A role of solvent in vibrational energy relaxation of metalloporphyrins

The formation of a vibrationally excited photoproduct of metalloporphyrins upon (π, π*) excitation and its subsequent vibrational energy relaxation were monitored by picosecond time-resolved resonance Raman spectroscopy. Stokes Raman bands due to a photoproduct of nickel octaethylporphyrin (NiOEP) instantaneously appeared upon the photoexcitation. Their intensities decayed with a time constant of 300 ps, which indicates electronic relaxation from the (d, d) excited state (B_1g) to the ground state (A_1g), being consistent with the results of transient absorption measurements by Holten and coworkers. Anti-Stokes ν₄ and ν₇ bands for vibrationally excited (d, d) state of NiOEP decayed with time constants of 10 and 300 ps. The former is ascribed to vibrational relaxation, while the latter corresponds to the electronic relaxation from the (d, d) excited state to the electronic ground state. While the rise of anti-Stokes ν₄ intensity was instrument-limited, the rise of anti-Stokes ν₇ intensity was delayed by 2.6±0.5 ps, which indicates that intramolecular vibrational energy redistribution has not been completed in subpicosecond time regime. To study a mechanism of intermolecular energy transfer, solvent dependence of the time constants of anti-Stokes kinetics was investigated using various solvents. No significant solvent dependence of the rise and decay constants was observed for NiOEP. For an iron porphyrin, we observed two phases in intermolecular energy transfer. The fast phase was insensitive to solvent and the slow phase depended on solvents. A model of classical thermal diffusion qualitatively reproduced this behavior. For solute-solvent energy transfer process, low-frequency modes of proteins seem to be less important.     

Stabilization of Bicontinuous Cubic Phase and Its Two-Sided Nature Produced by Use of Siloxane Tails and Introduction of Molecular Nonsymmetry

A recent intriguing finding that a helical network arrangement forms the bicontinuous cubic phase is attracting great attention for the possibility of new routes to asymmetric synthesis by achiral molecules. However, the design of the molecular structure for the cubic phase is still unrevealed. In this work, a nonsymmetric core molecule with larger naphthalene and smaller benzene moieties at each side of the central linkage and the same disiloxanyldecyloxy terminal at both terminals is shown to be the first example of molecule forming both single-layered and double-layered core assembly modes in the Ia3d phase as a single molecule system. The molecule forms the former mode at high temperatures as a thermodynamically stable phase, similarly to the symmetric naphthalene core system, whereas, on cooling below a temperature (∼350 K), a metastable Ia3d phase forms a double-layered core state down to room temperature, which is common to the benzene core system. As another effect of the nonsymmetric core, the cubic phase is maintained at room temperature for more than 100 days with slight distortion. Infrared spectral studies and quantum chemical calculations suggested the easy transformation between the two core assembly modes. The core nonsymmetry can be a versatile fine-tuning of the core assembly mode and phase stability for the cubic phase molecules.     

Insertion reactions of difluorocarbene generated by pyrolysis of hexafluoropropene oxide to OH bond

ROCHF₂-type fluorinated ethers were synthesized by the reaction of hexafluoropropene oxide (HFPO) with alcohol or phenol. In this reaction, although the insertion reaction of difluorocarbene to OH bond and the nucleophilic attack of alcohol or phenol to HFPO were competition, the insertion reaction proceeded predominantly to give fluorinated ether in the case of low nucleophilic alcohol or phenol. In addition, high reaction pressure is advantageous to the selectivity of the fluorinated ethers in the reaction of HFPO with (CF₃)₂CHOH or C₆F₅OH.     

Synthesis of polybenzimidazoles with sulfonic acid groups

2-Sulfoterephthalic acid (STA) and disulfoisophthalic acid (DSIA) were synthesized through the sulfonation and the oxidation of m- and p-xylene. The polycondensation reactions of STA and DSIA with aromatic tetraamines gave polybenzimidazoles which contained one or two sulfonic acid groups for each repeating unit. The polymer obtained was soluble in sulfuric acid, some organic solvents, and aqueous strong alkaline solution. The polymers were stable up to 400°C, but they gave polybenzimidazoles above 400°C by eliminating sulfonic acid groups, instead of ring closure.     

Modulation Transfer Function of Blazed Diffractive Optics Produced by Diamond Turning

In blazed diffractive optics produced by the diamond turning process, the finite size of the tool determines the decrease in diffraction efficiency of the desired order. Diffracted light of other orders degrades the image quality. To analyze the influence of the tool, we evaluate diffraction efficiency and phase of periodic gratings based on the electromagnetic theory and calculate modulation transfer function using a linear system approach.     

Extraction Mechanism of Metal Ion from Aqueous Solution to the Hydrophobic Ionic Liquid, 1-Butyl-3-methylimidazolium Nonafluorobutanesulfonate

Summary. We studied the extraction behavior of metal ionic species in aqueous solutions into the hydrophobic ionic liquid, 1-butyl-3-methylimidazolium nonafluorobutanesulfonate ([bmi][NfO]). The extraction ratios (E/%) of Li(I), Na(I), Cs(I), Ca(II), Sr(II), and La(III) species were found to be 39, 24, 5.0, 81, 79, and 98. This result is similar to the phenomena that the metal ions with larger charge are more easily adsorbed onto cation exchange resins. In order to examine the extraction mechanism, we studied the extraction behavior of La(III) species from the aqueous to the [bmi][NfO] phase. As a result, it was found that the E values of La(III) decrease remarkably with an increase in concentrations of HNO₃ (0–1 M) in the aqueous phase and that the amount of La(III) transferred into [bmi][NfO] phase increases linearly with an increase in the amount of [bmi] transferred into the aqueous phase. Furthermore, we investigated the extraction behavior of La(III) species using 1-pentyl- and 1-hexyl-3-methylimidazolium nonafluorobutansulfonate ([pmi][NfO], [hmi][NfO]), which are more hydrophobic than [bmi][NfO], and found out that the E values of La(III) decrease in order of [bmi][NfO] > [pmi][NfO] > [hmi][NfO]. From these results, it was proposed that the extraction of metal ionic species from the aqueous to the [bmi][NfO], [pmi][NfO], or [hmi][NfO] phase is mainly ascribed to the cation exchanges between two phases.     

Fabrication of steady junctions consisting of alpha,omega-bis(thioacetate) oligo(p-phenylene vinylene)s in nanogap electrodes

For obtaining molecular devices using metal-molecule-metal junctions, it is necessary to fabricate a steady conductive bridge-structure; that is stable chemical bonds need to be established from a single conductive molecule to two facing electrodes. In the present paper, we show that the steadiness of a conductive bridge-structure depends on the molecular structure of the bridge molecule for nanogap junctions using three types of modified oligo(phenylene vinylene)s (OPVs): alpha,omega-bis(thioacetate) oligo(phenylene vinylene) (OPV1), alpha,omega-bis(methylthioacetate) oligo(phenylene vinylene) (OPV2), and OPV2 consisting of ethoxy side chains (OPV3). We examined the change in resistance between the molecule-bridged junction and a bare junction in each of the experimental Au-OPV-Au junctions to confirm whether molecules formed steady bridges. Herein, the outcomes of whether molecules formed steady bridges were defined in terms of three types of result; successful, possible and failure. We define the ratio of the number of successful junctions to the total number of experimental junctions as successful rate. A 60% successful rate for OPV3 was higher than for the other two molecules whose successful rates were estimated to be approximately 10%. We propose that conjugated molecules consisting of methylthioacetate termini and short alkoxy side chains are well suited for fabricating a steady conductive bridge-structure between two facing electrodes.     

Effects of cannibalism on a basic stage structure

In this paper, we discuss the effects of cannibalism on a basic stage-structured population model for a single species. A threshold condition for extinction versus persistence is obtained, and numerical simulations of the population dynamics are presented. These simulations suggest that cannibalism has a stabilizing effect on the population, promoting equilibrium of the adult population level.     

Adsorptivity of silica-supported monoamide resins to U(IV) in nitric acid media

For the selective extraction of radionuclides from nitrate media, the extraction properties of organopolyphosphine polyoxides were examined in the form of impregnated adsorbents. It was found that the extraction property of 1,1,3,5,5-pentaphenyl-1,3,5-triphosphapentane trioxide (PPTPT) for U(VI) is quite unusual with very high values of the distribution ratio in nitric acid solutions of both low and high concentration ranges, which is not observed for other types of extractants. From the extraction properties for other metal ions, this type of extracant may be promising for the selective extraction of U(VI) from HNO₃ of very low and high concentrations.