Influence of Groove on Metal Vapour Behavior and Arc Characteristics in TIG Welding of High Manganese Stainless Steels

Plasma Chemistry and Plasma Processing - In arc welding, a groove is often used between metal pieces being welded. In tungsten inert gas welding of high-manganese stainless steels with arc voltage...     

Constituents of Holothuroidea, 18. Isolation and structure of biologically active disialo- and trisialo-gangliosides from the sea cucumber Cucumaria echinata

Three new disialo- and trisialo-gangliosides, CEG-6 (6), CEG-8 (8), and CEG-9 (9), were obtained, together with one known ganglioside, HLG-3 (7), from the lipid fraction of the chloroform/methanol extract of the sea cucumber Cucumaria echinata. The structures of the new gangliosides were determined on the basis of chemical and spectroscopic evidence to be 1-O-[alpha-L-fucopyranosyl-(1-->11)-(N-glycolyl-alpha-D-neuraminosyl)-(2-->4)-(N-acetyl-alpha-D-neuraminosyl)-(2-->6)-beta-D-glucopyranosyl]-ceramide (6) and 1-O-[(N-glycolyl-D-neuraminosyl)-(2-->11)-(N-glycolyl-D-neuraminosyl)-(2-->4)-(N-acetyl-D-neuraminosyl)-(2-->6)-D-glucopyranosyl]-ceramide (8, 9). The ceramide moieties of each compound were composed of an homogeneous sphingosine or phytosphingosine base and heterogeneous 2-hydroxy or nonhydroxylated fatty acid units. These gangliosides showed neuritogenic activity toward the rat pheochromocytoma cell line PC-12 in the presence of nerve growth factor.     

New efficient organic activators for highly enantioselective reduction of aromatic ketones by trichlorosilane

[reaction: see text] Aryl ketones were reduced to the corresponding alcohols with excellent enantioselectivity (up to 99.7% ee) by Cl3SiH in the presence of a catalytic amount of N-formyl-alpha'-(2,4,6-triethylphenyl)-L-proline as an activator. Both carboxyl group at the alpha-position of the activator and 2,4,6-triethylphenyl group at the alpha'-position were critical for the high enantioselectivity.     

Novel approach for catalytic cyclopropanation of alkenes via (2-furyl)carbene complexes from 1-benzoyl-cis-1-buten-3-yne

The reaction of conjugated ene-yne-ketones 3 with a variety of alkenes in the presence of a catalytic amount of Cr(CO)(5)(THF) at room temperature gives (2-furyl)cyclopropanes in good yields. These cyclopropanation reactions proceed via (2-furyl)carbene-chromium intermediates 4 formed in situ from ene-yne-ketones 3. Late transition metals, such as [RuCl(2)(CO)(3)](2), [RhCl(cod)](2), PdCl(2), and PtCl(2), also catalyze effectively the cyclopropanation of styrene with 3.     

Polymer chain conformation in the phase separation process of a binary liquid mixture

A polymer chain conformation change near the critical point of liquid-liquid phase separation was investigated. Poly(N-isopropylacrylamide) labeled with a small amount of carbazolyl group for a fluorophore (P(NIPA-Cz)) was prepared. A ternary system of P(NIPA-Cz)+cyclohexane+methanol was investigated by the fluorescence spectroscopic technique. A mixed solvent of cyclohexane+methanol (CH/MeOH) shows phase separation at the upper critical solution temperature. Light scattering intensity, fluorescence emission intensity and fluorescence anisotropy ratio, as a function of temperature, were measured with quasi statically approaching to the critical demixing point. The fluorescence intensity of the carbazolyl groups attached to the polymer chain decreases with approaching to the critical temperature. This result suggests that the radius of gyration of the polymer decreases upon approaching to the critical demixing point of the solvent. We discuss the collapse and aggregation processes of the polymer based on the fluorescence quenching method. The rotational diffusion coefficient of carbazolyl groups attached to the polymer chain was estimated by the fluorescence depolarization technique. The rotational motion of carbazolyl groups is slowed down upon approaching the critical point.     

Chemical interactions in noncontact AFM on semiconductor surfaces: Si(111), Si(100) and GaAs(110)

Total-energy pseudopotential calculations are used to study the imaging process in noncontact atomic force microscopy (AFM) on Si(111), Si(100) and GaAs(110) surfaces. The chemical bonding interaction between a localised dangling bond on the atom at the apex of the tip and the dangling bonds on the adatoms in the surface is shown to dominate the forces and the force gradients and, hence, to provide atomic resolution. The lateral resolution capabilities are tested in both the Si(100) and the GaAs(110) surfaces. In the first case, the two atoms in a dimer can be resolved due to the dimer flip induced by the interaction with the tip during the scan, while in the GaAs(110), we identify the anion sublattice as the one observed in the experimental images.     

Two‐dimensionally extended aromatic polyamines for optimization of charge‐transporting properties by partial oxidation

This article describes the synthesis of the two‐dimensionally extended aromatic polyamines by polycondensation between the tri‐sec‐amine monomer and p‐phenylenediamine‐based dibromide, the polyradical generation by chemical and electrochemical oxidations, and the hole‐transporting properties. The molecular weights (M_n) of the polyamines, 3a and 3b , were 7700 and 5000, respectively, and both polymers were very soluble in the typical organic solvents, ensuring a good film formation capability by a spin‐coating technique. The thermal stability of the aromatic polyamines, elucidated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), was quite high. More important, the cross‐conjugated structure is essential for the controlled radical generation and the maintenance of the radical stability. Cyclic voltammograms of the neutral polyamines in the presence of 1 vol % of trifluoroacetic acid and the intervalence bands of the partially oxidized polyamines with NOPF₆ revealed that the generated radicals delocalize over the p‐phenylenediamine moieties. The half‐life of the polyradicals was about 12 h even under ambient conditions, which allowed us to fabricate and measure the hole‐only devices. The charge‐transporting properties of the polyamines were dramatically changed by the partial oxidation (20 mol %/aminium unit) with NOPF₆. The neutral polyamines showed the conventional injection‐limit behaviors, whereas the hole‐transporting behaviors of the polyradicals are bulk‐limit and highly dependent on the chemical structure. The efficient hole‐transport of the all‐conjugated poly(aminium cationic radical)s was for the first time realized for the polyradical of 3b . © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4577–4586, 2009     

Syntheses of 6-O-ethyl/methyl-celluloses via ring-opening copolymerization of 3-O-benzyl-6-O-ethyl/methyl-α-d-glucopyranose 1,2,4-orthopivalates and their structure–property relationships

6-O-Alkyl-celluloses with well-defined ratio of ethyl and methyl groups at position 6 were prepared by ring-opening copolymerization of 6-O-ethyl and 6-O-methyl glucose 1,2,4-orthopivalate derivatives. An aqueous solution of 6-O-ethyl-cellulose having no methyl group was found to be thermo-responsive to be turbid at ~70 °C. An aqueous solution of 6-O-ethyl-cellulose with higher molecular weight showed endothermic and exothermic peaks in the heating and cooling curves of DSC measurements, respectively. However, 6-O-alkyl-cellulose having 10% methyl group lost its thermo-responsive character. 6-O-Alkyl-celluloses having more than ten percent of ethyl group at position 6 became water-soluble, though 6-O-methyl-cellulose is insoluble in water. Thus, 6-O-ethyl group was found to be of importance for the water solubility of regioselective 6-O-alkyl-celluloses. Furthermore, a small amount of methyl group introduced at C6 position was found to affect some of physical properties of 6-O-alkyl-celluloses such as thermo responsive property.