Z. B. Alfassi

Bio: Z. B. Alfassi is an academic researcher from National Institute of Standards and Technology. The author has contributed to research in topics: Radical & Reaction rate constant. The author has an hindex of 17, co-authored 30 publications receiving 780 citations. Previous affiliations of Z. B. Alfassi include Royal Institution & Duquesne University.

Electrospray ionization mass spectrometry of ionic liquids and determination of their solubility in water

Abstract: Electrospray ionization mass spectrometry is used to detect both the cations (C+) and the anions (A−) of ionic liquids (CA). In this study, the ionic liquids are diluted with aqueous methanol before injection. In addition to the main peaks of the parent ions, fragmentation products are observed upon increasing the cone voltage, whereas aggregates of the parent ion with one or more ionic liquid molecules (e.g., C(CA)n +, A(CA)n −) are observed upon decreasing the cone voltage. The ions of several ionic liquids in a mixture are also detected and the ratios of their concentrations estimated. A method is developed to determine quantitatively the concentration of an ionic liquid in solution by using the cation and anion of another ionic liquid as internal standards. By using this method, the solubilities in water at room temperature (22±1 °C) of three typical hydrophobic ionic liquids have been determined: 0.70±0.08 g L−1 for methyltributylammonium bis(trifluoromethylsulfonyl)imide (MeBu3NNTf2), 6.0±0.5 g L−1 for butylmethylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BuMePyrNTf2), and 18.6±0.7 g L−1 for 1-butyl-3-methylimidazolium hexafluorophosphate (BMIPF6).

Temperature dependence of the rate constants for reaction of inorganic radicals with organic reductants

Abstract: Rate constants for the reactions of several inorganic radicals with several organic reductants in aqueous solutions have been measured by pulse radiolysis as a function of temperature, generally between 5 and 75{degree}C. The reactions studied were those of the radicals N{sub 3}{sm bullet}, NO{sub 2}{sm bullet}, Br{sub 2}{sup {sm bullet}{minus}}, I{sub 2}{sup {sm bullet}{minus}}, and (SCN){sub 2}{sup {sm bullet}{minus}} reacting with several phenols and ascorbate. Rate constants were also measured for the reactions of Cl{sub 2}{sup {sm bullet}{minus}} with phenol and of ClO{sub 2}{sm bullet} with p-methoxyphenolate. The rate constants measured were in the range of 10{sup 5} to nearly 10{sup 10} M{sup {minus}1} s{sup {minus}1} and the calculated Arrhenius activation energies ranged from 7 to 41 kJ mol{sup {minus}1}. The preexponential factors also varied considerably, with log A ranging from 9.2 to 13.9. The temperature dependences of these reactions do not seem to relate to their exothermicities. Variations in rate constants appear to be more strongly dependent on changes in preexponential factors rather than on changes in activation energy.

Substituent effects on rates of one-electron oxidation of phenols by the radicals chlorine dioxide, nitrogen dioxide, and trioxosulfate(1-)

Abstract: Rate constants for the reactions of ClO/sub 2/, NO/sub 2/, and SO/sub 3//sup -/ radicals with several substituted phenoxide ions have been measured by pulse radiolysis. They vary from the immeasurably slow ( 10/sup 9/ M/sup -1/s/sup -1/) and depend on the redox potentials of the phenoxide ions and the inorganic radicals. With the weak oxidant SO/sub 3//sup -/ reverse reactions were observed in certain cases; i.e., the phenoxyl radical oxidizes sulfite ions. An attempt is made to correlate the rate constants with Hammett's substituent constants and the results are compared with those obtained previously for the reactions of various inorganic radicals with phenols and phenoxide ions.

Reduction Potential of the tert-Butylperoxyl Radical in Aqueous Solutions

Abstract: Rate constants for oxidation of tert-butyl hydroperoxide anion (t-BuO2-) by several oxidants were determined by pulse radiolysis. Rapid oxidation was found with N3• (4.4 × 108 L mol-1 s-1) and •O- ...

Superoxide Ion: Generation and Chemical Implications

Abstract: Superoxide ion (O2•–) is of great significance as a radical species implicated in diverse chemical and biological systems. However, the chemistry knowledge of O2•– is rather scarce. In addition, numerous studies on O2•– were conducted within the latter half of the 20th century. Therefore, the current advancement in technology and instrumentation will certainly provide better insights into mechanisms and products of O2•– reactions and thus will result in new findings. This review emphasizes the state-of-the-art research on O2•– so as to enable researchers to venture into future research. It comprises the main characteristics of O2•– followed by generation methods. The reaction types of O2•– are reviewed, and its potential applications including the destruction of hazardous chemicals, synthesis of organic compounds, and many other applications are highlighted. The O2•– environmental chemistry is also discussed. The detection methods of O2•– are categorized and elaborated. Special attention is given to the f...

Thermochemistry of Proton-Coupled Electron Transfer Reagents and its Implications

Abstract: Many, if not most, redox reactions are coupled to proton transfers. This includes most common sources of chemical potential energy, from the bioenergetic processes that power cells to the fossil fuel combustion that powers cars. These proton-coupled electron transfer or PCET processes may involve multiple electrons and multiple protons, as in the 4 e–, 4 H+ reduction of dioxygen (O2) to water (eq 1), or can involve one electron and one proton such as the formation of tyrosyl radicals from tyrosine residues (TyrOH) in enzymatic catalytic cycles (eq 2). In addition, many multi-electron, multi-proton processes proceed in one-electron and one-proton steps. Organic reactions that proceed in one-electron steps involve radical intermediates, which play critical roles in a wide range of chemical, biological, and industrial processes. This broad and diverse class of PCET reactions are central to a great many chemical and biochemical processes, from biological catalysis and energy transduction, to bulk industrial chemical processes, to new approaches to solar energy conversion. PCET is therefore of broad and increasing interest, as illustrated by this issue and a number of other recent reviews.

Biological Activity of Ionic Liquids and Their Application in Pharmaceutics and Medicine.

Abstract: Ionic liquids are remarkable chemical compounds, which find applications in many areas of modern science. Because of their highly tunable nature and exceptional properties, ionic liquids have become essential players in the fields of synthesis and catalysis, extraction, electrochemistry, analytics, biotechnology, etc. Apart from physical and chemical features of ionic liquids, their high biological activity has been attracting significant attention from biochemists, ecologists, and medical scientists. This Review is dedicated to biological activities of ionic liquids, with a special emphasis on their potential employment in pharmaceutics and medicine. The accumulated data on the biological activity of ionic liquids, including their antimicrobial and cytotoxic properties, are discussed in view of possible applications in drug synthesis and drug delivery systems. Dedicated attention is given to a novel active pharmaceutical ingredient-ionic liquid (API-IL) concept, which suggests using traditional drugs in ...

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.