Charge reduction potential

B Shen, DR Jollie, CD Stout, TC Diller, EA Armstrong, CM Gorst, GN La Mar, PJ Stephens, BK Burgess. Azotobacter vmelandii ferredoxm I Alteration of individual surface charges and the [4Ee-4S] cluster reduction potential. 1 Biol Chem 269 8564-8575, 1994. 

Table 5.1 lists some of the atomic properties of the Group 2 elements. Comparison with the data for Group 1 elements (p. 75) shows the substantial increase in the ionization energies this is related to their smaller size and higher nuclear charge, and is particularly notable for Be. Indeed, the ionic radius of Be is purely a notional figure since no compounds are known in which uncoordinated Be has a 2- - charge. In aqueous solutions the reduction potential of... 

Figures 12-12 and 12-13 document that trap-free SCL-conduction can, in fact, also be observed in the case of electron transport. Data in Figure 12-12 were obtained for a single layer of polystyrene with a CF -substituted vinylquateiphenyl chain copolymer, sandwiched between an ITO anode and a calcium cathode and given that oxidation and reduction potentials of the material majority curriers can only be electrons. Data analysis in terms of Eq. (12.5) yields an electron mobility of 8xl0 ycm2 V 1 s . The rather low value is due to the dilution of the charge carrying moiety. The obvious reason why in this case no trap-limited SCL conduction is observed is that the ClVquatciphenyl. substituent is not susceptible to chemical oxidation.

MEH-PPV and P3MBET, were used. As a measure of the efficiency of the photo-induced charge transfer, the degree of luminescence quenching and the ratio of the charged photoexcitation bands to the neutral photoexcitation bands were taken. These two numbers are plotted in Figure 15-15 versus the electrochemical reduction potential. A maximum in the photoinduced electron transfer was determined for Cbo. 

Another point of importance about the film structure is the degree to which it can be permeated by various ions and molecules. It is of course essential that supporting electrolyte ions be able to penetrate the film, else the electrical double layer at the electrode/polymer interface could not be charged to potentials that drive electron transfers between the polymer and the electrode. The electroneutrality requirements of porphyrin sites as their electrical charges are changed by oxidation or reduction also could not be satisfied without electrolyte permeation. With the possible exception of the phenolic structure in Fig. 1, this level of permeability seems to be met by the ECP porphyrins. 

We close this section with a note on the influence of pH on reduction potentials. Many redox reactions are pH-dependent, which can be understood with reference to the simple model in Figure 13.4, in which a redox compound in its oxidized state has a pK,t for proton dissociation that is different from (i.e., lower than) the corresponding value for its reduced state the positive charge of Xox is higher than that of Xred, so it is more difficult for Xox to accept a proton (i.e., its pKa is lower). The °(pH) is now... 

Interestingly, the methyl-transfer reaction between BMeT and 3-cyano-TV-methylpyridinium (with the highest reduction potential, see Table 7) occurs instantaneously and thus precludes the isolation of the charge-transfer salt. 

Photoinduced methyl transfer. The yellow mixture of 4-phenylpyridinium cation (with relatively low reduction potential) and tetramethylborate anion in tetrahydrofuran persists for 24 h without any reaction (in the dark). However, the deliberate irradiation of the charge-transfer band (at /exc = 370 nm)... 

The relationship between the herbicidal activity of 1,2,5-oxadiazole iV-oxides and some physicochemical properties potentially related to this bioactivity, such as polarity, molecular volume, proton acceptor ability, lipophilicity, and reduction potential, were studied. The semi-empirical MO method AMI was used to calculate theoretical descriptors such as dipolar moment, molecular volume, Mulliken s charge, and the octanol/water partition coefficients (log Po/w) <2005MOL1197>. 

The activity of a metal is based on how easily it oxidizes to positively-charged ions. Therefore, a more active metal loses electrons more readily, is more easily oxidized and is a better reducing agent. The strength of a reducing agent increases as its standard reduction potential becomes more negative. 

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