Ni‐Catalyzed [4+3+2] Cycloaddition of Ethyl Cyclopropylideneacetate and Dienynes: Scope and Mechanistic Insights

A detailed study of the Ni‐catalyzed [4+3+2] cycloaddition reaction between ethyl cyclopropylideneacetate and dienynes has been conducted, resulting in the development of a new method for the synthesis of compounds containing nine‐membered rings. We studied the reactivity of various dienynes, together with their substituent and conformational effects. The mechanism of the reaction was probed by examining the stoichiometric reactions of the Ni complexes and dienynes.     

Complete Photochromic Structural Changes in Ruthenium(II)?Diimine Complexes,Based on Control of the Excited States by Metalation

The thermal and photochemical reactions of a newly synthesized complex, [Ru^II(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 Ru^II center was occupied by a molecule of MeCN from the solvent to give a dissociated complex, [Ru^II(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 Ru^II(TPA)(tpphz) unit and either a Ru^II(bpy)₂ or Pd^IICl₂ 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.     

Chiral Photoresponsive Tetrathiazoles That Provide Snapshots of Folding States

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.     

Partial crystalline transformation of solvated cellulose IIII crystals, reproduced by theoretical calculations

In hot-water molecular dynamics simulation at 370 K, four cellulose III_I 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 III_I (1 ?1 0) models. The optimized structure of cellulose III_I (1 0 0) models deviated largely from the initial sheet form. It was proposed to the crystalline transformation from cellulose III_I to Iβ that conversion of the chain sheet structure first take place, followed by sliding of the chain sheet along the fiber axis.     

Development of continuous process enabling nanofibrillation of pulp and melt compounding

Microfibrillated cellulose (MFC), a mechanically fibrillated pulp mostly consisting of nanofibrils, is a very attractive material because of its high elastic modulus and strength. Although much research has been done on composites of MFC and polypropylene (PP), it has been difficult to produce such composites at an industrial level because of the difficulties in using MFC in such composites are not only connected to the polarity (that can be improved with compatibilizers), but also with the challenge to make a homogeneous blend of the components, and also the low temperature stability of cellulose that could cause problems during processing. We developed a new processing method which enables continuous microfibrillation of pulp and its melt compounding with PP. Never-dried kraft pulp and powdered PP were used as raw materials to obtain MFC by kneading via a twin-screw extruder. Scanning electron microscopy showed nano to submicron wide fibers entangled in the powdered PP. MFC did not aggregate during the melt compounding process, during which the water content was evaporated. Maleic anhydride polypropylene (MAPP) was used as a compatibilizer to reinforce interfacial adhesion between the polar hydroxyl groups of MFC and non-polar PP. We investigated the effect of MAPP content on the mechanical properties of the composite, which were drastically improved by MAPP addition. Needle-leaf unbleached kraft pulp (NUKP)-derived MFC composites had better mechanical properties than needle-leaf bleached kraft pulp (NBKP)-derived MFC composites. Injection molded NUKP-derived MFC composites had good mechanical and thermal properties. The tensile modulus of 50 wt% MFC composite was two times, and the tensile strength 1.5 times higher than that of neat PP. The heat distortion temperature of 50 wt% MFC content composite under 1.82 MPa flexural load was increased by 53 °C, from 69 to 122 °C. This newly developed continuous process using powder resin has the potential for application at an industrial level.     

Neutron Diffraction Study on the Structure of Aqueous LiNO3 Solutions

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.     

Optical properties of highly planar diketopyrrolopyrrole derivatives fixed by coordinate bonds

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.     

Oxidation of sulfides with hydrogen peroxide catalyzed by synthetic flavin adducts with dendritic bis(acylamino)pyridines

The catalytic activities of the cationic synthetic flavin adduct 1 with various dendritic and non-dendritic 2,6-bis(acylamino)pyridines 2 were examined for the oxidation of organic sulfides with H₂O₂. The adduct of 5-ethyllumiflavinium perchlorate 1a with 2b–d bearing poly(benzyl ether) dendron units acts as an efficient organocatalyst for the oxidative transformation of sulfides to the corresponding sulfoxides under mild conditions.     

Silk‐Pectin Hydrogel with Superior Mechanical Properties,Biodegradability, and Biocompatibility

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.     

Anion- and cation-exchange studies of Zr,Hf, and Th using ion-exchange resin and fiber in H2SO4 media for chemical characterization of sulfate complex of Rf

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...