Acidic layer-enhanced nanoconfinement of anions in cylindrical pore of single-walled carbon nanotube.

The adsorption of the nitrate ion by the cylindrical pore of single-walled carbon nanotubes (SWCNT) was found to be aided by an acidic adsorbed layer. Adsorbed water in the vicinity of the pore wall can supply protons through ionization, forming the acidic layer, according to Raman spectra and results of solution pH fluctuations caused by ion species adsorption. Such an acidic adsorbed layer leads to surplus adsorption of anionic species where the adsorbed amount of nitrate ions is much larger than that of cations. Also, we could observe the Raman bands being assignable to the symmetrical stretching mode at an extremely high-frequency region for nano-restricted nitrate ions compared to any other bulk phases. The abnormal band shift of adsorbed nitrate ions indicates that the nitrate ions are confined in the pore under the effects of nanoconfinement by the pore and the strong interaction with the acidic layer in the pore. Our results warn that we have to construct the adsorption model of aqueous electrolytes confined in carbon pores by deliberating the acid layer formed by the adsorbed water.

Isolation and identification of the antimicrobial substance included in tempeh using Rhizopus stolonifer NBRC 30816 for fermentation.

In this study, we focus on the antimicrobial properties of tempeh, a soybean fermented food, against oral bacteria. Tempeh showed antimicrobial activity against dental caries pathogenic bacterium Streptococcus mutans at a final concentration of 1 mg/mL. An antimicrobial substance contained in tempeh was present in the 100 kDa or greater fraction generated by ultrafiltration, but it was found not to be proteinaceous by native-PAGE, SDS-PAGE and protein degradation tests. Next, when the fraction was purified with an ODS column, the 80% and 100% methanol eluates showed antimicrobial activity against S. mutans. The 100% methanol eluate was further subjected to a 2nd column purification, and isolation of the target was confirmed by HPLC. When the isolated material was analyzed by ESI-MS, the m/z was 279.234. Further analysis by Raman spectroscopy revealed a peak similar to linoleic acid. This substance also possessed antimicrobial properties equivalent to linoleic acid.

Plasmon-mediated chemical transformation from alkane to alkene on a silver nanoparticle array under 532 nm excitation.

Surface-enhanced Raman scattering (SERS) spectra of organic compounds, para-methylthiophenol (p-MT), decylamine and 1-butanethiol (1-BT), were measured using a two-dimensional silver nanoparticle array at 532 nm excitation. For p-MT, it was observed that Raman peaks grew at 1580 and 1690 cm-1, which were never observed in the normal Raman spectrum, indicating oxidation from the methyl to carboxyl group. For both decylamine and 1-BT, an intensive SERS peak grew at 1580 cm-1. We measured the time-resolved SERS spectra of 1-BT at the laser intensity of 185 W mm-2 and confirmed that the spectral shapes changed as the total exposure increased. Another SERS peak was also observed at 3050 cm-1 for decylamine and 1-BT. From these results, it was considered that unsaturated bonds were formed in the alkanes, meaning that alkenes were produced from alkanes. Additionally, the SERS spectrum revealed that the chemically transformed alkane possesses a methyl group. The result indicates that dehydrogenation preferentially occurs at the secondary carbons, which is consistent with the stability of radicals on carbon atoms. The laser intensity threshold for plasmon-mediated chemical transformation was experimentally observed to be 2.7 and 40 W mm-2 for p-MT and 1-BT, respectively. The higher laser intensity is necessary for oxidation of alkanes compared with aromatic compounds, which is consistent with the chemical stability of organic compounds.

Enhanced Optical Collection of Micro- and Nanovesicles in the Presence of Gold Nanoparticles.

We describe a process for collecting micro- and nanovesicles on a glass substrate using the optical pressure of a laser beam. The laser beam was focused on a glass substrate that sandwiched a solution containing vesicles prepared using a phospholipid. The optical pressure generated at the surface of the vesicles pulled them into the center of the beam where they formed an aggregate on the glass surface. The vesicles prepared with a buffer solution were successfully collected via adsorption onto the glass surface, whereas the vesicles prepared with pure water exhibited no such tendency. The time required to collect a certain amount of vesicles was inversely proportional to their concentration. To enhance the collection efficiency, we added gold nanoparticles to the vesicle solution. The addition of gold nanoparticles into the solution reduced the collection time to one-tenth of that without it, and this was attributed to thermal mixing promoted by the heat generated by the absorption from the gold nanoparticles in the solution, as well as to an enhancement of light scattering induced by the gold nanoparticles. The optical collection of vesicles coupled with gold nanoparticles shows a promise for the collection of trace amounts of extracellular vesicles in biological fluids.

Temperature-induced Coalescence of Droplets Manipulated by Optical Trapping in an Oil-in-Water Emulsion.

Coalescence of oil droplets in an oil-in-water (O/W) emulsion was achieved with heating and optical trapping. Three types of O/W emulsions were prepared by adding a mixture of butanol and n-decane to an aqueous solution containing a cationic surfactant (cetyltrimethylammonium bromide, CTAB), an anionic surfactant (sodium dodecyl sulfate, SDS), or a neutral hydrophilic polymer (polyethylene glycol, PEG) as an emulsifier. Two oil droplets in the emulsions were randomly trapped in a square capillary tube by two laser beams in order to induce coalescence. Coalescence of the droplets could not be achieved at room temperature (25°C) regardless of the type of emulsifier. Conversely, the droplets prepared with PEG coalesced at a temperature higher than 30°C, although the droplets with ionic surfactants CTAB and SDS did not coalesce even at the elevated temperature due to their electrostatic repulsion. The size of the resultant coalesced droplet was consistent with that calculated from the size of the two droplets of oil, which indicated successful coalescence of the two droplets. We also found that the time required for the coalescence could be correlated with the temperature using an Arrhenius plot.

Speciation of arsenic in a thermoacidophilic iron-oxidizing archaeon, Acidianus brierleyi, and its culture medium by inductively coupled plasma-optical emission spectroscopy combined with flow injection pretreatment using an anion-exchange mini-column.

The thermoacidophilic iron-oxidizing archaeon Acidianus brierleyi is a microorganism that could be useful in the removal of inorganic As from wastewater, because it simultaneously oxidizes As(III) and Fe(II) to As(V) and Fe(III) in an acidic culture medium, resulting in the immobilization of As(V) as FeAsO4. To investigate the oxidation mechanism, speciation of the As species in both the cells and its culture media is an important issue. Here we describe the successive determination of As(III), As(V), and total As in A. brierleyi and its culture medium via a facile method based on inductively coupled plasma-optical emission spectroscopy (ICP-OES) with a flow injection pretreatment system using a mini-column packed with an anion-exchange resin. The flow-injection pretreatment system consisted of a syringe pump, a selection valve, and a switching valve, which were controlled by a personal computer. Sample solutions with the pH adjusted to 5 were flowed into the mini-column to retain the anionic As(V), whereas As(III) was introduced into ICP-OES with no adsorption on the mini-column due to its electrically neutral form. An acidic solution (1 M HNO3) was then flowed into the mini-column to elute As(V) followed by ICP-OES measurement. The same sample was also subjected to ICP-OES without being passed through the mini-column in order to determine the total amounts of As(III) and As(V). The method was verified by comparing the results of the total As with the sum of As(III) and As(V). The calibration curves showed good linearity with limits of detection of 158, 86, and 211 ppb for As(III), As(V), and total As, respectively. The method was successfully applicable to the determination of the As species contained in the pellets of A. brierleyi and their culture media. The results suggested that the oxidation of As(III) was influenced by the presence of Fe(II) in the culture medium, i.e., Fe(II) enhanced the oxidation of As(III) in A. brierleyi. In addition, we found that no soluble As species was contained in the cell pellets and more than 60% of the As(III) in the culture medium was oxidized by A. brierleyi after a 6-day incubation.

Determination of association constants between 5'-guanosine monophosphate gel and aromatic compounds by capillary electrophoresis.

Hydro gel formed by 5'-guanosine monophosphate (GMP) in the presence of a potassium ion is expected to exhibit interesting selectivity in capillary electrophoretic separations. Here, we estimated the conditional association constants between the hydro gel (G-gel) and aromatic compounds by capillary electrophoresis in order to investigate the separation selectivity that is induced by the G-gel. Several aromatic compounds were separated in a solution containing GMP and potassium ion at different concentrations. The association constants were calculated by correlating the electrophoretic mobilities of the analytes obtained experimentally using a concentration of G-gel. During semi-quantitative estimation, naphthalene derivatives had larger association constants (Kass=10.3-16.8) compared with those of benzene derivatives (Kass=3.91-5.31), which means that the binding sites of G-gel match better to a naphthalene ring than to a benzene ring. A hydrophobic interaction was also found when the association constants for alkyl resorcinol were compared with those of different hydrocarbon chains. The association constants of nucleobases and tryptophan ranged from 6.05 to 12.6, which approximated the intermediate values between benzene and naphthalene derivatives. Consequently, the selective interaction between G-gel and aromatic compounds was classified as one of three types: (1) an intercalation into stacked planar GMP tetramers; (2) a hydrophobic interaction with a long alkyl chain; or, (3) a small contribution of steric hindrance and/or hydrogen bonding with functional groups such as amino and hydroxyl groups.

C2v symmetrical two-photon polymerization initiators with anthracene core: synthesis, optical and initiating properties.

A series of C(2v) symmetrical two-photon absorption compounds with anthracene core, 2,7-bis[2-(4-substituted phenyl)-vinyl]-9,10-dipentyloxyanthracenes designated as I, II and III (the substituted groups at the 4-position of phenyl of I, II and III were dimethylamino, methyl and cyano, respectively) were designed and synthesized as initiators in two-photon induced polymerization (TPIP). The anthracene ring was modified by linking vinylphenyl groups to the 2,7-position to extend conjugation system length and two pentyloxy groups to the 9,10-position to serve as electronic donors. Two-photon absorption cross section of I was around 300 GM, which was much larger than the 10 GM of II and 29 GM of III at 800 nm. I of 0.18% molar ratio in resin composed of methacrylic acid and dipentaerythritol hexaacrylate exhibited a dramatically low threshold of 0.64 mW compared with commercial photoinitiator benzil at a scanning speed 10 µm s(-1). Moreover, the threshold of photoinitiator I was only increased to 2.53 mW at a scanning speed of 1000 µm s(-1). The dependency of threshold on the concentration and exposure time was in accordance with theoretical calculation. Finally, a reasonable mechanism of the two-photon initiating process was proposed. This study provides good prospects for developing low threshold photoinitiator in TPIP.

Three-dimensional fabrication of metallic nanostructures over large areas by two-photon polymerization.

An experimental protocol for the realization of three-dimensional periodic metallic micro/nanostructures over large areas is presented. Simultaneous fabrication of hundreds of three-dimensional complex polymer structures is achieved using a two-photon photopolymerization (TPP) technique combined with a microlens array. Metallization of the structures is performed through the deposition of thin and highly conductive films by electroless plating. A chemical modification of the photopolymerizable resin and the production of a hydrophobic coating on the glass surface supporting the structures are realized. This process prevents metal deposition on the substrate and restricts adhesion on polymer. Our technique can produce periodic and/or isolated metallic structures with arbitrary shape, created by more than 700 individual objects written in parallel.

A tunable picosecond dye laser for use in dioxin analysis.

A distributed-feedback dye laser with a quenching cavity was designed and constructed for generating a tunable picosecond pulse with a narrow spectral linewidth. This nearly transform-limited pulse was succeedingly amplified by a triple-pass off-axis amplifier. The pulse duration and the spectral linewidth were 60 ps and 9.4 pm, respectively. The amplified pulse was frequency-doubled by second-harmonic generation, producing a 0.5-mJ pulse with no background emission. The potential advantage of this laser in the analysis of dioxin based on supersonic jet/resonance-enhanced multiphoton ionization/mass spectrometry is discussed.