Spectrophotometric determination of yttrium in aluminium base alloys with 1-[(5-Methyl-2-pyridyl)azo]-2-naphthol

Summary A highly sensitive and selective Spectrophotometric method has been developed for the determination of yttrium in aluminium base alloys. The method is based on the red water-insoluble complex formed when yttrium and 1-[(5-methyl-2-pyridyl)azo]-2-naphthol (5-Me--PAN) react in a pH 9.5–11.2 solution. This complex could be extracted into ether (absorption maximum, 530 nm). Beer's law is obeyed up to 1 p. p. m. of yttrium and the molar absorptivity is 6.4 · 10⁴ l · mole^–1 · cm^–1 at 530 nm.

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Zusammenfassung Eine hochempfindliche und selektive spektrophotometrische Methode zur Bestimmung von Yttrium in Aluminiumlegierungen wurde ausgearbeitet. Sie beruht auf der Bildung der roten, wasserlöslichen Komplexverbindung des Yttriums mit 1-[(5-Methyl-2-pyridyl)azo]-2-naphthol(5-Me--PAN) bei pH 9,5–11,2. Diese Verbindung läßt sich mit Äther extrahieren und hat ein Absorptionsmaximum bei 530 nm. Das Beersche Gesetz ist bis zu 1 ppm Yttrium erfüllt. Die molare Extinktion beträgt 6,4 · 10⁴ 1 · Mol^–1 cm^–1 bei 530 nm.

     

Synthesis of perfluorochemicals for use as blood substitutes,Part I. Electrochemical fluorination of N-methyldecahydroquinoline and N-methyldecahydroisoquinoline

Electrochemical fluorination of N-methyldecahydroquinoline afforded mainly a mixture of $\text{cis}$ and $\text{trans}$ N-(F-methyl)-F-decahydroquinoline, their rearranged isomers and F-propyl-F-cyclohexane arising from the cleavage at carbon-nitrogen bonds, in a ratio of approximately 2:4:6:3. N-Methyldecahydroisoquinoline was also fluorinated electrochemically to give a mixture of $\text{cis}$ and $\text{trans}$ N-(F-methyl)-F-decahydroisoquinoline, their rearranged isomers and 1-(F-ethyl)-2-(F-methyl)-F-cyclohexane in a ratio of approximately 4:4:6:1. No correlation was found between the $\text{cis}$ and $\text{trans}$ ratio of starting materials and that of the corresponding perfluorinated amines. Fluorination of N-methyl-1,2,3,4-tetrahydroquinoline gave much lower yields.     

Separation of proteins by hydrophobic interaction chromatography at low salt concentration

We investigated protein separation by hydrophobic interaction chromatography (HIC) at low salt concentration on the supports of various hydrophobicities. Hydrophobic proteins could be successfully separated with more than 90% recovery by gradient elution of ammonium sulfate from 0.3-0.5 M to 0 in 50 mM phosphate buffer (pH 6.8) by using supports whose hydrophobicities were properly adjusted individually for each protein. Satisfactory results were also obtained by isocratic elution without ammonium sulfate and gradient elution of ethanol from 0 to 10%. HIC at low salt concentration was compatible with other modes of liquid chromatography like ion-exchange chromatography. On the other hand, it was not successful to separate hydrophilic proteins at low salt concentration. Recoveries of hydrophilic proteins decreased before they were retained enough as support hydrophobicity increased. Therefore, it is inevitable to use a higher concentration of salt, e.g., 1-2 M ammonium sulfate, on hydrophilic or moderately hydrophobic support in order to retain hydrophilic proteins without decrease in recovery.     

Synthesis of wholly aromatic polysulfonamides from aromatic disulfonyl chlorides and aromatic diamines

Wholly aromatic polysulfonamides of high molecular weight were prepared by the solution poly-condensation of aromatic disulfonyl chlorides with aromatic diamines in tetramethylene sulfone and substituted pyridines as the acid acceptor. Polysulfonamides with inherent viscosities as high as 1.2 were readily obtained by initiating polycondensation at a temperature of 5–10°C to control the side reactions. The polycondensation was fairly fast and was completed in 10 min at 60°C. All the aromatic polysulfonamides dissolved in a wide range of solvents, including acetone and tetrahydrofuran. These polymers were less thermally stable than the corresponding aromatic polyamides.     

Decisive role of electronic polarization of the protein environment in determining the absorption maximum of halorhodopsin

It is known that the absorption maximum of halorhodopsin is red shifted by 10 nm with the uptake of a chloride ion Cl(-). According to the X-ray structure, the ion is located at the position of the counterion of the chromophore, protonated retinal Schiff base. Thus, the direction of the observed spectral change is opposite to that expected from the pi-electron redistribution (an increase in the bond alternation) induced by the counterion. The physical origin of this abnormal shift is never explained in terms of any simple chemical analogues. We successfully explain this phenomenon by a QM/MM type of excitation energy calculation. The three-dimensional structure of the protein is explicitly taken into account using the X-ray structure. We reveal that the electronic polarization of the protein environment plays an essential role in tuning the absorption maximum of halorhodopsin.     

1-alkoxyvinyl esters: renaissance of half-century-old acyl donors with potential applicability

Among the various kinds of acyl donors, the 1-alkoxyvinyl esters have characteristic features, such as a high reactivity under nearly neutral conditions and the generation of neutral and volatile esters as single coproducts. Although their use in organic syntheses began in the middle of the 1950s, no significant progress has been seen. This is probably because the existing method of preparing alkoxyvinyl esters used toxic mercuric salts and was not totally applicable for those esters having functionalized acyl moieties. We have discovered that the use of a catalytic amount of the less toxic [RuCl2(p-cymene)]2 effectively accelerates the addition of carboxylic acids to ethoxyacetylene to give ethoxyvinyl esters bearing a variety of functionalized acyl groups in high yields. This discovery has opened a new avenue for developing new reactions and new synthetic methodologies based on the design and use of these acyl donors with suitable functional groups. Such examples include (i) the installation of hydrophilic acyl moieties on biologically active compounds, (ii) asymmetric Pummerer-type reactions, (iii) aromatic Pummerer-type reactions, (iv) the lipase-catalyzed desymmetrization of symmetrical 1,3-diols, and (v) lipase-catalyzed domino reactions. Future possibilities for these acyl donors are also discussed.     

The synthesis of crowned phenoselenazinone derivatives

Summary Several substituted crowned phenoselenazin-16-one derivatives were prepared by condensation of substituted zinc 2-amino-benzeneselenolates with 1,4-quinone of benzo[15]crown-5 or its dibromide in alcoholic solution. The dehalogenation of the bromoselenazinones was also investigated.

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Synthese von Kronen-Phenoselenazinon-Derivaten (Kurze Mitt.)

Zusammenfassung Es wurden einige substituierte Kronen-Phenoselenazin-16-on-Derivate mittels Kondensation von substituierten Zink-2-aminobenzolselenolaten mit dem 1,4-Chinon von Benzo[15]krone-5 oder seinem Dibromid in alkoholischer Lösung dargestellt. Die Dehalogenierung der Bromselenazinone wurde ebenfalls untersucht.

     

Boundary effect on the thermal degradation of copolymers

The mechanism of thermal degradation of vinyl-type copolymers at high temperatures was investigated theoretically and experimentally. A parameter β was proposed to account for the boundary effect. Values of β for acrylonitrile–styrene and methyl methacrylate–styrene copolymers were determined experimentally. It was ascertained that the value of β was independent of the distribution of monomer sequence lengths in a copolymer, but dependent on the pyrolysis temperature and on the nature of the copolymer. The boundary effect is attributed to differences in the dissociation energies of C? C bonds connecting terminal monomer units to adjacent monomer units in copolymer chain radicals.     

The mass spectrum of isopropyl o-toluate

The formation of an [M + 1]⁺ ion and the fragmentation of isopropyl o-toluate have been investigated by the deuterium labelling technique and kinetic energy release measurements. The hydrogen atom involved in the [M + 1]⁺ ion formation does not originate from a specific part of the molecule, but from all parts. A small amount of hydrogen exchange between the secondary carbon atom in the isopropyl group and the carbon atoms in the tolyl group takes place prior to decomposition of the molecular ion into the m/z 136 ion by a McLafferty rearrangement. Either almost complete scrambling of the hydroxyl hydrogen atom and the methyl hydrogen atoms in tolyl group or an almost equilibrated exchange of the hydroxyl hydrogen atom with one of the remaining hydrogen atoms in tolyl group also takes place prior to the elimination of a water molecule from the intermediate m/z 136 ion.     

Synthetic studies on mitomycins. 2. A synthesis of 9a-hydroxy-5,8-dideoxomitosane skeleton through a novel retroaldol type of ring-opening reaction.

A synthesis of 9a-hydroxy-5,8-dideoxomitosanes was accomplished by the transannular cyclization of hydro-1-benzazocinone intermediates derived from 3-(2,5-dioxo-1-methylcyclopentyl)-6-methyl-p-phenylenediamine derivatives. These mitosanes were led to the 8-membered ring system by an oxidative ring-opening reaction.