High oxygen-reduction activity of silk-derived activated carbon

Activated carbon prepared from silk fibroin, which is free of metal elements, showed a high catalytic activity for the oxygen-reduction reaction (ORR). The activated carbon had a very high onset potential of E_onset = 0.83 V (vs. RHE) in oxygen-saturated 0.5 M H₂SO₄ at 60 °C. The ORR on the activated carbon proceeded by a four-electron process in the high-electrode-potential region; this gradually decreased to a 3.5-electron reaction below about 0.6 V (vs. RHE). Only about 1% of nitrogen atoms (mostly quaternary) remained in the activated carbon by heat-treatment at up to 1200 °C are responsible for the high catalytic activity. The open circuit voltage of a polymer electrolyte fuel cell using the activated carbon as the cathode and a platinum/carbon black anode under pure oxygen and hydrogen gases, respectively, both at one atmosphere, was 0.96 V at 27 °C.     

13C NMR studies of the electronic structure of low-spin iron(III) tetraphenylchlorin complexes

A series of low-spin six-coordinate (tetraphenylchlorinato)iron(III) complexes [Fe(TPC)(L)2]+/- (L = 1-MeIm, CN-, 4-CNPy, and (t)BuNC) have been prepared, and their (13)C NMR spectra have been examined to reveal the electronic structure. These complexes exist as the mixture of the two isomers with the (d(xy))2(d(xz), d(yz))3 and (d(xz), d(yz))4(d(xy))1 ground states. Contribution of the (d(xz), d(yz))4(d(xy))1 isomer has increased as the axial ligand changes from 1-MeIm, to CN(-) (in CD2Cl2 solution), CN- (in CD(3)OD solution), and 4-CNPy, and then to tBuNC as revealed by the meso and pyrroline carbon chemical shifts; the meso carbon signals at 146 and -19 ppm in [Fe(TPC)(1-MeIm)2]+ shifted to 763 and 700 ppm in [Fe(TPC)(tBuNC)2]+. In the case of the CN- complex, the population of the (d(xz), d(yz))4(d(xy))1 isomer has increased to a great extent when the solvent is changed from CD2Cl2 to CD3OD. The result is ascribed to the stabilization of the d(xz) and d(yz) orbitals of iron(III) caused by the hydrogen bonding between methanol and the coordinated cyanide ligand. Comparison of the 13C NMR data of the TPC complexes with those of the TPP, OEP, and OEC complexes has revealed that the populations of the (d(xz), d(yz))4(d(xy))1 isomer in TPC complexes are much larger than those in the corresponding TPP, OEC, and OEP complexes carrying the same axial ligands.     

Sequential reaction intermediates in aliphatic C-H bond functionalization initiated by a bis(mu-oxo)dinickel(III) complex

The reaction of [Ni2(OH)2(Me2-tpa)2]2+ (1) (Me2-tpa = bis(6-methyl-2-pyridylmethyl)(2-pyridylmethyl)amine) with H2O2 causes oxidation of a methylene group on the Me2-tpa ligand to give an N-dealkylated ligand and oxidation of a methyl group to afford a ligand-based carboxylate and an alkoxide as the final oxidation products. A series of sequential reaction intermediates produced in the oxidation pathways, a bis(mu-oxo)dinickel(III) ([Ni2(O)2(Me2-tpa)2]2+ (2)), a bis(mu-superoxo)dinickel(II) ([Ni2(O2)2(Me2-tpa)2]2+ (3)), a (mu-hydroxo)(mu-alkylperoxo)dinickel(II) ([Ni2(OH)(Me2-tpa)(Me-tpa-CH2OO)]2+ (4)), and a bis(mu-alkylperoxo)dinickel(II) ([Ni2(Me-tpa-CH2OO)2]2+ (5)), was isolated and characterized by various physicochemical measurements including X-ray crystallography, and their oxidation pathways were investigated. Reaction of 1 with H2O2 in methanol at -40 degrees C generates 2, which is extremely reactive with H2O2, producing 3. Complex 2 was isolated only from disproportionation of the superoxo ligands in 3 in the absence of H2O2 at -40 degrees C. Thermal decomposition of 2 under N2 generated an N-dealkylated ligand Me-dpa ((6-methyl-2-pyridylmethyl)(2-pyridylmethyl)amine) and a ligand-coupling dimer (Me-tpa-CH2)2. The formation of (Me-tpa-CH2)2 suggests that a ligand-based radical Me-tpa-CH2* is generated as a reaction intermediate, probably produced by H-atom abstraction by the oxo group. An isotope-labeling experiment revealed that intramolecular coupling occurs for the formation of the coupling dimer. The results indicate that the rebound of oxygen to Me-tpa-CH2* is slower than that observed for various high-valence bis(mu-oxo)dimetal complexes. In contrast, the decomposition of 2 and 3 in the presence of O2 gave carboxylate and alkoxide ligands, respectively (Me-tpa-COO- and Me-tpa-CH2O-), instead of (Me-tpa-CH2)2, indicating that the reaction of Me-tpa-CH2* with O2 is faster than the coupling of Me-tpa-CH2* to generate ligand-based peroxyl radical Me-tpa-CH2OO*. Although there is a possibility that the Me-tpa-CH2OO* species could undergo various reactions, one of the possible reactive intermediates, 4, was isolated from the decomposition of 3 under O2 at -20 degrees C. The alkylperoxo ligands in 4 and 5 can be converted to a ligand-based aldehyde by either homolysis or heterolysis of the O-O bond, and disproportionation of the aldehyde gives a carboxylate and an alkoxide via the Cannizzaro reaction.     

In situ generation of 3,3,3-trifluoropropanal and its use for carbon-carbon bond-forming reactions

The DIBAL reduction of 2-phenylethyl 3,3,3-trifluoro-2-methylpropionate 2 at -78 degrees C afforded the aluminum acetal 3, and this intermediate, on worming up to 0 degrees C, was found to slowly decompose into the corresponding aldehyde 4, which smoothly reacted with appropriate nucleophiles in a one-pot manner in good to excellent yields with up to 93% diastereoselectivity.     

Effect of visual target blurring on accommodation under distance viewing

Purpose

To examine the effect of visual target blurring on accommodation.

Methods

We evaluated the objective refraction values when the visual target (asterisk; 8°) was changed from the state without Gaussian blur (15 s) to the state with Gaussian blur adapted [0(without blur)?→?10, 0?→?50, 0?→?100: 15 s each].

Results

In Gaussian blur 10, when blurring of the target occurred, refraction value did not change significantly. In Gaussian blur 50 and 100, when blurring of the target occurred, the refraction value became significantly myopic.

Conclusion

Blurring of the distant visual target results in intervention of accommodation.

     

Development of SI-traceable C-peptide certified reference material NMIJ CRM 6901-a using isotope-dilution mass spectrometry-based amino acid analyses

A certified reference material (CRM) is a higher-order calibration material used to enable a traceable analysis. This paper describes the development of a C-peptide CRM (NMIJ CRM 6901-a) by the National Metrology Institute of Japan using two independent methods for amino acid analysis based on isotope-dilution mass spectrometry. C-peptide is a 31-mer peptide that is utilized for the evaluation of β-cell function in the pancreas in clinical testing. This CRM is a lyophilized synthetic peptide having the human C-peptide sequence, and contains deamidated and pyroglutamylated forms of C-peptide. By adding water (1.00 ± 0.01) g into the vial containing the CRM, the C-peptide solution in 10 mM phosphate buffer saline (pH 6.6) is reconstituted. We assigned two certified values that represent the concentrations of total C-peptide (mixture of C-peptide, deamidated C-peptide, and pyroglutamylated C-peptide) and C-peptide. The certified concentration of total C-peptide was determined by two amino acid analyses using pre-column derivatization liquid chromatography-mass spectrometry and hydrophilic chromatography-mass spectrometry following acid hydrolysis. The certified concentration of C-peptide was determined by multiplying the concentration of total C-peptide by the ratio of the relative area of C-peptide to that of the total C-peptide measured by liquid chromatography. The certified value of C-peptide (80.7 ± 5.0) mg/L represents the concentration of the specific entity of C-peptide; on the other hand, the certified value of total C-peptide, (81.7 ± 5.1) mg/L can be used for analyses that does not differentiate deamidated and pyroglutamylated C-peptide from C-peptide itself, such as amino acid analyses and immunochemical assays.     

Hydroxylated surface of GaAs as a scaffold for a heterogeneous Pd catalyst

A novel use of GaAs, namely, as a scaffold for a heterogeneous palladium catalyst, is proposed. Hydroxy groups on the GaAs surface play important roles. During the adsorption of Pd(OAc)(2) on the GaAs surface, the hydroxy groups attract Pd(ii) species by anion exchange. A subsequent redox reaction proceeds to generate Pd(0) nanoparticles, which are stabilized on the GaAs surface. This process is confirmed by surface-sensitive measurements: diffuse reflection IR spectroscopy and X-ray photoelectron spectroscopy. Moreover, a more bulk-sensitive measurement, hard X-ray photoemission spectroscopy with synchrotron radiation, also supported our considerations. The amounts of Pd(0) nanoparticles on the surface were evaluated by catalytic activity, yield, and recyclability in the Heck reaction, in addition to the deposit test.     

Synthesis of α-amino ketones from terminal alkynes via rhodium-catalyzed denitrogenative hydration of N-sulfonyl-1,2,3-triazoles

N-Sulfonyl-1,2,3-triazoles react with water in the presence of a rhodium catalyst to produce α-amino ketones in high yield. An intermediary α-imino rhodium(II) carbenoid undergoes insertion into the O-H bond of water. This transformation formally achieves 1,2-aminohydroxylation of terminal alkynes in a regioselective fashion when combined with the copper(I)-catalyzed 1,3-dipolar cycloaddition with N-sulfonyl azides.     

Porphyrin nanochannels reinforced by hydrogen bonding

Carboxyl groups were introduced at the peripheral positions of dodecaphenylporphyrin to link nanochannel structures with intermolecular hydrogen bonds to make the supramolecular structures robust.     

Mechanofluorochromism of carbazole-type D–π–A fluorescent dyes

We have newly designed and synthesized unsymmetrical carbazole-type D–π–A fluorescent dyes. The dyes show a bathochromic shift-type mechanofluorochromism (MFC): grinding of as-recrystallized dyes induces a bathochromic shift of fluorescent color and the fluorescent color is recovered by heating or exposure to solvent vapor. In order to clarify the MFC mechanism for the carbazole-type D–π–A fluorescent dyes, time-resolved fluorescence spectroscopy, X-ray powder diffractometry, single-crystal X-ray structural analysis, IR spectroscopy, and differential scanning calorimetry are performed before and after grinding of the solids. On the basis of experimental results and semi-empirical molecular orbital calculations (AM1 and INDO/S), we have revealed that the MFC is attributed to a reversible switching between crystalline and amorphous states with changes of intermolecular hydrogen bonding and π–π interaction.