The development of new magnetic materials in which magnetic properties are combined with optical properties has been extensively studied. So far, several photo-responsive molecular solids have been reported. However, the strategies that are necessary to achieve photoinduced switching in a solid state are yet to be clarified. Here, I have focused on composite materials as a novel strategy for realizing such photo-functional magnetic systems. These include the incorporation of organic photochromes into magnetic systems, e.g., photo-controllable magnetic vesicles and LB films containing Prussian blue or iron oxide nanoparticles and azobenzene.
The 7-azaindole dimer (7AI2) is a prototype of double hydrogen-bonded molecules. 7AI2 has been considered as a model DNA base pair and has attracted much attention to the mechanism of the excited-state double-proton transfer (ESDPT). Two ESDPT mechanisms, stepwise and concerted mechanisms, have been proposed so far. Great efforts have been devoted to clarify the mechanism of ESDPT using experimental and theoretical methods. However, the reaction mechanism had been controversial for more than a decade. We provide the resolution of the two mechanisms on the basis of new data obtained from electronic spectroscopy and picosecond time-resolved spectroscopy in the gas phase. The initial state of the ESDPT reaction has been well characterized by investigating the exciton resonance interaction with UV–UV hole-burning spectroscopy for various 7AI2 isotopomers. The lowest-excited state of 7AI2 has been classified into the weak coupling case of the exciton theory. We have concluded that the ESDPT reaction in 7AI2 occurs via the concerted mechanism on the basis of the results of picosecond time-resolved experiments and the H/D kinetic isotope effect on ESDPT studied by measuring the vibronic-state selective dispersed fluorescence spectra. ESDPT of 7AI2 has a “dynamic cooperative” nature that may arise from the coupling of the two moving protons with the reorganization of electrons. We have provided a new paradigm of ESDPT, where two quantum effects, the exciton resonance interaction and the proton tunneling, are concerned with the ESDPT reaction.
Two spatially different nano-structured inorganic materials, titania nanosheets (TNS) and mesoporous silica (MPS), were integrated onto a glass substrate to form stacked composite thin films. Investigations were then carried out on photoinduced electron transfers between the tetrakis(1-methylpyridinium-4-yl)porphyrinatometal(4+) ion ([M(tmpyp)]4+); M = H2, Zn, and Co) and 1,1′-dimethyl-4,4′-bipyridinium (methyl viologen; MV2+) within the hybrid films. The [M(tmpyp)]4+ molecules were found to be adsorbed only in the MPS nano-cavities, while MV2+ was intercalated only in the TNS layer, i.e., the [M(tmpyp)]4+ and MV2+ molecules could be separately and selectively accommodated into the MPS nano-cavities and TNS layers of the hybrid films, respectively. Upon UV light irradiation (TNS excitation) of the films containing [H2(tmpyp)]4+, the decomposition of [H2(tmpyp)]4+ and the formation of a one-electron reduced MV2+ (MV+•) were observed, clearly indicating photoinduced electron transfers in the MPS/TNS films. Moreover, when the metal-complex [Zn(tmpyp)]4+ or [Co(tmpyp)]4+ was used in place of [H2(tmpyp)]4+, visible light-induced electron transfers could be observed in the present MPS/TNS hybrid films, the first report of such charge separation in consecutively stacked thin films by visible light.
Molecular dynamics simulations for a lithium cation surrounded with 100 water molecules as a solvent were carried out by using an ab initio integrated multicenter molecular orbitals method (IMiC MO) with HF/6-31G(d,p) level. For the temperature of both 293 and 323 K, the first hydration shell of the lithium cation is preferred to form a tetrahedral structure including four water molecules, and is well separated from the outer hydration shell. The mechanisms for the variation of the coordination number and the exchange of solvent molecules between the first and the second hydration shells were also studied.
The infrared intensities of the triclinic and monoclinic crystal modifications of quinhydrone (QH) have been measured, along with those of the parent molecules of p-hydroquinone (HQ) and p-benzoquinone (BQ) in solutions and in crystal form. The infrared spectra calculated by the density functional theory indicate that the hydrogen bond between HQ and BQ gives large changes in the infrared intensities of some bands of HQ, but gives rather small changes in the bands of BQ, even in ν(C=O). Charge-transfer interaction in QH is suggested to play an important role for the change in the infrared intensities of ν19a at 1520 cm−1 and τ(C–H) at 530 cm−1 in HQ. In the two crystal modifications of QH, the hydrogen bond is stronger in triclinic QH than in monoclinic QH, whereas the electrostatic interaction is stronger in monoclinic QH than in triclinic QH. The intensity differences of BQ between the CCl4 solution and the crystal are analyzed on the basis of the electrostatic model.
Circular dichroism (CD) signals of J-aggregates of 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS4) fixed on mesoporous TiO2 film were induced by adsorption of D-tartaric acid. The intensity of the induced CD signal at 477 nm derived from TPPS4 J-aggregates adsorbed on TiO2 film increased depending strongly on the concentration of D-tartaric acid dissolved in the surrounding water and the immersion time of TPPS4-adsorbed TiO2 film in acidic water. Especially, in acidic water with high concentrations of D-tartaric acid, the CD intensity increased enormously with the elapse of immersion time, accompanying a decrease of J-aggregates adsorbed on TiO2 film. The amount of D-tartaric acid adsorbed on TiO2 film should determine the CD intensity of J-aggregates. When D-tartaric acid dimethyl ester, which has an effect similar to D-tartaric acid on the induction of CD of TPPS4 J-aggregates in an aqueous solution, was used instead of D-tartaric acid, a slight CD at 477 nm was observed, clearly showing that the chemisorption of chiral molecules on the TiO2 surface through an anchoring group was critical for inducing the CD signal of J-aggregates.
A kinetic study was performed for edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one) in order to clarify the mechanism of its free-radical-scavenging and vitamin E-regenerating actions. The second-order rate constants for the radical-scavenging reaction of edaravone were measured in several organic solvents and in a water/methanol mixed solvent at various pH. The keto–enol tautomerism and the acid–base dissociation equilibrium of edaravone produce keto, enol, and anion forms in solutions, and their contributions and activities varied depending on the properties of the solutions. From the results of NMR and kinetic studies, it has been clarified that the keto–enol tautomerism of edaravone actually exists, and the keto form has larger radical-scavenging activity than the enol form. Furthermore, the pH dependence of the rate constants suggests that the anion form produced by the acid–base dissociation equilibrium of edaravone has the highest radical-scavenging activity in the keto, enol, and anion forms.
Well-formed crystals of barium chlorapatite [Ba5Cl(PO4)3] and strontium chlorapatite [Sr5Cl(PO4)3] were grown from a sodium chloride flux. The contact angle of water on the () face of each chlorapatite crystal was observed using a modified Wilhelmy method, where we measured the change of liquid weight instead of the crystal weight. The contact angle depends on the aspect ratio of the crystal. Both the advancing and receding contact angles were larger for Ba5Cl(PO4)3 and Sr5Cl(PO4)3 crystals with larger aspect ratios. The surface free energy of the () face was calculated using Neumann’s equation. The () face of the crystals of larger aspect ratios has a smaller surface free energy, indicating that such crystals have a more stable () face than the crystals of smaller aspect ratios. This result corresponds to the morphology of the chlorapatite crystals because the crystals have a tendency to elongate into the  direction.
A sensitive and simple method for the simultaneous determination of nutritionally important minerals including copper, nickel, and iron in real samples is in great demand. Atomic absorption spectrometry (AAS) coupled with a preconcentration method is shown to be an appropriate technique for this objective. The method is based on the formation of mineral complexes by α-benzyl dioxime (BDO) supported on sodium dodecyl sulfate (SDS)-coated alumina. The metal contents in the complexes are eluted using 5 mL of 6 mol L−1 HNO3, and then detected by AAS at respective maximum wavelengths. In this procedure, minerals such as Cu, Ni, Pb, Co, and Fe can be analyzed in one run by carrying out the simultaneous separation and quantification of them. The low detection limit of these elements makes it a superior alternative to UV–vis and in several applications, also an alternative to ICP-MS techniques. The method has been successfully applied for these metal content evaluations in some real samples including waste water, river water, spring water, tap water, vegetable, and baking powder.
A series of novel Cu(I) complexes with an s-binap ligand and a diimine ligand, [Cu(s-binap)(bpy)]PF6, [Cu(s-binap)(phen)]PF6, and [Cu(s-binap)(dmp)]PF6, were synthesized, where bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline, dmp = 2,9-dimethyl-1,10-phenanthroline, and s-binap = (S)-2,2′-bis(diphenylphosphino)-1,1′-binaphthyl. All three complexes show intense photoluminescence in the solid state, whereas [Cu(s-binap)(dmp)]PF6 is a comparatively good emitter in CH2Cl2 solutions. These luminescence bands have been assigned to the emission from 3MLCT states. The complexes [Cu(s-binap)(bpy)]PF6 and [Cu(s-binap)(dmp)]PF6 were characterized by X-ray structure analyses. Although the distorted tetrahedral structures around the central metals of the two complexes are similar, the photophysical properties of the dmp complex differ from those of the other complexes in solution. The structures and the photophysical properties of the three complexes have been discussed.
Iron(III) spin-crossover compounds with H3-OMe-salRen ligands [Fe(3-OMe-salRen)2]ClO4 (1–5) were prepared and characterized by single-crystal X-ray diffraction, Mössbauer spectra, magnetic susceptibilities, and electronic spectra, where 3-OMe-salRen is a tridentate ligand derived from 3-methoxysalicylaldehyde and N-R-ethylenediamine (R = H, Me, Et, Pr, and Bu for 1, 2, 3, 4, and 5). The structures of compounds 1, 2, 3, and 5 at 90 and 298 K, and that of compound 4 at 298 K were determined. Compounds 1, 2, 3, and 5 exhibited a spin transition depending on temperature; the transition temperatures for 1, 2, 3, and 5 were >400, 360, 196, and 223 K, respectively. Compound 4 was in the high-spin state in the temperature range of 5 to 400 K. σ–π or π–π interactions exist in compounds 1–5, and the structures of the compounds were made clear in both the high-spin and low-spin states. Compound 3 exhibited a spin transition with thermal hysteresis.
Solid-state 13C NMR characterization of cross-linkage formation between the exocyclic methylene groups of labdane polymers in amber demonstrated that the process is an apparent first-order reaction with a half-life of ≈13 million years.
An environmentally friendly and efficient synthesis of a series of 1,4-dihydropyridines was developed by the practical one-pot reactions of aldehydes with ammonium acetate and 1,3-dicarbonyl compounds such as alkyl acetoacetate, 5,5-dimethyl-1,3-cyclohexanedione, 1,3-cyclohexanedione, and 2,4-pentanedione in water without any additives under refluxing conditions.
1,4,7,10-Tetraisopropyldibenzo[c,g][1,2,5,6]tetrachalcogenocins that were readily synthesized from 4,7-diisopropyl-2,2-dimethyl-1,3,2-benzodichalcogenastannoles underwent selective ring contraction under irradiation with a high-pressure mercury lamp to give the corresponding 1,4,6,9-tetraisopropylchalcogenanthrenes having bulky substituents on the benzene ring at adjacent positions of the 6-membered dichalcogenin unit in moderate yields. X-ray crystal structure determination of 1,4,6,9-tetraisopropylthianthrene revealed that the substituents of bulky substituents such as isopropyl groups scarcely affected the structure of the parent dithiin framework. Measurements of the cyclic voltammetry of thianthrene showed a well-defined reversible redox property, whereas the voltammograms of selenium-containing analogues showed irreversible oxidation waves. In contrast to electrical observations, facile reversible one-electron redox reaction systems were observed between the chalcogenanthrenes and the corresponding chalcogenanthrenium radical cations by chemical oxidation or reduction reactions.
An asymmetric synthesis of the C1–C16 polyol subunit 2 of the macrolide antibiotic ossamycin (1) has been achieved through stepwise carbon-chain elongation reaction from D-glucose, based on a chiral pool approach. An outstanding point of this strategy is asymmetric induction by utilizing steric hindrance of neighboring groups. The stereogenic centers at the C4 and C5 positions of 2 were constructed by mCPBA epoxidation, and the C6 and C7 positions of 2 were produced by catalytic OsO4 dihydroxylation under highly stereoselective conditions.
An efficient and concise synthesis of the β-Man(1→4)GlcN linkage that exists in N-linked glycans has been established. Direct β-mannosylations of the 4-OH group of glucosamine derivatives by using 6-nitro-2-benzothiazolyl 3,6-di-O-allyl-2,4-di-O-benzyl-α-D-mannopyranoside (3α) proceed smoothly in the presence of a catalytic amount of HB(C6F5)4 in CH2Cl2 at −78 °C to afford the desired β-mannosides in high yields. The β-trisaccharide 14β, a key building block for the synthesis of the pentasaccharide core 20, is directly prepared from the mannosyl donor 3α and chitobiose acceptor 10 in high yield. In addition, this mannosylation method has successfully been applied to a wide range of glycosyl acceptors derived from glucosamine in a highly efficient manner. Further, the pentasaccharide core 20 that is commonly present in N-linked glycans can also be synthesized readily according to this direct mannosylation strategy.
The first general method for the synthesis of 4H-1,3-benzodioxin-2-one derivatives has been developed. Treatment of t-butyl 2-vinylphenyl carbonates with iodine in the presence of sodium hydrogencarbonate gave 4-iodomethyl-4H-1,3-benzodioxin-2-one derivatives in moderate to good yields. These iodides were reduced with tributyltin hydride to give the corresponding 4-methyl-4H-1,3-benzodioxin-2-one derivatives.
A functional group compatible palladium-catalyzed cross-coupling reaction between aryllithiums and aryl halides mediated by a five-membered cyclic silyl ether as a precursor for an activated arylsilane has been developed. The reaction proceeds under mild conditions without the addition of a fluoride salt or a base to activate the silyl reagent.
The selective deposition of SnS into/onto SnO2 nano-particle films was performed. The disposition of SnS was controlled by the pH of a source tin solution. The photocurrent of the photoelectrochemical cells using these SnS-deposited SnO2 films depended on where SnS was deposited.
It is shown that industrially available 2,3-dichloro-1,3-butadiene is a useful starting material for the synthesis of 2,3-diaryl-1,3-butadienes. Ni(II)-catalyzed cross-coupling reaction of 2,3-dichloro-1,3-butadiene with ArMgBr (Ar = 2-thienyl, phenyl, 4-dodecyloxyphenyl, and 4-fluorophenyl) gives the corresponding 2,3-diaryl-1,3-butadienes in good yields.