Effect of LET on radiolysis of C6−C8 cycloalkane systems

The - and -radiolysis of cyclohexane, cycloheptane and cyclooctane was investigated in the absence and presence of iodine scavenger. Comparison of the distributions of products formed revealed considerable differences between - and -radiolysis, and the decomposition of strainless cyclohexane and strained cycloheptane and cyclooctane.     

Spectral and kinetic characteristics of the α-propionic acid methyl ester radical in cyclohexane and water

The -propionic acid methyl ester radical was produced in dissociative electron capture reaction of 2-chloropropionic acid methyl ester. The absorption maxima of the radical are at 310 and 300 nm in cyclohexane and water with extinction coefficients of 440±50 and 400±50 mol^–1 dm³ cm^–1. The second order decay rate parameter in water is (2.3±0.5)×10⁹ mol^–1 dm³ s^–1. The peroxy radicals have the characteristics: _max=265–270 nm, _max=700–900 mol^–1 dm³ and 2k=(7±2)·10⁸ mol^–1 dm³ s^–1.     

Mechanism of OH radical-induced oxidation of <Emphasis Type="Italic">p</Emphasis>-cresol to <Emphasis Type="Italic">p</Emphasis>-methylphenoxyl radical

The OH radical-induced oxidation of p-cresol to p-methylphenoxyl radical was studied in aqueous solution in a wide pH range by means of pulse radiolysis combined with optical spectroscopy. OH-adduct cyclohexadienyl type radicals were identified as intermediates of the reaction. In the acidic pH range the first-order rate coefficient of phenoxyl radical formation was found linearly dependent on the H₃O⁺ concentration yielding a bimolecular rate coefficient of 1.8 × 10⁸ mol^–1 dm³ s^–1. In the alkaline range a linear dependence was found on the OH^– concentration with rate coefficient of 4.9 × 10¹⁰ mol^–1 dm³ s^–1. These findings were interpreted in terms of acid-base catalysis of the H₂O elimination from the OH-adduct. With the time resolution applied, 30 ns, the radical cation p-CH₃C₆H₄OH^+. was not observed as intermediate.     

Study of polymerization kinetics of acrylic and methacrylic acid esters at low conversions

The kinetics of high-energy radiation initiated polymerization of acrylate and methacrylate monomers were studied in dilute cyclohexane solutions. The absorption spectra of the intermediates were obtained by pulse radiolysis with optical detection. In solutions of acrylates at longer times after the pulse the presence of oligomer radicals was observed. In solutions of methacrylates the beginning of the oligomerization reaction was detected at higher monomer concentrations. From the kinetic curves the rate coefficients of termination were calculated.     

Calculated and measured transient product yields in pulse radiolysis of aqueous solutions: Concentration dependence

Pulse radiolysis of aqueous solutions was modeled by using 54 equations for the reaction of water radiolysis intermediates with carefully selected rate coefficients. Yields of products formed in the hydrated electron+solute and hydroxyl radical+solute reactions were calculated and compared with the measured yields in wide concentration range. These reactions are in competition with the reactions of the water radiolysis intermediates with each other and with H₂O, H⁺ and H₂O₂. An empirical equation was developed for the calculation of scavenged product yields that can be used in cases when due to low rate coefficient, low solubility or very high absorbance, low solute concentrations are applied and a considerable fraction of the water radiolysis intermediates does not react with the solute.     

Pulse radiolysis study of the initial steps of the polymerization of cyclohexyl acrylate and cyclohexyl methacrylate

Pulse radiolysis with kinetic spectroscopic detection was applied to study the kinetics of the first steps of radiation induced polymerization of cyclohexyl acrylate and cyclohexyl methacrylate in cyclohexane solvent. The reactions were initiated by cyclohexyl radicals produced in the radiolysis of the solvent. The transient absorption spectra of the -carboxyalkyl type radicals produced in addition reaction show maxima around 300 nm. This shifts to longer wavelength with time after the pulse. This phenomenon was explained by the oligomerization reaction. From the kinetic curves average rate coefficients of termination for the oligomer radicals (2k_t) were determined as a function of time elapsed after the electron pulse. The values obtained were compared with those calculated for other (acrylate and methacrylate type) monomers.     

Conservation of the skeletal conformation in the ring decomposition of dimethylcyclohexanes

By comparing the composition of products formed during the -radiolysis of structural and geometrical /cis and trans/ isomers of dimethylcyclohexanes, the relationship between molecular structure and ring decomposition reactions was investigated. The yields of products that exist in geometrical isomeric forms /e.g. 2-butenes, 2-octenes/ were considerably different in the irradiation of cis- and transdimethylcyclohexanes: the products reflected the conformation of the decomposed molecule. It was assumed that the ring decomposition is a very fast process taking place within about 1 ps. If biradical intermediates are involved in the reactions, their further transformations occur before attaining conformational equilibrium.     

Demonstration of a protein with enhanced resistance to proteinase K in transmissible cytopathic condition elicited by cell-free lysate of free-living ameba Naegleria gruberi

The cell-free lysate of free-living amebae Naegleria gruberi and Naegleria fowleri were reported to elicit cytopathic effect in various cell lines that could be indefinitely transmitted by the culture media. The causative agent showed sensitivity to treatments detrimental to proteins while resisted exposures damaging to nucleic acids. Here we demonstrate that subsequent to exposure to N. gruberi lysate mild digestion with proteinase K reveals the presence of a protein band in HeLa cells absent from control cell lines. Though the small quantity of this protein with enhanced resistance to proteinase K relative to the total protein content of the sample has proved to date insufficient for its purification, we suppose that it is a human cellular protein that assumed altered conformation in a prion-like fashion. The conformational conversion could have been trigerred by an ameba protein in the lysate. In addition, we showed that HeLa cells treated with N. gruberi lysate display elevated cathepsin B activity which is assumed to be a secondary response to the accumulation of the proteinase K-resistant protein. We propose that a number of degenerative sequelae following previous microbial infections in mammals could have a similar pathomechanism. Moreover, epidemiological data strongly suggest that natural prion disease in sheep, goat and cervids may also have an etiology linked to prior infection/colonization with a microbe, as it had already been proposed by one of us.     

Electron transfer from cresols to N3, BrO2, ClO2, NO2 and SO4 radicals: correlation between rate constants and one-electron reduction potentials

The rate constants of oxidation of phenol and the cresol isomers to phenoxyl or methylphenoxyl radicals by inorganic radicals (R√) were studied in aqueous solutions at pH=5.8 and 11.5 using pulse radiolysis. The oxidation was due to electron transfer. Using the Marcus theory the electron transfer data were evaluated on the basis of the energy difference, ΔE, between the one-electron reduction potential of the inorganic couple and the mid-point potential of the half-cell of the phenoxyl/phenolate(phenol) couple. The standard reduction potentials of (o-CH₃PhO√/o-CH₃PhO⁻) and (m-CH₃PhO√/m-CH₃PhO⁻) couples (vs. NHE) were determined as 760 and 800 mV, respectively. The electron transfer was found to be diffusion limited when ΔE500 mV independently of the inorganic radical, type of phenol or pH. Between 0ΔE500 mV the rate constants showed good correlation with ΔE. The rate constants were dependent on the isomeric position of the methyl substituent.     

Improvement of pesticide adsorption capacity of cellulose fibre by high-energy irradiation-initiated grafting of glycidyl methacrylate

Cellulose as a renewable raw material was used for preparation of adsorbent of organic impurities in wastewater treatment. Hydrophobic surface of cellulose substrate was developed by grafting glycidyl methacrylate in simultaneous grafting using gamma irradiation initiation. Water uptake of cellulose significantly decreased while adsorption of phenol and a pesticide molecule (2,4-dichlorophenoxyacetic acid: 2,4-D) increased upon grafting. Adsorption equilibrium data fitted the Freundlich isotherm for both solutes.