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51.
Takuya Sawaki Dr. Tomoya Ishizuka Prof. Dr. Masaki Kawano Dr. Yoshihito Shiota Prof. Dr. Kazunari Yoshizawa Prof. Dr. Takahiko Kojima 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(27):8978-8990
The thermal and photochemical reactions of a newly synthesized complex, [RuII(TPA)(tpphz)]2+ ( 1 ; TPA=tris(2‐pyridylmethyl)amine, tpphz=tetrapyrido[3,2‐a:2′,3′‐c:3′′,2′′‐h: 2′′′,3′′′‐j]phenazine), and its derivatives have been investigated. Heating a solution of complex 1 (closed form) and its derivatives in MeCN caused the partial dissociation of one pyridylmethyl moiety of the TPA ligand and the resulting vacant site on the RuII center was occupied by a molecule of MeCN from the solvent to give a dissociated complex, [RuII(η3‐TPA)(tpphz)(MeCN)]2+ ( 1′ , open form), and its derivatives, respectively, in quantitative yields. The thermal dissociation reactions were investigated on the basis of kinetics analysis, which indicated that the reactions proceeded through a seven‐coordinate transition state. Although the backwards reaction was induced by photoirradiation of the MLCT absorption bands, the photoreaction of complex 1′ reached a photostationary state between complexes 1 and 1′ and, hence, the recovery of complex 1 from complex 1′ was 67 %. Upon protonation of complex 1 at the vacant site of the tpphz ligand, the efficiency of the photoinduced recovery of complex 1 +H+ from complex 1′ +H+ improved to 83 %. In contrast, dinuclear μ‐tpphz complexes 2 and 3 , which contained the RuII(TPA)(tpphz) unit and either a RuII(bpy)2 or PdIICl2 moiety on the other coordination edge of the tpphz ligand, exhibited 100 % photoconversion from their open forms into their closed forms ( 2′ → 2 and 3′ → 3 ). These results are the first examples of the complete photochromic structural change of a transition‐metal complex, as represented by complete interconversion between its open and closed forms. Scrutinization by performing optical and electrochemical measurements allowed us to propose a rationale for how metal coordination at the vacant site of the tpphz ligand improves the efficiency of photoconversion from the open form into the closed form. It is essential to lower the energy level of the triplet metal‐to‐ligand charge‐transfer excited state (3MLCT*) of the closed form relative to that of the triplet metal‐centered excited state (3MC*) by metal coordination. This energy‐level manipulation hinders the transition from the 3MLCT* state into the 3MC* state in the closed form to block the partial photodissociation of the TPA ligand. 相似文献
52.
Dr. Takuya Nakashima Kyohei Yamamoto Yuka Kimura Prof. Tsuyoshi Kawai 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(50):16972-16980
Herein, we designed chiral photoresponsive tetra(2‐phenylthiazole)s, which induce a diastereoselective 6π‐electrocyclization reaction in a helically folded structure to freeze the conformational interconversions. The folding conformation with one helical turn of tetra(2‐phenylthiazole)s was supported by multiple intramolecular noncovalent interactions including vicinal S???N interheteroatom interactions and CH–π and π–π stacking interactions between nonadjacent units, as found in X‐ray crystal structures as well as quantum chemical calculations. The introduction of a chiral group at both ends of tetra(2‐phenylthiazole) dictates the preferential folding into a one‐handed helix conformation by the simultaneous operation of S???O and multiple CH–π interactions that involve the chiral end groups. Since the tetra(2‐phenylthiazole)s possess two equivalent photoreactive 6π‐electron systems and the folded conformation is suitable for photoinduced electrocyclization reaction, they undergo a photocyclization reaction in a stereoselective manner to memorize the chirality of the helix in a resulting diastereomeric closed form. 相似文献
53.
Takuya Uto Takashi Hosoya Sachio Hayashi Toshifumi Yui 《Cellulose (London, England)》2013,20(2):605-612
In hot-water molecular dynamics simulation at 370 K, four cellulose IIII crystal models, with different lattice planes and dimensions, exhibited partial crystalline transformations of (1 ?1 0) chain sheets, in which hydroxymethyl groups were irreversibly rotated from gt into tg conformations, accompanied by hydrogen-bond exchange from the original O3–O6 to cellulose-I-like O2–O6 bonds. The final hydrogen-bond exchange ratio was about 95 % for some of the crystal models after 50 ns simulation. The corrugated (1 ?1 0) chain sheet was converted to a cellulose-I-like flat chain sheet with a slightly right-handed twist. The 3D structures of the three types of isolated chain sheet models were optimized using density functional theory calculations to compare their stabilities without crystal packing forces. The cellulose Iβ (1 0 0) models were more stable than the cellulose IIII (1 ?1 0) models. The optimized structure of cellulose IIII (1 0 0) models deviated largely from the initial sheet form. It was proposed to the crystalline transformation from cellulose IIII to Iβ that conversion of the chain sheet structure first take place, followed by sliding of the chain sheet along the fiber axis. 相似文献
54.
Yasuo Kameda Takuya Miyazaki Toshiya Otomo Yuko Amo Takeshi Usuki 《Journal of solution chemistry》2014,43(9-10):1588-1600
Neutron diffraction measurements were carried out at 25 °C for aqueous LiNO3 heavy water solutions, (*LiNO3) x (D2O)1?x where x = 0.1, 0.05 and 0.01, in which the 6Li/7Li isotopic ratios were varied. Structural information on intermolecular nearest neighbor Li+···D2O interactions in the extensive concentration range was derived from the first-order difference function, ?Li(Q), obtained from the difference in scattering cross sections between 6Li- and 7Li-enriched sample solutions. The nearest neighbor Li+···O distance and coordination number for sample solution with x = 0.1 were determined to be r LiO = 1.969 (8) Å and n LiO = 4.12 (6), respectively, corresponding to the four-coordinated Li+ ion in the solution. On the other hand, those obtained for the solution with x = 0.01 are r LiO = 2.00 (2) Å and n LiO = 6.0 (2), respectively, indicating that hexaaqua Li+ is dominant in the dilute solution. These results clearly indicate that a concentration dependence of the hydration number of Li+ occurs in the aqueous solutions. 相似文献
55.
Diketopyrrolopyrrole (DPP) derivatives bearing 2-pyridyl groups were synthesized, which could serve as anionic N,N′-chelate ligands consisting of two nitrogen atoms of the lactam moieties and the pyridyl groups. Coordination of the DPP ligand to boron and platinum yielded the corresponding DPP complexes. Their crystal structures exhibited coplanar structures between the DPP core and the 2-pyridyl groups, which indicated extended π-conjugation. The maximum absorption wavelength of the DPP complexes was longer than that of the corresponding DPP ligands. The choice of the introduced element affects the optical properties of the DPP complexes; the platinum complex has a longer absorption wavelength than the boron complex. The theoretical calculation revealed that these absorptions can be attributed to the π–π* transition. The introduction of the coordinating elements predominantly lowers the band gap. In addition, the substituent on the 2-pyridyl group can also modulate the energy levels. 相似文献
56.
Silk‐Pectin Hydrogel with Superior Mechanical Properties,Biodegradability, and Biocompatibility
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Keiji Numata Shoya Yamazaki Takuya Katashima Jo‐Ann Chuah Naofumi Naga Takamasa Sakai 《Macromolecular bioscience》2014,14(6):799-806
A new method is developed to prepare silk hydrogels and silk‐pectin hydrogels via dialysis against methanol to obtain hydrogels with high concentrations of silk fibroin. The relationship between the mechanical and biological properties and the structure of the silk‐pectin hydrogels is subsequently evaluated. The present results suggest that pectin associates with silk molecules when the silk concentration exceeds 15 wt%, suggesting that a silk concentration of over 15 wt% is critical to construct interacting silk‐pectin networks. The silk‐pectin hydrogel reported here is composed of a heterogeneous network, which is different from fiber‐reinforced, interpenetrated networks and double‐network hydrogels, as well as high‐stiffness hydrogels (elastic modulus of 4.7 ± 0.9 MPa, elastic stress limit of 3.9 ± 0.1 MPa, and elastic strain limit of 48.4 ± 0.5%) with regard to biocompatibility and biodegradability. 相似文献
57.
Yokokita Takuya Yano Shinya Komori Yukiko Haba Hiromitsu 《Journal of Radioanalytical and Nuclear Chemistry》2022,331(2):1127-1134
Journal of Radioanalytical and Nuclear Chemistry - To investigate sulfate complex formation of Rf, we performed batch-wise ion-exchange experiments of its homologues Zr and Hf and its pseudo... 相似文献
58.
Cellulose - Cellulose I crystals swell on exposure to ethylenediamine (EDA) molecules to form a cellulose I–EDA complex, and successive extraction of EDA molecules converts the complex... 相似文献
59.
Dr. Neil J. Stewart Hitomi Nakano Shuto Sugai Mitsushi Tomohiro Yuki Kase Yoshiki Uchio Dr. Toru Yamaguchi Yujirou Matsuo Dr. Tatsuya Naganuma Dr. Norihiko Takeda Dr. Ikuya Nishimura Dr. Hiroshi Hirata Dr. Takuya Hashimoto Dr. Shingo Matsumoto 《Chemphyschem》2021,22(10):915-923
Hyperpolarized [1-13C]fumarate is a promising magnetic resonance imaging (MRI) biomarker for cellular necrosis, which plays an important role in various disease and cancerous pathological processes. To demonstrate the feasibility of MRI of [1-13C]fumarate metabolism using parahydrogen-induced polarization (PHIP), a low-cost alternative to dissolution dynamic nuclear polarization (dDNP), a cost-effective and high-yield synthetic pathway of hydrogenation precursor [1-13C]acetylenedicarboxylate (ADC) was developed. The trans-selectivity of the hydrogenation reaction of ADC using a ruthenium-based catalyst was elucidated employing density functional theory (DFT) simulations. A simple PHIP set-up was used to generate hyperpolarized [1-13C]fumarate at sufficient 13C polarization for ex vivo detection of hyperpolarized 13C malate metabolized from fumarate in murine liver tissue homogenates, and in vivo 13C MR spectroscopy and imaging in a murine model of acetaminophen-induced hepatitis. 相似文献
60.
Hiroki Yamamoto Takuya Fujiwara Takashi Funatsu Makoto Tsunoda 《Molecules (Basel, Switzerland)》2021,26(8)
Biothiols, such as cysteine and glutathione, play important roles in various intracellular reactions represented by the redox equilibrium against oxidative stress. In this study, a method for intracellular thiol quantification using HPLC-fluorescence detection was developed. Thiols were derivatized with a thiol-specific fluorescence derivatization reagent, viz. ammonium 7-fluoro-2,1,3-benzoxadiazole-4-sulfonate (SBD-F), followed by reversed-phase separation on an InertSustain AQ-C18 column. Six different SBD-thiols (homocysteine, cysteine, cysteinylglycine, γ-glutamylcysteine, glutathione, and N-acetylcysteine as an internal standard) were separated within 30 min using a citric buffer (pH 3.0)/MeOH mobile phase. The calibration curves of all the SBD-thiols had strong linearity (R2 > 0.999). Using this developed method, the thiol concentrations of human chronic myelogenous leukemia K562 cell samples were found to be 5.5–153 pmol/1 × 106 cells. The time-dependent effect of a thiol scavenger, viz. N-ethyl maleimide, on intracellular thiol concentrations was also quantified. This method is useful for elucidating the role of intracellular sulfur metabolism. 相似文献