Sonja Solar

Effect of γ-irradiation on agaritine, γ-glutaminyl-4-hydroxybenzene (GHB), antioxidant capacity, and total phenolic content of mushrooms (Agaricus bisporus).

Fresh mushrooms ( Agaricus bisporus ) were irradiated at doses of 1, 3, and 5 kGy to assess the effect of gamma-irradiation on the major aromatic compounds agaritine (beta-N-(gamma-L-(+)-glutamyl)-4-(hydroxymethyl)phenylhydrazine) and GHB (gamma-glutaminyl-4-hydroxybenzene) as well as on the total phenolic content and antioxidant capacity. Up to 3 kGy, agaritine was not affected. At 5 kGy, a significant reduction (p = 0.05) from 1.54 (0 kGy) to 1.35 g/kg dry weight (DW) was observed. gamma-Glutaminyl-4-hydroxybenzene decreased by 22% at 1 kGy and by 31% at 5 kGy. Additionally, agaritine standard solutions at concentrations of 10(-4) and 5 x 10(-5) mol/L were irradiated to compare the effect on agaritine content in aqueous solutions and in the sample matrix. A rapid decay was observed, 50% at 750 Gy (10(-4) mol/L) and 400 Gy (5 x 10(-5) mol/L). The total phenolic content and antioxidant capacity were not significantly (p = 0.05) influenced by irradiation.

Reactivity of OH and O– with aqueous methyl viologen studied by pulse radiolysis

The behaviour of aqueous MV2+ towards oxidizing radicals (OH and O–) has been investigated in the pH range from 6 to 14 by means of pulse radiolysis. A semi-linear optimization method was applied for resolving the complex reaction mechanism. In the pH range from 6 to 8 the rate constant for attack by OH is k=(2.5±0.2)× 108 dm3 mol–1 s–1. The resulting transient absorbs at λmax= 470 nm (Iµ470= 1600±70 m2 mol–1) and decays with 2k=(1.3±0.2)× 108 dm3 mol–1 s–1.In strongly alkaline solutions (pH 13.8) the O– radical anion reacts preferentially by hydrogen abstraction from the methyl group, k=(1.4±0.2)× 109 dm3 mol–1 s–1, forming a radical which then decays by reaction with OH–(k= 2.8 × 106 dm3 mol–1 s–1) to produce a modified radical cation; this has absorption maxima at 392 and 605 nm (Iµ392= 4300 m2 mol–1, Iµ605= 1500 m2 mol–1) and is relatively long lived.The remaining part (< 10%) of O– attacks MV2+ at the ring carbon atom, k=(1.0±0.4)× 108 dm3 mol–1 s–1, resulting in an O– adduct, which has λmax= 470 nm (Iµ470= 2200±100 m2 mol–1).

Pulse radiolysis of pyrene in aprotic polar organic solvents: simultaneous formation of pyrene radical cations and radical anions

Abstract Simultaneous formation of pyrene radical cations Py · + and radical anions Py · − was observed by pulse radiolysis of pyrene in DMSO or sulfolane solutions containing 10 vol % toluene. Using 5×10 −5 mol dm −3 pyrene in the oxygen-free solvent mixture of 90 vol % DMSO and 10 vol % toluene, the radical cation Py · + (λ max =450 nm ;e 450 =2.29×10 4 dm 3 mol −1 cm −1 ) was formed with the rate constant k=4.0×10 9 dm 3 mol −1 s −1 and decayed by a first-order reaction with k 1 =1.2×10 4 s −1 , forming the dimer radical cation ( Py ) 2 · + . Simultaneously, the radical anion Py · − (λ max =495 nm ; e 495 =2.17×10 4 dm 3 mol −1 cm −1 ) was produced with k=6.0×10 10 dm 3 mol −1 s −1 and disappeared by formation of the dimer radical anion ( Py ) 2 · − with k 1 =4.6×10 4 s −1 . The first-order rate constants (k1) for the decay of the species Py · + and Py · − with formation of the dimer radical ions ( Py ) 2 · + and ( Py ) 2 · − increased with raising the substrate concentration. By scavenging all radiolytically generated electrons with oxygen (k≈8×10 8 dm 3 mol −1 s −1 in 90 vol % DMSO and 10 vol % toluene), the formation of the Py · − transients was suppressed without interfering with the generation of the radical cations Py · + . In oxygen-free solutions of pyrene (5×10 −5 mol dm −3 ) in 90 vol % sulfolane and 10 vol % toluene the corresponding rate constants of the transient formation and the decay were for Py · + :k=1.5×10 10 dm 3 mol −1 s −1 and k 1 =0.9×10 4 s −1 , and for Py · − :k=2.3×10 10 dm 3 mol −1 s −1 and k 1 =4,1×10 4 s −1 .

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.

Radiation-induced C—C bond cleavage in 1,2-diarylethanes as model compounds of coal. Part 1.—Pulse and steady-state radiolysis of 1,2-di(1-naphthyl)ethane

1,2-Di(1-naphthyl)ethane (1,2-DNE) has been used to study the radiation-induced C—C bond cleavage of the ethane linkage. Pulse radiolysis was applied both in the absence and presence of NaAlH4 and NaAlH2(OR)2 used as scavengers for solvent cations. In the presence of the sodium aluminium hydrides the radical anions of 1,2-DNE are stabilized by the metal cation, resulting in the formation of radical anion/sodium cation pairs (Na+, 1,2-DNE˙–); these species have a rather long lifetime (τ > 2 ms) in DME as well as in THF, and show three absorption bands at 330, 370 and 750 nm. In THF Iµ370= 14000 dm3 mol–1 cm–1 and Iµ750= 5000 dm3 mol–1 cm–1 were established. Cleavage of the ethano bridge of 1,2-DNE was achieved by means of steady-state as well as multi-pulse radiolysis in the presence of alkali-metal aluminium hydrides. The efficiency of this process was studied by using NaAlH4, NaAlH2(OR)2, NaAlH2Et2, NaAlEt4 and LiAlH4 in THF as well as in DME. The most efficient C—C bond cleavage was found to occur with NaAlH4 in DME. Based on all the experimental results it is concluded that the C—C bond cleavage results from the successive attack of two sodium cation/electron ion pairs (Na+, e–), forming the unstable dianions (2 Na+, 1,2-DNE2–). These decompose under scission of the ethano bridge, producing naphthylmethyl carbanionic fragments C10H7CH–2Na+ which supposedly form aluminate salts, e.g. C10H7CH2AlH–3Na+, with AlH3 generated in the scavenging processes. From these aluminate salts 1-methylnaphthalene (1-MN) is obtained through hydrolysis.

A semi-linear optimization model for resolving fast processes

A new algorithmic procedure for resolving superimposed spectra and kinetic data of transients produced in fast complex chemical processes is presented. The optimization model allows partitioning of the unknown model parameters into two groups: linear spectroscopic parameters and non-linear kinetic parameters. When solving the inverse problem, the field of iterations is confined to the kinetic parameters and so no initial information regarding spectroscopic behaviour of the transients is required and the computing time is drastically reduced, as compared with a previous method. We illustrate the optimization model for the reaction of multisite hydrogen attack on three dyes (acridine, proflavin and acridine orange) studied by pulse radiolysis. The reliability of the optimized parameters (k, Iµ) is critically examined by means of a sensitivity matrix. The optimization procedure, combined with pulse radiolysis, laser or flash photolysis, will be helpful in providing an insight into the reaction mechanisms of fast complex chemical processes.

Photolyse von Monophenylphosphat und e aq ? -Bildung in wriger Lsung@@@Photolysis of monophenyl phosphate and formation of e aq ? in aqueous solution

At photolysis (253.7 nm) of monophenylphosphate (10−3m) in O2-free neutral aqueous solution were determined: orthophosphate (Φ=0.006), phenol (Φ=0.0029), besides of small amounts of phosphorous acid, benzene, 2.2′-dihydroxybiphenyl and traces of 2.4′- and 4.4′-dihydroxybiphenyl. The yield of the main products is smaller at pH 2 and 12. Polymers were formed at u.v.-doses >2·1019hv/ml. The electron yield determined by means of N2O increases from Φ (N2)= Φ(eaq−)=0.012 to 0.019 changing the ester concentration from 0.001 to 0.1m. Φ (N2)-value rises by addition of methanol or increasing pH. As electron ejecting state an excited complex is postulated. The effective ionization potential of phenylphosphate in aqueous solution is ≦4.9 e.v.

Photochemische Untersuchungen an vicinal-substituierten tertiären Alkylaziden

The photochemical behaviour of several of the title class of compounds was studied, and the results correlated with the various views concerning the mechanism of alkyl azide photolysis. The results of photolysis oft-butyl azide differ from those described in the literature.ZusammenfassungDas photochemische Verhalten einiger Titelverbindungen wird untersucht. Die Ergebnisse werden mit den verschiedenen mechanistischen Anschauungen über die Photolyse von Alkylaziden korreliert. Die Photolyse vont-Butylazid liefert andere Ergebnisse, als in der Literatur beschrieben.

Radiation-induced C—C bond cleavage in 1,2-diarylethanes as model compounds of coal. Part 2.—Pulse and steady-state radiolysis of 1,2-di(pyren-1-yl)ethane in tetrahydrofuran, dimethoxyethane and toluene in the presence of sodium dihydridobis(2-methoxyethoxy)aluminate

1,2-Di(pyren-1-yl)ethane (1,2-DPE) has been used as a model for coal to study the C—C bond cleavage of the ethano linkage in the radiolysis of solutions containing NaAlH2(OCH2CH2OCH3)2[NaAlH2(OR)2]. Transient species were investigated by pulse radiolysis of solutions of 1,2-DPE, 1-methylpyrene (1-MP) and pyrene (P) in THF, DME and toluene in the absence and the presence of NaAlH2(OR)2. In the presence of the latter stabilized and long-lived radical anion/sodium cation pairs of 1,2-DPE, 1-MP and P were generated even in the non-polar solvent toluene. The reaction mechanisms differ substantially for the ether solvents (THF or DME) and solutions in toluene. In the case of the ether solvents (SH) NaAlH2(OR)2 acts as a scavenger for solvent radical cations SH˙+ and solvent cations SH(H+) generated through ionization. This produces stabilized sodium cation/electron pairs (Na+, e–s) which reduce the aromatic substrates to their radical anion/sodium cation pairs. The prevailing species generated in the radiolysis of solutions in toluene are electronically excited molecules of the solvent and the substrate from which the excited triplet molecules are preferentially reduced to radical anions by NaAlH2(OR)2 in an electron-transfer process. Steady-state radiolysis (60Co γ-rays) of solutions of 1,2-DPE in THF, DME or toluene containing NaAlH2(OR)2 resulted in the C—C bond cleavage of the ethano linkage. This is attributed to the unstable dianion (1,2-DPE2–, 2Na+) formed in two successive reductions via(1,2-DPE˙–, Na+). UV–VIS spectroscopy and product analysis showed that the radiation-induced reduction of 1,2-DPE, 1-MP and P requires lower doses in THF and DME than in toluene. However, reactions of (1,2-DPE˙–, Na+) with THF and DME to form substrate–solvent addition products limit C—C bond cleavage (16% in THF and 32% in DME). The inertness of toluene towards such side reactions makes the radiation-induced cleavage process of 1,2-DPE in this solvent (despite of the higher dose required) much more efficient than in THF and DME, yielding after hydrolysis up to 52% 1-MP. Radiation-induced reduction of polycyclic arenes in the NaAlH2(OR)2–toluene system is very useful for investigating the radical anions of these arenes by UV–VIS and EPR spectroscopy, since essentially no other interfering species are formed.

Radiation-Induced C -C Bond Cleavage in 1,2-Diarylethanes as Model Compounds of Coal, Part 3. Pulse and Steady-State Radiolysis of 1,2-Di(9-anthryl)ethane in Organic Solvents

1,2-Di(9-anthryl)ethane (1,2-DAE) was used as a model for coal to study the C -C bond cleavage of the ethano linkage in the radiolysis of solutions containing NaAlH2(OCH2CH2OCH3)2 [NaAlH2(OR)2]. Transient species were investigated by pulse radiolysis of solutions of 1,2-DAE in THF, DME and toluene in the absence and the presence of NaAlH2(OR)2. In the presence of NaAlH2(OR)2 stabilized, long-lived radical anion/sodium cation pairs of 1,2-DAE were generated even in the non-polar solvent toluene. The reaction mechanisms differ substantially for solutions in the ether solvents (THF or DME) and for solutions in toluene. Steady-state radiolysis (60Co γ-rays) of solutions of 1,2-DAE in toluene containing NaAlH2(OR)2 resulted in the C -C bond cleavage of the ethano linkage. This is attributed to the unstable dianion (1,2-DAE2-, 2Na+) formed in two successive radiation- induced reductions via (1,2-DAE∙- , Na+). The resulting (9-anthryl)methyl carbanionic fragments C14H9CH2-, Na+ react with AlH(OR)2 generated in the process, to form the aluminate salts [C14H9CH2AlH(OR)2-, Na+]. From the aluminate salts, 9-methylanthracene (9- MA) was obtained by hydrolysis in yields up to 65 wt.%.