[en] For the present study of free-radical transfer in polymers pulse radiolysis and product studies have been carried out in aqueous solutions using thus far only the water-soluble polymers polyacrylic acid, polymethacrylic acid and polyvinyl alcohol. When OH radicals, generated in the radiolysis of N₂O-saturated aqueous solutions, react with polymers the lifetime of the polymer radical thus created very much depends on the number of radicals per polymer chain. When there are a large number of radicals per chain their bimolecular decay may be faster than the corresponding (diffusion controlled) decay of monomeric radicals, but when the macromolecule contains only few or even just one radical their lifetime is considerably prolonged. Highly charged polymers such as polyacrylic acid at high pH attain a rod-like conformation which again favors a long lifetime of the radicals. Under such conditions, radical transfer reactions can occur. For example, in polyacrylic acid OH radicals generate two kinds of radicals side by side. The radical in β-position to the carboxylate group converts into the thermodynamically more stable α-radicals by an H-transfer reaction as can be followed by spectrophotometry. Besides radical transfer reactions β-fragmentation reactions occur causing chain scission. Such reactions can be followed in a pulse radiolysis experiment by conductometry, because counter ions are released upon chain scission. Such a process is especially effective in the case of polymethacrylic acid, where it results in a chain depolymerization. An intramolecular H-abstraction is also observed in the γ-radiolysis of polyacrylic acid with the corresponding peroxyl radicals. This causes a chain reaction to occur. The resulting hydroperoxides are unstable and decarboxylate given rise to acetylacetone-like products. In polyvinyl alcohol the peroxyl radicals in α-position to the alcohol function undergo HO₂-elimination. This prevents a scission of the polymer chain in the bimolecular decay of the peroxyl radicals. (author)

[en] The yields of single- and double-strand breaks (SSB and DSB) in calf thymus DNA, after ⁶⁰Co gamma irradiation in dilute aqueous solution, have been determined via molecular weight measurements using a low-angle laser light scattering technique. The irradiations were administered to N₂O-containing solutions of DNA in the absence and presence of oxygen and with different concentrations of the OH radical scavengers phenol, tertiary butanol, and methanol. OH radicals were found to produce SSB linearly with dose with a G value of 55 nmol J-1 and 54 nmol J-1 in deoxygenated and oxygenated solutions, respectively. DSB were formed according to a linear-quadratic dose relationship and the G value of linearly formed DSB were GDSB alpha(r.t.) = 3.5 nmol J-1 in deoxygenated and 3.2 nmol J-1 in oxygenated solution. The ratio of GSSB/GDSB alpha(r.t.) = gamma of 19 +/- 6 was independent of the scavenger concentration in the case of tertiary butanol and methanol-containing solutions. GDSB alpha(r.t.) is interpreted to result from a radical site transferred from a sugar moiety of the cleaved strand to the complementary intact strand. This process of radical transfer and subsequent cleavage of the second strand occurs with a probability of about 6 +/- 2% in the presence of oxygen at all scavenger concentrations studied. These data on scavenging capacity on GDSB alpha(r.t.) suggest that the double-strand breakage produced via radical transfer remains higher than that resulting from direct effect, up to scavenging capacities of about 10(9) s-1

[en] Yields of radiation-induced single-strand breaks in double-stranded calf thymus DNA have been measured as a function of OH scavenger concentration in N₂O/O₂-saturated aqueous solution. The experimental data are well represented by a theoretical model based on non-homogeneous reaction kinetics, without the need to adjust any parameter. The good agreement between experimental and theoretical data is taken as evidence that, in the presence of oxygen, the main effect of added scavengers with respect to the formation of single-strand breaks in double-stranded DNA is OH radical scavenging. 30 refs., 3 figs., 1 tab

[en] The G values for single-strand breaks G(ssb) in γ-irradiated polyuridylic acid (poly U) have been measured by low-angle laser light scattering in aqueous solutions under various conditions (e.g. in the presence of N₂O, Ar and t-butanol). In N₂O-saturated solutions at room temperature and pH 5.6, the G(ssb) is 2.3. The efficiency of ssb formation was found to be 41 per cent for OH radicals, 19 per cent for H atoms and approx.= zero for e^-sub(aq). On the basis of 20 per cent and less than 5 per cent attack on the sugar moiety by OH radicals and H atoms, respectively, the large G(ssb) values obtained cannot be explained solely as resulting from radicals produced by reaction of OH radicals and H atoms on the sugar moiety. It is therefore proposed that base radicals produced by the reaction of OH radicals or H atoms with the uracil moiety can also lead to chain break formation in poly U via radical transfer to the sugar moiety. (author)

[en] Published in summary form only

[en] Pulsed irradiation was used in a study of the action of 2.8 MeV electron pulses on aqueous solutions containing an acetylene-oxygen mixture or an acetylene-oxygen-nitrous oxide mixture in order to investigate the reactions of the beta-hydroxy-vinyl-peroxyl radical. This radical is formed from acetylene by reaction with OH followed by addition of molecular oxygen. The results show that a highly acidic intermediate is formed with a pK value of greater or equal to 2. The decay of this intermediate leads to the observed products. 6 references, 2 figures, 1 table

[en] The thiyl radical derived from glutathione (GSH) is shown to decay rapidly in aqueous solution by intramolecular rearrangement reactions into the non-sulphur-centred radical 1. The reaction is induced by OH^- with a rate constant of 5 x 10⁹ dm³ mol^-1 and is also observable at near-neutral conditions (at physiological pH values around 7.5 the rate of formation of 1 amounts to ∼ 1 x 10³ s^-1). The activation enthalpy and entropy at pH 8.4 and 20^oC were found to be 26.7 kJ mol^-1 and -77 J mol^-1 K^-1, respectively. Radical 1 was unequivocally identified by EPR as the α-amino radical at the glutamyl residue of GSH. It is relatively long-lived with typical biomolecular decay rate constants of the order of (2-20) x 10⁶dm³ mol^-1 s^-1. At higher GSH concentrations the formation of 1 is retarded but not inhibited. All radicals, sulphur- as well as non-sulphur-centred ones are connected via equilibria, partly under the action of 'repair' processes of GSH. These repair processes, however, are slow (k << 1.4 x 10⁵ dm³ mol^-1 S ^-1). (Author)

[en] Conductivity changes were found which followed the reaction of radiolytically generated OH radicals with the potassium salt of polyuridylic acid (poly U) in aqueous solution. After ₆₀Co-ß-irradiation the observed increase of conductivity at pH=6.8 was shown to consist of the liberation of K⁺ ions from the stock of K⁺ ions electrostatically bound to the polyanion. The initial G(K⁺) is 36 and hence 6 times higher than the G value of OH radicals in N²O saturated solutions. At a poly U concentration of 60 mg l^-₁ half of the ion release occurred at 12 J kg^-₁ and nearly all ions are released at 40 J kg^-₁. The liberation of K⁺ is explained to be a consequence of the formation of chain breaks leading to an increase of the degree of dissociation. The rate of the ion release was studied under pulse radiolysis conditions. Because of the high G-value of counterion liberation and the use of conductivity as analytical quantity the method is very sensitive. With 6 mg l^-₁ poly U the rate could be measured even at a dose per pulse of 0.25 J kg^-₁. The kinetics of the ion release can be described in terms of two parallel first order reactions of comparable contribution with an average rate constant of 0.8 s^-₁ at 20₀C, 60 mg l^-₁ poly U and pH=6.8 with a small contribution of slower components. In more acidic solutions, besides K⁺ ions H⁺ are also liberated since at low pH values bound K⁺ is replaced by H⁺. (orig./AJ)

[en] Laser flash photolysis of polyuridylic acid (poly U) in anoxic aqeuous solutions leads to biphotonic photoionization of the uracil moiety followed by the formation of single strand breaks (ssb). The rate constant for ssb formation (1.0 s^-1, obtained from the slow component of conductivity increase at 23⁰C and pH 6.8) increases with decreasing pH to 235 s^-1 at pH 3.5. The activation energy (pre-exponential factor) was measured to be 66 kJ mol^-1 (5 x 10¹¹ s^-1) at pH 6.8. Addition of dithiothreitol (DTT) or glutathione (GSH) prevents ssb formation by reacting with a poly U intermediate (rate constant = 1.2 x 10⁶ and 0.16 x 10⁶ dm³ mol^-1 s^-1, respectively). Since with OH radicals as initiators very similar data have been obtained for the kinetics of ssb formation and for the reaction with DTT, it is concluded that photoionization of the uracil moiety in poly U leads eventually to the same chemical pathway for ssb formation as that induced by OH radicals. Furthermore, it is proposed that protection by DTT and GSH occurs via H donation to the C-4' radicals of the sugar moiety of DNA and to the C-4' and the C-2' radicals of poly U. (author)

[en] A radioimmunoassay capable of detecting 300 fg somatostatin has been developed and levels of the polypeptide in gastrointestinal tissues from man, dog, and rat have been measured. Rapid freezing of collected samples and careful control of extraction is necessary. Concentrations in different regions of dog antrum (425 +- 50 to 773 +- 254 ng/g tissue) are similar to those in antrum from duodenal ulcer patients and control subjects: 614 +- 125 and 465 +- 104 ng/g tissue respectively. Levels in histologically normal human pancreas (253 +- 43 ng/g tissue) are comparable with those in dog pancreas (333 +- 66 ng/g tissue), whereas in two cases of neonatal hypoglycaemia the concentration exceeded 3000 ng/g tissue. On gel chromatography the majority of immunoreactive somatostatin elutes as the synthetic tetradecapeptide and a small fraction as a larger species. (author)