Sebastian Beil

Nature, Published online: 13 November 2019; doi:10.1038/d41586-019-03231-x

Alkyne crossing: A new catalyst system for E‐selective cross‐dimerization of two terminal alkynes to access a variety of 1,3‐enynes is reported. A dichlorocobalt(II) complex bearing 2,9‐bis(2,4,6‐triisopropylphenyl)‐1,10‐phenanthroline serves as the catalyst. A catalytically active cobalt(0) complex was successfully isolated, strongly suggesting that cobalt(0/II) redox processes are involved in the catalytic cycle.

Abstract

A highly E‐selective cross‐dimerization of terminal alkynes with either terminal silylacetylenes, tert‐butylacetylene, or 1‐trimethylsilyloxy‐1,1‐diphenyl‐2‐propyne in the presence of a dichlorocobalt(II) complex bearing a sterically demanding 2,9‐bis(2,4,6‐triisopropylphenyl)‐1,10‐phenanthroline, activated with two equivalents of EtMgBr, gives a variety of (E)‐1,3‐enynes. A well‐characterized diolefin/cobalt(0) complex, with divinyltetramethyldisiloxane, acted as a catalytically active species without any activation, clearly indicating that a cobalt(0) species is involved in the catalytic cycle.

Segments: For the first time, two chiral conjugated macrocycles ([4]CAn_2,6 ), as (−)/(+)‐(12,4) carbon nanotube segments, are synthesized and the physical properties studied. The hoop‐shaped molecules can be directly viewed by an STM technique. Chiral enantiomers with (−)/(+) helicity of the [4]CAn_2,6 were successfully isolated. These new tubular chiral carbon nanotube segments exhibit strong circularly polarized luminescence (g _lum≈0.1).

Abstract

Carbon nanotubes (CNTs) have unusual physical properties that are valuable for nanotechnology and electronics, but the chemical synthesis of chirality‐ and diameter‐specific CNTs and π‐conjugated CNT segments is still a great challenge. Reported here are the selective syntheses, isolations, characterizations, and photophysical properties of two novel chiral conjugated macrocycles ([4]cyclo‐2,6‐anthracene; [4]CAn_2,6 ), as (−)/(+)‐(12,4) carbon nanotube segments. These conjugated macrocyclic molecules were obtained using a bottom‐up assembly approach and subsequent reductive elimination reaction. The hoop‐shaped molecules can be directly viewed by a STM technique. In addition, chiral enantiomers with (−)/(+) helicity of the [4]CAn_2,6 were successfully isolated by HPLC. The new tubular CNT segments exhibit large absorption and photoluminescence redshifts compared to the monomer unit. The carbon enantiomers are also observed to show strong circularly polarized luminescence (g _lum≈0.1). The results reported here expand the scope of materials design for bottom‐up synthesis of chiral macrocycles and enrich existing knowledge of their optoelectronic properties.

The biologically active nicotinamide adenine dinucleotide motif (NAD⁺) can facilitate reversible energy storage in lithium ion batteries (LIBs). Ex situ analysis and DFT calculations demonstrate that the intrinsically charged redox‐active system is capable of reversible lithium‐coupled electron transfer during the discharge/charge process.

Abstract

Nicotinamide adenine dinucleotide (NAD⁺) is one of the most well‐known redox cofactors carrying electrons. Now, it is reported that the intrinsically charged NAD⁺ motif can serve as an active electrode in electrochemical lithium cells. By anchoring the NAD⁺ motif by the anion incorporation, redox activity of the NAD⁺ is successfully implemented in conventional batteries, exhibiting the average voltage of 2.3 V. The operating voltage and capacity are tunable by altering the anchoring anion species without modifying the redox center itself. This work not only demonstrates the redox capability of NAD⁺, but also suggests that anchoring the charged molecules with anion incorporation is a viable new approach to exploit various charged biological cofactors in rechargeable battery systems.

Pyramid power: Owing to the drastic pyramidalization around the trivalent boron atom and the presence of a cationic phosphonium back‐side bridge, the Lewis acidity of the cage‐shaped 9‐bora‐10‐phosphonium triptycenes surpasses that of all trivalent boron Lewis acids generated to date.

Abstract

Bending the planar trigonal boron center of triphenylborane by connecting its aryl rings with carbon or phosphorus linkers gave access to a series of 9‐boratriptycene derivatives with unprecedented structures and reactivities. NMR spectroscopy and X‐ray diffraction of the Lewis adducts of these non‐planar boron Lewis acids with weak Lewis base revealed particularly strong covalent bond formation. The first Lewis adduct of a trivalent boron compounds with the Tf₂N⁻ anion illustrates the unrivaled Lewis acidity of these species. Increasing the pyramidalization of the boron center and using a cationic phosphonium linker resulted in an exceptional enhancement of Lewis acidity. Introduction of a phosphorus and a boron atom at each edge of a triptycene framework, allowed access to new bifunctional Lewis acid‐base 9‐phospha‐10‐boratriptycenes featuring promising reactivity for the activation of carbon‐halogen bonds.

Nature Communications, Published online: 08 November 2019; doi:10.1038/s41467-019-13072-x

Taking the strain: According to the isolated pentagon rule (IPR), fused pentagons in fullerene cages result in an increase in the local steric strain of the fullerene. The release of the strain arising from fused pentagons can be achieved by endohedral or exohedral functionalization. This Review gives an overview on fullerenes with fused pentagons, highlighting their role in the stability, electronic properties, and chemical reactivity of the fullerene cage.

Abstract

According to the isolated pentagon rule (IPR), for stable fullerenes, the 12 pentagons should be isolated from one another by hexagons, otherwise the fused pentagons will result in an increase in the local steric strain of the fullerene cage. However, the successful isolation of more than 100 endohedral and exohedral fullerenes containing fused pentagons over the past 20 years has shown that strain release of fused pentagons in fullerene cages is feasible. Herein, we present a general overview on fused‐pentagon‐containing (i.e. non‐IPR) fullerenes through an exhaustive review of all the types of fused‐pentagon‐containing fullerenes reported to date. We clarify how the strain of fused pentagons can be released in different manners, and provide an in‐depth understanding of the role of fused pentagons in the stability, electronic properties, and chemical reactivity of fullerene cages.

Silaboration of [1.1.1]propellane enabled direct introduction of B and Si functional groups onto the bicyclo[1.1.1]pentane (BCP) scaffold in high yield under mild, additive‐free conditions. The silaborated BCP can be obtained on a gram scale in a single step without the need for column chromatography purification, and is storable and easy to handle, providing a versatile synthetic intermediate for BCP derivatives.

Abstract

The silaboration of [1.1.1]propellane enables direct introduction of B and Si functional groups onto the bicyclo[1.1.1]pentane (BCP) scaffold in high yield under mild, additive‐free conditions. The silaborated BCP can be obtained on a gram‐scale in a single step without the need for column‐chromatographic purification, and is storable and easy to handle, providing a versatile synthetic intermediate for BCP derivatives. We also describe various conversions of the C−B/C−Si bonds on the BCP scaffold, including development of a modified Suzuki–Miyaura cross‐coupling reaction at the highly sterically hindered bridgehead sp³ carbon center of the BCP skeleton using a combination of highly activated BCP boronic esters, copper(I) oxide, and a PdCl₂(dppf) catalyst system.

Chemical pinching increases the distance between spin centers. This should result in reduced through‐space exchange spin coupling. In naphthalene‐bridged biscobaltocenes, the bridge plays a larger role than anticipated, with pinching leading to an increase of spin coupling. This is important for tuning interactions in spin wires for information transfer.

Abstract

Pinching molecules via chemical strain suggests intuitive consequences, such as compression at the pinched site and clothespin‐like opening of other parts of the structure. If this opening affects two spin centers, it should result in reduced communication between them. We show that for naphthalene‐bridged biscobaltocenes with competing through‐space and through‐bond pathways, the consequences of pinching are far less intuitive: despite the known dominance of through‐space interactions, the bridge plays a much larger role for exchange spin coupling than previously assumed. Based on a combination of chemical synthesis, structural, magnetic, and redox characterization, and a newly developed theoretical pathway analysis, we can suggest a comprehensive explanation for this non‐intuitive behavior. These results are of interest for molecular spintronics, as naphthalene‐linked cobaltocenes can form wires on surfaces for potential spin‐only information transfer.

Two‐in‐one : A three‐dimensional tetraphenylethene‐based octacationic cage (see structure), which successfully integrates the properties of fluorescence and host–guest recognition in one molecule, was synthesized in a straightforward manner. The cage was shown to bind polycyclic aromatic hydrocarbons, such as coronene, in organic media and the water‐soluble dye sulforhodamine 101 in aqueous media.

Abstract

We report the synthesis and characterization of a three‐dimensional tetraphenylethene‐based octacationic cage that shows host–guest recognition of polycyclic aromatic hydrocarbons (e.g. coronene) in organic media and water‐soluble dyes (e.g. sulforhodamine 101) in aqueous media through CH⋅⋅⋅π, π–π, and/or electrostatic interactions. The cage⊃coronene exhibits a cuboid internal cavity with a size of approximately 17.2×11.0×6.96 ų and a “hamburger”‐type host–guest complex, which is hierarchically stacked into 1D nanotubes and a 3D supramolecular framework. The free cage possesses a similar cavity in the crystalline state. Furthermore, a host–guest complex formed between the octacationic cage and sulforhodamine 101 had a higher absolute quantum yield (Φ _F=28.5 %), larger excitation–emission gap (Δλ _ex‐em=211 nm), and longer emission lifetime (τ =7.0 ns) as compared to the guest (Φ _F=10.5 %; Δλ _ex‐em=11 nm; τ =4.9 ns), and purer emission (Δλ _FWHM=38 nm) as compared to the host (Δλ _FWHM=111 nm).

Easy as 1, 2, 3: Under nickel catalysis, alkenyl carboxylic acids undergo selective 1,2‐diarylation. The resulting products can then be readily converted into diverse 1,2,3‐trifunctionalized motifs via classical carboxylic acid interconversions and modern decarboxylative cross‐couplings.

Abstract

A nickel‐catalyzed conjunctive cross‐coupling of alkenyl carboxylic acids, aryl iodides, and aryl/alkenyl boronic esters is reported. The reaction delivers the desired 1,2‐diarylated and 1,2‐arylalkenylated products with excellent regiocontrol. To demonstrate the synthetic utility of the method, a representative product is prepared on gram scale and then diversified to eight 1,2,3‐trifunctionalized building blocks using two‐electron and one‐electron logic. Using this method, three routes toward bioactive molecules are improved in terms of yield and/or step count. This method represents the first example of catalytic 1,2‐diarylation of an alkene directed by a native carboxylate group.

The recent research progress on antibacterial carbon‐based nanomaterials (CNMs) is reviewed, first focusing on the physicochemical parameters of CNMs, then introducing various antibacterial mechanisms and discussing the influence of physicochemical parameters on their antibacterial activity. Finally a conclusion is presented highlighting the current challenges and future perspectives for the development of more effective and safer antibacterial CNMs.

Abstract

The emergence and global spread of bacterial resistance to currently available antibiotics underscore the urgent need for new alternative antibacterial agents. Recent studies on the application of nanomaterials as antibacterial agents have demonstrated their great potential for management of infectious diseases. Among these antibacterial nanomaterials, carbon‐based nanomaterials (CNMs) have attracted much attention due to their unique physicochemical properties and relatively higher biosafety. Here, a comprehensive review of the recent research progress on antibacterial CNMs is provided, starting with a brief description of the different kinds of CNMs with respect to their physicochemical characteristics. Then, a detailed introduction to the various mechanisms underlying antibacterial activity in these materials is given, including physical/mechanical damage, oxidative stress, photothermal/photocatalytic effect, lipid extraction, inhibition of bacterial metabolism, isolation by wrapping, and the synergistic effect when CNMs are used in combination with other antibacterial materials, followed by a summary of the influence of the physicochemical properties of CNMs on their antibacterial activity. Finally, the current challenges and an outlook for the development of more effective and safer antibacterial CNMs are discussed.

Enzyme‐instructed supramolecular self‐assembly (EISA) is a new strategy to combat cancer. Differentiated by certain thresholds of enzyme activities between normal and cancer cells, EISA can selectively assemble in cancer cells only. This multistep dynamic process exhibits anticancer activity via the induction of dysfunction of cell activities, targeted drug delivery, and so on.

Abstract

Cancer remains one of the leading causes of death, which has continuously stimulated the development of numerous functional biomaterials with anticancer activities. Herein is reviewed one recent trend of biomaterials focusing on the advances in enzyme‐instructed supramolecular self‐assembly (EISA) with anticancer activity. EISA relies on enzymatic transformations to convert designed small‐molecular precursors into corresponding amphiphilic residues that can form assemblies in living systems. EISA has shown some advantages in controlling cell fate from three aspects. 1) Based on the abnormal activity of specific enzymes, EISA can differentiate cancer cells from normal cells. In contrast to the classical ligand–receptor recognition, the targeting capability of EISA relies on dynamic control of the self‐assembly process. 2) The interactions between EISA and cellular components directly disrupt cellular processes or pathways, resulting in cell death phenotypes. 3) EISA spatiotemporally controls the distribution of therapeutic agents, which boosts drug delivery efficiency. Therefore, with regard to the development of EISA, the aim is to provide a perspective on the future directions of research into EISA as anticancer theranostics.

Incorporating d‐chirality into supraparticles (SPs) enhances uptake by cancer cells and prolongs in vivo stability in circulation. These chiral‐selective interactions result from the energetically more favorable association of d‐SPs with cells, which have the same handedness, compared with endogenous proteins and proteases with opposite handedness.

Abstract

Chirality is ubiquitous in nature and hard‐wired into every biological system. Despite the prevalence of chirality in biological systems, controlling biomaterial chirality to influence interactions with cells has only recently been explored. Chiral‐engineered supraparticles (SPs) that interact differentially with cells and proteins depending on their handedness are presented. SPs coordinated with d‐chirality demonstrate greater than threefold enhanced cell membrane penetration in breast, cervical, and multiple myeloma cancer cells. Quartz crystal microbalance with dissipation and isothermal titration calorimetry measurements reveal the mechanism of these chiral‐specific interactions. Thermodynamically, d‐SPs show more stable adhesion to lipid layers composed of phospholipids and cholesterol compared to l‐SPs. In vivo, d‐SPs exhibit superior stability and longer biological half‐lives likely due to opposite chirality and thus protection from endogenous proteins including proteases. This work shows that incorporating d‐chirality into nanosystems enhances uptake by cancer cells and prolonged in vivo stability in circulation, providing support for the importance of chirality in biomaterials. Thus, chiral nanosystems may have the potential to provide a new level of control for drug delivery systems, tumor detection markers, biosensors, and other biomaterial‐based devices.

A supramolecular assembly of single‐chain magnets (SCM) is reported. The chains self‐organize to form chiral supramolecular nanotubes where their magnetic behavior is preserved. Magnetic relaxation with both finite and infinite size regimes is observed and confirms the validity of the Ising approximation.

Abstract

We report a single‐chain magnet (SCM) made of a terbium(III) building block and a nitronyl‐nitroxide radical (NIT) functionalized with an aliphatic chain. This substitution is targeted to induce a long‐range distortion of the polymeric chain and accordingly it gives rise to chains that are curled with almost 20 nm helical pitch. They self‐organize as a chiral tubular superstructure made of 11 chains wound around each other. The supramolecular tubes have a 4.5 nm internal diameter. Overall, this forms a porous chiral network with almost 44 % porosity. Ab initio calculations highlight that each Tb^III ion possesses high magnetic anisotropy. Indeed, notwithstanding the supramolecular arrangement each chain behaves as a SCM. Magnetic relaxation with both finite and infinite‐size regimes is observed and confirms the validity of the Ising approximation. This is associated with quite strong coercive field and magnetic remanence (H _c=2400 Oe M _R=2.09 μ_B at 0.5 K) for this class of compounds.

Alkynes in ring systems: Angle‐strained alkynes show specific reactivity and properties. An overview of angle‐strained alkynes in π‐conjugated macrocycles is presented. Their synthetic methods and transformations, photophysical, and supramolecular properties, and bond angles are summarized.

Abstract

Angle‐strained alkyne‐containing π‐conjugated macrocycles are attractive compounds both in functional materials chemistry and biochemistry. Their interesting reactivity as well as photophysical and supramolecular properties have been revealed in the past three decades. This review highlights the recent advances in angle‐strained alkyne‐containing π‐conjugated macrocycles, especially their synthetic methods, the bond angles of alkynes (∠_sp at C≡C−C), and their functions. The theoretical and experimental research on cyclo[n]carbons and para‐cyclophynes consisting of ethynylenes and para‐phenylenes are mainly summarized. Related macrocycles bearing other linkers, such as ortho‐phenylenes, meta‐phenylenes, heteroaromatics, biphenyls, extended aromatics, are also overviewed. Bond angles of strained alkynes in π‐conjugated macrocycles, which are generable, detectable, and isolable, are summarized at the end of this review.