F. Martinotti

ESR study of the direct radiolysis of DNA, DNA-histones and DNA-intercalators complexes

Abstract The nature of the radicals contributing to the room temperature spectrum of irradiated “dry” DNA, with special reference to the central structure, is discussed, and the thesis of their ionic origin tested by irradiation experiments with intercalators. The mechanism of spin transfer protein→DNA has been investigated through a comparative ESR study on the DNA-histones complex, the structureless random molecular mixture of the DNA-histones and the neat components. The yield of spin transfer is enhanced in the random mixture, presumably because of the greater efficiency of molecular contacts. Evidence of the scavenging of electrons by the thymine and cytosine bases, as a key mechanism for the spin transfer, has been obtained.

Alkoxyfluoroalkyl radicals: Structure and conformations from solid state esr spectra

Abstract The anisotropic components of the α and β Fluorine h.f. tensors of alkoxyfluoroalkyl radicals ROCF 2 and ROCF(CF 3 ) were experimentally determined and basic informations pertaining the geometry of the radical centres and the mechanism of magnetic interactions were obtained.

Radiolysis mechanisms in clathrates systems: EPR spectroscopy investigation of the long chain carboxylic esters urea adducts

Abstract The mechanism of the gamma radiolysis of long chain aliphatic carboxylic esters from decanoic and hexadecanoic acids, in the state of urea clathrates has been investigated by EPR spectroscopy. The major species identified are the carboxylate anion-radicals, trapped electrons, and the neutral primary alkyl radicals of type RCH · 2 arising from the OC and CCOOR bond scissions. Also present among the species trapped at 77 K are the secondary alkyl radicals CH 2 CHCH 2  formed by CH bond rupture in the aliphatic chains. On warming the radical anions are converted into RCH · 2 species and intermediate acyl type radicals RCO have been observed. At room temperature all the primary and secondary radicals gradually disappear, being partially converted into the α-carboxylate radicals RCH 2 CHCOOR. This process is thought to involve the intrachain migration of the free valences by hydrogen abstraction. The comparison with the neat compounds has shown that the clathrate structure has a profound influence on the radiolysis mechanism the major effects observed being the increase of the OC scission products, the increase of the radical anions yield and the decrease of the CH bond ruptures in the aliphatic chains.

Kinetic ESR for self reactions of perfluoroalkyl ether peroxyradicals

Abstract The rate constants for self-reactions of perfluoroalkyl ether peroxy radicals are found to be several order of magnitude greater as compared to the rate constants for their not fluorinated analogues. This difference of reactivity is interpreted in terms of fluorine substituents effects.

Decay constants of peroxy radicals from polypropylene and polypropylene model compounds: a kinetic ESR study

Abstract The rate constants and the activation energy for the mutual recombination of peroxy radicals generated from atactic polypropylene (PP) and for model compounds of PP and PP autoxidation products have been determined by kinetic ESR. The type of peroxy radicals and the preferred sites of attack for the hydrogen abstraction by t-butoxyl radicals were identified. The results are of interest in respect to the mechanism and the kinetic simulation of PP autoxidation.

Matrix isolation and ESR study of platinum(I) diolefin complexes—norbornadiene and (1,5-cyclooctadiene) platinum dichloride radical anions

Abstract The low temperature γ-irradiation of norbornadiene and (1,5-ciclooctadiene) platinum(II) dichloride in methyltetrahydrofurane matrix leads to a selective production of electron capture centres which were identified by ESR as platinum(I) diolefin radical anions. The Molecular Orbital calculations suggest that the unpaired electron is in a b 2 orbital (assuming an idealised C 2r symmetry) where the 5 d yz is the major metal orbital involved. The low contribution of 5 d yz to the SOMO (α 2 = 0.23 as derived from the analysis of the experimental ESR parameters) implies a high delocalization on the ligands. The electronic structure of the paramagnetic species and, in particular, the large negative contributions to the calculated g -tensor elements giving rise from the low energy empty levels, were rationalised by extended Huckel MO calculations.

ESR Study of radical cations from γ-irradiation of bicyclo[3.1.0]hex-2-ene in freon matrices

Abstract Bicyclo[3.1.0]hex-2-ene radical cation, generated by γ-irradiation of the parent compound in freon matrices at 77 K, undergoes ring opening to the 1,3-cyclohexadiene radical cation. In CF 2 ClCFCl 2 matrix both radical cations also undergo deprotonation to the corresponding neutral radicals.

Time Dependent Reactivity in the Post Irradiation Oxidation of Polypropylene

Abstract A kinetic model for the radiation induced oxidation of isotactic polypropylene film (38μ thick) has been developed which allows determination of the concentration profiles, rate constants and diffusion coefficients. The match with the experimental data is consistent with a distribution of reactivity that changes during the course of the reaction giving rise to time dependent fat? constants according to the Plonkas equation (k=ko (a-1). This equation can be rationalized within the framework of the random walk models under the assumption of temporal, geometric or energetic disorder. The origin and the characteristics of the reactivity distribution have been investigated by an ESR spectroscopy study of the degree of order and the molecular dynamics of the intermediate peroxy radicals.

Matrix isolation EPR study of novel radical cations from bicyclic[3.2.0] and monocyclic C7H8 and C7H10 compounds

The radical cations of bicyclo[3.2.0]hepta-2,6-diene and bicyclo[3.2.0]hept-2-ene have been obtained by γ-irradiation of the parent compounds in Freon matrices and their structures investigated by EPR spectroscopy and MNDO and INDO calculations. In a CFCl3 matrix, ring opening to the isomeric cycloheptatriene and cycloheptadiene radical cations occurred, whereas in a CF2ClCFCl2 matrix the prevalent reaction was deprotonation to the neutral bicyclo[3.2.0]hepta-2,6-dien-4-yl and bicyclo[3.2.0]hept-2-en-4-yl radicals, respectively.

The Molecular Dynamics of Peroxy Radicals in Irradiated Crystalline Aliphatic Amides

Abstract The molecular dynamics of peroxy radicals generated from several amides have been investigated as a function of temperature by ESR using a modified Bloch formalism. Rotation about the C-0 bond was found to be a mode of motion common to the peroxy radicals in the amides studied thus far. In the linear amides, we have also obtained preliminary evidence for rotation about the chain axis leading to inversion of the parallel and perpendicular principal g values. The frequence of motion at a given temperature decreases with increasing molecular size and with branching. The mobility parameters correlate reasonably well with the previously reported kinetics of post irradiation oxidation in the amides.