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2021
●Self-Sorting Behavior in Supramolecular Fullerene Polymerization Directed by Host-Guest Complexation between Calix[5]arene and C60
We describe self-sorting supramolecular polymerization that uses chiral calix[5]arene hosts and a dumbbell-shaped fullerene guest. In a solution containing the racemic host and the guest, the (S)-host and the (R)-host preferably formed their homomeric complexes to form helical supramolecular fullerene polymers in a self-sorting manner. The self-sorting behavior has been studied using diffusion-ordered 1H NMR (DOSY) and circular dichroism (CD) studies. The present findings show that it is possible to accomplish controlled supramolecular polymerization.
Takehiro Hirao, Naoka Fujii, Yoshiki Iwabe, and Takeharu Haino,Chemm.Commun., 2021, 57, 11831-11834.
●Synthesis and Conformational Characteristics of Calix[4]arene Oligomers
Lower- and/or upper-rim functionalization of calix[4]arene realized a variety of calix[4]arene systems. Compared to these monomeric calix[4]arenes, covalently linked calix[4]arene oligomers have not been studied well. Calix[4]arene oligomers can be utilized as building blocks of supramolecular complexes as well as for the synthesis of calix[4]arene polymers. This background motivated us to develop synthetic procedures for calix[4]arene oligomers and to conduct conformational analysis of these oligomers. We produce oligomers ranging from the monomer to the pentamer. The coupling of the pentamer with 2,3-dibenzyloxy-1,4-benzenedicarboxylic acid can access a decamer and oligomers. NMR measurements, X-ray crystal structure analysis, and computational studies demonstrate that calix[4]arene oligomers can regulate their length by changing the conformations of the calix[4]arene cores.
Masauki Morie, Ryo Sekiya, and Takeharu Haino, Bull. Chem. Soc. Jpn, 2021, 94, 2792-2799.(Selected Paper, Frontispiece)
●Gas-Phase UV Spectroscopy of Chemical Intermediates Produced in Solution: Oxidation Reactions of Phenylhydrazines by DDQ
In this study, we demonstrated cold gas-phase spectroscopy of chemical intermediates produced in solution. Herein, we combined an electrospray ion source with a T-shaped solution mixer for introducing chemical intermediates in solution into the gas phase. Specifically, the oxidation reaction of 2-(4-nitrophenyl)hydrazinecarboxaldehyde (NHCA) by 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) was initiated by mixing the methanol solutions of NHCA and DDQ in the T-shaped mixer, and the chemical species were injected into the vacuum apparatus for ultraviolet photodissociation (UVPD) spectroscopy. A cationic intermediate was strongly observed at m/z 150 in the mass spectrum, and the UVPD spectrum was observed under cold (∼10 K) gas-phase conditions. The UVPD spectrum showed a strong, broad absorption at ∼38,000 cm–1, accompanied by a relatively weak component at ∼34,000 cm–1. These spectral patterns can be ascribed to a diazonium cation intermediate, whose existence has been predicted in a previous study. This report indicates that cold gas-phase UV spectroscopy can be a useful method for identifying the structure of chemical intermediates produced in solution.
Shiori Machida, Motoki Kida, Satoru Muramatsu, Takehiro Hirao, Takeharu Haino, and Yoshiya Inokuchi, J. Phys. Chem. A, 2021, 125, 6697-6702.
●Solvent-Directed Formation of Helically Twisted Stacking Constructs via Self-Assembly of Tris(phenylisoxazolyl)benzene Dimers
Ureido-pyrimidinone (UPy)-appended tris(phenylisoxazolyl)benzenes were synthesized. The UPy moieties of the tris(phenylisoxazolyl)benzenes stably formed self-complementary dimers in solution. The dimers self-assembled to form helically twisted stacking constructs driven by π-π stacking interactions of UPy dimer moieties and dipole-dipole interactions of isoxazole units. Strong association affinity was seen within the stacking constructs compared with the previously reported isoxazole derivatives owing to the auxiliary π-π stacking interaction. Notably, tris(phenylisoxazolyl)benzenes showed an environmentally responsive nature. The absorption band, emission intensity, and size of ensembles significantly depended on the mixing ratio of CHCl3 and methylcyclohexazne (MCH). Also, a sharp on-off switching nature was seen in their circular dichroism (CD) and circularly polarized luminescence (CPL) spectra in response to the mixing ratio of CHCl3 and MCH. CD and CPL were activated only at a certain mixing ratio of CHCl3/MCH, thus showing potential for the creation of molecular sensors.
Yudai Ono, Takehiro Hirao and Takeharu Haino , Org. Biomol. Chem., 2021, 19, 7165-7171.
●Self-Complementary Structure of Bisporphyrin Dimer
The crystal structure of a bisporphyrin cleft molecule revealed that the head-to-head dimeric structure is directed by the intermolecular self-complementary hydrogen-bonding interactions of amide groups and π-π stacking interactions. The UV/Vis absorption spectrum of the homodimeric structure in the solid-state resulted in a broad Soret band. Time-dependent density functional theory (TD-DFT) calculation of the dimer indicated that an intra- and intermolecular charge transfer transition as well as a π-π* transition were responsible for the observed broad Soret bandThe crystal structure of a self-complementary bisporphyrin dimer is reported. The head-to-head dimeric structure was maintained by the assistance of hydrogen bonding interactions and π-π stacking interactions. The UV-Vis absorption spectrum of the dimer showed a broad Soret band in the solid state. TD-DFT calculation of the dimeric structure revealed that a local π-π* electronic transition and intra- and intermolecular charge transfer electronic transition most likely contribute to band broadening at the Soret band.
Naoyuki Hisano ,Takehiro Hirao , and Takeharu Haino, Chem. Lett., 2021, 50, 1844-1847.
●Negative Coorperativity in Guest Binding of Ditopic Self-Folding Biscavitand
A brand-new self-folding biscavitand was synthesized from a feet-to-feet-connected bisresorcinarene. The X-ray crystal structure of the biscaivtand showed that the two cavities are tightly connected with four butylene linkages. The conformationally coupled two cavities accommodated two cationic guests, showing a homotropic negative cooperativity in nonpolar solvents (toluene and chloroform). A polar tetrahydrofuran solvent weakened the cyclic hydrogen bonding interactions of the biscavitand, which resulted in noncooperative guest binding.
Haruna Fujimoto, Daisuke Shimoyama, Katsuo Katayanagi, Naomi Kawata, Takehiro Hirao, and Takeharu Haino, Org. Lett., 2021, 23, 16, 6217–6221.(Front Cover)
DOI:10.1021/acs.orglett.1c01837
●Polymerization of a Biscalix[5]arene Derivative
Recent decades have seen an increased interest in the preparation of polymers possessing host or guest moieties as the end group, which has enabled new polymeric materials such as self-healable, shape-memory, and stimuli-responsive materials. Such polymers are commonly synthesized by tethering the host or guest moieties to polymers. On the other hand, there are limited reports demonstrating the preparation of host- or guest-appended polymers by directly polymerizing the corresponding host- or guest-appended monomers, which is valuable for easy access to diverse polymers from single molecular species. However, reactive host and/or guest moieties of the monomer interfere with the polymerization reaction. Here, we report that a biscalix[5]arene host-appended molecule can be polymerized with various monomers to form the corresponding host-appended polymers. The host-guest complexation behavior of calix[5]arene-appended polymers with fullerene derivatives was studied by 1H NMR and UV/vis spectroscopic techniques, which revealed that the long polymer chains did not prevent host-guest complexation even when the fullerene derivative was equipped with a polymer chain. Thus, the present study shows the potential for developing polymers that have various combinations of polymer chains.
Takehiro Hirao, Kazushi Fukuta, and Takeharu Haino, RSC Adv., 2021, 11, 17587-17594.
●Self-assembly of neutral platinum complexes possessing chiral hydrophilic TEG chains
Neutral platinum complexes that possess chiral triethylene glycol (TEG) moieties were synthesized. The platinum complexes formed helically twisted stacked assemblies in chloroform and toluene, which were studied by 1H NMR, UV/vis spectroscopy, and emission spectroscopy. On the other hand, emissive micellar aggregates were observed in a THF/water mixed solvent. Dynamic light scattering (DLS) experiments revealed that micellar aggregates with a diameter (d) of ≈100 nm emitted strong light, whereas the monomeric form and large aggregates (d > 500 nm) did not show luminescence efficiently. Furthermore, the micellar aggregates were twisted chirally, where the twisted direction was determined by the chirality of the TEG moieties. The assemblies were observed to be solvent responsive, which allows for the modulation of the nanostructure by changing the solvent polarity.
Masaya Yoshida, Takehiro Hirao, and Takeharu Haino, Org. Biomol. Chem., 2021, 19, 5303-5311.(Front Cover)
●Self-Assembling Behavior and Chiroptical Properties of Carbazole-Cored Phenyl Isoxazolyl Benzenes
Carbazole-cored phenyl isoxazolyl benzenes possessing chiral moieties were synthesized. The molecules self-assembled to form stacked supramolecular assemblies in an isodesmic fashion in chloroform, whereas the molecules preferably assembled in a cooperative fashion in methylcyclohexane (MCH), which was determined by spectroscopic methods, including UV–vis absorption, fluorescence, and 1H NMR spectroscopy. Clear nucleation and elongation processes were observed in the plot of the degree of aggregation (αagg) against temperature, which allowed us to determine the elongation temperature (Te), the enthalpic gain in the elongation process (ΔHe), the equilibrium constant between nucleation and elongation (Ka), and the degree of polymerization at the elongation temperature ([Nn(Te)]). Circular dichroism (CD) and circularly polarized luminescence (CPL) studies revealed the formation of helically stacked assemblies in solution. Moreover, the majority-rule effect was clearly observed in the solutions of mixtures of (S)- and (R)-1, indicating the chiral amplification behavior of the helically stacked assemblies consisting of (S)- and (R)-1. AFM provided morphological insight into the assemblies on mica, which clearly indicates the formation of polymeric assemblies in the solid state.
Yudai Ono, Takehiro Hirao, Toshiaki Ikeda, and Takeharu Haino, J. Org. Chem., 2021, 86, 5499-5505.(Front Cover)
●Self-Assembly of Nanographenes
Suitably decorated small aromatic systems can organize stacked structures that display interesting properties arising from their unique morphologies. Although nanographenes produced by top-down methods have graphitic domains and can in principle be applied for such supramolecular systems, to the best of our knowledge, no such example has been reported thus far. This is partly because of their limited solubility in organic solvents and partly because of their wide lateral size distribution. To realize nanographene-based supramolecular aggregates, nanographenes carrying alkyl chains with narrow lateral size distributions are employed. We find that the nanographenes undergo self-assembly and that self-assembly is regulated by concentration, solvent polarity, temperature, and sonication. Optical measurements and AFM images indicate that stacked structures are possible candidates for aggregates. A molecular mechanics calculation suggests that graphitic domains inside the nanographenes can contact those of the nearest neighbors in the aggregates, while graphitic domains near the edge are difficult to make contact due to steric congestion. This model can rationalize a unique PL response to temperature. The nanographenes showed concentration-dependent morphologies on mica, stacked structures at low concentrations and polymer-like network structures on mica at higher concentrations.
Ikuya Matsumoto, Ryo Sekiya, and Takeharu Haino, Angew. Chem. Int. Ed., 2021, 60, 12706-12711.(Hot Paper, Frontispiece)
●Helically Organized Fullerene Array in a Supramolecular Polymer Main Chain
To date, supramolecular chemistry techniques have been applied to fullerene polymer synthesis, enabling the development of main-chain fullerene polymers whose primary structure is well regulated, including linear, dendritic, and net-like fullerene arrays. These research achievements have led to an intriguing scientific challenge to create main-chain fullerene polymers with higher structural regulation. Here, we report the fabrication of a helically organized fullerene array based on the supramolecular polymerization of chiral ditopic tetrakiscalix[5]arene hosts and a dumbbell-shaped fullerene. The molecular association between the chiral hosts and the dumbbell-shaped fullerene resulted in sizable supramolecular polymers in solution, with the highest degree of polymerization of more than 32. The achiral dumbbell-shaped fullerene exhibited circular dichroism in the π-π* transition bands arising from the fullerene moieties through supramolecular polymerization. End-capping experiments of the supramolecular helical polymers showed that the chirally twisted conformation of the dumbbell-shaped fullerene was directed by supramolecular polymerization. Finally, the helical morphology of the supramolecular polymer chain was visualized by atomic force microscopy. The successful development of helical main-chain fullerene polymers would break new ground in fullerene chemistry.
Tekehiro Hirao, Yoshiki Iwabe, Naoka Fujii, Takeharu Haino, J. Am. Chem. Soc., 2021, 143, 4339-4345.
●Folding and Unfolding of Acetoxy Group-Terminated Alkyl Chains Inside a Size Regulable Hemicarcerand
A resorcinarene-based hemi-carcerand, which consists of two cavitands covalently linked to each other by four alkyl chains, allows structural expansion and contraction by demetalation and metalation of Cu(I) cations with a size change of approx-imately 12 Å. This metal-mediated switching of the two states regulates the conformations of acetoxy group-terminated alkyl chains. A guest binding study reveals the encapsulation of heptyl to undecyl chains in metal-free and Cu(I)-coordinated capsules. The chemical shifts of the acetoxy groups of the bound guests are the same in the metal-free capsule, while those in the Cu(I)-coordinated one differ from each other. This indicates that the metal-free capsule regulates its size to the bound guests, while the bound guests adopt their conformations to the cavity of the Cu(I)-coordinated capsules. 1H NMR measurements and molecular mechanics calculations suggest that the bound guests have extended conformations in the metal-free capsule, while the Cu(I)-coordinated capsule forces the bound guests to adopt folded conformations. The presence of folded conformations is supported by the conformational study with structurally similar capsules and a non-symmetric guest, allowing us to observe NOEs stemming from folded conformations of the guest in the cavity.
Kentaro Harada, Ryo Sekiya, and Takeharu Haino, J. Org. Chem., 2021, 86, 4440-4447.(Front Cover)
●Translational Isomers of N-sulfonylated [3]Catenane: Synthesis and Isomerization
N-Sulfonylated [3]catenanes, which exist as two translational isomers, were synthesized. The X-ray crystal structure of the distal isomer of [3]catenane, which has higher symmetry, revealed hydrogen bonds involving the carboxylic acid moieties on the terminal rings. The thermodynamic parameters of the isomerization revealed that this hydrogen bonding influenced the isomerization process.
Hajime Iwamoto, Yuki Ishizu, Eietsu Hasegawa, Ryo Sekiya and Takeharu Haino , Chem. Commun., 2021, 57, 1915-1918.
●Nanographenes from Distinct Carbon Sources
This article reports the production protocol of nanographenes and the effect of the reaction conditions on their structures and optical properties. These fundamental studies are of value for exploring suitable reaction conditions for the production of nanographenes with desirable properties. Graphite, finely crushed graphite powders, and artificial graphite, all of which are commercially available, are employed. Nanographenes are produced by the acid-assisted oxidative cleavage of the parent carbons followed by neutralization and deionization. The use of dialysis membranes for the size separation of nanographenes offers nanographenes with a specific size distribution, thereby allowing their structures and optical properties to be compared. Experiments demonstrate that small amounts of acids (60 ml of conc. H2SO4 and 20 mL of 60% HNO3) and oxidation for 12 h promotes a more efficient and cost-effective production of nanographenes from 2 g of a carbon source. The functionalization of the nanographene edges with p-propargyloxybenzyl amine confirms that the armchair edge with two carboxy groups is the dominant edge structure, irrespective of the carbon source.
Ikuya Matsumoto, Ryo Sekiya, and Takeharu Haino, Bull. Chem. Soc., Jpn., 2021, 94, 1394-1399.(Selected Paper, Frontispiece)
●Blueish-white-light-emitting Nanographenes Developed by Pd-Catalyzed Suzuki-Miyaura Cross Coupling Reactions
Top-down methods produce nanographenes with many carboxy groups on their edges. These functional groups can be utilized for developing multichromophoric systems. As proof of concept, pyrene is installed on the edges by Pd-catalyzed cross-coupling reactions. The lack of monomer emissions from the functionalized nanographenes indicates that the neighboring chromophores are sufficiently distant to form the excimer. The pyrene-installed nanographene emits bluish-white-light. Its lipophilic nature allows fabricating a nanographene-dispersed polymethyl methacrylate film emitting visible light.
Shohei Nishitani, Ryo Sekiya, Ikuya Matsumoto, and Takeharu Haino, Chem. Lett., 2021, 50, 664-667.
●A Light‐Harvesting/Charge‐Separation Model with Energy Gradient Made of Assemblies of meta‐pyridyl Zinc Porphyrins
Self‐assembly of porphyrins is a fascinating topic not only for mimicking chlorophyll assemblies in photosynthetic organisms but also for the potential of creating molecular‐level devices. Herein we have prepared zinc porphyrin derivatives bearing a meta‐pyridyl group at the meso‐position and studied their assemblies in chloroform. Among porphyrins studied, one with a carbamoylpyridyl moiety (ZnPPyC) gave distinct 1H NMR spectrum in CDCl3, which allowed us to probe the supramolecular structure in solution in detail. Ring‐current induced chemical shift changes in 1H NMR, together with vapor pressure osmometry and diffusion‐ordered NMR spectroscopy, among other evidence, suggested that the porphyrin molecules form a trimer in a triangular cone structure. Further incorporation of a directly‐linked porphyrin‐ferrocene dyads with the same assembling properties in the assemblies lead to a rare light‐harvesting/charge‐separation model, in which an energy gradient is incorporated and reductive quenching occurs.
Joe Otsuki, Takumi Okumura, Kosuke Sugawa, Shin-ichiro Kawano, Kentaro Tanaka, Takehiro Hirao, Takeharu Haino, Yu Jin Lee, Seongsoo Kang, Dongho Kim, Chem. Eur. J. 2021, 27, 4053-4063.
●Stereoselectivity in Dehydrative Cyclic Trimerization of Substituted 4-Alkylaminobenzoic Acids
Cyclic trimerization of substituted 4-alkylaminobenzoic acids were investigated. From NMR analyses of DiMeO_C3A with two methoxy groups, which was obtained by using SiCl4 as a dehydrative condensation reagent and purified by preparative GPC, exhibited the syn/anti ratio of 60/40. On the other hand, 3Br_C3A with one bromine group at the ortho-position relative to the amide nitrogen was synthesized by using PPh3/Cl3CCCl3 as a dehydrative condensation reagent and isolated by SiO2 colum chromatography. 3Br_C3A showed an inverse stereoselectivity, namely, the syn/anti ratio of 25/75 was calculated based on the conprehensive NMR analyses. The population of stereoisomers had no relationship with the dehydrative condensation reagent and reaction temperature. Solvent character also had a negligible influence on the syn/anti ratio in solution reflecting the rigid structure of 3Br_C3A.
Koji Takagi, Hinako Yamaguchi, Daiki Miyamoto, Yuka Deguchi, Takehiro Hirao and Takeharu Haino, New J. Chem., 2021, 45, 1187-1193.
●Calix[4]arene-Based Triple-Stranded Metallohelicate in Water
The title complex is a triple-stranded metallohelicate organized by the self-assembly of 5,17-difunctionalized calix[4]arenes and metal cations with octahedral coordination geometry. Due to hydrophilic triethylene glycol chains on the lower rim of the calix[4]arene, the metallohelicate can encapsulate cationic guests in water. NMR and UV-vis titration experiments reveal that the metallohelicate captures a pyridinium guest with an alanine derivative to form a host-guest complex with a host-guest ratio of 1:1. CD spectroscopy confirms the bias of the P- and M-helical sense of the metallohelicate by the captured guest. The metallohelicate captures two molecules of dicationic N,N’-dimethyl-DABCO and monocationic N-methyl quinuclidine, exhibiting a positive allosteric effect. 1H NMR titration experiments indicate that the bound guests are in close proximately to the aromatic rings of the ligands. Molecular mechanics calculations based on the UV-vis and NMR observations suggest that the first guest preorganizes the conformation of the metallohelicate to facilitate access of the second guest to the cavity.
Masayuki Morie, Ryo Sekiya, and Takeharu Haino, Chem. Asian J., 2021, 16, 49-55.(Front Cover)