[en] Both the basic and applied aspects of radiation chemistry belong to the scope of the 26th Miller Conference on Radiation Chemistry. The main topics was the next: fundamental processes in radiation chemistry, electron beam-, ion beam-, photon-, laser-, plasma reactions, radiolysis of inorganic and organic systems, radiation chemistry of biological systems, biopolymers, radiation chemistry of nanoscale systems and macromolecular systems (polymerization kinetics, crosslinking, grafting, radiation stability, EB and UV curing of surface coating, etc.), biomedical materials, environmental protection, food irradiation, identification of irradiated food, packaging materials, radiation sterilization. (S.I.)

[en] Complete text of publication follows. Radicals are present at solid-solution interfaces of metals, semi-conductors and insulating oxides in a variety of processes, e.g.: 1. Catalytic processes 2. Electrochemical reactions 3. Photochemical processes in which the light is absorbed by solid Consequently, the mechanisms of reaction of radicals with surfaces are of utmost importance. Recent results show that alkyl radicals and alkyl-peroxyl radicals react in aqueous solutions with suspended metal- and semiconductor surfaces to form intermediates with metal-carbon or metal-oxygen bonds, respectively. The results suggest that the life time of these intermediates is considerably longer than expected. The mechanisms of decomposition of these intermediates depend on the nature of the metal, substituents on R, pH, temperature, and electrical potential bias.

[en] Complete text of publication follows. The main reaction of the HO^· radical with guanosine or 2'-deoxyguanosine (∼65%) is not the addition at the C4 position as previously thought, but the hydrogen abstraction from the NH₂ moiety to give a guanyl radical. This radical, characterized by a broad band in the visible region (around 610 nm), undergoes a water-assisted tautomerization to the most stable isomer, which is also known as one-electron oxidation species of the corresponding guanine derivatives. Moreover, one-electron reduction of 8-bromoguanine derivatives was found to give a radical anion that undergoes fast protonation at C8 by proton transfer from the solvent to afford a complex. This complex debrominates giving two short-lived intermediates, which are recognized to be the two-guanyl tautomers. The tautomerization is a general phenomenon of purine reactive intermediates that has been uncovered so far, and will add other important information to the general scenario of the radical transformations concerning DNA.

[en] Complete text of publication follows. The electron transfer in non-polar media (alkanes, alkyl chlorides) exhibits some essential peculiarities. For instance the reaction of hetero-substituted aromatics with parent solvent radical cations results in the parallel formation of metastable donor radical cations and fragmentation products, in comparable amounts. The fragmentation products originate from a dissociative donor radical cation which decays extremely rapidly, i.e., in some femtoseconds. This phenomenon is explained in terms of intramolecular dynamic motions which cause changes of the electron density (π and n-orbitals) in dependence on the deformation angle between the substituents and the aromatic ring. Hence femtosecond dynamics is reflected in the nanosecond time range and can be observed with real-time spectroscopy. Therefore, the process is named free electron transfer (FET) which corresponds to an unhindered electron jump occurring in the first approach of the reactants. From the FET mechanism some new aspects for chemical reaction kinetics can be derived.

[en] Complete text of publication follows. We have developed a new type of radiation dosimeter which is based on radio-fluorogenic co-polymerization 'RFCP'. In this method the dosimeter consists of a liquid monomer which polymerizes when exposed to high energy radiation, for example methylmethacrylate. Dissolved in this bulk monomer is a small (ca millimolar) concentration of a compound that is non-fluorescent but which becomes fluorescent when it is incorporated into a growing polymer chain. The resulting fluorescence is then proportional to the yield of initiating free-radicals formed and hence to the accumulated radiation dose. The method is illustrated by application to remote, real-time dose monitoring within a small (< 0.2 ml) volume. Using a semi-rigid gel form of the RFCP dosimeter, two and three dimensional fluorescent images of a masked 3 MeV electron beam and a 6 MeV X-ray beam have been created.

[en] Complete text of publication follows. Polythiophenes belong to group of conducting polymers which play an important role in electric and electronic industry. The oxidative polymerization mechanism involves several consecutive steps such as electron transfer, carbon - carbon bond formation and deprotonation. The identification of the reactive intermediates formed upon oxidation of thiophenes is complicated by the high reactivity of their radical cations, the primary products of one electron oxidation. Therefore, it is useful to investigate the initial steps of the polymerization in low-temperature organic matrices. Thiophene, 3,4-dimethoxythiophene (DMT), 3,4-ethylenedioxythiophene (EDOT) and 3,4-propylenedioxythiophene (PDOT) were chosen for this study. The mixture of ionic liquid 1-butylmethylimidazolium hexafluorophosphate (BMIMPF₆) and chloroform was used as the low temperature organic matrix. In this type of matrix annealing of irradiated frozen mixture triggers formation of peroxyl radicals which can play a role of secondary oxidizing agent. The observed steps of oxidative dimerization of thiophenes and the role of peroxyl radicals in 'delayed' oxidation of primary radiolysis products of thiophenes are discussed.

[en] Complete text of publication follows. Nitrous oxide is in widely use for converting reducing hydrated electrons into oxidizing hydroxyl radicals. The yield of hydroxyl radicals resulting from the very fast reaction of hydrated electrons with nitrous oxide in aqueous solution has been re-determined using the method of pulse radiolysis. For solutions saturated with nitrous oxide the half-life time of this reaction is about 3 ns, i.e., this reaction occurs on a time scale where spur reactions are still underway. At these times, the yield of hydrated electrons is definitely larger than the known value of 0.269 μmol J^-1 (2.6 molecules/100 eV) at about 100 ns after irradiation. Mimicking the experimental absorption vs. time curves of the hydrated electron at 700 nm for solutions either being purged with argon or being saturated with nitrous oxide reveals that hydroxyl radicals, due to the reaction of hydrated electrons with nitrous oxide, are generated with a yield of 0.33 μmol J^-1 (3.2 molecules/100 eV). Compared with the normally used value of 0.269 μmol J^-1 (2.6 molecules/100 eV), this new value is 23 % larger.

[en] Complete text of publication follows. Exciton decay dynamics in semiconductor quantum dots and single-walled carbon nanotubes are extensively studied experimentally. Excitons produced in these nanoobjects decay either by radiative process or by charge transfer to ligands bound to them or by Auger recombination. The number of excitons produced in each nanoobject is usually very small and fluctuations in the number of excitons in each nanoobject are comparable to the average number of excitons per nanoobject. In this situation the conventional bulk approach that considers only the average number of excitons per nanoobject is not sufficient to describe the dynamics of exciton decay. Instead one has to use a stochastic approach which properly takes into account fluctuations in the number of excitons in each nanoobject. In this talk I present a stochastic treatment of exciton decay dynamics in nanoobjects and analyse recent experiments on exciton decay in quantum dots by charge transfer to ligands, exciton decay in quantum dots and nanotubes by Auger recombination, and competition between charge transfer to ligands and Auger recombination in exciton decay in quantum dots. The quantized character of the number of excitons in each nanoobject turns out to be essential to understand exciton decay dynamics.

[en] Complete text of publication follows. Radiation processing has many advantages over other conventional methods. When using radiation for material processing, no catalysts or additives are needed in order to initiate the reaction. Polymeric films were modified by gamma-radiation grafting of pH and thermo sensitive monomers by one and two step methods, using the preirradiation and the direct methods. The effects of the absorbed dose, monomer concentration and reaction time were investigated. The surface chemistry of grafted samples was analyzed by FTIR-ATR spectroscopy, while their thermal properties were analyzed by TGA and DSC. The stimuli-responsive behavior was studied by swelling and contact angle in water, as well as by DSC. Sensitive films presented a critical pH point and low critical solution temperature. Temperature and pH stimuli-responsive macromolecular materials have attracted great attention because of their obvious applications in biomedicine and biotechnology. This work was supported by DGAPA-UNAM Grant IN200208.

[en] Complete text of publication follows. In the radiolysis and vacuum-ultraviolet photolysis of liquid cycloalkanes structural isomerizations to open-chain olefins, while in the cases of 1,2-, 1,3- and 1,4-dimethylcycloalkanes also geometrical (cis↔trans) isomerizations were observed. Biradicals are suggested as intermediates of these isomerizations. Iodine scavenging studies, similar to that previously performed for n-alkanes and isoalkanes, were made in the γ radiolysis of cyclopentane, cyclohexane, cycloheptane, cyclooctane and cyclodecane. Using gel permeation chromatography (GPC) for the separation of iodide scavenging products αω-diiodo alkanes were also found to form in addition to the usual scavenging products, cycloalkyl iodides and fragment iodoalkanes. The production of αω- diiodo alkanes was attributed to biradical scavenging. The diiodo alkane yields showed a strong dependence on iodine concentration revealing a Stern-Volmer type competition between unimolecular stabilization of the biradicals forming hydrocarbon products and the radical scavenging reaction. This competition allowed to estimate the biradical lifetimes, 100-600 ns, and the biradical yields, G = 0.06 - 0.25 biradical/100 eV.