Confinement effects on the structure and reactivity of encapsulated buckybowls in cycloparaphenylene.

We theoretically investigated the host-guest chemistry between belt-like cycloparaphenylenes (CPPs) and entrapped bowl-shaped sumanene and corannulene. Density functional theory calculations show that the buckybowls can be stabilized in a CPP host with an appropriately sized cavity (e.g., [10]CPP) through multi-site CH-π interactions. Arising from the confined intermolecular interactions within the cavity, the restrictive buckybowls display novel reactivity distinct from that in their free state.

Dehydrogenative oxidation of hydrosilanes using gold nanoparticle deposited on citric acid-modified fibrillated cellulose: unveiling the role of molecular oxygen.

Efficient and environmentally friendly synthesis of silanols is a crucial issue across the broad fields of academic and industrial chemistry. Herein, we describe the dehydrogenative oxidation of hydrosilane using a gold nanoparticle catalyst supported by fibrillated citric acid-modified cellulose (F-CAC). Au:F-CAC catalysts with various particle sizes (1.7 nm, 4.9 nm, and 7.7 nm) were prepared using the trans-deposition method, a technique previously reported by our group. These catalysts exhibited significant catalytic activity to produce silanols with high turnover frequency (TOF) of up to 7028 h-1. Recycling experiments and transmission electron microscopy (TEM) observation represented the high durability of Au:F-CAC under the reaction conditions, allowing kinetic studies on size dependency. Mechanistic studies were conducted, including isotope labelling experiments, kinetics, and various spectroscopies. Notably, the near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) of the model catalyst (Au:PVP) revealed the formation of catalytically active cationic Au sites on the surface through the adsorption of molecular oxygen, providing a new insight into the reaction mechanism.

Amplification sensing manipulated by a sumanene-based supramolecular polymer as a dynamic allosteric effector.

The synthesis of signal-amplifying chemosensors induced by various triggers is a major challenge for multidisciplinary sciences. In this study, a signal-amplification system that was flexibly manipulated by a dynamic allosteric effector (trigger) was developed. Herein, the focus was on using the behavior of supramolecular polymerization to control the degree of polymerization by changing the concentration of a functional monomer. It was assumed that this control was facilitated by a gradually changing/dynamic allosteric effector. A curved-π buckybowl sumanene and a sumanene-based chemosensor (SC) were employed as the allosteric effector and the molecular binder, respectively. The hetero-supramolecular polymer, (SC·(sumanene)n), facilitated the manipulation of the degree of signal-amplification; this was accomplished by changing the sumanene monomer concentration, which resulted in up to a 62.5-fold amplification of a steroid. The current results and the concept proposed herein provide an alternate method to conventional chemosensors and signal-amplification systems.

Sumanene-carbazole conjugate with push-pull structure and its chemoreceptor application.

The first-of-its-kind tetra-substituted sumanene derivative, featuring the push-pull chromophore architecture, has been successfully designed. The inclusion of both strong electron-withdrawing (CF3) and electron-donating (carbazole) moieties in this buckybowl compound has enhanced the charge transfer characteristics of the molecule. This enhancement was supported by ultraviolet-visible (UV-Vis) and emission spectra analyses along with density functional theory (DFT) calculations. The application of the title sumanene-carbazole push-pull chromophore as a selective recognition material for cesium cations (Cs+) was also presented. The title compound exhibited effective and selective Cs+-trapping ability, characterized by a high apparent binding constant value (at the level of 105) and a low limit of detection (0.09-0.13 µM). Owing to the tuned optical properties of the title push-pull chromophore, this study marks the first time in sumanene-tethered chemoreceptor chemistry where efficient tracking of Cs+ binding was possible with both absorption and fluorescence spectroscopies. This work introduces a new approach toward tuning the structure of bowl-shaped optical chemoreceptors.

Enhanced reactivity of Li+@C60 toward thermal [2 + 2] cycloaddition by encapsulated Li+ Lewis acid.

Lithium ion-endohedral fullerene (Li+@C60), a member of the burgeoning family of ion-endohedral fullerenes, holds substantial promise for diverse applications owing to its distinctive ionic properties. Despite the high demand for precise property tuning through chemical modification, there have been only a few reports detailing synthetic protocols for the derivatization of this novel material. In this study, we report the synthesis of Li+@C60 derivatives via the thermal [2 + 2] cycloaddition reaction of styrene derivatives, achieving significantly higher yields of monofunctionalized Li+@C60 compared to previously reported reactions. Furthermore, by combining experimental and theoretical approaches, we clarified the range of applicable substrates for the thermal [2 + 2] cycloaddition of Li+@C60, highlighting the expanded scope of this straightforward and selective functionalization method.

Strain-induced carbon-carbon bond cleavage of bowl-shaped sumanenone.

This study details a highly effective ring-opening reaction that involves acid-mediated carbon-carbon bond cleavage of the buckybowl, sumanenone. The reaction of the bowl-shaped sumanenone with AcOH and TfOH results in the formation of a planar carboxylic acid. The examination of reactivity in comparison to planar analogues, along with theoretical calculations, suggests that the release of curved strain is a crucial factor for the success of this reaction.

Biased Bowl-Direction of Monofluorosumanene in the Solid State.

A new curved π-conjugated molecule 1-fluorosumanene (1) was designed and synthesized that possesses one fluorine atom on the benzylic carbon of sumanene. This compound can exhibit bowl inversion in solution, leading to the formation of two diastereomers, 1endo and 1exo, with different dipole moments. Experimental and theoretical investigation revealed an energetical relationship among 1exo, 1endo, and solvent to realize the various endo:exo ratios in the single crystals of 1 depending on the crystallization solvent. Significantly, the molecular dynamics (MD) simulations revealed that 1exo positively worked for the elongation of the stacking structure and the final endo:exo ratio was affected by the relative stability difference between 1endo and 1exo derived by solvation. Such an arrangeable endo:exo ratio of 1 realized the preparation of unique materials showing a different dielectric response from the same molecule 1 just by changing the crystallization solvent.

Expanding the library of sumanene molecular receptors for caesium-selective potentiometric sensors.

This paper reports the synthesis and characterization of eight sumanene molecular receptors for the selective recognition of caesium cations (Cs+). The sumanene derivatives differed in the number (from one to nine), type (electron donating or electron withdrawing) and method of the attachment (functionalization of sumanene at the benzylic or aromatic carbons) of substituents in the sumanene skeleton. The ultimate goal of this work was to investigate the prospective use of various sumanene derivatives in the design of Cs+-selective potentiometric sensors, thus, expanding the library of sumanene receptors for such applications. Spectroscopic fluorescence titration with caesium hexafluorophosphate revealed that the formation of sandwich complexes is highly favourable, but the steric hindrance of bulky substituents can disrupt this preference. In the case of triaryl-substituted sumanene derivatives, theoretical calculations show that, indeed, sandwich complexes are energetically more advantageous by 2.3 times than 1 : 1 complexes. Furthermore, such functionalization significantly increases receptor solubility in the polymeric membrane of the potentiometric sensors, which was quantitatively evaluated with the COSMO model.

Oxidation-derived anticancer potential of sumanene-ferrocene conjugates.

An effective synthetic protocol towards the oxidation of sumanene-ferrocene conjugates bearing one to four ferrocene moieties has been established. The oxidation protocol was based on the transformation of FeII from ferrocene to FeIII-containing ferrocenium cations by means of the treatment of the title organometallic buckybowls with a mild oxidant. Successful isolation of these ferrocenium-tethered sumanene derivatives 5-7 gave rise to the biological evaluation of the first, buckybowl-based anticancer agents, as elucidated by in vitro assays with human breast adenocarcinoma cells (MDA-MB-231) and embryotoxicity trials in zebrafish embryos supported with in silico toxicology studies. The designed ferrocenium-tethered sumanene derivatives featured attractive properties in terms of their use in cancer treatments in humans. The tetra-ferrocenium sumanene derivative 7 featured especially beneficial biological features, elucidated by low (<40% for 10 µM) viabilities of MDA-MB-231 cancer cells together with a 1.4-1.7-fold higher viability of normal cells (human mammary fibroblasts, HMF) for respective concentrations. Compound 7 featured significant cytotoxicity against cancer cells thanks to the presence of sumanene and ferrocenium moieties; the latter motif also provided the selectivity of anticancer action. The biological properties of 7 were also improved in comparison with those of native building blocks, which suggested the effects of the presence of the sumanene skeleton towards the anticancer action of this molecule. Ferrocenium-tethered sumanene derivatives exhibited potential towards the generation of reactive oxygen species (ROS), responsible for biological damage to the cancer cells, with the most efficient generation of the tetra-ferrocenium sumanene derivative 7. Derivative 7 also did not show any embryotoxicity in zebrafish embryos at the tested concentrations, which supports its potential as an effective and cancer-specific anticancer agent. In silico computational analysis also showed no chromosomal aberrations and no mutation with AMES tests for the compound 7 tested with and without microsomal rat liver fractions, which supports its further use as a potent drug candidate in detailed anticancer studies.

Ultra-Rapid and Specific Gelation of Collagen Molecules for Transparent and Tough Gels by Transition Metal Complexation.

Collagen is the most abundant protein in the human body and one of the main components of stromal tissues in tumors which have a high elastic modulus of over 50 kPa. Although collagen has been widely used as a cell culture scaffold for cancer cells, there have been limitations when attempting to fabricate a tough collagen gel with cells like a cancer stroma. Here, rapid gelation of a collagen solution within a few minutes by transition metal complexation is demonstrated. Type I collagen solution at neutral pH shows rapid gelation with a transparency of 81% and a high modulus of 1,781 kPa by mixing with K2 PtCl4 solution within 3 min. Other transition metal ions also show the same rapid gelation, but not basic metal ions. Interestingly, although type I to IV collagen molecules show rapid gelation, other extracellular matrices  do not exhibit this phenomenon. Live imaging of colon cancer organoids in 3D culture indicates a collective migration property with modulating high elastic modulus, suggesting activation for metastasis progress. This technology will be useful as a new class of 3D culture for cells and organoids due to its facility for deep-live observation and mechanical stiffness adjustment.

Sumanene-stacked supramolecular polymers. Dynamic, solvation-directed control.

In this study, we found that a pristine buckybowl, sumanene, can form solution-state supramolecular polymers. We also demonstrated that sumanene supramolecular polymers can be dynamically controlled by external stimuli, in which solvation plays a significant role. This study not only provides new guidelines for the rational design of supramolecular polymers, particularly for the use of buckybowls, but also presents interesting dynamic behaviors of supramolecular polymerization.

Reversible Modulation of the Electronic and Spatial Environment around Ni(0) Centers Bearing Multifunctional Carbene Ligands with Triarylaluminum.

Designing and modulating the electronic and spatial environments surrounding metal centers is a crucial issue in a wide range of chemistry fields that use organometallic compounds. Herein, we demonstrate a Lewis-acid-mediated reversible expansion, contraction, and transformation of the spatial environment surrounding nickel(0) centers that bear N-phosphine oxide-substituted N-heterocyclic carbenes (henceforth referred to as (S)PoxIms). Reaction between tetrahedral (syn-κ-C,O-(S)PoxIm)Ni(CO)2 and Al(C6F5)3 smoothly afforded heterobimetallic Ni/Al species such as trigonal-planar {κ-C-Ni(CO)2}(µ-anti-(S)PoxIm){κ-O-Al(C6F5)3} via a complexation-induced rotation of the N-phosphine oxide moieties, while the addition of 4-dimethylaminopyridine resulted in the quantitative regeneration of the former Ni complexes. The corresponding interconversion also occurred between (SPoxIm)Ni(η2:η2-diphenyldivinylsilane) and {κ-C-Ni(η2:η2-diene)}(µ-anti-SPoxIm){κ-O-Al(C6F5)3} via the coordination and dissociation of Al(C6F5)3. The shape and size of the space around the Ni(0) center was drastically changed through this Lewis-acid-mediated interconversion. Moreover, the multinuclear NMR, IR, and XAS analyses of the aforementioned carbonyl complexes clarified the details of the changes in the electronic states on the Ni centers; i.e., the electron delocalization was effectively enhanced among the Ni atom and CO ligands in the heterobimetallic Ni/Al species. The results presented in this work thus provide a strategy for reversibly modulating both the electronic and spatial environment of organometallic complexes, in addition to the well-accepted Lewis-base-mediated ligand-substitution methods.

A sumanene-containing magnetic nanoadsorbent for the removal of caesium salts from aqueous solutions.

Sumanene was covalently immobilised onto the surface of cobalt nanomagnets to obtain a magnetic nanoadsorbent. This nanoadsorbent was specifically designed to efficiently and selectively remove caesium (Cs) salts from aqueous solutions. The nanoadsorbent's application potential was evidenced by the removal of Cs from model aqueous solutions, simulating the concentrations of radioactive 137Cs in the environment. Additionally, Cs was effectively removed from aqueous wastes generated by routine chemical processes, including those used in drug synthesis.

Dihydroxyacetone production by glycerol oxidation under moderate condition using Pt loaded on La1-xBixOF solids.

Pt/La1-xBixOF/SBA-16 (SBA-16: Santa Barbara Amorphous no. 16) catalysts were prepared to produce dihydroxyacetone (DHA) from glycerol under moderate conditions. By using 7 wt% Pt/16 wt% La0.95Bi0.05OF/SBA-16, the DHA yield reached up to 78.4% (glycerol conversion: 100%) after reacting for 6 h at 30 °C in an atmospheric open-air system.

Collective bending motion of a two-dimensionally correlated bowl-stacked columnar liquid crystalline assembly under a shear force.

Stacked teacups inspired the idea that columnar assemblies of stacked bowl-shaped molecules may exhibit a unique dynamic behavior, unlike usual assemblies of planar disc- and rod-shaped molecules. On the basis of the molecular design concept for creating higher-order discotic liquid crystals, found in our group, we synthesized a sumanene derivative with octyloxycarbonyl side chains. This molecule forms an ordered hexagonal columnar mesophase, but unexpectedly, the columnar assembly is very soft, similar to sugar syrup. It displays, upon application of a shear force on solid substrates, a flexible bending motion with continuous angle variations of bowl-stacked columns while preserving the two-dimensional hexagonal order. In general, alignment control of higher-order liquid crystals is difficult to achieve due to their high viscosity. The present system that brings together higher structural order and mechanical softness will spark interest in bowl-shaped molecules as a component for developing higher-order liquid crystals with unique mechanical and stimuli-responsive properties.

Derivatization of sumanenetrione through Lewis acid-mediated Suzuki-Miyaura coupling and an unprecedented ring opening.

A series of sumanenetrione derivatives were synthesized through Lewis acid-mediated Suzuki-Miyaura cross-coupling. Their optical properties reflected the significantly strong electron-accepting ability of sumanenetrione. The bowl strain of the 2-hydroxyphenyl derivative brought the ring-opening response adjacent to the substituent even at room temperature without any activation, which generally requires harsh conditions.

Application of Monoferrocenylsumanenes Derived from Sonogashira Cross-Coupling or Click Chemistry Reactions in Highly Sensitive and Selective Cesium Cation Electrochemical Sensors.

This paper reports the synthesis and characterization of novel monoferrocenylsumanenes obtained by means of the Sonogashira cross-coupling or click chemistry reaction as well as their application in cesium cation electrochemical sensors. A new synthetic protocol based on Sonogashira cross-coupling was developed for the synthesis of monoferrocenylsumanene or ethynylsumanene. The click chemistry reaction was introduced to the sumanene chemistry through the synthesis of 1,2,3-triazole containing monoferrocenylsumanene. The designed synthetic methods for the modification of sumanene at the aromatic position proved to be efficient and proceeded under mild conditions. The synthesized sumanene derivatives were characterized by detailed spectroscopic analyses of the synthesized sumanene derivatives. The supramolecular interactions between cesium cations and the synthesized monoferrocenylsumanenes were spectroscopically and electrochemically investigated. Furthermore, the design of the highly selective and sensitive cesium cation fluorescence and electrochemical sensors comprising the synthesized monoferrocenylsumanenes as receptor compounds was analyzed. The tested cesium cation electrochemical sensors showed excellent limit of detection values in the range of 6.0-9.0 nM. In addition, the interactions between the synthesized monoferrocenylsumanenes and cesium cations were highly selective, which was confirmed by emission spectroscopy, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and cyclic voltammetry.

Synthesis of π-extended and bowl-shaped sumanene-ferrocene conjugates and their application in highly selective and sensitive cesium cations electrochemical sensors.

Carbon-carbon bond formation, condensation or click chemistry reactions were used to synthesize novel bowl-shaped sumanene-ferrocene conjugates, along with the extended π-electron framework in good yields. For the first time, the present study uses sumanene derivatives tris-substituted at the benzylic positions as the materials to begin the study on the click chemistry or the metal-catalyzed coupling reactions, Suzuki-Miyaura or Sonogashira couplings. The synthesized conjugates exhibited the property of selective recognizing cesium cations. As a result, this led to the development of highly sensitive and selective fluorescent or electrochemical sensors dedicated to the recognition of cesium cations (Cs+) in water. We successfully designed the Cs+ electrochemical sensors, which exhibited an acceptable limit of detection (LOD) values at 0.05-0.38 µM. Spectrofluorimetry, voltammetry, and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) were used to perform the selectivity studies. The results revealed that the designed sensors are highly Cs+-selective. This work significantly contributes to the design of new methods of sumanene modification. It also provides further information on the electrochemical properties and innovative applications of metallocene-tethered sumanene derivatives.

Thermodynamic Differentiation of the Two Sides of Azabuckybowl through Complexation with Square Planar Platinum(II).

The precise control of the two faces, concave/convex faces, is an attractive challenge to realizing novel dynamic molecular systems. Herein, we report the synthesis, X-ray crystal structure, and bowl-to-bowl inversion behavior of a platinum complex with azabuckybowl as a monodentate ligand. X-ray crystallography revealed that the azabuckybowl is orthogonally coordinated to the plane containing the Pt center and other ligands. One and two-dimensional NMR studies have also confirmed that this complex was observed as mixtures of two isomers, although the isomeric ratio was highly biased. Theoretical calculations indicate that the difference in thermodynamic stability of these isomers is due to the direction of the concave/convex face of an azabuckybowl ligand.

Acceleration Effect of Bowl-Shaped Structure in Aerobic Oxidation Reaction: Synthesis of Homosumanene ortho-Quinone and Azaacene-Fused Homosumanenes.

An oxidation reaction of hydroxyhomosumanene on silica gel providing homosumanene ortho-quinone and its synthetic application for azaacene-fused homosumanenes is described. Hydroxyhomosumanene is photochemically oxidized by air, when it is coated on silica gel; this aerobic oxidation proceeds faster than that of planar analogues. The difference of such reactivity was attributed to the unusual keto-enol tautomerization due to structural difference between planar and curved π-system. The homosumanene ortho-quinone was used in the synthesis of several azaacene-fused homosumanenes, azaacenohomosumanenes. X-ray diffraction analysis of the single crystals revealed their columnar stacking structures due to the interactions between each bowl. Azaacenohomosumanenes exhibited high electron affinity due to the combination of buckybowl and electron-deficient azaacene moieties.