoxin; and v) a reengineered Cu storage protein into a Ni binding protein. Aspects of key design considerations in the construction of these artificial biocatalysts and insights gained into their chemical reactivity are discussed.

Nature, Published online: 08 June 2020; doi:10.1038/s41586-020-2406-6

Photoenzymatic enantioselective intermolecular radical hydroalkylation

Inspired by nature: Inspired by solar‐energy harvesting in biological systems, artificial membrane technologies are being increasingly applied in converting light to actively regulate proton and ion transport. During the past decades, artificial photo‐induced active transport systems defined as “chemical” and “physical” modes that are capable of transporting protons or metal ions have been successfully constructed. Toward practical, effective and selective light‐driven active ion transport, appropriate photoactive materials, structures and interfacial adjustments are still needed before artificial ion pumps become attractive for solar energy conversion and storage, bio‐interfaces and water treatment applications.

Abstract

Solar energy can be harvested by biological systems to regulate the directional transport of protons and ions across cells and organelles. Structural and functional bio‐mimic photo‐active ion nanofluidic conductors, usually in the forms of ion channels and ion pumps, have been increasingly applied to realize active ion transport. However, progress in attaining effective light‐driven active transport of ions (protons) has been constrained by the inherent limitations of membrane materials and their chemical and topological structures. Recent advances in the construction of photo‐responsive physical ion pump in all‐solid‐state membranes could potentially lead to new classes of membrane‐based materials for active ion transport. In this concept, the development of the state‐of‐the‐art technologies for manufacturing artificial light‐driven active ion transport systems are presented and discussed, which mainly involves the utilization of solar energy to realize two types of active ion transport, chemically and physically active ion transport. Afterward, we summarize the key factors towards culminating highly effective and selective membranes for active ion transport. To conclude, we highlight the promising application perspectives of this light‐driven active ion transport technique in the field of energy conversion, bio‐interfaces and water treatment.

Here we show how a simple inorganic salt can spontaneously form autocatalytic sets of replicating inorganic molecules that work via molecular recognition based on the {PMo12} ≡ [PMo12O40]3– Keggin ion, and {Mo36} ≡ [H3Mo57M6(NO)6O183(H2O)18]22– cluster. These small clusters are able to catalyze their own formation via an autocatalytic network, which...

Nature, Published online: 29 May 2020; doi:10.1038/d41586-020-01618-9

Abdelrahman Y. Fouda shares six things he learnt from interviewing online.

Nature, Published online: 27 May 2020; doi:10.1038/s41586-020-2278-9

Water splitting with an internal quantum efficiency of almost unity is achieved using a modified semiconductor photocatalyst that selectively promotes the hydrogen and oxygen evolution reactions on separate crystal facets.

Ribosomes can produce proteins in minutes and are largely constrained to proteinogenic amino acids. Here, we report highly efficient chemistry matched with an automated fast-flow instrument for the direct manufacturing of peptide chains up to 164 amino acids long over 327 consecutive reactions. The machine is rapid: Peptide chain elongation is complete in hours. We demonstrate the utility of this approach by the chemical synthesis of nine different protein chains that represent enzymes, structural units, and regulatory factors. After purification and folding, the synthetic materials display biophysical and enzymatic properties comparable to the biologically expressed proteins. High-fidelity automated flow chemistry is an alternative for producing single-domain proteins without the ribosome.

Nature Chemistry, Published online: 25 May 2020; doi:10.1038/s41557-020-0467-7

A naturally occurring stand-alone and intermolecular Diels–Alderase, MaDA, has been identified from Morus alba cell cultures. MaDA is a FAD-dependent enzyme, which catalyses the intermolecular [4+2] cycloaddition via a concerted but asynchronous pericyclic pathway between morachalcone A and a diene generated from moracin C. Characterization revealed that MaDA possesses good substrate promiscuity towards both dienes and dienophiles.

Many of us are alleviating the boredom of lockdown during COVID-19 by getting out and exercising. How does the body produce the energy it needs, is there any science behind ‘runner’s high’, and what causes the aches and pains afterwards? This month’s edition of Periodic Graphics in Chemical & Engineering News takes a look. View […]

Nature Chemistry, Published online: 18 May 2020; doi:10.1038/s41557-020-0477-5

Chemistry is now starting to embrace preprints, with more and more researchers in chemical and materials sciences posting their manuscripts online prior to peer review. Preprints can speed up the dissemination of scientific results and lead to more informal exchanges between researchers, hopefully accelerating the pace of research as a whole.

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.

Herein, we report the synthesis of three short‐chained anthracene strapped porphyrins and their corresponding endoperoxides, formed by a cycloaddition reaction between in situ generated singlet oxygen and the anthracene moiety. We also synthesized Zn(II)complexes of the strapped porphyrins. X‐ray crystallography and UV/Vis analysis confirmed macrocyclic distortion in the strapped systems.

The syntheses of short‐chained anthracene‐strapped porphyrins and their Zn(II)complexes are reported. The key synthetic step is a [2+2] condensation between a dipyrromethane and an anthracene bisaldehyde, 2,2'‐((anthracene‐9,10‐diylbis(methylene))bis(oxy))dibenzaldehyde. Following exposure to white light, self‐sensitized singlet oxygen and the anthracene moieties underwent [4+2] cycloaddition reactions to yield the corresponding endoperoxides. ¹H NMR studies demonstrate that the endoperoxide readily formed in [D]chloroform and decayed at 85 °C. X‐ray crystallography and absorption spectroscopy were used to confirm macrocyclic distortion in the parent strapped porphyrins and endoperoxides. Additionally, X‐ray crystallography indicated that endoperoxide formation occurred exclusively on the outside face of the anthracene moiety.

Switch and tune ! The trans –cis conformational switching of 2,2’‐bipyridine in response to acid was exploited to tune supramolecular polymerization processes. For this purpose, the aqueous self‐assembly of a bipyridine‐based linear bolaamphiphile that self‐assembles under standard conditions into cooperative supramolecular polymers was investigated. Interestingly, acid‐triggered protonation of the bipyridine unit induces a molecular conformational change from linear (trans ) to cis (V‐shaped) that leads to an attenuated supramolecular growth into shorter fibers.

Abstract

Besides their widespread use in coordination chemistry, 2,2’‐bipyridines are known for their ability to undergo cis–trans conformational changes in response to metal ions and acids, which has been primarily investigated at the molecular level. However, the exploitation of such conformational switching in self‐assembly has remained unexplored. In this work, the use of 2,2’‐bipyridines as acid‐responsive conformational switches to tune supramolecular polymerization processes has been demonstrated. To achieve this goal, we have designed a bipyridine‐based linear bolaamphiphile, 1 , that forms ordered supramolecular polymers in aqueous media through cooperative aromatic and hydrophobic interactions. Interestingly, addition of acid (TFA) induces the monoprotonation of the 2,2’‐bipyridine moiety, leading to a switch in the molecular conformation from a linear (trans ) to a V‐shaped (cis ) state. This increase in molecular distortion along with electrostatic repulsions of the positively charged bipyridine‐H⁺ units attenuate the aggregation tendency and induce a transformation from long fibers to shorter thinner fibers. Our findings may contribute to opening up new directions in molecular switches and stimuli‐responsive supramolecular materials.

Sheets and tubes : The syntheses of amphiphilic 5,5′,6,6′‐tetrachlorobenzimidacarbocyanine dye derivatives with aminopropanediol head groups, which only differ in stereochemistry (chiral enantiomers, meso form and conformer), are reported. The experiments demonstrate that the aggregation behaviour of compounds can be controlled solely by head group stereochemistry.

Abstract

The syntheses of novel amphiphilic 5,5′,6,6′‐tetrachlorobenzimidacarbocyanine (TBC) dye derivatives with aminopropanediol head groups, which only differ in stereochemistry (chiral enantiomers, meso form and conformer), are reported. For the achiral meso form, a new synthetic route towards asymmetric cyanine dyes was established. All compounds form J aggregates in water, the optical properties of which were characterised by means of spectroscopic methods. The supramolecular structure of the aggregates is investigated by means of cryo‐transmission electron microscopy, cryo‐electron tomography and AFM, revealing extended sheet‐like aggregates for chiral enantiomers and nanotubes for the mesomer, respectively, whereas the conformer forms predominately needle‐like crystals. The experiments demonstrate that the aggregation behaviour of compounds can be controlled solely by head group stereochemistry, which in the case of enantiomers enables the formation of extended hydrogen‐bond chains by the hydroxyl functionalities. In case of the achiral meso form, however, such chains turned out to be sterically excluded.

Reproducing to better understand : The calculational method electrostatically embedded generalized molecular fractionation is a full quantum mechanical (FQM) approach that can nearly reproduce the experimental optical absorption and emission spectra of the prototype fluorophore di(p‐methoxylphenyl)dibenzofulvene, which displays aggregation‐induced emission, in both condensed phases.

Abstract

Full quantum mechanical (FQM) calculation of the excited state of aggregation‐induced‐emission (AIE) materials is highly sought but still a challenging task. Herein, we employed the recently developed electrostatically embedded generalized molecular fractionation (EE‐GMF) method, a method based on the systematic fragmentation approach, to predict, for the first time, the spectra of a prototype AIE fluorophore: di(p‐methoxylphenyl)dibenzofulvene (FTPE). Compared to the single molecular or QM/MM calculations, the EE‐GMF method shows significantly improved accuracy, nearly reproducing the experimental optical spectra of FTPE in both condensed phases. Importantly, we show that the conventional restriction of the intramolecular rotation mechanism cannot fully account for AIE, whereas the two‐body intermolecular quantum mechanical interaction plays a crucial role in AIE.