Charge annihilation

The decomposition of dioxetanone may involve the chemically initiated electron-exchange luminescence (CIEEL) mechanism (McCapra, 1977 Koo et al., 1978). In the CIEEL mechanism, the singlet excited state amide anion is formed upon charge annihilation of the two radical species that are produced by the decomposition of dioxetanone. According to McCapra (1997), however, the mechanism has various shortfalls if it is applied to bioluminescence reactions. It should also be pointed out that the amide anion of coelenteramide can take various resonance structures involving the N-C-N-C-O linkage, even if it is not specifically mentioned. 

Therefore, the sequence of reactions illustrated in Fig. 1 catalytically (the anthraquinone is regenerated) injects a radical cation into a DNA oligonucleotide that does not simultaneously contain a radical anion. As a result, the lifetime of this radical cation is determined by its relatively slow bimolecular reaction with H20 (or some other diffusible reagent such as 02- ) and not by a rapid intramolecular charge annihilation reaction. This provides sufficient time for the long distance migration of the radical cation in DNA to occur. 

Since its discovery in 1964 electrogenerated chemiluminescence (ECL) has been an active area of chemical research O ). The light producing mechanism common to all ECL systems consists of an oxidation and reduction, followed by charge annihilation to produce the excited state of an emitting compound. 

Equations (2a) and (2b) have been applied widely to organic-based dyads where forward ET involves charge separation (e.g., D-A — D+-A- ) and back ET charge annihilation (e.g., D+-A D-A). In this situation the CSE term... 

The electron-transfer chemiexcitation is shown schematically in molecular orbital terms in Fig. 2. Although other electron-transfer reactions are potentially chemiluminescent (Tokel-Takvoryan et al., 1973), the charge annihilation reaction of oppositely charged aromatic radical ions is the prototypical case and has been most extensively studied. This is due to the convenient preparation of the radical ions by electrochemical means, the large range of redox potentials which are available, and the high fluorescence... 

Figure 1. Energy level diagram for charge annihilation processes. Relative energies are shown for the DPA+, DPA pair, the TMPD, DPA pair and the singlet and triplet excited states of DPA. The allowed recombination processes are indicated by the arrows.

Charge-annihilation processes preceding emission may occur from solvent-separated or contact ion pairs, and there is a possibility that excited-state dimers... 

Subatomic particles with equal mass and opposite charge —> Annihilate each other upon encounter, producing energy... 

Adsorbed humate of arei close to 0.5 produces complex layers of zero potential in all situations. This reveals surface charge annihilation where Al3+ (main component), Al(OH)2+, and Al(OH)2 paired with acid groups exactly compensate for the remaining dissociated acid groups R-COCT. 

The reaction mechanism proposed by Koo and Schuster [4], is that of a cage charge annihilation ... 

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