Ruth Maria Quint

Degradation of monochlorophenols by γ-irradiation

Abstract The degradation of aqueous 5 × 10 −4 mol dm −3 2-, 3- and 4-chlorophenol (2-CIP, 3-CIP, 4-CIP) under reducing and oxidizing conditions has been studied by steady state γ-radiolysis. The reaction with e aq − leads to reductive dechlorination which equals the degradation of the chlorophenols. Solely phenol is the major organic compound formed. In N 2 O saturated solutions the dehalogenation is much less effective. In the case of 4-CIP 40% and in that of 2- and 3-CIP only 20% of the decomposed substrates are resulting in chlorine free organic compounds. From these pyrocatechol for 2-CIP and hydroquinone for 4-CIP could be identified in minor amounts. Main products are the hydroxylated substrates originating from the primarily formed ortho- and para OH-adducts. These are for 2-CIP: chlorohydroquinone and 3-chlorocatechol, for 3-CIP: chlorohydroquinone, 3- and 4-chlorocatechol and for 4-CIP: 4-chlorocatechol. In the presence of oxygen, where the OH-adducts are converted into peroxyl radicals, the degradation yield of the substrates corresponds to that of OH radicals up to doses of 0.5 kGy. The dechlorination process in this dose range is 50% for 4-CIP, and 33% for 2- and 3-CIP. The position of chlorine on the aromatic ring strongly influences the dehalogenation and degradation process. A pronounced dependency of the dose/yield curves on the oxygen concentration was observed. This indicates that for an efficient degradation process of chlorophenols oxygen supply is necessary during irradiation.

γ-radiolysis and pulse radiolysis of aqueous 4-chloroanisole

Abstract Using pulse radiolysis and steady state γ-radiolysis in combination with product analysis by HPLC the radiolytic degradation mechanism of 4-chloroanisole (4-ClAn) has been elucidated. Pulse radiolysis experiments show that OH radicals react in neutral aqueous N2O saturated solutions with 4-ClAn by addition to all aromatic ring positions to yield hydroxycyclohexadienyl radicals (OH-adducts), k(OH + 4-ClAn) = 6.5 × 109dm3mol−1s−1. Those OH-adducts formed on ipso positions of the molecule subsequently undergo HCl or CH3OH elimination forming methoxyphenoxyl- and chlorophenoxyl radicals. Their yield corresponds to ∼ 20% of the OH-radicals, whereby the distribution is roughly 3:1 in favor of the methoxyphenoxyl radicals, which reflects the stronger ortho-, para-directing activity of the methoxy group. The OH-adducts decay second order, 2k = 1 × 109dm3mol−1s−1. The presence of oxygen leads to its addition on the hydroxycyclohexadienyl radicals, k(OH-adduct + O2) = 3.2 × 108dm3mol−1s−1. In airfree solution the reaction of H-atom with the substrate, k(H + 4-ClAn) = 1.2 × 109dm3mol−1s−1, results in H-adducts which decay in bimolecular reactions, 2k = 8.2 × 108dm3mol−1s−1. The rate constant for the reaction of the solvated electrons has been determined to k(eaq− + 4-ClAn) = 2 × 109dm3mol−1s−1. The absorption spectra of H- and OH-adducts were measured in the range of 280–450 nm. The products analysed by HPLC after γ-radiolysis in dependence of dose (100–600 Gy) are given for N2O-, air-, oxygen- and argon saturated neutral aqueous solutions. In conditions favoring the OH radical oxidation 4-chlorophenol, 4-methoxyphenol, 5-chloro-2-methoxyphenol and 2-chloro-5-methoxyphenol were determined as final products. In the presence of Ar, where about equal amounts of OH and eaq− are present, additionally anisole could be detected. Under both reaction conditions the amount of identified products is about 20% of decomposed 4-ClAn. The reaction of eaq− leads to reductive dechlorination which corresponds quantitatively to the degradation of the substrate. In the presence of air or solutions saturated with pure oxygen predominantly hydroquinone, 4-chlorophenol and muconic acids are formed and the material balance is ∼50%. The efficient dechlorination (∼60% of the decomposed 4-ClAn) as well as ring fragmentation products as intermediates en route to complete mineralization in oxygenated solution indicate that high energy radiation is a promising method for degradation of halogenated aromatic compounds in water. Variation of dose rates from 79 Gy min−1 to 266 Gy min−1 did not show any influence on the product distribution.

The 4-hydroxyestrone: Electron emission, formation of secondary metabolites and mechanisms of carcinogenesis

4-Hydroxyestrone (4-OHE(1)), a typical cancer-inducing metabolite, originating from 17beta-estradiol (17beta-E2), was chosen as a model for the studies. The aim was to get a deeper insight in the mechanisms of its ability to initiate cancer. It was found, that 4-OHE(1) can eject electrons (e(aq)(-)), when excited in the singlet state by monochromatic UV-light (lambda=254 nm) in polar media (water:ethanol=40:60 vol.%). The quantum yield Q(e(aq)(-)), determined for various 4-OHE(1) concentrations, is found to be as high as that previously observed for 17beta-E2. It decreases with increasing substrate concentration, but it is enhanced at higher temperature. The ability of 4-OHE(1) to eject as well as to consume and to transfer electrons to other biological systems, classifies it as an electron mediator, similar to 17beta-E2. The 4-OHE(1) transients resulting of the electron emission process are leading to the formation of secondary metabolites. Surprisingly, it was established that the secondary metabolites possess likewise the ability to eject as well as to consume electrons. Hence, they behave similar like 17beta-E2. However, the structure of the secondary formed metabolites, which determinates their biological properties and carcinogenity, depends on the nature of the available reaction partners involved in their formation. A probable reaction mechanism explaining the subject matter is discussed.

One-electron oxidation of Mitomycin C and its corresponding peroxyl radicals. A steady-state and pulse radiolysis study

Abstract The one-electron oxidation of Mitomycin C (MMC) as well as the formation of the corresponding peroxyl radicals were investigated by both steady-state and pulse radiolysis. The steady-state MMC-radiolysis by OH-attack followed at both absorption bands showed different yields: at 218 nm G i (-MMC) = 3.0 and at 364 nm G i (-MMC) = 3.9, indicating the formation of various not yet identified products, among which ammonia was determined, G(NH 3 ) = 0.81. By means of pulse radiolysis it was established a total κ (OH + MMC) = (5.8 ± 0.2) × 10 9 dm 3 mol −1 s −1 . The transient absorption spectrum from the one-electron oxidized MMC showed absorption maxima at 295 nm ( ϵ = 9950 dm 3 mol −1 cm t -1 ), 410 nm ( ϵ = 1450 dm 3 mol −1 cm −1 ) and 505 nm ( ϵ = 5420 dm 3 mol −1 cm −1 ). At 280–320 and 505 nm and above they exhibit in the first 150 μs a first order decay, κ 1 = (0.85 ± 0.1) × 10 3 s −1 , and followed upto ms time range, by a second order decay, 2 κ = (1.3 ± 0.3) × 10 8 dm 3 mol -1 s −1 . Around 410 nm the kinetics are rather mixed and could not be resolved. The steady-state MMC-radiolysis in the presence of oxygen featured a proportionality towards the absorbed dose for both MMC-absorption bands, resulting in a G i (-MMC) = 1.5. Among several products ammonia-yield was determined G(NH 3 ) = 0.52. The formation of MMC-peroxyl radicals was studied by pulse radiolysis, likewise in neutral aqueous solution, but saturated with a gas mixture of 80% N 2 O and 20% O 2 . The maxima of the observed transient spectrum are slightly shifted compared to that of the one-electron oxidized MMC-species, namely: 290 nm ( ϵ = 10100 dm 3 mol −1 cm −1 ), 410 nm ( ϵ = 2900 dm 3 mol −1 cm −1 ) and 520 nm ( ϵ = 5500 dm 3 mol −1 cm −1 ). The O 2 -addition to the MMC-one-electron oxidized transients was found to be at 290 to 410 nm gk (MMC·OH + O 2 ) = 5 × 10 7 dm 3 mol −1 s −1 , around 480 nm κ = 1.6 × 10 8 dm 3 mol −1 s −1 and at 510 nm and above, κ = 3 × 10 8 dm 3 mol −1 s −1 . The decay kinetics of the MMC-peroxyl radicals were also found to be different at the various absorption bands, but predominantly of first order; at 290–420 nm κ 1 = 1.5 × 10 3 s −1 and at 500 nm and above, κ = 7.0 × 10 3 s −1 . The presented results are of interest for the radiation behaviour of MMC as well as for its application as an antitumor drug in the combined radiation-chemotherapy of patients.

Pulsed laser-induced oxidation of phenol in acid aqueous TiO2 sols

Transient formation in aqueous acid unprotected TiO2 sols containing phenol has been studied by timeresolved absorption spectroscopy upon irradiation with 10 ns laser pulses at 355 nm. Four types of sol were studied, differing in the starting compound used for colloid preparation [TiCl4 or titanium(IV) tetraisopropylate] and in the acid used for pH adjustment (HCl or HClO4). Phenoxyl radical formation is demonstrated, the major part of which involves Cl˙–2 radical anions as intermediates which oxidize phenol. The formation of Cl˙–2, in turn, occurs by valence-band hole oxidation of Cl–, which is either introduced into the solution as HCl to adjust the pH or is present on the particle surface if TiCl4 is used as starting compound. Laser pulse energy-dependent measurements of transient formation were performed to determine oxidation quantum yields and concentrations of surface-adsorbed Cl–.

The effect of homocysteine thiolactone and its α-alkylated derivative on the survival of irradiated E. coli AB1157

Abstract The radiation induced decomposition of homocysteine thiolactone (HCTL) and α-methyl-homocysteine thiolactone (α-MHCTL) was studied in aqueous solution (pH = 5.4) as a function of dose (up to 1.55 kGy) in the absence and presence of oxygen as well as in solutions saturated with N 2 O. The strongest radiolysis of both substances was observed in oxygenated solution, because of the peroxide transient formation. E. coli AB1157 were used as model of living systems for toxicity studies of α-MHCTL in the range of 6 × 10 -9 to 6 × 10 -3 mol dm -3 . Comparative survival curves of E. coli bacteria using α-MHCTL, HCTL and cysteamine in the presence of air showed that α-MHCTL is the most efficient radiation protector. Rather high radiation protective effect on bacteria was also observed in absence of oxygen. The corresponding D 37 data (kGy) are reported.

Influence of Temperature and Oxygen Concentration on the Radiation Induced Oxidation of Phenylalanine

Abstract The formation of tyrosine isomers by γ-radiolysis of neutral aqueous phenylalanine solutions was found to be strongly dependent on oxygen concentration and temperature. Changing the dose rate did not influence the degradation process. In the presence of 0.25 x 10-3 mol dm-3 oxygen at room temperature the yields of o-tyrosine as well as of m- and p-tyrosine drop from G(o-Tyr) = 0.5 and G(m-Tyr) = G(p-Tyr) = 0.4 at a dose of 0.3 kGy to 0.18 and 0.16 at 2.5 kGy, respectively. In solutions containing 1.25 x 10-3 mol dm-3 oxygen the initial yields remain unchanged but decrease at 2.5 kGy only to G(o-Tyr) = 0.3 and G(m-Tyr) = G(p-Tyr) = 0.20. Under the latter reaction conditions also 3,4-dihydroxyphenylalanine was found. Samples irradiated in frozen state did not show remarkable radiolysis of phenylalanine and tyrosine formation. In the range between 5 and 20°C no essential influence of temperature on the phenylalanine radiolysis and tyrosine yields was observable. The obtained results are important for methods using the tyrosine yields as markers for the detection of irradiated food. Storage conditions and irradiation temperature play an essential role on radiation induced changes of food.

Flash Photolysis and ESR Studies on Hematoporphyrin and Photofrin II in Polar and Microheterogeneous Environment

Hematoporphyrin (HP) and its derivatives (HPD; e.g. photofrin II) are used as efficient sensitizers in the photodynamic treatment of tumors. The photoinduced formation of various transients resulting from these substrates at pH 12 and 7.4 were studied by conventional flash photolysis and by ESR techniques in the presence of various additives. EDTA is acting as an efficient reducing agent for the triplet state of the substrates. The absorption spectra of some transients (HP·-, HP -OH, HPD·-, HPD -OH) were obtained. Further, ESR studies (pH 4-7) showed that 3HP is mostly converted into HP·- - in the presence of EDTA, but this is not the case with 3HPD. In airfree HPD solutions a longlived transient was registered, which was attributed to HPD·+ species. In aerated substrate solutions the singlet oxygen ( 1O2) and peroxyradicals are formed. The discussed transients very likely are involved in the photodynamic treatment of tumors in man.

Electron emission and product analysis of estrone: progesterone interactions studied by experiments in vitro.

Recent studies showed that hormones like progesterone, testosterone, etc. can eject (solvated electrons). By means of electron transfer processes via the brain, the hormones communicate with other biological systems in the organism. The present study proves that also estrone is able to emit electrons. Their yield strongly depends on the concentration of the hormone, temperature and on the absorbed energy. The metabolites resulting from this process are likewise able to generate electrons, however with much smaller yields. The formation of the estrone metabolites is studied by HPLC-analyses. In vitro experiments with MCF-7 cells demonstrate the distinct effect of progesterone on the carcinogenity of estrone metabolites. Probable reaction mechanisms for explanation of the observed effects are postulated.

Effects of food store quality on hibernation performance in common hamsters

Hibernating animals can adjust torpor expression according to available energy reserves. Besides the quantity, the quality of energy reserves could play an important role for overwintering strategies. Common hamsters are food-storing hibernators and show high individual variation in hibernation performance, which might be related to the quality of food hoards in the hibernacula. In this study, we tested the effects of food stores high in fat content, particularly polyunsaturated fatty acids (PUFAs), on hibernation patterns under laboratory conditions. Control animals received standard rodent pellets only, while in the other group pellets were supplemented with sunflower seeds. We recorded body temperature during winter using subcutaneously implanted data loggers, documented total food consumption during winter, and analysed PUFA proportions in white adipose tissue (WAT) before and after the winter period. About half of the individuals in both groups hibernated and torpor expression did not differ between these animals. Among the high-fat group, however, individuals with high sunflower seeds intake strongly reduced the time spent in deep torpor. PUFA proportions in WAT decreased during winter in both groups and this decline was positively related to the time an individual spent in deep torpor. Sunflower seeds intake dampened the PUFA decline resulting in higher PUFA levels in animals of the high-fat group after winter. In conclusion, our results showed that common hamsters adjusted torpor expression and food intake in relation to the total energy of food reserves, underlining the importance of food hoard quality on hibernation performance.