An ESR study on gamma-irradiated poly(vinyl alcohol)

The formation of radicals in poly(vinyl alcohol), PVA, powder irradiated at 77 K by gamma -rays and the transformations of these radicals during photolysis with visible wavelengths and on thermal annealing have been studied. After irradiation a four-line ESR spectrum was observed. It was assigned to a triplet of the C-alpha-radical (38%), with a splitting of 3.27 mT, superimposed on a doublet (62%) with a splitting of 2.7 mT. The doublet appears to be composed of two radicals, one of which is photo-bleachable (58%) and the other which is not photo-bleachable (42%). This suggests that the latter radical is a neutral radical. The photo-bleachable component of the doublet has been assigned to a carbonyl anion radical. but the second doublet due to a neutral radical is unassigned. The total G-value for formation of radicals at 77 K was found to be 2.41 +/- 0.03. Upon illumination with visible light, the anion radicals were removed and the doublet components or the spectrum diminished in intensity, while the three-line spectrum of the C-alpha-radical became more clearly visible. This transition was due to the photo-detachment of electrons from traps which were proposed to be located on carbonyl groups in the polymer resulting from incomplete hydrolysis of the vinyl acetate. The photo-decay of the anion radicals could be satisfactorily described by a two-stage process. The first stage comprised the decay of approximately 80% of the anion radicals present, while the second stage was associated with the decay of the remaining 20%. Subsequent thermal annealing of a photolysed sample to 290 K led to a change in the shape of the spectrum to form a more clearly defined triplet, As the doublet of the neutral radical decays on thermal annealing between 150 and 250K, the C-alpha-radical is formed. (C) 2001 Elsevier Science Ltd. All rights reserved.

An ESR study of irradiated poly(tetrafluoroethylene-co-perfluoropropyl vinyl ether) (PFA)

Poly(tetrafluoroethylene-co-perfluoropropyl vinyl ether) (PFA) with 2 mol% perfluoropropyl vinyl ether (PPVE) was exposed to gamma -irradiation in vacuum at both 77 K and room temperature and the ESR spectra recorded. Both the main chain, similar to CF2-(CF)-F-.-CF(2)similar to, and end chain, similar to (CF2CF2)-F-. radicals were identified at both temperatures and their thermal stabilities measured, No radicals unique to the radiolytic cleavage at the PPVE units were observed at room temperature, either due to the low concentration of the comonomer or beta -scission to form a chain end radical and a nonradical species. G-values for radical formation at room temperature and 77 K were found to be 0.93 and 0.16, respectively. (C) 2001 Elsevier Science Ltd. All rights reserved.

The use of NMR for determination of new structures in irradiated TFE/PMVE fluoropolymers

The radiation chemistry of two TFE/PMVE copolymers with TFE mole fractions of 0.66 and 0.81 has been studied under vacuum using Co-60 gamma -radiation over absorbed dose ranges up to 4.2 MGy. The radiolysis temperature was 313 K for both TFE/PMVE copolymers. New structure formation in the copolymers was identified by solid-state F-19 NMR and the G-values for new chain ends of 2.1 and 0.5 and for branching sites of 0.9 and 0.2 have been obtained for the TFE/PMVE with TFE mole fractions of 0.66 and 0.81, respectively. The relative yields of-O-CF3 and -CF2-CF3 chain ends were found to be proportional to the copolymer composition, but the yields of the -CF2-CF3 chain ends and -CF- branch points mere not linearly related ia the composition. rather they wets correlated with the radical yields measured at 77 K. (C) 2001 Elsevier Science Ltd. All rights reserved.

High-speed MAS F-19 NMR analysis of an irradiated fluoropolymer

The effect of gamma-radiation on a perfluoroalkoxy (PFA) resin was examined using solid-state high-speed magic angle spinning (MAS) F-19 NMR spectroscopy. Samples were prepared for analysis by subjecting them to gamma-radiation in the dose range 0.5-3 MGy at either 303, 473, or 573 K. New structures identified include new saturated chain ends, short and long branches, and unsaturated groups. The formation of branched structures was found to increase with increasing irradiation temperature; however, at all temperatures the radiation chemical yield (G value) of new chain ends was greater than the G value of long branch points, suggesting that chain scission is the net process.

Chain scission and branching in irradiated poly(tetrafluoroethylene-co-hexafluoropropylene)

The radiation chemistry of poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) with a TFE mole fraction of 0.90 has been studied under vacuum using Co-60 gamma-radiation over a range of temperatures and absorbed doses. The radiolysis temperatures were 300, 363, 423, 523 and 543 K. New structure formation in the copolymers was analysed by solid-state F-19 NMR spectroscopy. The new structures formed in the copolymers have been identified and the G-values for the formation of new chemical structures have been investigated at 363 and 523 K. These two temperatures are just above and just below the polymer T-g and T-m, respectively. At the lower temperature, there was no evidence for any chain branching and an estimate of G(S) of 1.0 was obtained. A value of G(S) of 1.3 and a minimum value of G(X)(Y) of 1.3 were obtained at 523 K. (C) 2003 Society of Chemical Industry.

The impact of carboxy nitroxide antioxidants on irradiated ataxia telangiectasia cells

Three water-soluble carboxy nitroxide antioxidants, 5-carboxy-1,1,3,3-tetramethylisoindolin-2-yloxyl, 4-carboxy-2,2,6,6-tetramethylpiperidin-1-yloxyl, and 3-carboxy-2,2,5,5-tetramethylpyrrolidin-1-yloxyl, show significant impact on the postirradiation survival rates of ataxia telangiectasia (A-T) cells compared to normal cells, an assay which represents a model for understanding the impact of ROS damage on the A-T phenotype. The effects of these antioxidants are much more significant than those of vitamin E or Trolox (a water-soluble vitamin E analog), studied using the same cell survival model. (C) 2004 Elsevier Inc. All rights reserved.

Performance of a substratum-irradiated photosynthetic biofilm reactor for the removal of sulfide from wastewater

The performance of a sulfide-removal system based on biofilms dominated by green sulfur bacteria (GSB) has been investigated. The system was supplied with radiant energy in the band 720-780 nm, and fed with a synthetic wastewater. The areal net sulfide removal rate and the efficacy of the incident radiant energy for sulfide removal have been characterized over ranges of bulk sulfide concentration (1.6-11.5 mg L-1) and incident irradiance (0.21-1.51 W m(-2)). The areal net sulfide removal rate increased monotonically with both increasing incident irradiance and increasing bulk sulfide concentration. The efficacy of the radiant energy for sulfide removal (the amount of sulfide removed per unit radiant energy supplied) also increased monotonically with rising bulk sulfide concentration, but exhibited a maximum value with respect to incident irradiance. The maximum observed values of this net removal rate and this efficacy were, respectively, 2.08 g m(-2) d(-1) and 2.04 g W-1 d(-1). In-band changes in the spectral composition of the radiant energy affected this efficacy only slightly. The products of sulfide removal were sulfate and elemental-S. The elemental-S was scarcely released into the liquid, however, and reasons for this, such as sulfur reduction and polysulfide formation, are considered. Between 1.45 and 3.85 photons were needed for the net removal of one electron from S-species. Intact samples of the biofilm were characterized by microscopy, and their thicknesses lay between 39 +/- 9 and 429 +/- 57 mum. The use of the experimentally determined rates and efficacies for the design of a pilot-scale system is illustrated. (C) 2004 Wiley Periodicals, Inc.

Cryosections of pre-irradiated adult rat spinal cord tissue support axonal regeneration in vitro

Neonatal X-irradiation of central nervous system (CNS) tissue markedly reduces the glial population in the irradiated area. Previous in vivo studies have demonstrated regenerative success of adult dorsal root ganglion (DRG) neurons into the neonatally-irradiated spinal cord. The present study was undertaken to determine whether these results could be replicated in an in vitro environment. The lumbosacral spinal cord of anaesthetised Wistar rat pups, aged between 1 and 5 days, was subjected to a single dose (40 Gray) of X-irradiation. A sham-irradiated group acted as controls. Rats were allowed to reach adulthood before being killed. Their lumbosacral spinal cords were dissected out and processed for sectioning in a cryostat. Cryosections (10 mum-thick) of the spinal cord tissue were picked up on sterile glass coverslips and used as substrates for culturing dissociated adult DRG neurons. After an appropriate incubation period, cultures were fixed in 2% paraformaldehyde and immunolabelled to visualise both the spinal cord substrate using anti-glial fibrillary acidic protein (GFAP) and the growing DRG neurons using anti-growth associated protein (GAP-43). Successful growth of DRG neurites was observed on irradiated, but not on non-irradiated, sections of spinal cord. Thus, neonatal X-irradiation of spinal cord tissue appears to alter its environment such that it can later support, rather than inhibit, axonal regeneration. It is suggested that this alteration may be due, at least in part, to depletion in the number of and/or a change in the characteristics of the glial cells. (C) 2000 ISDN. Published by Elsevier Science Ltd. All rights reserved.

The crosslinking mechanism in gamma irradiation of polyarylsulfone: Evidence for Y-links

Measurements of molecular weights, soluble fractions and examination of NMR spectra of bisphenol-A polysulfone, after gamma irradiation in vacuum at 150 degrees C were used to elucidate the mechanism of crosslinking. Excellent agreement was obtained between G(S) and G(X) determined from measurements above and below the gel dose when a Y-linking mechanism was assumed, whereas poor agreement was obtained when an H-link mechanism was assumed, which is the mechanism normally believed to be responsible for crosslinking. New resonances were observed in the C-13 NMX spectra of the irradiated polymer which were consistent with the formation of Y-links involving phenylene units in the backbone chain. (C) 1998 John Wiley & Sons, Ltd.