Showing papers on "Radical ion published in 1969"

An identification of the radical giving rise to the light‐induced electron spin resonance signal in photosynthetic bacteria

Abstract: — A reaction-center fraction isolated from Rhodopseudomonas spheroides chromatophores exhibits light-induced changes in its optical and electron spin-resonance (ESR) spectra. In particular, a bleaching at 870nm (P870) has been found to be closely correlated with the appearance of an ESR signal with a g factor of 2.0025 and a peak-to-peak line width of 10 G. The ESR signal is indistinguishable from light-induced signals found in chromatophores or whole cells. A careful measurement of the spin concentration showed that the ratio of the light-induced spins to bleached P870 molecules is 1.1 ± 0.1. In addition the formation and decay kinetics are identical within experimental error under a variety of experimental conditions. Previous work has shown that P870 is a bacteriochlorophyll molecule in a specialized environment and that the bleaching signifies oxidation. The present work provides strong evidence that the photo-bleaching of P870 produces the radical cation of bacteriochlorophyll, P870+, and that this radical is the source of the ESR signal in whole cells. The quantum yield for the bleaching of P870 in reaction centers has been measured, using actinic light of wavelengths 880, 800, 760 and 680 nm. For light absorbed at 880 or 800 nm the efficiency is close to 100 per cent. In a coupled reaction, the oxidation of mammalian cytochrome c by P870+ proceeds with nearly the same efficiency. The above results place definite limits on the possibilities for the identity of the primary acceptor. These possibilities are discussed.

Complex Radical–Ion Salts of TCNQ (Tetracyanoquinodimethan) with Cyanine Dye and Related Cations

Abstract: The electrical conductivities of the complex radical–ion salts of TCNQ (tetracyanoquinodimethan) with cyanine dye and related cations generally increase with an increase in the polarizability of the cation. With large cations, however, the increase expected from the high polarizability is offset by the size of the cation. From the change in conductivity of the complex TCNQ salts accompanying the variation in structure of the corresponding cations, a plausible structure for the complex salts can be postulated.

Electrochemical methoxylation of vinyl ethers: a novel anodic dimerization reaction

Abstract: Electrolysis of vinyl ethers in methanol using a platinum anode and nickel cathode was found to yield the corresponding 1,2-dimethoxylation products (60–66%) and products resulting from a tail-to-tail dimerization to succindialdehyde acetals (20–22%). A mechanism involving radical cation intermediates is proposed.

Charge-transfer properties of some paraquat salts

Abstract: A series of salts of the dication, NN′-dimethyl-4,4′-bipyridyl, with anions of the type MX4n–, where M can be a unibi-, or ter-valent cation and X is chloride, bromide, or iodide, has been prepared. Their formulae have been obtained chemically and in certain cases by complete structure analyses. The absorption spectra of the solids have been measured and an intermolecular charge-transfer band, from anion to cation, has been assigned. E.p.r. spectra of the FeCl42– and of the Cu2Cl42– compound shows that these solids contain some of the reduced radical cation and some oxidised anion. The electrical conductivity of this type of compound is high. The relevance of the observations to the effect of the cation (paraquat) on electron-transfer in photosynthesis and oxidative phosphorylation is discussed.

ESR Studies of Trapped CO2− Radicals in X‐Irradiated Succinic Acid

Abstract: Studies of the g tensor of the singlet in x‐irradiated succinic acid suggest that this line is due to the CO2− radical ion. Temperature‐variation studies indicate that this CO2− fragment arises from the decomposition of the anionic species [HOOCCH2CH2COOH]− which appears to be formed in the initial radiation‐damage process. A mechanism rationalizing the ESR data on all irradiated carboxylic acids is proposed.

Radiolysis in Naphthalene Single Crystals

Abstract: Experimental studies of optical absorption and electron paramagnetic resonance of naphthalene single crystal irradiated at liquid nitrogen, dry ice and room temperatures have been made. It is found that the epr spectrum associated with the l-hydronaphthyl radical is produced at all temperatures studied. Optical absorption bands at 337, 395 and 530 nm are assigned to be associated with the l-hydronaphthyl radical. Irradiation at liquid nitrogen temperature produces a broad doublet epr spectrum as well as that associated with the l-hydronaphthyl radical; the former is considered to be caused by the naphthyl radical. Irradiation at dry ice and room temperatures produces optical absorption bands which are associated neither with the hydronaphthyl nor the naphthyl radical. It is suggested that the radiation products at higher temperature are the hydronaphthyl radical and the naphthalene dimer which is formed as the result of reaction of the naphthyl radical with a neighboring molecule.

The photoreactions of aromatic ketones with arylamines

Abstract: Photoreduction of aromatic ketones by N-alkyl-arylamines gives α-hydroxyarylmethyl radicals, which have been characterised by their e.s.r. spectra and u.v. absorption spectra, while photolysis of benzophenone in the presence of tri-p-tolylamine in acetonitrile gives the radical cation of the amine.

Paramagnetic resonance of SO2 - radical-ion in solution: Spin-rotational relaxation mechanism

Abstract: The E.P.R. linewidth of the SO2 - radical-ion in water solution has been studied as a function of temperature and viscosity. A strict dependence of the linewidth on T/η has been observed over the range of temperature and viscosity examined. The analysis of all possible broadening mechanisms shows that the spin-rotational interaction is the only process effective on the linewidth. The theory extended by Atkins and Kivelson [3] to E.P.R. relaxation has been checked quantitatively. From the slope of ΔH versus T/η and the principal values of the g tensor of the SO2 - radical-ion, the value of the hydrodynamic radius is r = 0·91 a. Comparison with the linewidth of the ClO2 isoelectronic radical has been made.

The photoreactions of aromatic hydrocarbons in the presence of amines

Abstract: Irradiation of benzene solutions of anthracene and acenaphthylene containing tertiary amines gives photodimers, whereas acetonitrile solutions give photoreduction: these results are interpreted in terms of excited charge transfer complex and radical ion formation.

Electron impact studies. Part XXXIX. Proximity effects in the mass spectra of aromatic carbonyl compounds containing adjacent methoxy-substituents

Abstract: Peaks due to M– H2O are observed in the mass spectra of aromatic carbonyl compounds which contain an ortho(or peri) methoxy-substituent. This process is of diagnostic value for simple systems, but cannot be extended to those systems which have a large number of oxygen-containing substituents. The fragmentation has been studied by 2H and 18O labelling. The properties of the M– 18 fragment in the spectrum of o-methoxybenzaldehyde correspond to those of a benzofuran radical ion.

Evidence for Activated Carrier Mobility in Organic Solids

Abstract: STEADY state space charge limited currents (SCLC) were obtained at different temperatures for a series of dipyridy-lium model compounds (Fig. 1) into which one TCNQ molecule (tetracyanoquinodimethane), in the form of a radical ion, was introduced. Some compounds were produced containing two molecules of TCNQ, one associated with each ring. Polymers of these compounds were also produced and SCLC measured (details of preparation will be published elsewhere).

Radical intermediates. Part I. Spectroscopic studies on the alkali-metal nitrobenzenides

Abstract: Alkali-metal derivatives of the nitrobenzene radical anion have been prepared as stable solids, and their e.s.r. and u.v. spectra interpreted in terms of the radical and its decay products. Solutions of the radical show remarkable stability in a wide range of solvents including water. The e.s.r. spectra of such solutions indicate that significant amounts of tightly bound ion pairs are present in solvents such as acetonitrile and acetone even at radical concentrations of around 10–4M.

Interaction of the stable radical 2,2,6,6-tetramethylpiperidone-4-oxy-1 with acids

Abstract: 1. The nitroxide free radical reacts with trichloroacetic and trifluoroacetic acids in benzene solution, forming a salt of the hydroxylamine and an unsaturated nitroso-compound. 2. A hypothesis on the occurrence of a reaction between radicals and acid through the intermediate formation of ionic forms of the radical was advanced.

An electron spin resonance study of quinone di-imide radical anions

Abstract: The e.s.r. spectra of the NN′-bisphenylsulphonyl-p-benzoquinone di-imine radical anion, its 2,3- and 2,5-di-chloro-substituted analogues, and the NN′-dicyano-p-benzoquinone di-imine radical anion are reported. The observation of two sets of equivalent protons in the bisphenylsulphonyl-p-benzoquinone di-imine and the NN′-di-cyano-derivative radical anions is interpreted on the basis of slow rotational isomerism of the para-substituents.

An identification of the radical giving rise resonance signal in photosynthetic bacteria to the light-induced electron spin

Abstract: A reaction-center fraction isolated from Rhodopseudomonas spheroides chromato- phores exhibits light-induced changes in its optical and electron spin-resonance (ESR) spectra. In particular, a bleaching at 870 nm (P870) has been found to be closely correlated with the appearance of an ESR signal with a g factor of 24025 and a peak-to-peak line width of 10 G. The ESR signal is indistinguishable from light-induced signals found in chromatophores or whole cells. A careful measurement of the spin concentration showed that the ratio of the light-induced spins to bleached P870 molecules is 1.1 20.1. In addition the formation and decay kinetics are identical within experimental error under a variety of experimental conditions. Previous work has shown that P870 is a bacteriochlorophyll molecule in a specialized environment and that the bleaching signifies oxidation. The present work provides strong evid- ence that the photo-bleaching of P870 produces the radical cation of bacteriochlorophyll, P870+, and that this radical is the source of the ESR signal in whole cells. The quantum yield for the bleaching of P870 in reaction centers has been measured, using actinic light of wavelengths 880, 800, 760 and 680 nm. For light absorbed at 880 or 800 nm the efficiency is close to 100 per cent. In a coupled reaction, the oxidation of mammalian cytochrome c by P870+ proceeds with nearly the same efficiency. The above results place definite limits on the possibilities for the identity of the primary acceptor. These possibilities are discussed.