Diagnostics of an inductively coupled plasma in oxygen

Spatial time-integrated and space-time resolved profiles of excited atoms of oxygen were measured by optical emission spectroscopy for inductively coupled plasma (ICP) in oxygen. The discharge was sustained by a single turn coil supplied by 13.56 MHz RF generator delivering 100 and 200 W of power. The spatial emission profiles give the anatomy of the discharge required in order to understand the basic kinetics of ICP. Two types of nonuniformities are observed, azimuthal anisotropy and radial nonuniformity, both caused by spatially dependent energy supply to the electrons. Our experimental results show that oxygen is much more affected by azimuthal anisotropy and radial nonuniformity than argon. It is due to a different role of metastable atoms in kinetics of excitation, whereby stepwise excitation in oxygen is less probable than in argon. Optical emission data are supplemented by Langmuir probe measurements of electron densities and plasma potentials. Electrons gain energy from the time varying fields close to the coil, and the energy is not redistributed along the radius before it is dissipated in excitation, thus the observations are not consistent with the nonlocal theory predictions for the range of pressures, geometry, and power covered in this paper     

Magnetic properties of stable N-[(dichlorophenyl)thio]-2,4,6-triphenylphenylaminyl and N-[(dichlorophenyl)thio]-2,4,6-tris(chlorophenyl)phenylaminyl radical crystals

The magnetic properties of N-[(dichlorophenyl)thio]-2,4,6-triarylphenylaminyl radical crystals are reported. The three stable thioaminyls show ferromagnetic behaviors described using the one-dimensional Heisenberg model with the large ferromagnetic interaction of 2J/k_B = 28.0, 11.4, and 3.6 K. The other two radicals show the antiferromagnetic alternating chain behaviors with 2J/k_B = −16.8 K, = 0.55 and 2J/k_B = −128.8 K, = 0.90. The low-temperature susceptibility and heat capacity measurements of the crystal showing 2J/k_B = 28.0 K reveal a magnetic phase transition at 0.4 K. The ordered phase shows spin-flop transition which reveals an antiferromagnetic long range order.     

The influence of wavelength of light on cyanobacterial asymmetric reduction of ketone

Asymmetric reduction of ketone by a microalga, Synechocystis sp. PCC 6803, smoothly afforded to the corresponding (S)-alcohol in excellent enantiomeric excess by the aid of illumination of orange and red LED lights which are more effective than other LEDs such as blue and green lights. The condition under minimum energy flux (1.0 W/m²) of orange-red LEDs is enough for the reduction of ketone, and it seems that orange-red light rather effectively forwarded the regeneration of coenzyme.     

Solid-Phase Total Synthesis of Yaku'amide B Enabled by Traceless Staudinger Ligation

We report a solid-phase strategy for total synthesis of the peptidic natural product yaku'amide B ( 1 ), which exhibits antiproliferative activity against various cancer cells. Its linear tridecapeptide sequence bears four β,β-dialkylated α,β-dehydroamino acid residues and is capped with an N-terminal acyl group (NTA) and a C-terminal amine (CTA). To realize the Fmoc-based solid-phase synthesis of this complex structure, we developed new methods for enamide formation, enamide deprotection, and C-terminal modification. First, traceless Staudinger ligation enabled enamide formation between sterically encumbered alkenyl azides and newly designed phosphinophenol esters. Second, application of Eu(OTf)₃ led to chemoselective removal of the enamide Boc groups without detaching the resin linker. Finally, resin-cleavage and C-terminus modification were simultaneously achieved with an ester–amide exchange reaction using CTA and AlMe₃ to deliver 1 in 9.1 % overall yield (24 steps from the resin).     

Coupling of Titanacyclopentadienes with a Cp Ligand and Elimination of One Substituent

Titanacyclopentadienes, prepared from [Cp₂TiBu₂] and either two equivalents of an alkyne or a diyne, were treated with PMe₃ (3 equiv) at 50 °C for 3 h and then with azobenzene at room temperature for 12 h to give 4,5,6‐trisubstituted indene derivatives with the loss of one substituent in good yields. This reaction contrasts sharply with our previously reported reaction for the formation of 4,5,6,7‐tetrasubstituted indene derivatives without the loss of substituents by the treatment of titanacyclopentadienes with azobenzene without PMe₃. ¹³C NMR spectroscopy of the product derived from a ¹³C‐enriched complex revealed that the five carbon atoms originating from a Cp ligand were arranged linearly in the trisubstituted indene derivatives, in contrast to the 4,5,6,7‐tetrasubsituted indene derivatives, in which the corresponding five carbon atoms are arranged in a ring.     

Convenient Preparation of 1,4-Dibenzylbenzene using Zinc Chloride in the Presence of Polar Solvents

1,4-Dibenzylbenzene was successfully synthesized by the Friedel-Crafts benzylation of benzene with 1,4-bis(chloromethyl)benzene using zinc chloride in the presence of polar solvents. In particular, zinc chloride dissolved in primary alcohols or ketones with a molar ratio of 1 was a highly effective catalytic system in the reaction.     

2-Phenylbenzimidazoline as a Reducing Agent in the Preparation of Malononitriles from α,β-Unsaturated Dinitriles

The development of methods applicable to the selective reduction of carbon-carbon double bonds conjugated with strong electronwithdrawing group such as cyano, nitro, ester or sulfonate group has been a synthetic subject. Although several procedures¹⁾ have been employed for such selective reduction, virtually no sufficient method is known. Recently we have found²⁾ that benzylmalononitriles and 2-nitroethylbenzenes were obtained in good yields by the reactions of benzylidene-malononitriles and β-nitrostyrenes with a half molar amount of o-phenylenediamine (1), and showed that the products resulted from the reduction of the olefins by 2-phenylbenzimidazolines formed from equimolar amounts of the olefins and diamine (1). However, this reaction mode is not effective as a synthetic procedure for the reduction of the olefins because a half molar amount of the olefins is consumed to form 2-phenylbenzimidazolines.     

Extended Hypervalent 5c–6e Interactions: Linear Alignment of Five C─Z- - -O- - -Z─C (Z = S,Se) Atoms in Anthraquinone and Anthracene Systems

Abstract

Structures of 1,8-(ArZ)₂C₁₄H₆O₂ and 9-(MeO)-1,8-(ArZ)₂C₁₄H₇ (Z = S, Se) are determined by X-ray crystallographic analysis. Five C─Z- - -O- - -Z─C atoms of the compounds align linearly, which are analyzed by the extended hypervalent 5c–6e model, based on QC calculations. CT of the 5c–6e occurs as the σ^*(C─Z) ← n _p (O)→ σ*(Z─C) direction.     

Synthesis and properties of fullerene (C70) complexes of 2,6-bis(porphyrin)-substituted pyrazine derivatives bound to a Pd(II) ion

2,6-Bis(porphyrin)-substituted 3,5-dimethylpyrazine and its zinc complex bound C₇₀ to yield 1:1 inclusion complexes, which were characterised by ESI-MS, UV–vis, fluorescence and NMR spectroscopies. Association constants of the C₇₀ complexes were determined by fluorescence and NMR spectral analyses. A decrease in absorbance of the Soret band of the pyrazine derivative by the effect of C₇₀ was observed, suggesting the existence of a charge transfer interaction between C₇₀ and porphyrin. Experimentally reliable values for the association constants were obtained by the NMR method and were about six times larger than those of the corresponding C₆₀ complexes. Palladium complexation of the porphyrin–pyrazine ligand was found to enhance the association with fullerene. The association constant of 2,6-bis(porphyrin-Zn)-substituted 3,5-dimethylpyrazine-Pd(II) complex with C₇₀ was determined to be 8400 ± 900 M^? 1. From the comparison of the association constants, it was found that inclusion room for C₇₀ in the Pd(II) complex was maintained, juxtaposed between porphyrins attached to the opposite sides of the pyrazine ligands.

     

Antioxidant Activity of Polymers Bearing Hindered Phenolic Groups

Abstract

Polyallylamine and polystyrene beads were allowed to react with 3,5-dibutyl-4-hydroxybenzaldehyde (BHB) and t-butylhydroquinone (BHQ), respectively. The polymeric products, poly-Aa(BHB) and polySt(BHQ) beads worked functionally as antioxidants. The antioxidant effect of the polymer beads in the oxidation of linoleic acid suspensions was investigated by both the ferric thiocyanate and thiobarbituric acid methods. The antioxidant activity of poly-St(BHQ) beads was higher than that of poly-Aa(BHB) ones. It was found that the antioxidant activity for 2 mg of 3, 5-dibutyl-4-hydroxytoluene (BHT) corresponded to that for 11.7 g of poly-Aa(BHB) and that of 0.6 g of poly-St(BHQ). The polymer beads are potential antioxidants for foods since their separation from a food oil after their use is easy because of their insolubility.