Ozonation of drinking water: part I. Oxidation kinetics and product formation.

Generation and propagation of radical reactions on proteins.

Chemical Science Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352; Department of Chemistry, ShelbyHall, University of Alabama, Box 870336, Tuscaloosa, Alabama 35487-0336; Notre Dame Radiation Laboratory, University of Notre Dame,Notre Dame, Indiana 46556; Department of Chemistry, Yale University, P.O. Box 208107, New Haven, Connecticut 0520-8107; Argonne NationalLaboratory, 9700 South Cass Avenue, Argonne, Illinois 60439; Department of Computer Science and Department of Physics, 2710 University Drive,Washington State University, Richland, Washington 99352-1671; Lawrence Berkeley National Laboratory, 1 Cyclotron Road Mailstop 1-0472,Berkeley, California 94720; Department of Chemistry and Biochemistry, University of Texas at Austin, 1 University Station A5300,Austin, Texas 78712; Office of Basic Energy Sciences, U.S. Department of Energy, SC-141/Germantown Building, 1000 Independence Avenue,S.W., Washington, D.C. 20585-1290; Department of Physics and Engineering Physics, Stevens Institute of Technology, Castle Point on Hudson,Hoboken, New Jersey 07030; Department of Chemistry, Johns Hopkins University, 34th and Charles Streets, Baltimore, Maryland 21218;Department of Chemistry, University of Southern California, Los Angeles, California 90089-1062; Department of Chemistry, The Ohio StateUniversity, 100 West 18th Avenue, Columbus, Ohio 43210-1185; Department of Chemistry, Columbia University, Box 3107, Havemeyer Hall,New York, New York 10027; Department of Chemistry, University of Pittsburgh, Parkman Avenue and University Drive,Pittsburgh, Pennsylvania 15260; Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973-5000; Department of Physics andAstronomy, Rutgers, The State University of New Jersey, 136 Frelinghuysen Road, Piscataway, New Jersey 08854-8019; Department of Chemistry,516 Rowland Hall, University of California, Irvine, Irvine, California 92697-2025; Stanford Synchrotron Radiation Laboratory, Stanford LinearAccelerator Center, 2575 Sand Hill Road, Mail Stop 69, Menlo Park, California 94025; School of Chemistry and Biochemistry, Georgia Institute ofTechnology, 770 State Street, Atlanta, Georgia 30332-0400; Geology Department, University of California, Davis, One Shields Avenue,Davis, California 95616-8605; Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue,Cambridge, Massachusetts 02139-4307; Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907-2084Received July 23, 2004

http://casey.brown.edu/chemistry/research/LSWang/publications/194.pdf

Role of water in electron-initiated processes and radical chemistry: issues and scientific advances.

Methionine oxidation by reactive oxygen species: reaction mechanisms and relevance to Alzheimer's disease

This review describes the PARTRAC suite of comprehensive Monte Carlo simulation tools for calculations of track structures of a variety of ionizing radiation qualities and their biological effects. A multi-scale target model characterizes essential structures of the whole genomic DNA within human fibroblasts and lymphocytes in atomic resolution. Calculation methods and essential results are recapitulated regarding the physical, physico-chemical and chemical stage of track structure development of radiation damage induction. Recent model extension towards DNA repair processes extends the time dimension by about 12 orders of magnitude and paves the way for superior predictions of radiation risks.

Track structures, DNA targets and radiation effects in the biophysical Monte Carlo simulation code PARTRAC.

Radiation chemical methods were used to investigate the reactions of glycine anions, H2NCH2CO2- (Gly-), with •OH, (CH3)2C•OH, and •CH3 radicals. A major and most significant product from all of these processes is CO2. Pulse-radiolysis revealed that the initial step in the •OH-induced mechanism is oxidation of the amino group, producing +H2N•-CH2-CO2- and HN•-CH2-CO2- with yields of 63% and 37%, respectively. The amino radical cation, +H2N•-CH2-CO2-, suffers fast (≤100 ns) fragmentation into CO2 + •CH2NH2. The other primary radical, HN•-CH2-CO2-, can also be converted into the decarboxylating +H2N•-CH2-CO2- by reaction with proton donors such as phosphate (H2PO4-/k = 7.4 × 107 M-1 s-1, and HPO42-/k = 2.5 × 105 M-1 s-1) or the glycine zwitterion, Gly± (k = 3.9 × 105 M-1 s-1), but only on a much longer (typically μs to ms) time scale (k ≈ 4 × 105 M-1 s-1). Competitively, the HN•-CH2-CO2- transforms into a carbon-centered radical H2N-C•H-CO2- either by an intramolecular 1,2-H-atom shift (k = (1.2 ± 1.0) × 103...

Glycine Decarboxylation: The Free Radical Mechanism

The radiation chemical yield of hydrogen peroxide has been determined in the γ-radiolysis of water at neutral pH. Methanol, ethanol, and bromide have been used as OH radical scavengers in order to explore the temporal dependence of hydrogen peroxide formation at elevated temperatures. The scavenger results at all temperatures confirm that OH radicals are the sole source of hydrogen peroxide at short times in the γ-radiolysis of water. Variation in dose rate by a factor of 20 shows no influence on the yield. With increasing temperature the yield of hydrogen peroxide is found to decrease, and the microsecond radiation chemical yields at low scavenger concentrations are found to be G (H2O2) = 0.78−2.43 × 10-3 T (°C) molecules/100 eV for methanol as a scavenger, and G (H2O2) = 0.74−2.40 × 10-3 T (°C) molecules/100 eV for bromide. The scavenger concentration dependence of the yields at elevated temperatures is discussed. Assuming an activation energy of 71 kJ mol-1 the thermal decomposition reaction rate const...

Temperature Dependence of the Hydrogen Peroxide Production in the γ-Radiolysis of Water

Experimental measurements coupled with Monte Carlo track simulations have been used to examine the yields of hydrated electrons in the radiolysis of water with protons, helium ions, and carbon ions. Glycylglycine, in concentrations ranging from 10(-4) to 1 M, was employed as a scavenger and the production of the ammonium cation used as a probe of hydrated electron yields from about 2 ns to 20 mus. Monte Carlo track simulations employing diffusion-kinetic calculations of product yields are found to reproduce experimental observations satisfactorily. Model details are used to elucidate the heavy ion track physics and chemistry. Comparison of the heavy ion results with those found in gamma radiolysis shows intratrack reactions are significant on the nanosecond to microsecond time scale as the ion track relaxes, and that a constant (escape) yield is never attained on this time scale. Numerical interpolation techniques are used to obtain both track average and track segment yields for use in practical applications or comparison with other models. The model results give the first hints that initial ( approximately 5 ps) hydrated electron yields, and possibly other water decomposition products, are dependent on the type and energy of the incident radiation.

Hydrated electron yields in the heavy ion radiolysis of water.

The reaction of the amino acid anions, R2N−CR2−CO2- (R = H or methyl), with •OH radicals and H• atoms was quantified with respect to the site of attack, the respective absolute rate constants, and the yields of the primary transients generated in these processes. The method applied was pulse radiolysis with time-resolved optical detection. Specifically investigated amino acids were glycine, alanine, α-methylalanine and N,N-dimethylglycine. Absolute overall rate constants, as determined from the growth of UV absorptions and competition with carbonate, ranged from (1.7−3.6) × 109 M-1 s-1 for the reaction of •OH with the anions of these amino acids, and (0.1−1) × 108 M-1 s-1 for the corresponding reaction with the respective zwitterions. H• atoms react with amino acid anions containing Cα−H bonds with a rate constant of 1.4 × 108 M-1 s-1, whereas k < 107 M-1 s-1 was estimated for the reaction with α-methylalanine. The primary transient radicals from these reactions include aminyl radicals (RN•-CR2−CO2-), α-a...

Absolute Rate Constants and Yields of Transients from Hydroxyl Radical and H Atom Attack on Glycine and Methyl Substituted Glycine Anions

A pulse radiolysis study was carried out of the reaction rate constants and kinetic isotope effects of hydroxyl-radical-induced H/D abstraction from the most-simple α-amino acid glycine in its anionic form in water. The rate constants and yields of three predominantly formed radical products, glycyl (NH2–˙CH–CO2−), aminomethyl (NH2–˙CH2), and aminyl (˙NH–CH2–CO2−) radicals, as well as of their partially or fully deuterated analogs, were found to be of comparable magnitude. The primary, secondary, and primary/secondary H/D kinetic isotope effects on the rate constants were determined with respect to each of the three radicals. The unusual variety of products for such an elementary reaction between two small and simple species indicates a complex mechanism with several reactions taking place simultaneously. Thus, a theoretical modeling of the reaction mechanism and kinetics in the gas- and aqueous phase was performed by using the unrestricted density functional theory with the BB1K functional (employing the polarizable continuum model for the aqueous phase), unrestricted coupled cluster UCCSD(T) method, and improved canonical variational theory. Several hydrogen-bonded prereaction complexes and transition states were detected. In particular, the calculations pointed to a significant mechanistic role of the three-electron two-orbital (σ/σ* N∴O) hemibonded prereaction complexes in the aqueous phase. A good agreement with the experimental rate constants and kinetic isotope effects was achieved by downshifting the calculated reaction barriers by 3 kcal mol−1 and damping the NH(D) stretching frequency by a factor of 0.86.

A surprisingly complex aqueous chemistry of the simplest amino acid. A pulse radiolysis and theoretical study on H/D kinetic isotope effects in the reaction of glycine anions with hydroxyl radicals.

Igor Štefanić

Papers

Glycine Decarboxylation: The Free Radical Mechanism

Temperature Dependence of the Hydrogen Peroxide Production in the γ-Radiolysis of Water

Hydrated electron yields in the heavy ion radiolysis of water.

Absolute Rate Constants and Yields of Transients from Hydroxyl Radical and H Atom Attack on Glycine and Methyl Substituted Glycine Anions

A surprisingly complex aqueous chemistry of the simplest amino acid. A pulse radiolysis and theoretical study on H/D kinetic isotope effects in the reaction of glycine anions with hydroxyl radicals.