Aqueous solution properties of disulfide linked gemini and cleaved monomeric thiol surfactants

Monomeric thiol surfactants, [C(n)H(2n+1)N(CH(3))(2)CH(2)CH(2)SH]Br, were produced by the cleavage of gemini surfactant containing a disulfide bond in the spacer chain, [C(n)H(2n+1)N(CH(3))(2)CH(2)CH(2)SSCH(2)CH(2)N(CH(3))(2)C(n)H(2n+1)]2Br. The disulfide bond was completely reduced by the addition of four times moles of dithiothreitol in water at room temperature. The critical micelle concentrations of monomeric surfactants were significantly increased in comparison with original gemini surfactants. The monomeric thiol surfactants were stable in the presence of dithiothreitol, whereas they returned gradually to their original gemini surfactants within several days due to air oxidation in water without dithiothreitol. The micelle formation induced by the disulfide linkage formation was suggested by the fluorescence intensity ratio of pyrene. The time course of decrease in thiol concentration associated with the recovery of gemini surfactants was confirmed by the absorption spectra utilizing the reactions with 4,4'-dithiopyridine.     

Reinvestigation of positional distribution of fatty acids in docosahexaenoic acid-rich fish oil triacyl-sn-glycerols

Positional distribution of fatty acids in triacyl-sn-glycerols of docosahexaenoic acid (DHA)-rich tuna orbital and bonito head oils has been reanalyzed by a method based on chromatographic separation of isomeric and enantiomeric monoacyl-sn-glycerol (MAG) derivatives. When boric acid thinlayer chromatography (TLC) was used for separation of 1(3)- and 2-MAG analytical intermediates, the stereospecific analysis showed the preferential association of DHA to the sn-2 position followed by the sn-3 position. This distribution pattern differed from that obtained by silicic acid LTC of their bis-3,5-dinitrophenylurethane (DNPU) derivatives. Reversed-phase high-performance liquid chromatography elution profiles of 1(3)- and 2-MAG intermediates revealed that 1(3)- and 2-MAG made up of both short- and long-chain lengths cannot be clearly resolved by TLC after preparation of the DNPU derivatives. The 1(3)- and 2-MAG must be resolved by boric acid TLC prior to derivatization.     

The relationship between solid-state fluorescence intensity and molecular packing of coumarin dyes

The solid-state fluorescence intensity of coumarin dyes depends on the substituents present at the 4- and 7-positions. 7-(Diethylamino)coumarins showed higher solid-state fluorescence quantum yield (Φ_f(ss) = 0.29–0.40) than 7-aminocoumarins (0.01). In the case of julolydyl coumarins, a 4-methyltetramethyljulolydyl derivative also displayed high Φ_f(ss) (0.34), this being greater than that observed for both 4-(perfluoroalkyl)tetramethyljulolydyl (0.09 and 0.10) and 4-methyljulolydyl derivatives (0.01). X-ray crystallographic analysis suggested that coumarin dyes bearing network hydrogen bonds and/or π–π stacking show weak solid-state fluorescence whereas coumarin dyes having isolated monomer- and dimer-type stacking show intense fluorescence. 4-(Perfluoroalkyl)tetramethyljulolydyl derivatives displayed medium fluorescence intensity owing to isolated monomer-type packing with little intermolecular interactions operating between adjacent molecules.     

Optical and thermal properties of methyl methacrylate and pentafluorophenyl methacrylate copolymer: Design of copolymers for low-loss optical fibers for gigabit in-home communications

As a novel base material for low-loss graded index plastic optical fibers (GI POFs) in gigabit home networks, a copolymer of methyl methacrylate (MMA) and pentafluorophenyl methacrylate (PFPMA) was prepared and its thermal and optical properties were investigated. When the PFPMA content in the monomer feed was 0-50 mol%, both the glass transition temperature (T_g) and the decomposition temperature of the copolymer were higher than that for PMMA, which is the base material for many commercially available POFs. The transmittance of the copolymer was also found to be higher than that of PMMA since it has fewer C-H bonds per unit volume. As the core material of GI POFs, MMA-co-PFPMA (65/35 mol%), which had the highest T_g of 118 °C was utilized. A low-loss GI POF with an attenuation of 172-185 dB/km at the emission wavelengths of a high-speed light source (670-680 nm) was successfully obtained for the first time.     

Physicochemical approach to nanobubble solutions

Small bubbles of nitrogen, methane, or argon with an average radius of 50 nm, as measured by scanning electron microscopy, were prepared under atmospheric conditions. The lifetime of the nanobubbles extended to more than two weeks. The total amount of gases in the nanobubble solutions reached 600 cm³ per 1 dm³ of water, and the liquid density was about 0.988 g/cm³. The internal pressure of the nanobubbles was estimated to be 6 MPa. The number of nanobubbles was 1.9×10¹⁶ bubbles per 1 dm³ of water. These findings show that almost no gas samples are dissolved homogeneously in the aqueous solution and that the vast majority is present in the form of nanobubbles, that is, nanobubbles should be thermodynamically unstable. Attenuated total reflectance infrared spectroscopy showed that the surfaces of the nanobubbles contain hard hydrogen bonds that may reduce the diffusivity of gases through the interfacial film.     

Spatial patterns of greenhouse gas emission in a tropical rainforest in Indonesia

Spatial patterns of CO₂, CH₄, and N₂O flux were analyzed in the soil of a primary forest in Sumatra, Indonesia. The fluxes were measured at 3-m intervals on a sampling grid of 8 rows by 10 columns, with fluxes found to be below the minimum detection level at 12 points for CH₄ and 29 points for N₂O. All three gas fluxes distributed log-normally. The means and standard deviations of CO₂ and CH₄ fluxes calculated by the maximum likelihood method were 3.68 ± 1.32 g C m^–2 d^–1 and 0.79 ± 0.60 mg C m^–2 d^–1, respectively. The mean and standard deviation of N₂O fluxes using a maximum likelihood estimator for the censored data set was 2.99 ± 3.26 g N m^–2 h^–1. The spatial dependency of CH₄ fluxes was not detected in 3-m intervals, while weak spatial dependency was observed in CO₂ and N₂O fluxes. The coefficients of variation of CH₄ and N₂O were higher than that of CO₂. Some hot spots where high levels of CH₄ and N₂O were generated in the studied field may increase the variability of these gases. The resulting patterns of variability suggest that sampling distances of >10 m and > 20 m are required to obtain statistically independent samples for CO₂ and N₂O flux in the studied field, respectively. But because of weak or no spatial dependency of each flux, a sampling distance of more than 10 m intervals is enough to prevent a significant problem of autocorrelation for each flux measurement.     

Novel Conjugated Polymers Containing [2.2]Paracyclophane and Carbazole Units with Efficient Photoluminescence

Summary Novel through-space conjugated polymers based on PPE having [2.2]paracyclophane and N-alkylcarbazole units in the main chain were synthesized by Sonogashira-coupling reaction. All polymers were quite soluble in a variety of organic solvents. Transparent and uniform thin films of the polymers were obtained easily by casting or spin-coating from toluene solution. These polymers possessed good thermal stability. The polymers exhibited strong blue photoluminescence in solution and bluish-green photoluminescence in the solid state.     

Effect of surface properties of silica nanoparticles on their cytotoxicity and cellular distribution in murine macrophages

Surface properties are often hypothesized to be important factors in the development of safer forms of nanomaterials (NMs). However, the results obtained from studying the cellular responses to NMs are often contradictory. Hence, the aim of this study was to investigate the relationship between the surface properties of silica nanoparticles and their cytotoxicity against a murine macrophage cell line (RAW264.7). The surface of the silica nanoparticles was either unmodified (nSP70) or modified with amine (nSP70-N) or carboxyl groups (nSP70-C). First, the properties of the silica nanoparticles were characterized. RAW264.7 cells were then exposed to nSP70, nSP70-N, or nSP70-C, and any cytotoxic effects were monitored by analyzing DNA synthesis. The results of this study show that nSP70-N and nSP70-C have a smaller effect on DNA synthesis activity by comparison to unmodified nSP70. Analysis of the intracellular localization of the silica nanoparticles revealed that nSP70 had penetrated into the nucleus, whereas nSP70-N and nSP70-C showed no nuclear localization. These results suggest that intracellular localization is a critical factor underlying the cytotoxicity of these silica nanoparticles. Thus, the surface properties of silica nanoparticles play an important role in determining their safety. Our results suggest that optimization of the surface characteristics of silica nanoparticles will contribute to the development of safer forms of NMs.     

Catalytic Asymmetric Mannich‐Type Reactions Using a Novel Chiral Iron Complex

Catalytic asymmetric Mannich‐type reactions using a novel chiral iron complex have been developed. The reactions proceeded smoothly in the presence of a catalyst prepared from iron(II) chloride, a BINOL derivative, and i‐Pr₂NEt. The desired products were obtained in good yield with good to high enantioselectivity, when 3,3′‐I₂BINOL was employed as a chiral ligand. A protic additive such as methanol facilitated the reactions effectively.     

EXTRACTIVE FERMENTATION OF PHENYLALANINE USING UNCHARGED POLYMERIC BEADS

Extractive fermentation was employed for the production of phenylalanine using an agitated and aerated fermenter. Uncharged polystyrene beads (Amberlite XAD-16) were packed in an external column and used to extract the phenylalanine in an intermittent fashion during the fermentation. Even though no cell separator was used and the fermentation broth was fed directly to the column, the overall system performed well without any clogging of the column. It was found that 43% of the phenylalanine could be extracted during the fermentation, and it was thus proved that extractive fermentation is an effective way to prevent the crystallization of phenylalanine. In addition, fermentation performance as also improved due to the relief of self-inhibition by phenylalanine. When 1.2 L of the beads was used and sufficient hydrophobic nutrients were present, the concentration and productivity increased 18% and 55% greater than in the control fermentation, respectively. These results show that extractive fermentation is a very attractive method to enhance production as well as to avoid crystallization. Numerical simulation modeling was also performed in this study for extractive fermentation. The results from the modeling corroborated the experimental data, thus confirming the reliability of the model.