INT. J. RADIAT. BIOL ., 1991, VOL . 59, NO. 2, 285-289

Meeting report

Journees d'Etudes sur la Chimie sous Rayonnement (JECR-90)

(Received 25 October 1990)

The Fifth `Journees d'Etudes sur la Chimie sous Rayonnement' were held in theCheribourg resort, near Sherbrooke, Quebec, Canada, 1-6 July 1990 . There wereabout 100 participants from 14 different countries. This radiation chemistryworkshop was organized by Jean-Paul Jay-Gerin, Thomas Goulet and DanielHoude of the Departement de Medecine nucleaire et de radiobiologie, Universite deSherbrooke, and Monique Gardes-Albert of the Laboratoire de Chimie-Physique,Universite Rene Descartes, Paris . It was dedicated to Professor Christiane Ferra-dini (Paris) on the occasion of her 65th birthday . In the tradition of the workshop,the oral presentations, posters and discussions were in French . The topics includedthe chemical physics of the early events in the interaction of radiation with matter,radiation chemistry in homogeneous and heterogeneous systems, biochemicalaspects of radiation chemistry, food irradiation, radiotherapy and phototherapy,along with numerous industrial and medical applications . There were 24 invitedpapers, 26 short talks and 27 posters presented . The atmosphere of the meeting wasfriendly and informal, which encouraged the participants to establish personalcontacts and conduct many discussions . Another characteristic was a relativelylarge proportion of young participants .

The conference started with five sessions dedicated to the chemical physics ofthe interaction of high-energy radiation with matter, and the chemical processesthat occur at times less than 10 -9 s. The invited papers began with a description byLeon Sanche (Sherbrooke) of energy loss processes of low-energy electrons (1-20eV, or 0 . 2-3 aJ) in thin solid films deposited on a metal surface. He showed, forexample, that the formation of a transient negative ion is an important mechanismfor the vibrational excitation of a molecule by an electron that has an energy below20 eV (3 aJ) .

Gilles Duplatre (Strasbourg) discussed the capture of an electron by a positroninjected into a liquid, thereby forming positronium. It appears that most of thepositronium is formed by the combination of the de-energized positron with aquasifree or shallowly trapped electron in the densely ionized microzone that thepositron forms at the end of its track .

Ugo Fano (Chicago) spoke of energy loss processes of - 1 eV (0 . 2 aJ) electrons .An important consideration is the dependence of the dielectric function 8(w,4) ofthe medium on the phase angular speed w (rad/s) of its oscillations and the radianvector q (rad/m) of the system structure . It will probably be necessary to considerthe non-linearity of the polarizability of the system at the large electric fieldstrengths near the projectile electron .

0020-7616/91 $3 .00 © 1991 Taylor & Francis Ltd

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Norman Klassen (Ottawa) presented the main species in liquid water and theirreactions during the period up to 10 - ' s after the passage of a high-energy particle .The species include quasifree electrons eqf , electrons localized in shallow, incom-pletely relaxed traps e ir , and completely solvated electrons about which the solventhas relaxed to an equilibrium state . Analogous ions are H 2O + , H,O :, and H30'Other species are H, OH, OHS , H 2 and H2O 2i the latter being formed by reactionsin microzones that initially contain several of the other species .

Daniel Houde (Sherbrooke) described a laser apparatus that permits timeresolution of about 10-13S in optical studies. He also honoured the 15-year-oldmeasurements of John Baxendale (Manchester), which demonstrated the samespectral relaxations in low-temperature liquid alcohols, at appropriately longertimes (-.10 -*7 s), recently the subject of so much interest in the physics communitythrough femtosecond laser technology .

Rene Voltz (Strasbourg) discussed the `large polaron - small polaron' model ofelectron localization and relaxation . The first form of this model was suggested byJortner and Onsager and others more than 15 years ago . The outside (1-2 nm fromthe centre of charge) - inwards relaxation of the solvent probably occurs as the laststage of electron solvation, and is probably not the initial localization process . Theinitial localization event is probably an inelastic interaction of the quasifree electronwith molecules at a defect in the local structure in the liquid . The initial stage ofsolvent reorientation probably moves as a shock of charge-dipole torque from thedefect outwards, and is followed by a backwash of final relaxation to equilibrium,from the distant solvent equilibrium configuration toward the centre of charge .

Nicholas Green (Oxford) presented Monte Carlo and independent reaction timesimulations of rapid chemical reactions in the initial stages after the passage of ahigh-energy particle through a liquid . There is remarkable agreement betweenresults from the two models .

Gordon Freeman (Edmonton) described the effects of molecular structure andliquid density on the distance that an electron moves away from its parent ion whileit is transferring its excess energy to the molecules of the liquid . The large amountof experimental data could guide future theoretical treatments of energy lossprocesses at energies in the region 0 . 1 to 0 . 01 aJ. This is an order of magnitudelower than the processes discussed by Fano and Sanche . The mobilities of thermalelectrons vary with molecular structure and liquid density in a manner similar tothe thermalization distances, but the former variations are much greater owing tothe lower energies involved .

Gianni Ascarelli (West Lafayette) explained electronic bands in crystals andspeculated about the validity of the concept as frequently used in descriptions ofelectron transport in liquids. Seven short talks and four posters completed thecoverage of the chemical physics of radiation effects .

An entire session was dedicated to the application of pulse and steady-stateradiolysis in the study of quantum size effects in metal clusters and in the synthesisof stable metal molecular clusters and aggregates . Jacqueline Belloni (Orsay) gavean overview of the principles of the radiolytic reduction of metal ions and of thecompetitive processes that enhance or inhibit the formation of metal atoms, theircoalescence and the growth of clusters . Selecting the growth of Age , due to itsimportance in photography, she explained how electron transfer from a photo-graphic developer to pre-existing silver aggregates is dependent on their size, and isrestricted to centres undergoing autocatalytic growth . The redox potential of the

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silver ion-aggregate system was shown to be the governing quantity . A video film`Magic of the Image' summarized the history and mechanism of the photographic

process .Three other oral presentations and four posters also came from the Orsay

laboratory of J . Belloni, dealing with the formation and properties of Cu, Rh and Agaggregates and complexes, and their practical applications . One of these talks wasconcerned with reconstruction of the first photographic process discovered byNicephore Niepce .

Three sessions were devoted to biochemical applications of radiation chemistry .The first invited speaker in this section, Christiane Ferradini (Paris), gave anoverview of the reactions of free radicals containing oxygen (02 , OH, R02) knownto be formed in normal and abnormal biological reactions (respiration and somediseases) . For example, it was stated that if 1 % of oxygen consumed in therespiratory process is converted to OZ , this is equivalent to the generation of OZ bya dose rate of 300 Gy per hour of high-energy radiation . She also presented some ofher group's recent results within the growing field of free radical biochemistry,covering the one-electron activation of biological compounds such as : drugs(sulfarlem, nifurtimox, daunorubicin, ellipticin-substituted derivatives), peptides(glutathione, oxidized glutathione-Cu II complex), proteins (collagen, haemocya-nin, riboflavin binding protein), lipoproteins (low-density lipoproteins), and amodel of vitamin K .

Rene-Victor Bensasson (Paris) discussed the generation of oxygen-containingradicals, the study of their chemical reactions with antioxidants and the determina-tion of the one-electron oxidation potentials of the compounds using pulseradiolysis and flash photolysis . It was established that the toxicity of 02 could bemainly due to HO2 (or any cation-OZ complex) which is a good oxidant .Superoxide dismutase (SOD), the natural protein that destroys the 02 , is found inall living organisms, and a good correlation is found between the SOD content andthe life-span of living species .

Moshe Faraggi (Beer-Sheva) reviewed long-range electron transfer reactionsbetween two redox centres attached to the same molecule in proteins and modelcompounds . The intramolecular electron migration over a distance greater than10 A, found in many proteins and peptides, plays an important role in biologicalprocesses such as photosynthesis, respiration and radiation inactivation . Electrontransfer in proteins may be anisotropic and there are potential through-bondpathways, for example ionic contacts (hydrogen bonds), alpha-helix, beta sheet,imide bond, etc . M. Faraggi described evidence for the through-bond electrontransfer in peptides .

Clemens von Sonntag (Mulheim/Ruhr) discussed the free-radical chemistry ofthiols, including recent data from his group about reactions involving thiyl radicalsand oxygen . For example, the reaction of the superoxide radical and dithiothreitolin alkaline solution is a decisive step in an oxidative chain .

Jean Cadet (Grenoble) reviewed the radiation- and photo-induced reactionsinvolving DNA bases . Recent results from his group show that OH radicalsgenerated by ionizing radiation and by the Fenton reagent may yield quite differentproducts, probably due to the presence of iron in the latter system, so thatobservations made with the Fenton reagent cannot be directly applied to iron-freeOH radical reactions . J . Cadet also presented a new method for detecting hydroper-oxides by HPLC .

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A rich selection of related subjects was presented in nine short talks and 13posters, a large proportion of them from the group of C . Ferradini (Paris) .

The radiobiology and therapy section comprised two sessions . John B . Little(Harvard University) described studies of the mutagenic effects of internallyemitting radionuclides in human cells . He reported that residual molecular damagefollowing the decay of labelled analogues covalently bound to DNA were importantin mutagenic effects. Mutagenesis appeared to be the result of energy directlydeposited in cellular DNA, rather than mediated by aqueous free radicals .

Madeleine Carreau (Sherbrooke) presented evidence that at least two DNArepair pathways exist in human cells one dependent on transcription and the otherindependent . Xeroderma pigmentosum (XP) group C cells are deficient in the latterbut not the former process, implicating a role for transcription in dimer recognitionand excision repair .

Monique Vuillaume (Paris) showed that catalase levels were reduced in fibro-blasts and keratinocytes from a large group of patients with XP including someheterozygotes . These results suggest that abnormalities in oxygen metabolism maybe involved in certain genetic disorders such as XP .

Two papers were presented relating to cancer therapy . Pierre Chauvel (Nice)reviewed the potential advantages of `light' ion therapy (such as protons, c6+ ,

Neio+, etc.) in the radiotherapy of tumours, and described the planned EULIMA(EUropean Light Ion Medical Accelerator) facility in Nice-a generator marked byits relative simplicity and ability to treat large numbers of patients . Johan E . vanLier (Sherbrooke) reviewed the methods of phototherapy and discussed currentcompounds used as photosensitizers . He described a promising new class ofcompounds for photodynamic therapy, the phthalocyanines . These agents arerelatively stable, are good generators of singlet oxygen, and allow good tissuepenetration of therapeutic light .

The remaining three sessions of the meeting concerned industrial applicationsof radiation and the chemical analysis of irradiated products . Bernard Tilquin(Louvain-en-Woluwe) and collaborators have, over the years, refined the tech-niques of high-performance capillary gas chromatography, often coupled with massspectrometry, for the identification and measurement of trace hydrocarbon prod-ucts of alkane radiolysis in order to help understand free radical reactions . Doses aslow as 1 kGy have made the analyses difficult but have simplified the interpretation .B . Tilquin gave a report on the products of pulse-irradiated alkanes . The combina-tion of high dose rate, low dose and low temperature allowed early reactions to beprobed, in particular the abstraction of H atoms from the solvent by primaryradicals to produce secondary radicals . Thierry Baudson (Louvain-en-Woluwe)used the same analytical techniques to study the radiation products of long-chainalkanes with a view to using them as model compounds for the radiolysis ofpolymers, especially of polyethylene . Selective cross linking was demonstrated .

Bernard Hickel (Saclay) described how the increase in radical yields in theradiolysis of water between 20°C and 200°C posed problems related to the size ofthe spurs and the primary yield of ionization of water . Both present and futurenuclear reactors require that the 02 concentration be kept low in order to reducecorrosion. To do this effectively requires a knowledge of the G-values of eaq , H,OH, H2 and H 202 , and the rate constants of important reactions .

John Swallow (Manchester) reviewed briefly the history of food irradiationbetween the first patents in the early part of the century and the beginning of

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commercialization. He distinguished between processes intended to alter the foodand those intended to destroy harmful organisms. With appropriate radiation thefood does not become radioactive and no toxic products are formed . Vitamin lossesand microbiological problems exist, but do not differ in principle from those withother processes . To control food irradiation it would be helpful if there weremethods of detecting whether foods have been irradiated or not . Jacques Raffi(Cadarache) discussed methods now being studied . One set of methods was basedon changes in DNA, either detected by chemical analysis or via microbiological orbiological consequences . Physical methods included ESR, thermoluminescenceand impedance. Chemical methods included measuring characteristic productsfrom lipids and o-tyrosine formed from proteins . Comparisons of results fromdifferent laboratories are in progress .

Five other short talks were also presented on applications, and there were twoposters concerned with related topics . The proceedings of the JECR-90 will bepublished in a special issue of the Journal de Chimie Physique, which should containabout 50 refereed contributions from those represented at the workshop .

The next (sixth) JECR workshop will be held in the summer of 1992 in thesouth of France . For details, please contact: Dr Jacques Raffi, Centre d'EtudesNucleaires de Cadarache, Departement de Biologie, 13108 Saint-Paul-lez-DuranceCedex, France .

Contributions to this report: J . Belloni, M. Faraggi, G . R. Freeman, E . Keszei,N . Klassen, J . B . Little, C . von Sonntag and A . J. Swallow .

JEAN-PAUL JAY-GERIN,Universite de Sherbrooke,

Departement de medecine nucleaireet de radiobiologie,

Centre hospitalier universitaire de Sherbrooke,Sherbrooke, Quebec,Canada J1 H 5N4

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