Large-scale separation of metallic and semiconducting single-walled carbon nanotubes

In the applications of single-walled carbon nanotubes (SWNTs), it is extremely important to separate semiconducting and metallic SWNTs. Although several methods have been reported for the separation, only low yields have been achieved at great expense. We show a separation method involving a dispersion-centrifugation process in a tetrahydrofuran solution of amine, which makes metallic SWNTs highly concentrated to 87% in a simple way.     

Speciation of mercury in salmon egg cell cytoplasm in relation with metallomics research

Speciation of mercury in salmon egg cell cytoplasm was investigated by surfactant-mediated high-performance liquid chromatography/inductively coupled plasma mass spectrometry (HPLC/ICP-MS), where an ODS (octadecylsilica) column coated with a bile acid derivative, CHAPS (3-[(3-cholamidopropyl)-dimethylammonio]-1-propane sulfonate), was used for species separation. Prior to the speciation analysis, total Hg in the cell cytoplasm was determined by ICP-MS at m/z 202 in a flow injection mode. For the precise measurement, salmon egg cell cytoplasm was diluted five-fold with 0.1 M Tris (Tris(hydroxymethyl)aminomethane)-HNO₃ buffer solution, and the standard addition method was employed. Thus, the total concentration of Hg in cell cytoplasm was estimated to be 12.4 ng g⁻¹ on the wet weight basis. Next, the cell cytoplasm diluted five-fold with 0.1 M Tris-HNO₃ buffer solution was analyzed by surfactant-mediated HPLC with the dual detection system of a UV absorption detector and an ICP-MS instrument. Two peaks corresponding to some proteins and small molecules were mainly observed in those chromatograms. When salmon egg cell cytoplasm was diluted five-fold with 0.01 M Tris buffer solution or pure water, some precipitates appeared probably because of precipitation of hydrophobic proteins in cytoplasm. After the precipitates were eliminated with a membrane filter, the filtrate was subjected to the analysis by surfactant-mediated HPLC/UV/ICP-MS. As a result, the peaks for small molecular species of Hg were clearly observed at the retention time near 4.0 min (corresponding to low-molecular weight zone) in the chromatograms with UV absorption detection as well as with Hg- and S-specific ICP-MS detections. The small molecule bound with Hg was identified as cysteine through the cysteine-spiked experiment. In addition, the protein fraction on the chromatogram obtained by using the CHAPS-coated ODS column was further analyzed by SEC (size exclusion chromatography). Consequently, several protein peaks with molecular weight of 300, 50 and 12 kDa were observed in all the detections of UV absorption, Hg and Se, although two peaks among them were coincident in the case of S. These results indicate that Hg in salmon egg cell cytoplasm binds with proteins containing selenocysteine and/or cysteine residues in proteins.     

Dynamic kinetic resolution of amino acid amide catalyzed by D-aminopeptidase and alpha-amino-epsilon-caprolactam racemase

Amino acid amide racemizing activity was discovered in alpha-amino-epsilon-caprolactam (ACL) racemase (EC 5. 1. 1. 15) from Achromobacter obae. The enzymatic synthesis of d-alanine from l-alanine amide has been demonstrated by use of d-aminopeptidase (DAP; EC 3. 4. 11. 19) from Ochrobactrum anthropi C1-38 and ACL racemase. The conversion of 45 mM l-alanine amide was carried out at 30 degrees C for 7 h; l-alanine amide was completely converted to d-alanine, and no l-alanine was detected. The result of successive enzymatic reaction shows that the combination of ACL racemase and DAP can be applied for dynamic kinetic resolution of dl-amino acid amides to yield d-amino acids.     

Flow injection determination of iodide ion in a photographic developing solution using iodide ion-selective electrode detector

A potentiometric flow injection determination method for iodide ion in a photographic developing solution was proposed by utilizing a flow-through type iodide ion-selective electrode detector. The sensing membrane of the electrode was Ag₂S–AgI membrane. The response of the electrode detector as a peak-shape signal was obtained for injected iodide ion in a photographic developing solution. A linear relationship in the subnernstian zone was found to exist between peak height and the concentration of the iodide ion in a photographic developing solution in a concentration range from 0 to 6.0×10⁻⁵ mol l⁻¹. The relative standard deviation for ten injections of 2×10⁻⁵ mol l⁻¹ iodide ion in a photographic developing solution was 0.96% and the sampling rate was approximately 12–13 samples h⁻¹. The iodide ion could be determined under coexisting of an organic reducing reagent and inorganic electrolytes of high concentration in a photographic developing solution sample solution by the present method.     

The complexation of 2,3-anthracenedicarboxylate by β- and γ-cyclodextrins in mixed solvent systems as studied by induced circular dichroism. The role of cosolvent hydrophobicity

The complexation of 2,3-anthracenedicarboxylate (ADC) by- and-cyclodextrins in water containing an organic solvent has been studied by induced circular dichroism. It has been shown that an increase of organic solvent ratio causes the degradation of the 1:1 ADC:-CD complex and the liberation of one guest molecule from the 2:1 ADC:-CD complex in water. The higher the hydrophobicity of the cosolvent, the weaker the complexation of ADC by-CD.     

2,6-Diphenylbenzo[1,2-b:4,5-b']dichalcogenophenes: a new class of high-performance semiconductors for organic field-effect transistors

2,6-Diphenylbenzo[1,2-b:4,5-b']dichalcogenophenes including thiophene, selenophene, and tellurophene analogues as organic semiconductors for field-effect transistors were effectively synthesized in three steps from commercially available 1,4-dibromobenzene. All three benzodichalcogenophenes acted as good p-type semiconductors, and particularly the selenophene analogue, 2,6-diphenylbenzo[1,2-b:4,5-b']diselenophene, showed high FET mobility of 0.17 cm2 V-1 s-1.     

Fluorescent Molecular Recognition and Sensing System of Bis-Dansyl Modified γ-Cyclodextrins

Flexible hosts, 6A,6B-; 6A,6C-; 6A,6D-; and 6A,6E-bis dansylglycine-modified -cyclodextrins (-1, -2, -3, and -4, respectively) have been synthesized as a sensing molecule for organic guests including terpenoids and bile acids. These host compounds show a pure monomer fluorescence whose intensity is decreased or enhanced upon addition of guest species. The value I/I₀, where I and I₀ are fluorescence intensities in the presence and absence of a guest and I is I₀- I, was used as a parameter of sensitivity. These hosts exhibit highly sensitive and selective molecular recognition ability, particularly, for lithochoic acid, chenodeoxycholic acid, and ursodeoxycholic acid. The behaviors of the appended moieties of these hosts when host–guest complexation occurs are studied by induced circular dichroism (ICD) spectra and fluorescence spectral change on accommodation of a guest. The ICD pattern of these hosts alone or on accommodation of a guest is very similar, indicating that the behavior of the appended moieties are very similar. The guest-induced variations in the fluorescence or ICD intensity suggest that the appended moieties act as a hydrophobic cap that enables the cyclodextrin to form 1 : 1 host–guest complexes.     

Properties of aqueous solution of sodium glycocholate and a nonionic surfactant,and their mixtures

The micellar properties of aqueous binary mixed solutions of sodium glycocholate, NaGC, and octa-oxyethylene glycol mono-n-decyl ether, C₁₀E₈, have been studied on the basis of surface tensions, the mean aggregation number and the polarity of the interior of the micelles. The mean aggregation number, measured by steady state quenching method, decreased with the increase of the mole fraction of NaGC in the mixed system. The polarity of the interior, estimated by the ratio of first and third vibronic peak in a monomeric pyrene fluorescence emission spectrum, suggested that the hydrophobicity of intramicelles increased with the increase of the mole fraction of NaGC in the mixed system. These are considered to be caused by the differences in the chemical structure and the hydrophobic nature between NaGC and C₁₀E₈. The mean aggregation number and the polarity of the interior for each micelle near the CMC in lower total concentration of surfactants showed the tendency approaching those of pure micelle of the nonionic surfactant. This suggests that the ratio of NaGC in the initial micelles in the range of lower total concentration near the CMC is lower than that of the corresponding prepared mole fraction in the mixed system. This lower value was confirmed also from theoretical calculation of the ratio of NaGC at the CMC in the mixed micelle by regular solution treatment of Rubingh in the solution.     

Electrochemical formation of stable ferrocene anion and the formal rate constant of the ferrocene0/− electrode

A reversible cyclic voltammogram for the one-electron reduction of ferrocene in 1,2-dimethoxyethane is recorded under experimental conditions that enable the ferrocene anion to exist for a few minutes. The formal rate constant of the ferrocene^0/? electrode, determined by cyclic voltammetry at ?45°C, ca. 10^?3 cm s^?1, is in striking contrast with that of ferrocene^+/0, > 10^?1 cm s^?1. The distortion of the ferrocene molecule caused by reduction may be a reason for this difference in electron-transfer rate.     

Redox-responsive molecular switches based on azoterpyridine-bridged Ru/Os complexes

Three new terpyridine-based dinuclear complexes, [(tpy)Ru(azotpy)Ru(tpy)]4+ (tpy = 2,2':6',2'-terpyridine, azotpy = bis[2,6-bis(2-pyridyl)-4-pyridyl]diazene), [(tpy)Os(azotpy)Os(tpy)]4+, and [(tpy)Ru(azotpy)Os(tpy)]4+ were prepared and their electrochemical and photophysical properties investigated. The bridging ligand, azotpy, in these complexes is reduced at less negative potentials than the unsubstituted tpy ligand. These complexes exhibit absorption bands due to the metal-to-ligand charge-transfer transitions both to the unsubstituted tpy ligand and the bridging azotpy ligand, the latter absorption being observed at the lower energy side of the former. These observations are consistent with the lower lying pi* level of the azotpy ligand than that of the tpy ligand. These complexes are nonluminescent, since the excited electron is trapped in this lower lying pi* level of the azotpy ligand in the excited state. Reduction of this bridging ligand by constant potential electrolysis renders the shape of absorption spectra for these complexes nearly identical to those of the parent complexes, [M(tpy)2]2+ (M = Ru, Os). In this reduced state, the homodinuclear Os complex becomes luminescent at room temperature, whereas the homodinuclear Ru complex becomes luminescent at 77 K, thus establishing their photoswitching behavior. The reduced heterodinuclear complex exhibits luminescence from the Os center, which is sensitized by the Ru center in the same molecule as evidenced by the excitation spectra. Thus, the intramolecular energy transfer can be switched on and off by the redox reaction of the bridging component.