Electron transfer reactions negative charge

Constants for Electron Transfer Reactions Negatively Charged Reactants0... 

Several processes are unique to ions. A common reaction type in which no chemical rearrangement occurs but rather an electron is transferred to a positive ion or from a negative ion is tenued charge transfer or electron transfer. Proton transfer is also conunon in both positive and negative ion reactions. Many proton- and electron-transfer reactions occur at or near the collision rate [72]. A reaction pertaining only to negative ions is associative detaclunent [73, 74],... 

Let s look at the little strip cartoon in Figure 7.7, which shows the surface of a copper electrode. For clarity, we have drawn only one of the trillion or so atoms on its surface. When the cell of which it is a part is permitted to discharge spontaneously, the copper electrode acquires a negative charge in consequence of an oxidative electron-transfer reaction (the reverse of Equation (7.7)). During the oxidation, the surface-bound atom loses the two electrons needed to bond the atom to the electrode surface, becomes a cation and diffuses into the bulk of the solution. 

We now consider a slightly different cell in which the copper half-cell is the positive pole. Perhaps the negative electrode is zinc metal in contact with Zn2+ ions. If the cell discharges spontaneously, then the electron-transfer reaction is the reduction reaction in Equation (7.7) as depicted in the strip cartoon in Figure 7.8. A bond forms between the surface of the copper electrode and a Cu2+ cation in the solution The electrons needed to reduce the cation come from the electrode, imparting a net positive charge to its surface. 

As the quencher is negatively charged, this electron transfer reaction and the subsequent reactions involving the negatively charged SO " radical, are less efficient when the complex binds to DNA than when it remains in solution, nevertheless SO and the oxidised complex oxidise the bases (B) of nucleic acid, eventually leading to strand scissions (see Sect. 5). 

Next we turn to the interpretation of the rate constants for electron-transfer reactions of cytochrome c that are accompanied by a net chemical change (Tables III and IV). The rate constants for the reaction of cytochrome c with both negatively charged (Fe(CN)5L3" and Ru[-(OSO30)2phen]34 ) and positively charged (Fe(bipy)2(CN)2+ and Ru(bipy)32+) complexes can be very great. 

The reaction centre found in many purple non-sulphur bacteria is a simple example of a group of proteins that are natureis solar batteries. The reaction centre uses the energy of sunlight to generate positive and negative charges on opposite sides of the bacterial cytoplasmic membrane. This potential difference drives a circuit of electron transfer reactions that are linked to proton translocation across this membrane. 

The occurrence of a reaction at each electrode is tantamount to removal of equal amounts of positive and negative charge from the solution. Hence, when electron-transfer reactions occur at the electrodes, ionic drift does not lead to segregation of charges and the building up of an electroneutrality field (opposite to the applied field). Thus, the flow of charge can continue i.e., the solution conducts. It is an ionic conductor. 

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