Zeev B. Alfassi

Bio: Zeev B. Alfassi is an academic researcher from Ben-Gurion University of the Negev. The author has contributed to research in topics: Radical & Neutron temperature. The author has an hindex of 24, co-authored 240 publications receiving 2546 citations. Previous affiliations of Zeev B. Alfassi include National Institute of Standards and Technology & SRI International.

Reaction of azide radicals with aromatic compounds. Azide as a selective oxidant

Abstract: In basic aqueous solution the N/sub 3/.radical is found to oxidize aromatic systems such as aniline and phenoxide ions and their derivatives at rate constants of (3-5) x 10/sup 9/ M/sup -1/s/sup -1/. In contrast to the reactions of OH radicals, where addition to the ring dominates, oxidation appears to be directly by electron transfer. Compounds such as benzene, toluene, and anisole are not observably oxidized by N/sub 3/. Phenol, in its neutral form in acidic solution, is oxidized several orders of magnitude more slowly than is the phenoxide anion. The rate of oxidation of phenols is strongly dependent on substitution, with activating groups increasing the rate in the order para > ortho > meta. N/sub 3/. can be readily prepared radiolytically by OH oxidation of azide. Being a neutral radical which does not absorb significantly above 300 nm it is very promising as a selective oxidant for pulse radiolysis studies. 27 references, 6 figures, 3 tables.

Reactivities of chlorine atoms and peroxyl radicals formed in the radiolysis of dichloromethane

Abstract: Radiolysis of dichloromethane (DCM) leads to formation of primary oxidizing radicals and carbon-centered radicals. The latter react with oxygen to yield peroxyl radicals. The yields and chemical behavior of these intermediates were studied by pulse radiolysis of DCM solutions containing various solutes: phenols, anilines, dimethoxybenzene, hexamethylbenzene, cyclohexene, dimethyl sulfoxide, and zinc tetratolylporphyrin. At low concentrations, some of these solutes were found to be oxidized by two peroxyl radicals, CH{sub 2}ClO{sub 2}{sup {sm bullet}} and CHCl{sub 2}O{sub 2}{sup {sm bullet}}, with different rate constants. At higher concentrations, the solutes react also with the primary radicals: Cl atoms and the radical cations CH{sub 2}Cl{sub 2}{sup +{sm bullet}}, with diffusion-controlled rate constants. The rates of these reactions were determined by competition kinetics because of the very short lifetimes of the species. Cl atoms were found to have a half-life of about 5 ns in DCM, reacting predominantly with the solvent by hydrogen abstraction. The radical cations decay within a fraction of a nanosecond. The total yield of these primary radicals was determined to be G = 3.6 and appears to be divided about equally between Cl and the radical cations. The total yield of oxidation, by the primary and the peroxyl radicals, wasmore » found to be G = 7.5. Cl atoms were found to be very reactive in electron transfer as well as addition and hydrogen abstraction reactions.« less

General aspects of the chemistry of radicals

Abstract: EPR Spectroscopy: The Basics (G. Buettner). Measurements of Rate Constants for Radical Reactions in the Gas Phase (T. Wallington & O. Nielsen). Measurements of Rate Constants for Radical Reactions in the Liquid Phase (G. Buxton). Models for Abstraction and Addition Reactions of Free Radicals (E. Denisov). Combination and Disproportionation of Free Radicals (Z. Alfassi). Radical Ions: Generation, Characterization and Reactions (J. Gebicki & A. Marcinek). Free Radical Polymerization and Chain Reactions (O. Ito). Reactions of Free Radicals in Supercritical Fluids (J. Chateauneuf). Numerical Simulations of Free Radical Dynamics (E. Bittner). Thermochemistry of Organic Free Radicals (N. Cohen). Measurement of Reduction Potentials of Inorganic Radicals in Aqueous Solution (D. Stanbury). Measurement and Estimation of Redox Potentials of Organic Radicals (K. Daasbjerg, et al.). Correlations Between Rate Parameters and Molecular Properties (G. Marston, et al.). Empirical Correlational Solvent Effect on Free Radical Chemistry (Z. Alfassi). Organic Synthesis by Radical Reactions (C. Chatgilialoglu & P. Renaud). Index.

Chemical analysis by nuclear methods

Abstract: Basic Background in Nuclear Physics and Chemistry Elemental Analysis with Neutron Sources Elemental Analysis with Particle Accelerators Use of Radioactive (Alpha, Beta and Gamma) Sources Use of Radio Tracers.

The redox potential of the azide/azidyl couple

Abstract: Pulse radiolysis experiments were carried out with neutral aqueous solutions containing azide with iodide, bromide, or thiocyanate to examine possible one-electron transfer rates and equilibria involving the N/sub 3//N/sub 3//sup -/ couple. The N/sub 3/ radical was found to oxidize I/sup -/ with a rate constant of 4.5 x 10/sup 8/ M/sup -1/ s/sup -1/. No reaction was observed between I/sub 2//sup -/ and N/sub 3//sup -/. With Br/sup -/, however, the system reached equilibrium, Br/sub 2//sup -/ + N/sub 3//sup -/ in equilibrium 2Br/sup -/ + N/sub 3/, with k/sub f/ = 4.0 x 10/sup 8/ M/sup -1/ s/sup -1/ and k/sub r/ = 7.3 x 10/sup 3/ M/sup -2/ s/sup -1/. From the equilibrium constant K = 5.5 x 10/sup 4/ M and the redox potential E(Br/sub 2//sup -//2Br/sup -/) = 1.63 V the authors calculate E(N/sub 3//N/sub 3//sup -/) = 1.35 +/- 0.02 V vs. NHE. Cyclic voltammetry experiments with N/sub 3//sup -/ showed a single peak on the anodic scan and no peak on the cathodic scan due to the rapid decay of the N/sub 3/ radicals. From the dependence of peak potential on scan rate they derive E/sub 1/2/ for the N/sub 3//N/sub 3//sup -/more » couple, 1.32 +/- 0.03 V vs. NHE.« less

Heavy metals in soils : trace metals and metalloids in soils and their bioavailability

Abstract: Preface.- Contributors.- List of Abbreviations.- Section 1: Basic Principles: Introduction.-Sources of Heavy Metals and Metalloids in Soils.- Chemistry of Heavy Metals and Metalloids in Soils.- Methods for the Determination of Heavy Metals and Metalloids in Soils.- Effects of Heavy Metals and Metalloids on Soil Organisms.- Soil-Plant Relationships of Heavy Metals and Metalloids.- Heavy Metals and Metalloids as Micronutrients for Plants and Animals.-Critical Loads of Heavy Metals for Soils.- Section 2: Key Heavy Metals And Metalloids: Arsenic.- Cadmium.- Chromium and Nickel.- Cobalt and Manganese.- Copper.-Lead.- Mercury.- Selenium.- Zinc.- Section 3: Other Heavy Metals And Metalloids Of Potential Environmental Significance: Antimony.- Barium.- Gold.- Molybdenum.- Silver.- Thallium.- Tin.- Tungsten.- Uranium.- Vanadium.- Glossary of Specialized Terms.- Index.

Flavonoids as antioxidants: determination of radical-scavenging efficiencies.

Abstract: Publisher Summary This chapter discusses the radical-scavenging efficiencies of flavonoids as antioxidants To test whether a certain substance acts as radical scavenger, the clearest evidence comes from the determination of reaction rate constants with a set of different specifically produced radicals In the tests discussed in the chapter, hydroxyl, azide, superoxide, linoleic acid peroxyl, tert-butoxyl, and sulfite radicals are used The spectral observation of radical reactions with flavonoids is assisted by the strong absorption characteristics of both the parent compounds and their respective aroxyl radicals Owing to the low solubility of flavonoids, conditions for pseudo-first order reactions with radical species can rarely be achieved for flavonoid aglycones Therefore, kinetic modeling calculations are employed The radical chemistry of flavonoids not only is of interest from a kinetic or mechanistic point of view but also offers considerable insight into structural relationships of highly evolved plant components First, the consistently high rate constants for attack by different types of radicals demonstrate the effective radicals scavenging capabilities of most flavonoids Second, owing to extensive electron delocalization as a prerequisite for radical stabilization, multiple mesomeric structures exist for aroxyl radical species of flavonoids

Air and water stable ionic liquids in physical chemistry

Abstract: Ionic liquids are defined today as liquids which solely consist of cations and anions and which by definition must have a melting point of 100 °C or below. Originating from electrochemistry in AlCl3 based liquids an enormous progress was made during the recent 10 years to synthesize ionic liquids that can be handled under ambient conditions, and today about 300 ionic liquids are already commercially available. Whereas the main interest is still focussed on organic and technical chemistry, various aspects of physical chemistry in ionic liquids are discussed now in literature. In this review article we give a short overview on physicochemical aspects of ionic liquids, such as physical properties of ionic liquids, nanoparticles, nanotubes, batteries, spectroscopy, thermodynamics and catalysis of/in ionic liquids. The focus is set on air and water stable ionic liquids as they will presumably dominate various fields of chemistry in future.