Yael Ilan

The one-electron transfer redox potentials of free radicals. I. The oxygen/superoxide system

The method of determination of Redox potentials of radicals, using the pulse radiolysis technique, is outlined. The method is based on the determination of equilibrium constants of electron transfer reactions between the radicals and appropriate acceptors. The limitations of this technique are discussed. The redox potentials of several quinones-semiquinones are calculated, as well as the standard redox potential of the peroxy radical. EO2/O2=-0.33 V and the redox oxidation properties of the peroxy radical in various systems and pH are discussed. The value determined for the redox potentials of O2/O2 is higher by more than 0.2 V than earlier estimates, which has important implications on the possible role of O2 in biological processes of O2 fixation.

ON THE GENERATION OF THE HYDROXYLATION AGENT FROM SUPEROXIDE RADICAL. CAN THE HABER–WEISS REACTION BE THE SOURCE OF OH RADICALS?

Abstract— In many biological systems, the role of O2‐ in hydroxylation and toxic processes was assumed to be due to the formation of OH radicals. The Haber‐Weiss reaction (Haber and Weiss, 1934)—(H2O2+ O2‐→ OH + OH‐+ O2) was suggested as the origin of this activity.

Radiation-Induced Damage in T4 Bacteriophage: The Effect of Superoxide Radicals and Molecular Oxygen

The sensitivity of T4 bacteriophage toward ..gamma.. irradiation has been studied in phosphate buffer suspensions. The spectrum of the water radicals was controlled by a careful choice of the appropriate saturating gas and the addition of radical scavengers. Thus, it was possible to distinguish between the effects of molecular oxygen and the superoxide radicals formed through its reactions. About 90% of the damage was caused by the water radicals formed in the bulk suspensions. These probably affected the phage proteins; only the remainder of the damage involved the viral DNA. The oxygen enhancement ratio observed was not connected in any way with the formation of the superoxide radicals. The results confirmed that the OH radicals are the reactive species, while e/sub aq//sup -/ as well as the superoxide radical do not contribute to the radiodamage.

On some fundamental reactions in radiation chemistry: Nanosecond pulse radiolysis

Abstract Several fundamental reactions have been investigated using nanosecond pulse radiolysis. The following reaction rate constants were measured: k ( N2O − →N2+O − )>10 8 s −1 , k ( H + +O2 − )= (5 ± 1) × 10 10 dm 3 mol −1 s −1 . k ( HO2→H + +O2 − ) = (7 ± 2) × 10 5 s −1 , k ( CO2 − +O2 ) = (4.2 ± 0.4) × 10 9 dm 3 mol −1 s −1 .

Reactions of the ferri-ferrocytochrome-c system with superoxide/oxygen and CO2−/CO2 studied by fast pulse radiolysis

The reduction of ferricytochrome c by O2- and CO2- was studied in the pH range 6.6-9.2 and Arrhenius as well as Eyring parameters were derived from the rate constants and their temperature dependence. Ionic effects on the rate indicate that the redox process proceeds through a multiply-positively charged interaction site on cytochrome c. It is shown that the reaction with O2- (and correspondingly with O2 of ferrocytochrome c) is by a factor of approx. 10(3) slower than warranted by factors such as redox potential. Evidence is adduced to support the view that this slowness is connected with the role of water in the interaction between O2-/O2 and ferri-ferrocytochrome c in the positively charged interaction site on cytochrome c in which water molecules are specifically involved in maintaining the local structure of cytochrome c and participate in the process of electron equivalent transfer.

Superoxide dismuting activity of an iron porphyrin

Abstract The efficiency of tetrakis-(4-N-methylpyridyl)porphineiron(III) as a superoxide dismuting catalyst has been determined using a pulse radiolysis technique.

Do copper ions influence the reduction of ferricytochrome C by O−2?

Recently, it was suggested that the measured rate of reduction of ferricytochrome C by O-2 below pH 8, was too high in the presence of high concentrations of formate (Koppenol, W.H., Van Buuren, K.J.H., Butler J. and Braams, R. (1976) Biochim. Biophys. Acta 449, 157-168). The high values were attributed to the presence of impurities of copper, which compete for O-2. This assumption is consistent with either a decrease in the reduction yield of ferricytochrome C in the presence of copper, or with a very fast reaction of Cu(I) with ferricytochrome C. It was previously shown by us and by others that the reduction yield of ferricytochrome C by O-2 IS 100%. We measured the rate of reduction of ferricytochrome C by Cu(I), and found that this reaction is slow: k = (1.5 +/- 0.5) . 10(3) M-1 . s-1. Therefore, our results rule out the possibility that below pH 8 copper impurities affect the measured rate constant of the reduction of ferricytochrome C by O-2.

Economic evaluation of remuneration from patents and technology transfers

ECONOMIC EVALUATION OF REMUNERATION FROM PATENTS AND TECHNOLOGY TRANSFER September 1986 Yale Han Technlon, Haifa and Dan Galai The Hebrew University of Jerusalem and Graduate School of Management University of California, Los Angeles CA