Nanostructures and properties of ultrathin polymer films prepared by repeated deposition of monolayers have been investigated with emphasis on single chain morphology in two dimensions. The particular characteristics of ultrathin films were successfully revealed by novel optical microscopy and fluorescence spectroscopy techniques. A single polymer chain, which is confined into a two-dimensional plane, takes a contracted conformation, being segregated from other chains in the monolayer. Unlike three dimensional bulk polymers, there is little entanglement of polymer chains even for large molecular weight samples. These characteristics at the molecular level result in the entropy relaxation of individual chains with a small activation energy of diffusion, when the segmental motions are allowed at elevated temperatures. These understandings of structures and properties in two dimensions are indispensable for fabrication and application of polymeric thin films because the fine structures in low dimensions play critical roles in the production of advanced functions.
Diarylethene is a photochromic molecule, which is potentially applicable to various optoelectronic devices. In diarylethenes the π-system of the two aryl rings is separated in the open-ring isomer, while the π-system is delocalized throughout the molecule in the closed-ring isomer. Based on this idea the exchange interaction between two nitronyl nitroxide radicals connected by a diarylethene unit was photocontrolled reversibly along with photochromism. The switching efficiency is more than 150-fold and thiophene spacer transmits the interaction more efficiently. When diarylethene dimer is used for the switching unit, the electric circuit-like behavior was observed. Moreover, reversed switching is achieved by reversing the thiophene ring. Magnetochemical and photochemical behavior of the radical-substituted diarylethene is described extensively.
In this account, the synthesis, structure, and reactions of cyclic, spiro-conjugated, and cumulative silicon–silicon doubly-bonded compounds are described. Photochemical and thermal interconversion among Si4R6 isomers including cyclotetrasilene 1, cyclotrisilene 2, and bicyclo[1.1.0]tetrasilane 7 occur without apparent participation of the corresponding tetrasila-1,3-diene, in contrast to the related interconversion among C4H6 isomers. Whereas parent spiropentadiene, the simplest spiroconjugation system, is known to survive only below −100 °C, spiropentasiladiene 3 is thermally very stable and shows remarkable spiroconjugation between the two ring π systems. The skeleton of isolable trisilaallene 4, the first stable silicon compound with tetracoordinate divalent (formally sp-hybridized) silicon atom, is not linear but remarkably bent. The considerable conjugation between two cumulative Si=Si double bonds was observed. The structural feature of 4 is quite different from that of carbon-based allenes having linear structure without conjugation between two π-bonds.
Photochemical and photophysical properties of the triplet excited states of dendritic multiporphyrins arrays (nPZn, n = 1, 3, and 7) have been investigated by measuring the nanosecond transient absorption spectra in the visible and near-IR regions with changing the generation number. Intermolecular triplet–triplet annihilation rates decrease with the dendrimer generation, which was interpreted on a proposed kinetic model assuming that the excited triplet energy almost localizes in one PZn unit in nPZn. In the presence of C60, intermolecular electron-transfer takes place via the excited triplet states of nPZn (3nPZn*), yielding the cation radical of nPZn (nPZn•+) and the anion radical of C60 (C60•−) in PhCN. Deceleration of the electron-transfer rate-constants from 1PZn to 3PZn and the acceleration from 3PZn to 7PZn were observed, in which the latter tendency was interpreted by considering an increase in effective encounter radius for 37PZn*. The observed small change of the rate constants for back electron transfer between the oppositely charged species with the dendrimer generation was also reasonably interpreted by taking a smaller effective radius due to electrostatic attraction into consideration. Dendrimer generation effect was also observed for the intermolecular hole-transfer process.
Time-of-Flight (TOF) neutron diffraction measurements were carried out for 12 mol% *HCOO7Li solutions in D2O. The H/D isotopic substitution technique was applied to the formyl-hydrogen atom of the formate ion in order to determine both the hydration structure around the formyl-hydrogen atom and the intramolecular structure of HCOO− in the aqueous solution. The hydration structure around the formyl-hydrogen atom was analyzed by applying a least-squares refinement procedure to the observed intermolecular difference function. The intramolecular distances within the formate ion were determined to be r(Hf–C) = 1.072(2) Å and r(Hf···Of) = 2.015(8) Å.
Hydroquinone, showing a melanogenesis inhibitory effect, formed crystalline molecular complexes with two cationic surfactants of benzyl(hexadecyl)dimethylammonium chloride and ethyl(hexadecyl)dimethylammonium bromide from an methanol solution at low temperatures, lower than 15 °C. The crystal structures were analyzed by X-rays at 223 K. There are two crystallographically independent hydroquinone molecules and one surfactant molecule in each crystal. One of the hydroquinone molecules is sandwiched by the surfactant molecules and makes a “common packing pattern,” which has been observed in complex crystals between aromatic compounds and surfactant molecules. Another hydroquinone occupies an inversion center surrounded by the benzyldimethylammonium or ethyldimethylammonium moiety of the surfactant molecule. Such a close packing makes hydroquinone in the molecular complex stable in open air at room temperature.
The 17O NMR spin–lattice relaxation times (T1) of solvent water molecules in aqueous solutions of amino alcohols (AA), charged amino alcohols (AA+), and charged diamines (DA2+) were determined as a function of concentration at 298 K. The values of the dynamic hydration number, nDHN = nh(τch/τc0−1), were determined from the concentration dependence of T1. The ratios (τch/τc0) of the rotational correlation times (τch) of the water molecules around each solute molecule in the aqueous solutions to that of pure water (τc0) were obtained from the nDHN and the hydration number (nh), which was calculated from the water accessible surface area (ASA) of the solute molecule. The hydrophobic hydration is disturbed by the adjacent polar groups. The effect of disturbance decreases in the following order: NH3+ > OH > NH2. The ASA dependence of the τch/τc0 value for diamines (DA), AA, and diols decreases in the following order: DA > AA > diols. When DA and AA are in a charged state, this order is reversed, namely, diols > AA+ > DA2+. The thermodynamic quantities of hydration for AA and AA+ are linearly dependent on their nDHN values.
A coarse grain molecular dynamics simulation method was applied to polystyrenesulfonate in aqueous solution to investigate the conformational and orientational behavior of flexible polyion under an external electric field. When the electric field was applied, the deviation of the counter-ion distribution and the rotational orientation of the polyion toward the direction of the electric field were observed. The orientation behavior of flexible polyelectrolytes depended on the field strength, and two typical orientational motions were detected. That is, at low electric field strength, elongation of the whole polyion chain conformation occurs at first stage and subsequently rotationally orients toward the field direction. On the other hand, segment orientation occurs at the high field because of the fast displacement of the counter ions on each polymer segment. The ionic polarization of the flexible polyion was evaluated by the component analysis of the counter-ion deviation. Results showed that the loosely-bound counter ions contribute largely to the ionic polarization.
We have prepared microfabricated α-Sb2O4 thin films on VSbO4 by electron lithography. The VSbO4 thin films were prepared on a Si substrate by a sol–gel method combined with a spin coating. The size, separation and arrangement of the α-Sb2O4 overlayer were controlled by electron-beam lithography. We could successfully draw 0.5 μm wide lines with a separation of 2 μm. A preliminary study on the catalysis showed an enhancement of the selectivity in a propene conversion reaction to acrolein on a microfabricated α-Sb2O4/VSbO4.
For the purpose of construction of the hydrogen-bonded and coordination-bonded supramolecular network, MnII complex bridged by squarate molecules was synthesized, and their structural and magnetic properties were studied. X-ray structure determination revealed that MnII complex, [MnII4(C4O4)4(C4H4N2)(H2O)8], had a three-dimensional network structure bridged by squarates with cavities which trap pyrazine molecules. Pyrazine molecules have an orientational disorder even at 10 K in the cavities. They are stabilized by weak hydrogen bonds with a network formed by squarates. A weak antiferromagnetic exchange interaction is observed between magnetic moments on Mn2+ ions through squarate. In the case of one-dimensional polymer chain complexes, MII(C4O4)(C4H4N2)(H2O)4 (where MII = FeII, NiII, CuII), which are bridged by pyrazine molecules, the temperature dependence of magnetic susceptibility follows Bonner–Fischer’s one dimensional chain model. The antiferromagnetic exchange parameter for CuII complex is slightly larger than those for FeII and NiII complexes. This difference is considered to be caused by the difference of the metal to metal distances. In the case of [CoII(C4O4)(C4H4N2)(H2O)4], clear anisotropy of the magnetic properties was observed, which was caused by large zero-field splitting.
A new zinc(II) complex, bis(6-ethylpicolinato)zinc(II) ([Zn(6epa)2]), was prepared by introducing an electron-donating ethyl group on the pyridine ring. [Zn(6epa)2] was crystallized from an aqueous solution, and its structure was determined by X-ray analysis, in which both carboxylate O and pyridine N atoms of 6epa coordinated to a Zn2+ ion, forming a distorted trigonal bipyramidal geometry with two 6epa and a water. In an in vitro evaluation with regard to the inhibition of free fatty acid (FFA) release from isolated rat adipocytes in the presence of epinephrine, the insulinomimetic activity (IC50 = 0.37 mM) of [Zn(6epa)2] was found to be higher than that (0.64 mM) of the bis(picolinato)Zn(II) complex in terms of the IC50 value. When the [Zn(6epa)2] complex was injected daily at a dose of 3 mg Zn/kg of body weight of KK-Ay mice for 14 d, the blood glucose levels of the mice were lowered to approximately 200 mg/dL (11.1 mM) from 400–500 mg/dL (22.2–27.8 mM). Based on the results, the [Zn(6epa)2] complex was proposed to be a new candidate for treating type-2 diabetes in animals. However, it was proven that [Zn(6mpa)2] has an advantage in having no side effect over [Zn(6epa)2], when the effects on their serum parameters were considered.
Dialkyl ethers and alkyl fluoroalkyl ethers are obtained in excellent yields by the reaction of alcohols and carbonyl compounds in the presence of Pd/C under the atmospheric pressure of hydrogen, when water produced by the reaction is continuously removed by bubbling hydrogen through the reaction mixture.
A chiral pyrromethene–BF2 complex dye, showing absorption (λmax) and emission maxima (λem) at 499 and 518 nm in acetonitrile, respectively, was synthesized. Racemic mexiletine smoothly reacted with this reagent in the presence of EDC to preferentially produce the corresponding diastereomeric amides, which were nicely separated by a non-chiral reverse phase column. The detection limit (S/N > 3) of mexiletine was ca. 0.3 pmol.
The reaction of phenols with ethyl acrylates in the presence of a Pd(OAc)2 catalyst in trifluoroacetic acid did not yield dihydrocoumarins but gave coumarins, in contrast to the reaction of phenols with propiolates. The addition of K2S2O8 as an oxidant increased the yield of coumarins. The reaction of several phenols with ethyl cinnamate, ethyl crotonate, or ethyl acrylate gave the corresponding coumarin derivatives in moderate to good yields. The coumarin formation competed with the oxidative coupling of electron-rich phenols, which reduced the product yield.
Cationic model peptides containing simple repeats, H-(LARL)3-(LRAL)n-NH2 (n = 0, 1, 2, and 3), were synthesized, and their antibacterial and hemolytic activities were investigated. Antibacterial activity decreased with an increase in the chain length of the peptides, whereas the reverse situation was found for hemolytic activity. As a result of measuring the bacterial membrane permeabilization, it was indicated that the complicated surface membrane structure of bacteria prevented the penetration of the long and rigid peptides into the inner membrane portion. Another peptide, H-(LARL)3-PRAL-(LRAL)2-NH2, which has a kink in the middle portion of the molecule, showed some antibacterial activity in spite of its long peptide chain.
A catalytic acylation of vinylsilane with acid anhydride is accomplished by the use of [RhCl(CO)2]2, in which the transmetalation between vinylsilane and rhodium(I) carbonyl complex plays a key role. The application of this acylation reaction to (1-acyloxyvinyl)silanes provides synthetic methods for α-acyloxy enones, α-diketones, and their derivatives.
Static and dynamic stereochemistry of several tris(9-triptycyl)stannane derivatives Tp3SnX (X = H, halogens, and alkyl groups) were studied. X-ray crystallography of the bromo and methyl compounds showed that the Sn atom was fundamentally tetrahedral and that the three Tp groups meshed with each other like bevel gears and formed a near-C3 chiral conformation. The rate constants for enantiomerization of the chiral conformation in solution could be obtained by the lineshape analysis of the aromatic proton signals, even when a direct probe for enantiomerization such as a benzyl group was absent. The energy barrier to enantiomerization decreased as the substituent X became bulkier, suggesting that the ground state is more destabilized than the transition state upon introduction of a bulkier group.
Monohydrolyses of symmetric diesters were carried out using several aqueous inorganic bases, LiOH, NaOH, KOH, and CsOH. The more reactive bases showed higher selectivities in the monohydrolyses of acyclic symmetric diesters.
Colloidal gold nanoparticles self-assembled into macroscopic aggregates by a charge-transfer interaction between a 9-carbazolyl unit as an electron-donor immobilized on the surface of the gold nanoparticles and a bivalent linker containing two dinitrophenyl units as electron-acceptors. Transmission electron microscopy and scanning electron microscopy images showed spherical aggregates consisting of the gold nanoparticles.
Polypyrrole films prepared from aromatic ester solutions of tetrabutylammonium tetrafluoroborate (TBABF4), tetrabutylammonium hexafluorophosphate (TBAPF6), tetrabutylammonium trifluoromethanesulfonate (TBACF3SO3), and tetrabutylammonium perchlorate (TBAClO4) exhibited large electrochemical strain (11.2–14.0%) and stress (10.6–22.0 MPa) when cycled between −0.9 V and +0.7 V vs Ag/Ag+ at 2 mV s−1 and 10 mV s−1, respectively, in an aqueous NaPF6 solution, amongst which PPy-CF3SO3− solely elongated mechanically by 60–100%. It is therefore more suitable for practical artificial muscle devices. Although polypyrrole actuators doped with ClO4− exhibited moderate strains for a decade, a PPy-ClO4− actuator prepared from an aromatic ester solution has showed large electrochemical strain (11.2–13.5%) and stress (12.3–15.2 MPa). When cycled at 100 mV s−1, polypyrrole actuators exhibited approximately twice as large electrochemical stress as those measured at 10 mV s−1, because the PPy strip was kept in the doped state (the weakest state) for a shorter time, and early breakage did not occur to give a larger electrochemical stress. Polypyrrole actuators might not be very stable when showing the maximum performance, but the electrochemical strain remained almost constant up to 100 cycles under moderate conditions, such as being driven at 0.1 Hz.
Wastewater contaminated with iron-complex cyanides was processed by UV photodecomposition accompanied by an iron elimination process using an iron-adsorbent. The wastewater processed by UV photodecomposition was oxidized by ozone combined with UV irradiation. The treated water was deionized by an ion-exchange resin method. This combined processes further increased the production of the pure water volume compared to a single process using an ion-exchange resin. The technique developed in this study can be summarized as follows. First, the iron-complex cyanides in plating wastewater were converted into aquapentacyanoferrate(III) [Fe(CN)5(H2O)]3− ion. Following the application of UV irradiation, it was decomposed into iron and cyanide (CN−) ion. The iron was removed from the water in the form of Fe(OH)3 by processing the wastewater with ozone and an iron-adsorbent. The CN− ion was oxidized to the cyanate (OCN−) form by UV ozone oxidation in a relatively short time. The processed water was de-ionized by passing through cation and anion-exchange resins. The deionized water could be reused as rinsing water in a plating process. The results reported here suggest that wastewater contaminated with chemically stable iron-complex cyanides can be effectively recycled.
An amphiphilic tetrathiafulvalene (1) was prepared by condensation of tetrathiafulvalene-4-carboxylic acid with reduced Triton X-100 to avoid crystallization. Its charge-transfer (CT) complexation behaviors were examined with a strong electron acceptor, i.e., 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), in solutions. Although tetrathiafulvalene, (4-tetrathiafulvalenyl)methyl acetate (2), and methyl tetrathiafulvalene-4-carboxylate (4) reacted with DDQ to produce a dark red precipitates in CHCl3 and (4-tetrathiafulvalenyl)methyl stearate (3) with DDQ formed black red colloidal dispersions in CHCl3, an equimolar amount of DDQ with 1 in CHCl3 formed a dark red solution without any precipitates. The UV spectrum of the solution of 1 and DDQ in CHCl3 shows a broad peak in near-IR regions. The absorption maximum at 1300 nm (ε = 3.8 × 102 M−1 cm−1) that is tailing to beyond 2000 nm is derived from π-stacked arrangement of the TTF moiety and DDQ. UV–vis absorption spectra of 1 with DDQ in several organic solvents, i.e., acetonitrile, acetone, CH2Cl2, toluene, and CCl4, show that the CT complexation behavior of 1 was highly dependent on the solvent polarity.
The liquid crystallinity values of 2-fluorenyl 4-alkyl (pentadecyl, n-, or s-butyl)-benzoates were compared with those of biphenyl homologues. Cyano group or hydrogen was used as the end group at the 7-position of 2-fluorenol moiety. Methoxy and hydroxy groups in addition to hydrogen were examined as a lateral substituent at the 2-position of 4-alkylbenzoic acid unit. 7-Cyano-2-fluorenyl 2-hydroxy-4-pentadecylbenzoate shows very similar properties to those of 4′-cyanobiphenyl-4-yl 2-hydroxy-4-pentadecylbenzoate.
Micelles of poly(styrene-b-2-vinylpyridine-b-ethylene oxide) (PS-b-P2VP-b-PEO) triblock copolymer were prepared in aqueous solutions. The physicochemical properties of the micelles were investigated by dynamic light scattering, zeta-potential measurements, atomic-force microscopy, and fluorescence spectroscopy. The micelles had an average diameter of about 200 nm under acidic conditions. The addition of dextran sulfate to a micellar solution under acidic conditions resulted in a significant decrease in the micelle size. This was due to a conformational change in the P2VP block form extended to shrunken forms after the cationic P2VP block was electrically neutralized with negative dextran sulfate. The release of anionic dye (Eosin Y) from the micelle particles was studied by a dialysis method, and proved to take tens of hours.
Dehalogenative homopolymerization and copolymerization of 2,5-dibromothiophene and 2,4-dibromothiophene were carried out by using a Ni(II) complex catalyst. Nitration of the polymers gave soluble nitrated polymers which provided information about the degree of polymerization (DP = 58–88) of the original polymers. Chemical properties of the polymers and their nitrates are reported.