Leslie H. Sutcliffe

An evaluation of the antioxidant and potential pro-oxidant properties of food additives and of Trolox C, vitamin E and probucol.

The food additives propyl gallate and vanillin inhibited iron ion-dependent lipid peroxidation in rat-liver microsomes, but stimulated formation of a deoxyribose degrading species, probably hydroxyl radical, from ferric-EDTA and hydrogen peroxide. Propyl gallate accelerated DNA damage by the anti-tumour antibiotic bleomycin, although vanillin did not. The water-soluble vitamin E analogue Trolox C also stimulated bleomycin-dependent DNA damage, but not hydroxyl radical generation from ferric-EDTA and H2O2. Indeed, Trolox C was found to be a powerful scavenger of hydroxyl radical (rate constant greater than 10(10) M-1s-1). Probucol did not stimulate oxidative damage in any of the systems tested, and is a powerful inhibitor of lipid peroxidation in rat liver microsomes. The ESR spectrum of the radical produced by one electron-oxidation of probucol in ethanol is described.

Electron spin resonance study of CH3CNSSN˙, C6H5CNSSN˙, and SNSSN˙+ free radicals

Isotropic and powder e.s.r. spectra have been recorded for CH3[graphic omitted]˙, C6H5[graphic omitted]˙, and [graphic omitted]˙+. Isotropic labelling with nitrogen-15 and sulphur-33 has been accomplished for [graphic omitted]˙+ and it has been possible to prepare 33[graphic omitted]˙+. Sulphur-33 satellites have been observed for C6H5[graphic omitted]˙. MNDO and Gaussian 76 calculations have been used to calculate the minimum-energy structures of the radicals, while INDO calculations have provided values for the hyperfine coupling constants. Unfortunately, poor agreement was obtained between the latter and the corresponding experimental values. All the radicals dimerise in solution at low temperatures and we have been able to measure the energetics of dimerisation for C6H5[graphic omitted]˙ and [graphic omitted]˙+. The dimers exist as crystalline solids which contain readily detectable amounts of the monomeric free radical.

Paramagnetic liquids: the preparation and characterisation of the thermally stable radical ButCNSNS· and its quantitative photochemically symmetry allowed rearrangement to a second stable radical ButCNSSN

The new thermally stable paramagnetic liquid 5-t-butyl-1,3,2,4-dithiadiazolyl has been isolated in the dark and quantitatively photochemically isomerised to the paramagnetic liquid 5-t-butyl-2,3,1,4-dithiadiazolyl (non-systematic numbering for ease of comparison).

The high yield preparation, characterisation, and gas phase structure of the thermally stable CF3CSNSCCF3·, 4,5-bis(trifluoromethyl)-1,3,2-dithiazolyl and the X-ray crystal structure of benzo-1,3,2-dithiazolyl

The very thermally stable, but photochemically sensitive radical, 4,5-bis(trifluoromethyl)-1,3,2-dithiazolyl has been prepared, isolated, and fully characterised including a gas phase structure, and found to be paramagnetic in the liquid state at room temperature; the X-ray structure of benzo-1,3,2-dithiazolyl has been obtained for comparison.

The benzobisdithiazole system in its various oxidation states: a new building block for organic conductors

Abstract The title compound can be isolated in at least three distinct oxidation states. Synthesis and characterization of these species are presented in this paper. The dication is easily reduced to the radical cation by a variety of reducing agents. Partial reduction occurs during its preparation, yielding a mixed valence compound showing a conductivity of ≈2 × 10 −1 S cm −1 . Further reduction yields a neutral paramagnetic species that forms a conducting 2:1 complex with TCNQ.

Electron spin resonance spectroscopy, stability and spin-probe properties of dithiazolyl, dithiadiazolyl, benzodithiazolyl and disulphenimidyl free radicals

A comparative investigation has been made of the e.s.r. spectra of 1,3,2-dithiazol-2-yl, 1,3,2,4-dithiadiazol-2-yl, 1,3,2-benzodithiazol-2-yl and dibenzenesulphenimidyl free radicals, both in solution and in rigid matrices. The powder spectra were analysed to give values for the anisotropic g-factors and hyperfine coupling constants, and, in turn, these results were used by means of a simple e.s.r. tumbling theory to calculate radical radii from low-temperature fluid e.s.r. spectra. A simple correction was incorporated into the theory to include a contribution from ‘slip’ rotation. The values of the nitrogen isotropic coupling constants provide a useful guide to the electronic and spatial structures of the radicals. It is shown that the 1,3,2-dithiazol-2-yl radicals have the greatest potential as spin probes.

NMR DETERMINATION OF EPR HYPERFINE COUPLING CONSTANTS OF SOME 5-(N-ALKYL)-1,1,3,3-TETRAKIS(TRIDEUTERIOMETHYL)ISOINDOLIN-2-YLOXYLS

2D 1H–13C chemical shift correlation spectroscopy has been used to determine some small 1H and 13C EPR hyperfine interaction constants in some 5-(n-alkyl)isoindolin-2-yloxyl radicals. In the methodology used, it was necessary to measure the chemical shifts of both the isoindolines and of the cognate isoindolin-2-yloxyl radicals. The latter n-alkyl-substituted radicals have considerable potential as EPR spin probes in lipid systems.

Molecular motion of a water-soluble nitroxyl radical in gelatin gels

Electron spin resonance spectroscopy (ESR) has been used to measure the rotational correlation times and translational diffusion constants of a radical spin probe in gelatin gels. The radical used is NaTMIOS, the sodium salt of sulphonated 1,1,3,3-tetramethylisoindolin-2-yloxyl. It was found that the mobility of the radical was influenced by the gelatin concentration and by temperature. It was concluded that the spin probe was constrained by the polymer chains and, when conditions were such that the distance between the chains was of the order of the size of the probe, rotational motion was severely impeded.

ESR measurements of the partitioning of some new spin probes in n-octanol–water

The stable free radical 1,1,3,3‐tetramethylisoindolin‐2‐yloxyl (TMIO) has proved to be very suitable for use as a spin probe for a number of applications. Because it is soluble mainly in non‐polar liquids, there is a need for new derivatives that can be used in a variety of environments. This has been done by introducing substituents in the 5‐position of the aromatic ring, namely carboxyl (CTMIO), trimethylamino (TMTMIOI) and sodium sulphonate (NaTMIOS). An accurate ESR method was developed for the measurement of partition coefficients in n‐octanol–water. For comparison purposes the method was also applied to some Tempo derivatives. The effect of temperature on the rotational correlation times and the nitrogen‐14 hyperfine coupling constant of some of the spin probes was investigated. There is evidence for dimerization of CTMIO to form a biradical. Copyright

The evaluation of two correlation times for methyl groups from carbon-13 spin-lattice relaxation times and NOE data

The purpose of this Note is to offer experimental evidence for the validity of using the two-correlation-time approach to methyl groups in two near-spherical molecules and one semirigid molecule, namely, tri-n-octylamine, polydecene (an oligomer of the alpha olefin decene, having between 30 and 70 carbon atoms), and DCMP (2,4-dicyclohexyl-2-methyl-n-pentane), which is a traction fluid