AE-368 UDC 541:1S 061:3(485) Scandinavian Radiation Chemistry Meeting Studsvik and Stockholm, September 17-19, 1969 H. Christensen, Editor AKTIEBOLAGET ATOMENERGI STUDSVIK, NYKOPING, SWEDEN 1969 AE-368 SCANDINAVIAN RADIATION CHEMISTRY MEETING STUDSVIK AND STOCKHOLM, SEPTEMBER 17-19, 1969' ABSTRACTS The report contains the abstracts of papers, which are intended for presentation at the meeting. The complete papers will not be published collectively. The following subjects .are discussed in the abstracts: Pulse radiolysis, water and aqueous solutions including vapour, inorganic systems, organic systems, monomers and polymers and biochemical sys­ tems. Printed and distributed in August 1 969. - 2 - LIST OF CONTENTS Page Authors ' Index 3 Pulse radiolysis 4 Water and aqueous solutions 1 8 Inorganic systems 24 Organic systems 27 Monomers and polymers 28 Biochemical systems 31 3 - Auth ors'Index P age Andersen, L-O 31, 32 Andersen, T 20 Andersson, U 21 Autio, Timo 30 Bellquist, B 14 Christensen, H C 4, 5, 11 , 12 Cserép, G 13 Edlund, Ove 24 Ehrenberg, A 35 Eriksen, Jytte 15 Fricke, H 19 Friis, Nils 29 Genske, Preben 15 Gillbro, Tomas 28 Gräslund, A 35 Carlson, F • 21 Kasche, Volker 34 Kinell, P-O 27, 31 Kops, Jørgen 29 Lund, Anders 26 Nielsen, S O 4, 5, 11 , 12 Nilsson, Gösta 4, 5, 12 Nilsson, Robert 7 Olsen, K J 20 Pagsberg, P 4, 5, 9, 12 Pedersen, Kai O 31 Reitberger, T 13, 14, 17 Rupprecht, A 35 Said, F 5 Sehested, K 19 Singer, Klaus 29 Stenström, T 22 Ström, G 35 S^r ensen, G 20 Thomsen, P V 20 Österdahl, Bengt 18 - 4 - ABSORPTION SPECTRA OF HYDROGEN ATOMS, HYDROXYL RADICALS AND SOLVATED ELECTRONS IN AQUEOUS SOLUTION FROM 200 TO 250 nm S O Nielsen', P Pagsberg , H C Christensen' ' and G Nilsson' *) Danish Atomic Energy Commission Research Establishment Riso, Roskilde, Denmark ' AB Atomenergi, Studsvik, Nykoping, Sweden It has been shown that in aqueous solutions hydrogen atoms, H, and hydroxyl radicals, OH, exhibit a previously unnoticed absorption band 1 2 with an absorption maximum below 200 nm ' . A similar absorption band was recently observed in the far-ultraviolet absorption spectrum, of - 3 2 4 the hydrated electron, e . Present techniques ' do not allow accu­ rate measurements to be made below 200 nm. At this wavelength all three species show molar absorptivities of comparable magnitude which suggests that the optical transitions involved in the three cases are sim- 1 2 3 ilar in nature. It has been proposed ' ' that the enhanced absorptivity of H, OH and e aq in aqueoux s solution at about 200 nm is due to a red shift of the water absorption beginning at ~ 1 86 nm. This shift is as­ cribed to perturbation of the first excited singlet state of "neighboring" water molecules which involves a partial electron transfer to H, OH and e aq , respectively. This model will be described in detail, References 1 . Nielsen S O et al. , Pulse radiolytic determination of the ultraviolet absorption of hydrogen atoms in aqueous solution. Chem. Commun. (1968)1523. 2. Pagsberg P et al. , Far-ultraviolet spectra of hydrogen and hydroxyl radicals from pulse radiolysis of aqueous solutions. Direct measurement of the rate of H + H. J. Phys. Chem. 73 (1969) 1029. 3. Nielsen S O et al. , Absorption spectrum of the hydrated electron from 200-250 nm. J. Phys. Chem. 1969. 4. Christensen H C et al. , Pulse radiolysis apparatus for monitoring at 2000 A. Rev. Sci. Instr. 40 (1969)786. - 5 - DIRECT SPECTROPHOTOMETRIC MEASUREMENT OF THE RATE OF H + OH IN AQUEOUS SOLUTIONS F Said ', P Pagsberg ^ S O Nielsen*', H C Christensen ' and G Nilsson ' *)' Danish Atomic Energy Commission Research Establishment Riso, Roskilde, Denmark ' AB Atomenergi, Studsvik, Nykoping, Sweden _3 Pulse radiolytic studies involving 10 M HC1 0. + 0.027 M H2 [P(H_) = 35 atm. J have revealed the existence of a transient species with a second order decay the amplitude of which diminishes monotonically 1 2 from 2000 to 2400 A ' . There is sound experimental evidence for as­ signing these transients to H atoms. This is contrary to the earlier assumption that solutions of free hydrogen atoms in water do not absorb light in the far ultraviolet spectral region (> 2000 A). If the absorption spectrum of free hydrogen atoms is assumed to be known, direct measurement of the rate constants 2k.r, „, 2.\a , ^TT and Jrl + rl Orl + UJri ^H + DM becomes possible by means of pulse radiolysis of deaerated so­ 3 lution of 1 0" M HC1 04. Results to date indicate that the measured optical transients from 2000-2600 A due to H, OH and H?0? can be approximated within the ex­ perimental error, by computer calculated transients based on the yields and extinction coefficients of H, OH and H70? together with previously found values of 2kTT , TT = (1 . 55 + 0. 1 0) x 1 0' ^ M" sec and 2.\<L ,_„ = rl + rl - Drl + Uri = (1 .04 + 0. 1 0)1 01 ° M"1 sec"1 . ] > Z The rate constant ku ^„ was used as the only variable parameter rl + OH to fit the computer calculated transients to the measured transients. The value thus obtained for k„ _„ in the region 2 000-2600 A was found H + OH i . to be somewhat smaller than 1 0 M sec Details are given of the experimental procedure employed and the results obtained together with results obtained in the computer calcula­ tions . - 6 - References 1 . Pagsberg P et al, , Far-ultraviolet spectra of hydrogen and hydroxyl radicals from pulse radiolysis of aqueous solutions. Direct measurement of the rate of H + H. J. Phys. Chem. 73 (1969) 1029. 2. Nielsen S O et al. , Pulse radiolytic determination of the ultraviolet absorption of hydrogen atoms in aqueous solution. Chem. Commun. (1968)1523. - 7 - PULSE RADIOLYTIC STUDIES OF THE O' ION-RADICAL Robert Nils son Division of Radiobiology, Institute of Biochemistry, Royal University of Stockholm, Stockholm, Sweden The formation of O" has been postulated in a number of biologi­ cal oxidations which occur under physiological conditions. Although this radical has been directly identified in certain inorganic sys­ tems, direct and conclusive evidence for its formation in most enzymic systems is lacking. Recently, Knowles et al. were able to identify an intermediate by means of ESR using the "rapid freezing" technique developed by Bray . By combining this rapid freezing with ESR and pulse radiolytic techniques the identity of the 0? radical could definitely be established. Our results provided confirmation that the en- zymically generated radical and the long-lived "alkaline stabilized form of 0?" described by Czapski and Dorfman are identical and correspond, moreover, to 0? itself. Using pulse radiolysis of alkaline aqueous solu­ tions in a flow system provided with facilities for rapid mixing after irradiation, tetranitromethane was found to act as an efficient scavenger 3 for Oy. Czapski and Dorfman showed that the optical absorption at 250 nm was appreciably increased in the presence of methanol. We have found that this increase in absorption is accompanied by an increase in the strength of the ESR signal, demonstrating that the yield of 0? is in­ creased in the presence of the alcohol. It is well established that the reduction of cytochrome c occurs in the presence of xanthine oxidase, substrate and oxygen 4 ' 5 . It has been proposed that 07 serves as the reducing agent in this system. The radio- lytic work of Rabani and Stein gives indication for the occurence of such a process. To study this reaction, 0? was generated by pulse radiolysis both in the presence and in the absence of cytochrome c, following which the kinetics of decay were analyzed. The results of this study and their implications are discussed. - 8 - References 1 . Knowles P. F. et al. , Electron-spin-resonance evidence for enzymic reduction of oxygen to a free radical, the superoxide ion. Biochem. J. 1 11 (1969) 53. 2. Bray R. C. , Sudden freezing as a technique for the study of rapid reactions. Biochem. J. 81 (1961) 189. 3. Czapski G. and Dorfman L. M. , Pulse radiolysis studies. 5. Transient spectra and rate constants in oxygenated aqueous solutions. J. Phys. Chem. 68 (1964) 1169. 4. Horecker B. L. and Heppel L. A. , Reduction of cytochrome c by xanthine oxidase. J. Biol. Chem. 178 (1949) 683. 5. McCord J. M. and Fridovich I. , Reduction of cytochrome c by milk xanthine oxidase. J. Biol. Chem. 243 (1968) 5753. 6. Rabani J. and Stein G. , The radiation chemistry of aqueous solutions of cytochrome c. Radiation Res. 17 (1962) 327. - 9 - PULSE RADIOLYSIS OF AMMONIA IN AQUEOUS SOLUTIONS IN THE PRESENCE OF NITROUSOXIDE* P B Pagsberg Danish. Atomic Energy Commission Research Establishment Riso, Roskilde, Denmark 7 -1 • Ammonia reacts with OH radicals with a rate constant k = 7xl0 M s the OH band thereby being replaced by a new band at 525 nm, which is assigned to the NH? radical. It has an extinction coefficient of 7 5M~ cm" at 525 nm. The yields of the products, NH?OH and N?H. were studied as a function of ammonia concentration. G(N?H.) increases steadily whereas G(NH?OH) passes through a maximum and a minimum with in­ creasing ammonia concentration, indicating the presence of at least two different NH?OH-producing reactions. The maximum yields obtained at high ammonia concentrations were 2(GNH?OH) = 0. 93 - 0. 05 and G(N?H.) = = 2.23 + 0. 07. G(NH2OH) + G(N2H4) =£(G(e" ) + G(OH) ) + G(H2Oz). The 525 nm band decays with a second order rate constant 2k(NH?) = 3. 5 x 9-1-1 x 10 M s .