Electron transfer between two stable radicals

Electron spin resonance (ESR) is a sensitive tool to detect the electron-transfer processes in some specified systems from the change of the ESR signals. In this paper, the interaction between poly(N,N-dimethylaniline) (PDMA) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) was investigated by ESR spectra based on the stability of their radicals in ethanol. It is shown that an electron-transfer process occurs from nitrogen atoms of PDMA molecules to those of DPPH molecules which makes PDMA form more stable radical cations and eliminates the radicals on DPPH.     

Magnetic interaction of pyridyl-substituted thioaminyl stable free radicals

N-(2-Pyridylthio)-2,6-diaryl-4-R-phenylaminyls (R = Ph, 4-ClC(6)H(4), MeCO, CN, EtOCO) and N-(4-pyridylthio)-2,6-diaryl-4-R-phenylaminyls (R = Ph, 4-ClC(6)H(4), EtOCO) were prepared and isolated as radical crystals. Their ESR spectra were measured, and the NS and pyridyl nitrogen and anilino meta and pyridyl ortho and para proton hyperfine coupling constants were determined. The spin-density calculations based on the density functional theory were performed by the UBecke 3LYP hybrid method using the STO 6-31G basis set. X-ray crystallographic analyses were performed for three radicals, and their structures were discussed in detail. The magnetic susceptibility measurements were carried out for the nine kinds of isolated radicals with a SQUID magnetometer. One radical showed ferromagnetic coupling (2J/k(B) = 44 K), and the others showed antiferromagnetic behavior. The magnetic interactions observed are explained on the basis of the crystal structures.     

A new polyphenylene derivative bearing two stable radicals

Hydroxylization of poly(N,N-dimethylaniline) (PDMA) by using H₂O₂ in base medium gives rise to a new polyphenylene derivative containing a high concentration of stable phenoxy radicals in the solid state. In solution, hydroxylated PDMA can have two forms of stable radicals, phenoxy radical and radical cation, and these two forms can be converted reversibly into each other by adjusting the pH value of the solution.     

Rate constants of the reaction between alkyl radicals and oxygen and stable nitroxyl radicals

Conclusions The rate constants of the reaction between the alkyl radicals of hydrocarbons (R^.) and of vinyl monomers (M^.) and O₂ and stable nitroxyl radicals were determined at 50C. The low-molecular-weight radicals react with O₂ (k₁) and the (k₃) more rapidly than the M^. do. For polar R^. and M^. k₁ and k₃ are close, and for the nonpolar ones k₁>k₃.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2446–2450, November, 1979.The authors express their appreciation to V. A. Golubev for submitting the nitroxyl radicals and A. P. Moravskii for help in running the experiment.     

Electrospray ionization mass spectrometry of stable nitroxide free radicals and two isoindoline nitroxide dimers

Electrospray ionization (ESI) mass spectra were recorded for a range of substituted isoindoline nitroxides, two isoindoline nitroxide dimers and two piperidinyl nitroxides. In all cases the dominant molecular species arise from oxidation rather than protonation, an unusual process in ESI. Fragment ion spectroscopy was used to establish fragmentation mechanisms for the nitroxides under ESI conditions.     

Mechanical properties of vanadium-base binary alloys

The fabricability and tensile properties of solid-solution-strengthened vanadium-base binary alloys containing aluminium, titanium, niobium, tantalum, chromium, molybdenum or iron were studied. The alloys were prepared by non-consumable arc melting and contained 150–370 ppm O, 20–250 ppm N and 40–130 ppm C. The VTi, VNb and VTa alloys were superior to the other alloys in their fabricabilities into sheet. The tensile properties were examined between room temperature and 1000 °C. The tensile strength values of the VNb and the VTa alloys were higher than those of the VAl and the VCr alloys. The tensile strengths of the VAl, VCr and VMo alloys increased in proportion to the increase in atomic per cent of alloying element, while those of the VNb, VTa and VFe alloys increased with the square root of the atomic per cent of the alloying element.     

The analysis of zirconium-thorium binary alloys

Thorium-zirconium binary alloys are analysed by complexometric procedures. For alloys containing more than 20% thorium or 5% zirconium by weight, the sum of the constituents is obtained by a back titration procedure at pH 2.6–2.8 with bismuth nitrate using xylenol orange as indicator. Thorium is then masked with sulphate and the liberated EDTA is titrated with bismuth at pH 1.2–1.3. For alloys containing less than 20% of thorium, thorium fluoride is precipitated on lanthanum fluoride to effect its separation before titration. For alloys containing less than 5% of zirconium, the zirconium is separated by precipitation with p-bromo-mandelic acid.     

Polarographic study of some stable phenoxyl radicals

Conclusions A study was made of the polarographic reduction of phenoxyl radicals.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2844–2845, December, 1971.     

Ferromagnetic behavior of formyl-group-carrying stable thioaminyl radicals

Four formyl-group-carrying thioaminyl radicals were generated, and one radical could be isolated as radical crystals. Magnetic susceptibility measurements of the isolated radical showed a ferromagnetic regular linear-chain interaction of 2J/k(B) = 3.2 K, which was explained in terms of the X-ray crystallographic results.     

Galactose oxidase models: tuning the properties of CuII-phenoxyl radicals

Four tripodal ligands with an N(3)O coordination sphere were synthesized: (2-hydroxy-3-tert-butyl-5-nitrobenzyl)bis(2-pyridylmethyl)amine (LNO(2)H), (2-hydroxy-3-tert-butyl-5- fluorobenzyl)bis(2-pyridylmethyl)amine (LFH), (2-hydroxy-3,5-di-tert-butylbenzyl)bis(2-pyridylmethyl)amine (LtBuH) and (2-hydroxy-3-tert-butyl-5-methoxybenzyl)bis(2-pyridylmethyl)amine (LOMeH). Their square-pyramidal copper(II) complexes, in which the phenol subunit occupies an axial position, were prepared and characterized by X-ray crystallography and UV/Vis and EPR spectroscopy. The phenolate moieties of the copper(II) complexes of LtBuH and LOMeH were electrochemically oxidized to phenoxyl radicals. These complexes are EPR-active (S=1), highly stable (k(decay)=0.008 min(-1) for [Cu(II)(LOMe(.))(CH(3)CN)](2+)) and stoichiometrically oxidise benzyl alcohol. Two additional tripodal ligands providing an N(2)O(2) coordination sphere were also studied: (2-pyridylmethyl)(2-hydroxy-3-tert-butyl-5-methoxybenzyl)(2-hydroxy-3-tert-butyl-5-nitrobenzyl)amine (L'OMeNO(2)H(2)) and (2-pyridylmethyl)bis(2-hydroxy-3-tert-butyl-5- methoxy)benzylamine (L'OMe(2)H(2)). Their copper(II) complexes were isolated as dimers ([Cu(2II)(L'OMe(2))(2)], [Cu(2II)(L'OMeNO(2))(2)]) that are converted to monomers on addition of pyridine. The complexes were investigated by X-ray crystallography and UV/Vis and EPR spectroscopy. Their one-electron electrochemical oxidation leads to copper(II)-phenoxyl systems that are less stable than those of the N(3)O complexes. The N(2)O(2) complexes are more reactive than the N(3)O analogues: they aerobically oxidize benzyl alcohol to benzaldehyde at a higher rate, as well as ethanol to acetaldehyde (40-80 turnovers).     

Determination of niobium and tantalum in binary alloys and zirconium alloys

Recent developments in the metallurgy of niobium, tantalum and zirconium have necessitated provision of analytical procedures for determining niobium and tantalum in the presence of each other and in the presence of zirconium. For this purpose, absorptioinetric procedures based on the formation of yellow coloured complexes, between pyrogallol and niobium or tantalum, have been critically examined. Direct absorptiometric procedures are described, which are suitable for determining niobium or tantalum in the range 2 to 7%; when either of these metals exceeds 7%, differential absorptiometric procedures are recommended. Corrections must lie made for absorption due to the presence of other metals which form complexes with pyrogallol. In tlie determination of niobium or tantalum up to 5%, the precision of the method is about ±0.05%. About 12 determinations can be made in a day, by one analyst.