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2023
●Molecular Recognition Process in Resorcinarene-based Coordination Capsules
Cu and Ag capsules can take up various organic molecules. Their molecular recognition possibly involves partial dissociation and slippage. We investigated molecular recognition processes in Cu and Ag capsules by CD and 1H NMR spectroscopy and employed 4,4’-diacetoxy biphenyl carrying two benzothiadiazole groups as a probe. CD and 1H NMR measurements reveal that the host-guest complexation proceeds under second-order reactions and that these capsules undergo partial dissociation to take up the probe in [D1]chloroform and [D8]THF. Slippage also contributes to host-guest complexation for a Cu capsule that carries p-methoxyphenyl groups on the 2,2’-bipyridiyl arms. DFT calculations suggest that π/π stacking interactions between the electron-rich p-methoxyphenyl group and the electron-poor 2,2’-bipyridyl arm elongate the capsule, allowing the guest to access the cavity without partial dissociation.
Kentaro Harada, Ryo Sekiya, and Takeharu Haino, Chem. Eur. J., 2023, 29, e202302581.
●A robust heterodimeric bis-Rh(iii)–porphyrin macrocycle for the self-assembly of a kinetically stable [2]-rotaxane
We report the self-assembly of a robust di-nuclear tetralactam macrocyle based on two symmetric components: a Rh(III) bis-porphyrin and a bis-pyridyl ligand. We probe the binding properties of the tetralactam macrocycle with adipamide derivatives using 1H NMR spectroscopy. On the one hand, we show that the binding of the adipamide having linear alkyl chains that can thread through the intact macrocycle's cavity produces a weakly bound 1 : 1 complex stabilized by four intermolecular hydrogen bonds and featuring a preferred binding geometry of [2]pseudorotaxane topology. On the other hand, we detect the formation of two different complexes in the binding of an analogous adipamide possessing bulky stoppers (dumb-bell axle). The initial addition of the dumb-bell guest induces the formation of a 1 : 1 complex featuring fast exchange kinetics on the 1H chemical shift timescale and exo-cyclic (non-threaded) binding geometry. Notably, in the presence of a large excess of the dumb-bell guest and at suitable concentrations of the macrocycle (>5 mM) we observe the emergence of a second species displaying slow exchange kinetics. This observation allows the undisputed assignment of a [2]rotaxane topology to the second complex. The significant increase in kinetic stability featured by the di-nuclear Rh(III) [2]rotaxane complex contrasts with its reduction in thermodynamic stability (more than one order of magnitude) compared to the previously described di-nuclear Zn(II) counterpart.
Naoyuki Hisano, Virginia Valderrey, Gemma Aragay, Pablo Ballester, Dalton Trans., 2023, 52, 8344-8352.
●Induction of Chirality on Nanographenes
Chirality induction is an important topic in studies of nanographenes (NGs). We report chirality enhancements of NGs through postsynthetic chemical modifications of NGs with pyrene and m-terphenyl groups. These substituents were installed into N-(p-bromophenylethyl)imides on the edges of the NGs with Pd-catalyzed cross-coupling reactions. Circular dichroism (CD) spectra demonstrated that these bulky substituents improved the induced CD signal of the NGs compared to those previously reported and suggested that they induced the opposite chirality. Density functional theory calculations indicated possible edge structures for the NGs and indicated that π/π and CH/π interactions among the neighboring substituents influenced the orientations of the imides. These imides distorted the edges, and the distorted edges eventually generated the chiral environments of the NGs. The interactions among the substituents are, therefore, likely to allow detection of the CD signals in the visible region and induction of the opposite chirality.
Saki Arimura, Ikuya Matsumoto, Shohei Nishitani, Ryo Sekiya, and Takeharu Haino, Chem. Asian J., 2023, 18, e202300126.
●Negative Homotropic Cooperativity in Guest Binding of a Trisporphyrin Double Cleft
The negative homotropic allostery of a triple-layered trisporphyrin cleft with two guest binding sites was confirmed. The X-ray crystal structures of the 1:2 host-guest complexes showed that the trisporphyrin accommodated two guest molecules within the cleft via π–π stacking and donor-acceptor interactions. In solution, 1H NMR and Job plots showed 1:2 host-guest complexes. Isothermal titration calorimetry (ITC) and UV/vis absorption spectroscopy were employed to evaluate the binding constants and cooperativities. The guest binding of the trisporphyrin showed negative cooperativity and noncooperativity depending on the structures of the guest molecules. The correlations between the interaction parameters (α) and Hill constants were determined. ITC experiments showed that the host-guest complexation of trisporphyrin with electron-deficient guests incurred an enthalpy penalty in the successive guest binding process. DFT calculations revealed that the first guest binding reduced the electron density of the central porphyrin plane, which led to an energetic penalty that weakened the successive binding process.
Naoyuki Hisano, Tomoki Kodama, and Takeharu Haino, Chem. Eur. J., 2023, 29, e202300107(Front Cover)
●Effects of Edge Functionalization of Nanographenes with Small Aromatic Systems
Regulation of the physical properties of nanographenes (NGs) by edge functionalization is an active research area. We conducted a computational study of the effects of edge functionalization on the physical properties of NGs. The computed NGs were models of experimentally obtained NGs and composed of a C174 carbon framework with from one to four 3,5-dimethylnaphthalene units on the edge. The effects were assessed structurally, magnetically, and electronically by the least square planarity index, harmonic oscillator model of aromaticity, nucleus-independent chemical shift, and HOMO-LUMO (H-L) gaps. Density functional theory calculations indicated that although the structures of the model NGs were not very sensitive to edge functionalization, the magnetic and electronic properties were. The installed substituents narrowed the H-L gap and induced a redshift of the PL band by the π conjugation between NG and the substituent. These results were consistent with the extension of the absorption band and the redshift of the PL bands of the experimentally modified NGs. Furthermore, the calculations confirmed the contribution of the charge transfer character to the absorption spectra.
Shusaku Takahashi, Ryo Sekiya, and Takeharu Haino, ChemPhysChem, 2023, 24, e202300066.
●Substituent-Induced Supramolecular Aggregates of Edge Functionalized Nanographenes
Precisely controlled molecular assemblies often display intriguing morphologies and/or functions arising from their structures. The application of the concept of the self-assembly for controlling the aggregation of nanographenes (NGs) is challenging. The title NGs are those carrying both long alkyl chains and tris(phenylisoxazolyl)benzene (TPIB) on the edge. The former group secures the affinity of NGs for organic solvents, and the latter group drives the one-dimensional arrangement of NGs through the interactions between the TPIB units. The concentration-dependent and temperature variable 1H NMR, UV-vis, and PL spectra demonstrate the aggregation of NGs in 1,2-dichloroethane, and the aggregation is controllable by the regulation of the solvent polarity. AFM images give the stacked structures of the NGs, and these aggregates turn out to be network polymeric structures at a high concentration. These observations demonstrate that the synergy of the face-to-face interactions between the surfaces and the interactions between the TPIB units is effective for controlling the self-assembly of the NGs.
Haruka Moriguchi, Ryo Sekiya, and Takeharu Haino, Small, 2023, 19, 2207475.(Frontispiece)
●Synthesis of Supramolecular A8Bn Miktoarm Star Copolymers by Host–Guest Complexation
We report a brand-new synthetic method to construct supramolecular A8Bn (n = 1, 2, 4) miktoarm star copolymers via host–guest complexation between a resorcinarene-based coordination capsule possessing eight polystyrene chains and 4,4-diacetoxy biphenyl guest molecules keeping one, two and four polymethyl acrylate chains. The formation of the supramolecular A8Bn (n = 1, 2, 4) miktoarm star copolymers was confirmed by dynamic light scattering (DLS), size exclusion chromatography (SEC), and diffusion-ordered NMR spectroscopy (DOSY). Differential scanning calorimetry (DSC) measurements revealed that the miktoarm copolymers were phase-separated in bulk. The micro Brownian motion of the capsule surrounded by polymethyl acrylate arms and polystyrene arms in the A8B4 structure was markedly enhanced in bulk due to a weak segregation interaction between the immiscible arms.
Natsumi Nitta, Shin-ichi Kihara, Takeharu Haino, Angew. Chem. Int. Ed, 2023, 62, e202219001.(Inside Cover)
●Supramolecular Chiral Sensing by Supramolecular Helical Polymers
A tetrakis(porphyrin) with branched side chains self-assembled to form supramolecular helical polymers both in solution and in the solid state. The helicity of the supramolecular polymers was determined by the chirality of solvent molecules, which permitted the polymer chains to be used in chiral sensing.
Takehiro Hirao, Sei Kishino and Takeharu Haino, Chem. Comm, 2023, 59, 2421-2424.(Inside Front Cover)
●Lanthanide and Actinide Ion Complexes Containing Organic Ligands Investigated by Surface-Enhanced Infrared Absorption Spectroscopy
A new technique, surface-enhanced infrared absorption (SEIRA) spectroscopy, was used for the structural investigation of lanthanide (Ln) and actinide (An) complexes containing organic ligands. We synthesized thiol derivatives of organic ligands with coordination sites similar to those of 2-[N-methyl-N-hexanethiol-amino]-2-oxoethoxy-[N′,N′-diethyl]-acetamide [diglycolamide (DGA)], Cyanex-272, and N,N,N′,N′-tetrakis(2-pyridinylmethyl)-1,2-ethanediamine (TPEN), which have been used for separating Ln and An through solvent extraction. These ligands were attached on a gold surface deposited on an Si prism through S–Au covalent bonds; the gold surface enhanced the IR absorption intensity of the ligands. Aqueous solutions of Ln (Eu3+, Gd3+, and Tb3+) and An (Am3+) ions were loaded onto the gold surface to form ion complexes. The IR spectra of the ion complexes were obtained using Fourier transform infrared spectroscopy in the attenuated total reflection mode. In this study, we developed a new sample preparation method for SEIRA spectroscopy that enabled us to obtain the IR spectra of the complexes with a small amount of ion solution (5 μL). This is a significant advantage for the IR measurement of radiotoxic Am3+ complexes. In the IR spectra of DGA, the band attributed to C═O stretching vibrations at ∼1630 cm–1 shifted to a lower wavenumber by ∼20 cm–1 upon complexation with Ln and An ions. Moreover, the amount of the red shift was inversely proportional to the extraction equilibrium constant reported in previous studies on solvent extraction. The coordination ability of DGA toward Ln and An ions could be assessed using the band position of the C═O band. The Cyanex-272- and TPEN-like ligands synthesized in this report also showed noticeable SEIRA signals for Ln and An complexes. This study indicates that SEIRA spectroscopy can be used for the structural investigation of ion complexes and provides a microscopic understanding of selective extraction of Ln and An.
Sakiko Hirata, Ryoji Kusaka, Shogo Meiji, Seita Tamekuni, Kosuke Okudera, Shoken Hamada, Chihiro Sakamoto, Takumi Honda, Kosuke Matsushita, Satoru Muramatsu, Takayuki Ebata, Daisuke Kajiya, Ken-ichi Saitow, Toshiaki Ikeda, Takehiro Hirao, Takeharu Haino, Masayuki Watanabe, and Yoshiya Inokuchi, Inorg.Chem., 2023, 62, 1, 474–486.
DOI:10.1021/acs.inorgchem.2c03618
●Computational Studies on the Structures of Nanographenes with Various Edge Functionalities
Computational studies have often been carried out on hydrogen-terminated nanographenes (NGs). These structures are, however, far from those deduced from experimental observations, which have suggested armchair edges with two carboxy groups on the edges as dominant. We conducted computational studies on NGs consisting of C42, C60, C78, C96, C142, and C174 carbon atoms with hydrogen, carboxy, and N-methyl imide-terminated armchair edges. DFT calculations inform distorted basal planes and similar HOMO-LUMO gaps, indicating that the edge oxidation and functionalization do not very influence the electronic structure. Comparison of observed UV-vis spectra of carboxy- and N-octadecyl chain terminated NGs with calculated spectra of model NGs informs the contribution of pi-pi* transitions on the basal plane to the absorptions in the visible region. A dimeric structure of NG and octadecyl-installed NG demonstrate that both the distorted basal planes and the steric contacts among the functional groups widen the surface-to-surface distance thereby allowing the invasion of solvent molecules between the surfaces. This picture is consistent with the improved solubility of edge-modified NGs.
Shusaku Takahashi, Ryo Sekiya, and Takeharu Haino, ChemPhysChem, 2023, e202200465.