Redox potential calculations quinones

The one-electron oxidation of iV-benzylphenothiazine by nitric acid occurs in the presence of /i-cyclodextrin, which stabilizes the radical cation by incorporation into its cavity. The reaction is inhibited by adamantane, which preferentially occupies the cavity. Novel Pummerer-type rearrangements of / -sulfinylphenyl derivatives, yielding /7-quinones and protected dihydroquinones, and highly enantioselective Pummerer-type rearrangements of chiral, non-racemic sulfoxides have been reviewed. A comprehensive study has demonstrated that the redox potential for 7- and 8-substituted flavins is linearly correlated with Hammett a values. DFT calculations in [3.3.n]pro-pellanes highlight low ionization potentials that favour SET oxidative cleavage of the strained central C-C bond rather than direct C-H or C-C bond attack. Oxidations and reductions in water have been reviewed. ... 

An ab initio study using the 6-31G basis set was used to investigate the vibrational and electronic structures of a benzodithiophene and benzodifuran quinone as potential redox switches. The calculated and experimental data were... 

The redox chemistry of PQQ has been investigated by a number of research groups. Duine et al. [14,15] performed potentiometric titrations of PQQH2 at several pHs and measured the redox potential of PQQ/PQQH2. Eckert et al. [16,17] compared the redox properties of PQQ with those of o-phenanthroline quinones. Kano et al. [18] performed cyclic voltammetry at acidic pH. Bergethon [19] investigated the amperometric detection of PQQ as a tool for HPLC. From pulse radiolysis experiments, McWhirter and Klapper [20] derived a value of -122 mV (NHE) for Em PQQ/PQQH at pH 7, as compared to the value of - 218 mV calculated from mediator-linked potentiometric titrations [15],... 

Figure 11.25. Photocurrent dependence on the Gibbs free energy of electron transfer for the photo-oxidation of ferrocene derivatives (a) and photoreduction of quinone-type molecules (h) at the water/DCE interface. AG ( is evaluated from Equation (11.47), employing the formal redox potentials summarised in Table 11.1 and the applied Galvani potential difference. A deconvolution of the photocurrent relaxation in the presence of the electron acceptors was performed in order to estimate the flux of election injection g. The second-order rate constant for the photoninduced heterogeneous electron transfer is also calculated assuming values of 1 nm for dec and 5 x 10 s for A ,. The trends observed in both set of data were rationahsed in terms of a single solvent reorganisation energy and activation-less limit for the rate constant. Reprinted with permission from refs.[101] and [60]. Copyright (2002/2003) American Chemical Society.

Thermodynamics of electron transfer. It should become possible to specifically alter reduction potentials by suitable modification of proteins and/or redox groups. The shifts in E° arising from these modifications should also be accurately predictable from theoretical calculations. Reasonable agreement between observation and theory has been already reported for the effects of certain electrostatic modifications on E° (49, 53, 54, 59). The more difficult problem of ab initio calculations of E° values will take longer to accomplish, although encouraging results have been described for quinones (194). 

Solvation free energy calculations in combination with quantum mechanical calculations have been utilized to reproduce and predict the aqueous redox properties of quinones and the aqueous one-electron reduction potential of trimethyl-p-benzoquinone and plastoquinone-1 and selected p-benzoquinones. Shifts in the redox pair potential on mutation of the reaction center of Rhodobacter sphaerodes calculated using the FEP method have been reported by Apostolakis et al. ... 

Permeability through the monolayer of cyclodextrin derivative 4 has been estimated from the accessibility of electroactive markers to the electrode surface, which in turn can be estimated from the peak potential and area of cyclic voltammograms (Figure 4). The calculation of the voltammogram area has been made by an integration of either the oxidation or reduction peak that corresponds to the initial process of the redox cycle, i,e, the oxidation peak in the cases of [Co(phen)3]2+ and [Mo(CN)g]4", and the reduction peak in the case of p-quinone. 

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