60Co Γ-irradiation Research Articles

Biodegradable polymers for use in surgery — poly(ethylene oxide)/poly(ethylene terephthalate) (PEO/PET) copolymers: 2. In vitro degradation

The degradation mechanism of a series of poly(ethylene oxide)/poly(ethylene terephthalate) (PEO/PET) copolymers, synthesized as described in Part 1 1, has been studied in vitro. The need for the development of in vitro test methods for candidate biomaterials is set down. The effect of time, temperature, pH and selected enzymes on the rate and mechanism of degradation is elucidated. The degradation products are identified. The degree of degradation was monitored molecularly by gel permeation chromatography (g.p.c.) and end-group titration techniques. The composition of the copolymers was obtained using infra-red (i.r.) and nuclear magnetic resonance (n.m.r.) spectroscopy. Mass loss and water uptake data are also given. The mechanism of degradation is shown to be by hydrolysis. The effect of ethylene oxide (EO) and 60Co γ-irradiation sterilization on the copolymers was investigated.

Reactions of 1,1-dialkoxyalkene radical cations in aqueous solution with OH–, HPO42–, and H2O. Electron spin resonance spectroscopic, pulse conductometric, and product analytical studies

The reactions of H2O, HPO42–, and OH– with eight, 1,1-dialkoxyalkene radical cations have been studied in aqueous solution by e.s.r. spectroscopy and in part by pulse conductometry and product analysis. Hydroxide ion reacts with the radical cations with rate constants ranging from k 2 × 108 for species (5) to 6 × 109 l mol–1 s–1 for (6), producing mainly alkoxycarbonylalkyl radicals. With (1) and with (6), in addition, the formation of 1,1-dialkoxy-2-hydroxyethyl radicals was observed and e.s.r. parameters are given. The HPO42– anion was found to react with four of the radical cations to form phosphato-dianion-substituted radicals, (RO)2(PO42–)C–ĊH2(e.s.r. parameters are given), with k values ranging from 2 × 106 for (1) to 3 × 108 l mol–1 s–1 for (6). Water reacted analogously with rate constants ranging from k 3 × 102 for (1) to 104 s–1 for (27) at 20 °C, the reaction yielding 2,2-dialkoxy-2-hydroxyethyl radicals (e.s.r. parameters are given) and protons. Attack of water occurs virtually only at the dioxygen-substituted carbon as is shown in one example. Product analysis by g.l.c.–m.s. of the higher boiling material from 60Co γ-irradiation of N2O-saturated aqueous solutions of (CH3O)2CH–CH2Cl gave evidence for the formation of dimers and cross-dimers of the radicals ĊH2OCH(OCH3)CH2Cl, CH3OCOĊH2, (CH3O)2CHĊHCl, (CH3O)2ĊHCH2, and (CH3O)2ĊH2OH. Structures and yields of the products agree with the conclusions drawn from e.s.r. spectroscopic and conductometric measurements.

Effect of Mitomycin C and 60Co -Irradiation on the Replication of SV40 in Cell Lines of Varying Permissivity for SV40 Replication

The effects of mitomycin C and 60Co gamma-irradiation, which induce production of SV40 from SV40-transformed hamster cells, on the replication of superinfecting SV40 or virus DNA in cells varying in permissivity for SV40 replication have been examined. These agents enhance replication of SV40 in an uninducible line of SV40-transformed hamster kidney cells and in nonpermissive secondary hamster kidney cells. The same treatments do not affect SV40 replication in semipermissive hamster (BHK21) and human (HEL, HEK) cells and inhibit SV40 replication in permissive monkey (TC-7) cells. We conclude that forms of induction treatment, such as mitomycin C or 60Co gamma-irradiation, modify the expression of host cell factors which determine the level of permissivity for SV40 infection.

Effect of dose rate on intestinal tolerance in mice. Implications in radiotherapy

The effect of dose rate on intestinal tolerance after 60Co γ-irradiation has been studied in BALB/c mice. Intestinal tolerance was assessed from LD50, after either selective abdominal irradiation or total-body irradiation. Three dose rates were compared: 0.6 Gy/min (“acute irradiation” taken as reference), 0.05 Gy/min and 0.025 Gy/min.; the corresponding irradiation times were then about 20 min, 5 h and 12 h respectively. Irradiations were performed simultaneously, at these dose rates, with three telecobalt therapy units; the dose rates were adjusted with lead shields and by increasing the distances. For abdominal irradiations the animals were immobilized with legs stretched by means of wooden clothes-pegs (Wambersie et al., 1974). The immobilization times were the same (about 12 h) for all animals; they could bear it without anaesthesia.

Dosimetry studies related to irradiation of some insects with 60Co γ-rays and 1.0 MeV electrons, at different dose rates

The paper describes the dosimetry procedures carried out with a 60Co γ-source Gammabeam 650 and 1.0 MeV Van de Graaff electron accelerator, in connection with studies to determine the susceptibility to different dose rates of two species of insects which commonly infest maize in Mexico. Results showed good uniformity in dose rate per source in the 60Co γ-irradiation device providing a dose rate range from 1.8 Gy/min to 139 Gy/min. The results with 1.0 MeV electrons gave a dose rate value of 78 ± 7.5 Gy/(min/μA) for the irradiation device considered.

Reactions of presolvated electrons and hydrogen atoms with benzyl chloride in methanol. A pulse radiolysis study

On pulse radiolysis at room temperature of acidic methanolic solutions of benzyl chloride, the absorption spectrum of the benzyl radical is observed to be completely developed within 20 ns with a Gε value at 315 nm of (2.27 ± 0.04)× 104. 60Co γ-irradiation of an acid solution with [C6H5CH2Cl]= 0.36 mol dm–3 resulted in the formation of chloride ion with G(Cl–)= 4.25 ± 0.30. At temperatures between 125–213 K some absorption due to benzyl radical was observed at the end of the pulse but further absorption developed after the pulse. The spectrum of the species formed after the pulse was resolved and shown to be different from that of the benzyl radical. The species formed after the pulse is ascribed to ·C6H7CH2Cl formed by addition of H atom to the aromatic ring of benzyl chloride. Studies on the kinetics of the growth of absorption at 315 nm permitted the determination of the rate constants, k4 and k7, of reactions (4) and (7) H·+CH3OH → H2+·CH2OH (4), H·+ C6H5CH2Cl →·C6H7CH2Cl (7), and also their dependence on temperature, which conformed to the Arrhenius expression. The dependences of the yields of C6H5CH2· and ·C6H7CH2Cl on the concentration of benzyl chloride were determined and are explained by a model which involves reaction of benzyl chloride with presolvated electrons.

Effect of γ-irradiation on the thermal decomposition of barium bromate

The kinetics of the solid state decomposition of barium bromate and the influence thereon of 60Co γ-irradiation have been investigated at different temperatures between 290 and 315°C. The decomposition is characterised by (i) initial rapid gas evolution followed by (ii) a short induction period, (iii) a slow linear reaction and finally by (iv) acceleratory and (v) decay stages. Both the acceleratory and the decay stages analyse according to the Prout-Tompkins as well as the contracting square kinetics with two different constants in each case. Irradiation shortens the duration of the induction and the linear reaction stages but enhances the decomposition rate constants in all the stages, the effect in each case increasing with the irradiation dose. The activation energy for the linear stage is decreased slightly on irradiation but that for the acceleratory and the decay stages is not significantly affected.

Cytogenetic effects of protracted exposures to alpha-particles from plutonium-239 and to gamma-rays from cobalt-60 compared in male mice

Adult C3H × 101 hybrid male mice were injected intravenously with 4 μCi of 239Pu citrate per kg body weight and examined for evidence of cytogenetic damage to the testis after exposures of 21, 28 and 34 weeks, with average doses from α-particles estimated as 13, 18 and 18 rad respectively (mean dose rate 0.00006 rad/min). Results were compared with those obtained when equivalent males were exposed continuously and concurrently to 1128 rad 60Co γ-irradiation over 28 weeks (0.004 rad/min). The following estimates of the relative effectiveness of the α- and γ-radiation were made: 24 for reciprocal translocations and for chromosome fragments, 22 for dominant lethal mutations acting after implantation. These values (with mean of 23) are based on average testis doses, with no correction for probable non-homogeneity of α dose distribution. In the mice exposed to γ-irradiation there were significant reductions in testis mass and epididymal sperm-count. Although corresponding differences from control were not significant in the α series, consideration of results from a previous experiment by the same authors [2] allowed the relative effectiveness of the α- and γ-irradiation for testis mass reduction to be estimated as roughly 10–15. Existing data on translocation induction in mouse spermatogonia by low dose-rates of γ-rays (down to 0.003 rad.min) were analysed. They suggested that minimum rates of induction at very low intensities were not less than 1 × 10 −5 translocations per rad. A comparison of the frequencies of induction of fragments and of sperm-head abnormalities obtained after chronic γ-ray exposures in the present experiment with those found by other workers after acute X-ray exposures suggested that there were no marked dose-rate effects with these types of mutational effect. Finally, the special problems associated with cytogenetic studies on α-emitters are discussed.

Enhanced tumor cell radiosensitivity in artificial pulmonary metastases of the lewis lung carcinoma

The influence of tumor size on radiation response was studied in the Lewis lung carcinoma as a model to evaluate the radiosensitivity of “microscopic” or subclinical metastatic tumor deposits. Tumor cell survival analysis following in situ 60Co γ-irradiation showed that cells in 1 mm diameter (0·5 mm 3) pulmonary metastases were markedly more radiosensitive ( D 0 = 106 rad, hypoxic fraction < 0·005) than those in 500 mm 3 subcutaneous tumors (final D 0 = 309 rad, hypoxic fraction = 0·36). Thus, unlike the large subcutaneous tumors, the 1 mm diameter metastases were nearly fully perfused with oxygen by an in situ tumor microvasculature. In addition the oxygenated cells from the small tumors were more radiosensitive ( D 0 = 89 rad) than those from the large subcutaneous tumors ( D 0 = 111 rad). These results may in part help explain and predict the success of regional radiotherapy in controlling subclinical regional deposits of metastatic carcinoma.

Isolation of simian virus 40-transformed inbred hamster cell lines heterogeneous for virus induction by chemicals or radiation

Cloned cell lines have been isolated after simian virus 40 (SV40) transformation of kidney cells of an inbred hamster strain. Considerable heterogeneity for the induction of infectious virus was observed between the lines, ranging from the spontaneous production of infectious virus to nonproducer characteristics. In spite of their differences in virus inducibility, all the clones were found to contain equivalent small numbers of SV40 genomes (1–2) per cell as measured by C 0 t analysis. The induction of infectious virus was studied after treating these clones with four agents that cause strand breakage either directly or indirectly in DNA: mitomycin C, BrdU and visible light, uv irradiation or 60Co γ-irradiation. A direct dose-response relationship was established between virus yield and dose of inducing agent used. Yields of infectious virus in induced cells were increased by factors of 10 3–10 4 compared to untreated cultures. In producer cell lines the percentage of induced cells was estimated to be 2–6% as determined by V antigen production or infectious center formation after treatment with the most effective inducing agent, mitomycin C. Our studies suggest that DNA damage and single-strand break formation may be early events in the induction of infectious SV40 from transformed cells by chemical and physical agents.

Radiation-induced chromosomal aberrations in human lymphocytes after partial-body exposure to60Co gamma-irradiation andin vitroexposure to 230 kV X-irradiation

Small yields of chromosome aberrations were present in lymphocytes from 12 patients observed at first metaphase in culbure. Blood samples were obtained at various times, up to three days, after single partial-body therapeutic exposure ranging from 75 to 400 rads of 60Co gamma-irradiation. When all patients were considered there was no correlation between treatment dose and aberration frequency, but on subdivision into two groups on the basis of whether the reticuloendothelial system was involved in the cancer, linear regression analysis could be fitted to the data for each group. An in vitro dose response curve for dicentrics induced by 230 kV X rays at a dose rate of 23.3 rads per minute was constructed for use as a standard calibration curve for 48 hour cultures. The yield of dicentric aberrations was best fitted by a power law model, Y = kDn in which k = (1.59 +/- 0.66) 10(-4) and n= 1.49 +/- 0.08, (P =0.96).

Ionic processes in cumene and p-xylene

Pulse radiolysis and γ-radiolysis data are presented which indicate that ions play a more significant role in the production of excited states in the liquid alkyl benzenes than previously thought. A lower limit to the excited state yield produced via ion precursors in the condensed phase is G≈1·0. The 60Co γ-irradiation of pure cumene glass at 77 K gives rise to trapped species which are shown to be the cation and anion of cumene both having spectral maxima at 400 and 555 nm. Ion neutralization results in the formation of the excited single state of cumene. Excitation of p-xylene to the third excited state by two photon laser excitation with γ = 3471 A ̊ light shows that this state may be quenched by the ion scavengers methanol and N 2O.

Radiation effects on aryl glycosides. Part VII. Radiolysis of aqueous solutions of p-nitrophenyl β-D-glucopyranoside

Pulse radiolysis experiments demonstrate that reactions of eaq–(k2= 4 x 1010 I mol–1) and OH (k2= 2.1 x 109 I mol–1 s–1) with p-nitrophenyl β-D-glucopyranoside (pNPG) yield transient species with absorption maxima near 300 nm. The results indicate that reactions occur mainly at the nitro-group. A transient species with absorption maximum at 450 nm in N2O-saturated and in acidic solution is considered to be the nitrocyclohexadienyl radical. p-Nitrophenol, 4-nitrocatechol, glucose, 2-hydroxy-4-nitrophenyl β-D-glucopyranoside, and traces of αβ-unsaturated carbonyl compounds are produced during steady state 60Co γ-irradiation of pNPG solutions, as a result of initial reaction of hydroxyl radicals. A mechanism is advanced for the formation of these products.

Haemoglobin, a sulphhydryl-protein in the binding reaction with radioprotective MEG.

SummaryHaemoglobin (Hb) in the form of oxyhaemoglobin as a SH protein binds SH radioprotector MEG through its reactive SH-groups. Prolonged reaction time, alkaline pH and urea are able to enhance the reactivity of the unreactive (‘masked’) SH-groups of Hb to the radioprotector. The binding of MEG to the β-93 SH-groups of Hb increases the chromatographic and electrophoretic heterogeneity of the macromolecule.On 60Co γ-irradiation, the mixed disulphide bond between Hb and MEG is not broken but stabilized, thus provoking structural changes, resulting in denaturation. The denatured protein retains the firmly bound radioprotector; the mixed disulphide bond resists splitting with thiols after being irradiated.

Attempted triploid induction in Atlantic salmon ( Salmo salar) using cold shocks

Radiation gynogenesis was used to investigate the effect of sub-zero cold shocks in inhibiting the second meiotic division of eggs of Atlantic salmon ( Salmo salar). If cold shocks were successful in giving rise to diploid gynogenesis they could be used to produce triploids from eggs fertilized with non-irradiated spermatozoa. Different concentrations of saline and glycerol solution were used to depress the freezing point of water, enabling eggs to be cold-shocked at temperatures below 0°C. Control experiments using eggs fertilized with unirradiated spermatozoa were made to assess the effect of saline and glycerol on normal egg development. A 4 h immersion in saline solution following dry fertilization was lethal to eggs, and haploid development was observed in some experiments when eggs were pre-treated for short periods in fresh water before immersion in saline. No such anomalies in development were observed using glycerol. Eggs fertilized with sperm receiving 60Co γ-irradiation at a dose of 10 5 rad were cold-shocked at between −0.2 and −1.7°C, at varying time intervals up to 40 min after fertilization, for a duration of 4 h. No treatments were particularly successful in inducing diploid gynogenesis. These findings are discussed in relation to studies in which cold shocks are highly successful in inducing diploid gynogenesis and triploidy in eggs of plaice ( Pleuronectes platessa).

Measurements of Optical Absorption Spectra under 60Co-γ Irradiation. Aqueous Methylene Blue Solutions Containing Oxygen

Abstract Aerated aqueous solutions of methylene blue (MB+; 3×10−7 m) were subjected to 60Co-γ rays in the presence of added methanol, ethanol, or d-glucose at dose rates up to 4×1015 eV g−1s−1, and the change in the optical absorption spectrum in the 300–700 nm region was studied using a rapid-scan spectrophotometer (scanning speed: 30 ms/100 nm). In the presence of high concentrations (&amp;gt;10−2 m) of organic substances, it was found that radiation caused a decrease in the absorption due to MB+ at 650 nm (the magnitude of the decrease was proportional to the radiation intensity), and that, on the removal of the radiation source, the original absorption spectrum was restored. This was interpreted as meaning that the radiation-produced leuco-form of methylene blue (MBH) was rapidly oxidized by oxygen. The rate constant, k(MBH+O2), was estimated to be (0.6±0.2)×104 m−1s−1 at neutral pH. In the absence of added organic substances, the permanent decoloration of MB+ took place; this was interpreted as being due to the reaction of MB+with OH-radicals. From the competition kinetic study using 10−4 m methanol, the rate constant, k(OH+MB+), was estimated to be 1.1×10−10 m−1s−1.

Effects of Irradiation or Traumatic Injuries on Propionate Metabolism in Rats

Abstract The rate of 14CO2 production in vivo by rats after injection with 10 µCi of 1-14C-propionate is useful in selecting uniform groups of animals for studies of experimental injuries and in investigating dose—response relationships in animals exposed to injury. The response appeared to be most sensitive to lung injury induced by air-blast, but was also sensitive to critical levels of irradiation or thermal exposure. Irradiation with 60Co γ-irradiation significantly depressed 14CO2 production, the degree and persistence being doserelated. Critical burn injuries resulted in decreased rates of 14CO2 production, which decreased as the clinical condition of animals deteriorated. Because the most significant decrease occurred within the first 30 min, measurement of the initial rate of 14C-propionate utilization was sufficient to detect altered metabolic states. High-resolution radioanalyses of urinary organic acids show the major ones excreted to be propionate and its immediate catabolites, methylmalonate and succinate, in both control animals and animals exposed to experimental injuries. These results suggest that propionate metabolism may be one of the sites in intermediary metabolism that is sensitive to alteration by experimental injuries and thus may be one of the more sensitive metabolic indicators.

Radiation dosimetry with acetylene

The suitability of acetylene as a gas-phase radiation dosimeter has been studied. Yields were obtained on an absolute basis, using ionization current dosimetry. Radiolysis of acetylene produces two products, benzene and polymer. The yield of benzene is dependent on dose, dose rate, presence of hydrogen or free radical scavengers, and temperature, and is of no value for estimating dose. ��� For 60Co γ irradiation at a dose rate of 4.1 x 1013 eV cm-3 mmHg-1 hr-1 and acetylene pressure 500 mmHg (6.6x104 N m-2) at 30�C, G(-C2H2) = 82.1�0.5. ��� 1-MeV electron irradiation at a dose rate of 3.9 x 1016 eV cm-3 mmHg-1 hr-1 gave a much lower yield, G(-C2H2) = 55.0�1.9, believed to be due to a dose rate effect. G(-C2H2) increased by about 67% when the temperature was increased from 25�C to 125-250�C. ��� Comparison with ethylene indicates the latter is the more useful dosimeter, as the yields do not vary significantly over a wide range of dose rates and temperatures.

NMR Measurements on 60Co γ-Ray Irradiated Polytetrafluoroethylene with High Radiation Doses

The effects of 60Co γ-irradiation and post-irradiation heat treatment on NMR line of PTFE are studied over the temperature range -50°C to 50°C for a total dose of 8.9×108R. Lowering of transition temperature associated with crystalline regions of PTFE, narrowing of the line width of broad component, broadening of the line width of narrow component, and appearance of very sharp line component are observed in the NMR line shape of the irradiated PTFE. When the irradiated PTFE is annealed near the melting temperature, the very sharp line component disappears and the transition temperature shifts to higher temperature, differing from that of the unirradiated PTFE. This difference is considered to be associated with the decrease in the average molecular weight of the irradiated PTFE. Changes resulting from post-irradiation heat treatment can be attributed to the removal of defects and low molecular weight products trapped within PTFE. No charge is observed in the line width or narrow component by post-irradiation heat treatment.

Radiolysis of Hydrogen Cyanide in an Aqueous System. II. Effects of Additives and Reaction Mechanism

Abstract The 60Co γ-irradiation of dilute aqueous solutions of hydrogen cyanide (6 mm) in the absence of oxygen yielded mainly ammonia with G=1.9, formaldehyde with G=1.1, and carbon dioxide with G=0.8, while G(–HCN)=5.8 molecules per 100 eV. Polymeric hydrogen cyanide was also observed with the G(–HCN(polymer))\simeq4, which showed an intense broad absorption band in the UV region upon γ-irradiation. The following material balances were observed with the main products: G(-HCN)\simeqG(NH_3)+G(-HCN(polymer))\simeqG(CO_2)+G(HCHO)+G(-HCN(polymer)) The results can be interpreted in terms of a mechanism involving HCN−, H2CN, and H(OH)CN radicals. The ratio of the rate constants for the reactions of e−aq and H atoms with hydrogen cyanide to those with several scavengers have been determined as k(e−aq + HCN)/k(e−aq + NO3−)=0.019 and k(H + HCN)/k(H + 2-propanol)=1.4, all at 17°C.