Aqueous solutions of, radiolysis

The radiolysis of dilute aqueous solutions can be summed up by the equation (3-5)  

Thus a mixture of strong single electron oxidizing- and reducing-agents is formed. However the hydrated electrons can be transformed into hydroxyl radicals via (7)  

In pulse radiolysis experiments these radicals are formed by a short pulse, 10-12-10-6 s depending on the experimental set up, in concentrations enabling their physical observation. The linear electron accelerator of the Hebrew University of Jerusalem, which is used, forms up to 

2 x 10 M of radicals within 1.5 x 10 s. The reactions of the radicals thus formed, or their reaction products, can be followed by a variety of physical techniques including spectrophotomety (this technique is used most commonly), EPR, electrical conductivity, polarography, resonance Raman, NMR etc. (3-5). The primary radicals formed can be transformed via the addition of different solutes into a variety of secondary inorganic radicals (e.g., 02 H02 0 s C02 CO s CN NH2 NO N02 N03 NCO POrf POf HS RSSR S02 SOr SOU SOU  

The organic radicals are produced essentially by one of the following methods Aliphatic carbon-centered radicals are formed mainly from saturated aliphatic compounds via hydrogen atom abstraction by OH and H radicals ( H radicals react with solutes to produce the same radicals as OH radicals, but the rate constants are usually considerably smaller (7))  

In pulse radiolysis experiments these radicals are formed by a short pulse, s depending on the experimental set up, in concentra- 

These reactions are fast for a-hydrogens to -OH, OR, or -NH2 substituents and considerably slower for a-hydrogens to -CO2 and NHJ substituents (7). A small part of the primary radicals react with hydrogens at the p-position. OH/ H radicals react very fast with aliphatic unsaturated compounds and aromatic compounds via addition to a double bond  

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Meissner and coworkers36 studied the pulse radiolysis of aqueous solutions of dimethyl sulfoxide. It was found that hydrated electrons react with DMSO with a rate constant of... 

In the case of diaryl sulfoxides the formation of both the aryl radical and the hydroxycyclohexadienyl radical was observed optically. Veltwisch and coworkers45 studied also the reaction of OH radicals from radiolysis of aqueous solutions of mixed (alkyl phenyl) sulfoxides (PhSOR). They found the formation of both alkylsulfinic and phenylsulfinic acids. 

Nelson54 studied the products of radiolysis of aqueous solution by variable-field CIDNP pulse radiolysis. On the basis of the chemical shifts the following products were identified methyl methanesulfinate, methanol, l,2-bis(methylsulfinylethane) [CH3S(0)CH2CH2S(0)CH3], dimethyl sulfone, dimethyl sulfide, methane and ethane. The high field polarization was used to study the mechanism of formation of polarized products. 

Nishimura and coworkers57-59 studied the y-radiolysis of aqueous solutions of sulfoxide amino acids. Sulfoxide amino acids are the precursors of the flavors of onions (S-propyl-L-cysteine sulfoxide, S-methyl-L-cysteine sulfoxide and S-(l-propenyl)-L-cysteine sulfoxide) and garlic (S-allyl-L-cysteine sulfoxide). In studies on sprout inhibition of onion by /-irradiation it was found that the characteristic flavor of onions became milder. In the y-radiolysis of an aqueous solution of S-propyl-L-cysteine sulfoxide (PCSO)57,58 they identified as the main products alanine, cysteic acid, dipropyl disulfide and dipropyl sulfide. In the radiolysis of S-allyl-L-cysteine sulfoxide (ACSO) they found that the main products are S-allyl-L-cysteine, cysteic acid, cystine, allyl alcohol, propyl allyl sulfide and diallyl sulfide. The mechanisms of formation of the products were partly elucidated by the study of the radiolysis in the presence of N20 and Br- as eaq - and OH radicals scavengers, respectively. 

In contrast with irradiation of ACSO and PCSO, where volatile products were formed (sulfides, disulfides and alcohols), no volatile products were formed in the radiolysis of aqueous solutions of S-(cis- l-propenyl)-L-cysteine. Here the authors found that reactions of OH" radicals are responsible for the formation of propyl-1-propenyl sulfides (cis and trans). 

Sumiyoshi and coworkers studied the radiolysis of aqueous solution of methyl methylthiomethyl sulfoxide [ H3S(0) H2S H3 MTMSO] at various pH by pulse radiolysis. They found that the reaction of e with MTMSO (in the presence of 1M t-butyl alcohol to scavenge OH" radicals) leads to formation of a transient with a broad absorption band of = 375 nm. The absorbance at 375 nm as a function of pH are of S shape, indicating an equilibrium due to reaction with H. Similar to the finding in dimethyl sulfoxide they suggested the scheme. 

FIGURE 7.2 Relative molecular yields of H2 and H202 in the radiolysis of aqueous solutions (Schwarz, 1955). Full curve is theoretical for solute concentrations (X axis) in different experiments multiplied by suitable normalization factors. Notice that even after normalization experimental points remain considerably higher than theoretical at high concentrations (x > 0.1). From Schwarz (1955), with permission of Am. Chem. Soc. ... 

Michael and Hart10 found that the reaction of OH radicals (formed by pulse radiolysis of aqueous solutions saturated with N20) with 1,3- and 1,4-cyclohexadienes leads to formation of an intermediate absorbing at 310 nm. In the case of 1,4-cyclohexadiene, another band at A, < 240 nm was also found. In this system there are both H atoms and OH radicals, however the yield of the OH radicals is 10 times higher than that of the H- atoms. Michael and Hart10 assumed that the band at 310 nm is due to CeWi ... 

The results of y-radiolysis of aqueous solutions of thymine in the presence of MNP exemplify the unusual, but by no means unprecedented, occurrence of accumulation of spin adduct after reaction has ceased . Thus, when irradiation is discontinued, and the sample is examined spectroscopically, the signal attributed to the MNP adduct of [38] slowly increases in intensity (Joshi et al., 1978). The explanation advanced in this instance was that the spin adduct itself scavenges radicals very efficiently during radiolysis, giving a diamagnetic product which is thermally unstable, and which slowly cleaves,... 

Several peroxidative reactions initiated by OH radical that may be generated by either y- and X-radiolysis of aqueous solutions or by transition metal-catalyzed reduction of H2O2 have been identified in free amino acids and short peptides. In this respect we may distinguish oxidizing reactions that involve the polypeptide backbone on the one hand... 

Scholes, G. Willson, R.L. Ebert, M. Pulse radiolysis of aqueous solutions of deoxyribonu-cleotides and of DNA reaction with hydroxyl radicals. Chem. Commun. 1969, 17. 

Pikaev, A.K. Shilov, V.P. Spitsyn, V.I. Radiolysis of Aqueous Solutions of Lanthanides and Actinides Nauka Moscow, 1983. in Russian. 

Re-examination of the radiolysis of aqueous solutions of alanine (absence of oxygen) shows that electrons react rapidly with the cationic form, less rapidly with the zwitterion, and much less rapidly with the anionic form. These conclusions have been confirmed by pulse radiolysis. Rate constants for amino acids, peptides, proteins, and numerous other substances have been obtained. Critical evaluation of these and correlation with molecular properties is now well under way. In living systems the reactions of the hydrated electron vary with the part of the cell concerned, with the developmental stage of the cell, and possibly with the nature of any experimentally added substances. 

Draganic, Z.D., Negro-Mendoza, A., Sehested, K., Vujosevic, S.I., Navarro-Gonzales, R., Albarran-Sanchez, M.G., and Draganic, I.G., Radiolysis of aqueous solutions of ammonium bicarbonate over a large dose range, Radiat. Phys. Chem., 38(3), 317-321, 1991. 

Schuler MA, Bhatia K, Schuler RH (1974) Radiation chemical studies on systems related to ascorbic acid. The radiolysis of aqueous solutions of a-bromotetronic acid. J Phys Chem 78 1063-1074 Schuler RH, Hartzell AL, Behar B (1981) Track effects in radiation chemistry. Concentration dependence for the scavenging of OH by ferrocyanide in NqO-saturated solutions. J Phys Chem... 

Barker GC, Fowles P (1970) Pulse radiolytic induced transient electrical conductance in liquid solutions, part 3. Radiolysis of aqueous solutions of some inorganic systems. Trans Faraday Soc 66 1661-1669... 

Thomas JK (1967) Pulse radiolysis of aqueous solutions of methyl iodide and methyl bromide. The reactions of iodine atoms and methyl radicals in water. J Phys Chem 71 1919-1925 Tsang W, Hampson RF (1986) Chemical kinetic data base for combustion chemistry, part I. Methane and related compounds. J Phys Chem Ref Data 15 1086-1279 UlanskiP, von Sonntag C (1999) The OFI-radical-induced chain reactions of methanol with hydrogen peroxide and with peroxodisulfate. J Chem Soc Perkin Trans 2 165-168 Ulanski P, Bothe E, Hildenbrand K, von Sonntag C, Rosiak JM (1997) The influence of repulsive electrostatic forces on the lifetimes of polyfacrylic acid) radicals in aqueous solution. Nukleonika 42 425-436... 

Isildar M, Schuchmann MN, Schulte-Frohlinde D, von Sonntag C (1982) Oxygen uptake in the radiolysis of aqueous solutions of nucleic acids and their constituents. Int J Radiat Biol 41 525-533 Jacobsen F, Flolcman J, Sehested K (1997) Manganese(ll)-superoxide complex in aqueous solution. J Phys Chem A 101 1324-1328... 

Table 10.28. Gvalues(unit 10 7molJ ) of inorganic phosphate release in they-radiolysis of aqueous solutions of some 3 - and 5 -monoucleotides (Raleigh et al. 1974). Data from...

Bansal KM, Patterson LK, Schuler RH (1972) Production of halide ion in the radiolysis of aqueous solutions of the 5-halouracils. J Phys Chem 76 2386-2392 Barnes JP, Bernhard WA (1994) One-electron-reduced cytosine in acidic glasses conformational states before and after proton transfer. J Phys Chem 98 887-893 Barvian MR, Greenberg MM (1992) Independent generation of the major adduct of hydroxyl radical and thymidine. Examination of intramolecular hydrogen atom transfer in competition with thiol trapping.Tetrahedron Lett 33 6057-6060... 

Grachev SA, Kropachev EV, Litvyakova Gl (1983) Synthesis of 5-S-cysteamine-6-hydroxythymine and evidence of its formation in the y radiolysis of aqueous solutions of thymine and cyste-amine. Bull Acad Sci USSR, Chem Ser (Engl Trans) 1595-1600 Grachev SA, Kropachev EV, Litvyakova Gl (1986) Addition of cysteamine to thymine and thymidine monophosphate initiated by y-irradiation. Bull Acad Sci USSR, Chem Ser (Engl Trans) 10 2178-2184... 

Flayon E, Simic M (1973) Addition of hydroxyl radicals to pyrimidine bases and electron transfer reactions of intermediates to quinones. J Am Chem Soc 95 1029-1035 Flaysom FIR, Phillips JM, Scholes G (1972) Formation of carbonium ions from dihydropyrimidyl radicals in they-radiolysis of aqueous solutions of dihydropyrimidines. J Chem Soc Chem Commun 1082-1083... 

Flaysom FIR, Phillips JM, Richards JT, Scholes G, Willson RL (1975) Pulse radiolysis of aqueous solutions of dihydropyrimidines the role of carbonium ions. In Adams GE, Fielden EM, Michael BD (eds) Fast processes in radiation chemistry and biology. Wiley, London, pp 241-246 Flazra DK, Steenken S (1983) Pattern of OFI radical addition to cytosine and 1-, 3-, 5- and 6-substi-tuted cytosines. Electron transfer and dehydration reactions of the OFI adducts. J Am Chem Soc 105 4380-4386... 

IV. Radiolysis of aqueous solutions of lactose and cellobiose. J Gen Chem USSR 35 1195-1197 Kochetkov NK, Kudryashov LI, Yarovaya SMB, Chizhov OS (1968) Radiation chemistry of the carbohydrates. IX. Formation of deoxysugars in the radiolysis of aqueous solutions of cellobiose and lactose. J Gen Chem USSR 38 2297-2303... 

Bibler, N.E. 1972. Gamma and alpha radiolysis of aqueous solutions of diethylene tri-aminepentaacetic acid, J. Inorg. Nucl. Chem. 34 1417-1425. 

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