One electron oxidation potentials

The competition between antioxidant and prooxidant activity of flavonoids depends firstly on their chemical structure. If we suppose that the oxidation of flavonoids (Reaction (17)) takes place by one-electron transfer mechanism, then it must depend on the capacity of flavonoids to donate an electron, i.e., on their one-electron oxidation potentials. 

Bors et al. [175] determined the rate constants and equilibrium constants for the reactions of flavonoids with ascorbate (Reaction (18)) by a pulse-radiolysis method and on their basis calculated the one-electron oxidation potentials of flavonoids (Table 29.9). 

Rate Constants (I mol-1 s-1) and Equilibrium Constants for the Reactions of Flavonoids with Ascorbate and One-Electron Oxidation Potentials (mV) of Flavonoids... 

An example of the use of these standard states for working with solvation effects on one-electron oxidation potentials is provided elsewhere.11... 

P. Winget, E. J. Weber, C. J. Cramer, and D. G. Truhlar, Computational electrochemistry Aqueous one-electron oxidation potentials for substituted anilines, Phys. Chem. Chem. Phys. 2 1231 (2000). 

The presence of a base is also essential for the efficient reductive dehalogenation of RX by 1-benzyl-1,4-dihydronicotinamide (BNAH) via photoinduced electron transfer [121,122], Since the one-electron oxidation potential of the singlet excited state of BNAH ( BNAH ) is —3.1 V (vs. SCE) [50], which is more negative than the one-electron reduction potential of benzyl bromide (PhCH2Br), photoinduced electron transfer from BNAH to PhCH2Br occurs efficiently with the diffusion-limited rate [122]. This fast process needs no base catalyst to accelerate the electron transfer rate further. However, the photoinduced electron transfer results in... 

The Mg2+ ion also shows an acceleration effect on the photoreduction of dimethylfumarate and some other related olefins by 1-benzyl-1,4-dihydro-nicotinamide (BNAH) used as an NADH model compound via photosensitized electron transfer from BNAH to [Ru(bpy)3]2+ (Scheme 16) [160]. In this case, however, the complex formation of BNAH with Mg2+ results in an increase in the one-electron oxidation potential of BNAH [87]... 

Enhancement of fluorescence due to the complexation of metal ions with fluoroionophores has been used as a well-precedented technique to analyze for the presence of metal ions [189-191], A number of studies have reported chelating fluorophores whose emission spectra change upon the addition of metal ions [192-198]. One remarkable result of this emission intensity enhancement is shown in Scheme 23, where the chelation of zinc chloride to 9,10-bis(((2-(dimethylamino)ethyl)methylamino)methyl)anthracene drastically enhances the observed fluorescence by a factor greater than 1000-fold [199], In the absence of Zn2+, the singlet excited state of anthracene moiety is strongly quenched by intramolecular photoinduced electron transfer from the amine to the anthracene moiety. The complex formation of Zn2+ with the amine moiety may result in the largely positive shift of the one-electron oxidation potential. Thus, intramolecular photoinduced electron transfer is strongly suppressed by the complexation of the amine moiety with Zn2+,... 

Figure 1. Correlation of one-electron oxidation potentials for Chl a and Chl b in the ground (So) and excited singlet (S,) and triplet (T,) states with redox potentials of some donor and acceptor species at pH 7 ((MV) methylviologen (H%Q) hydro-...

Methylquinolinium ion derivatives are reduced regioselectively to 1,4-dihydroqui-nones by (TMS SiH under photochemical conditions42. Mechanistic studies demonstrated that the reactions are initiated by photoinduced electron transfer from silane to the singlet excited states of 1-methylquinolinium ion derivatives to give the silane radical cation—quinolinyl radical pairs, followed by hydrogen transfer in the cage to yield 1,4-dihydroquinones and silicenium ion. The one-electron oxidation potential of (TMS SiH is 1.30 V42. 

Nucleophilic substitution reactions are driven by (1) the difference between the electron affinity of the electrophile ( E, one-electron reduction potential) and the electron-donating propensity of the nucleophile ( N, one-electron oxidation potential) (Ee - N) and (2) the bond energy of the newly formed bond.27 For example, the nucleophilic attack by HO- in MeCN ... 

Measurements of one-electron oxidation potentials of NADH and other dihydropyridines would be extremely useful in establishing the feasibility of... 

Koyama has examined the sensitization behavior of a series of pheophorbide sensitizers (112-117) with similar structure. The results indicate that the short-circuit current density as well as the overall solar energy-to-electricity conversion efficiency increased with the increasing Qy absorption and with the decreasing one electron-oxidation potential. Two empirical models are built based on the experimental results. One model suggests a parallel electron injection from both excited and ground states to the conduction band of Ti02 whereas the other one supports an electron injection via the excited state only, in which both the Qy absorption and the Qy-state one electron-oxidation potential can contribute [110]. 

Wang, J. Rivas, G. Ozsoz, M. Grant, D.H. Cai, X. Parrado, C. Microfabricated electrochemical sensor for the detection of radiation-induced DNA damage. Anal. Chem. 1997, 69, 1457-1460. Steenken, S. Jovanovic, S.V. How easily oxidizable is DNA One-electron oxidation potentials of adenosine and guanosine radicals in aqueous solution. J. Am. Chem. Soc. 1997, 119, 617-618. 

Of utmost import is the correlation which is found between the magnitude of kcat and the one-electron oxidation potential of the activator, the more easily oxidized activators having the larger values of kcar This indicates that a one-electron transfer from the activator to [26] may occur in the ratedetermining step of the bimolecular reaction and determine, in part, the magnitude of kcat. The mechanism proposed to account for the experimental observations on the chemiluminescence of [26] is shown in Fig. 10. 

Kocar and Inskeep [73] have examined the photochemical oxidation of As(III) in ferrioxalate solutions and conclude that the hydroxyl radical is the major oxidising species. The difference between the findings of Kocar and Inskeep [73] and Hug et al. [68] may relate to the nature of the ligand and their ground-state one electron oxidation potentials which determine... 

The fluorescence intensity of ZnP CONH Q is significantly quenched compared to the reference ZnP compound without Q due to efficient ET from the singlet excited state ( ZnP ) to Q in ZnP—CONH—Q (68). Such efficient ET results from the large driving force of electron transfer (—AGej = 0.91 eV in PhCN), which is determined from the one-electron oxidation potential of the ZnP moiety (Eox = 0-78V vs SCE), the one-electron reduction potential of the Q moiety (Ered = —0.36 V vs SCE), and the singlet excited-state energy of ZnP (2.05 eV). 

The same mechanism as Scheme 25 can be applied to the disproportionation of semiquinone radical anion (Q ) by the imidazolate-bridged Cu —Zn complex (155), (Scheme 25). Since the one-electron oxidation potential (Lqx vs SCE) of Q (—0.51 V), which is equal to the one-electron reduction potential of Q (135), is more negative than the one-electron reduction potential ( red vs SCE) of the Cu(II)... 

---