Lucigenin reaction mechanism

Lucigenin produces a weak light in an alkaline solution, and the intensity of its light is substantially increased by the addition of hydrogen peroxide [49], As to the reaction mechanism, it has been postulated [50, 51] that lucigenin is oxidized to form a peroxide, which is then decomposed to yield an excited state of A-methylacridine, as shown in Figure 6. 

The analytical method described here can predict the relative sensitivity detected by the chemiluminescence reactions of luminol and lucigenin, and computational chemical analysis can help to predict sensitive detection in liquid chromatography and ion chromatography. In the latter, reaction products are not easily obtained. Moreover, the reaction mechanisms of other compounds under similar conditions should be the same as those described for the above compounds. Further computational chemical study will elucidate the reaction mechanisms of chemiluminescence and the sensitivity differences, and facilitate further improvement of sensitivity. 

One of the more efficient CL substances, lucigenin (10,10 -dimethyl-9,9 -biscridinium nitrate), was discovered by Gleu and Petsch in 1935 (Fig. 5). They observed an intense green emission when lucigenin was oxidized in an alkaline medium [72], Other acridinium derivatives were shown to produce CL emission upon hydrogen peroxide oxidation of aqueous alkaline solutions. The main reaction product was /V-mcthylacridone, acting as an active intermediate in the mechanism proposed by Rauhut et al. [73, 74] (Fig. 6). 

For analysis in solutions, the most frequently used CL reaction is alkaline oxidation of luminol and lucigenin in the presence of hydrogen peroxide as oxidant, although sodium hypochlorite, sodium perborate, or potassium ferricyanide may also be used. CL reactions involving alkaline oxidation have been used to indicate acid-base, precipitation, redox, or complexometric titration endpoints either by the appearance or the quenching of CL when an excess of titrant is present [114, 134], An example of these mechanisms is shown in Figure 14. 

Thus, LOX-catalyzed oxidative processes are apparently effective producers of superoxide in cell-free and cellular systems. (It has also been found that the arachidonate oxidation by soybean LOX induced a high level of lucigenin-amplified CL, which was completely inhibited by SOD LG Korkina and TB Suslova, unpublished data.) It is obvious that superoxide formation by LOX systems cannot be described by the traditional mechanism (Reactions (1)-(7)). There are various possibilities of superoxide formation during the oxidation of unsaturated compounds one of them is the decomposition of hydroperoxides to alkoxyl radicals. These radicals are able to rearrange into hydroxylalkyl radicals, which form unstable peroxyl radicals, capable of producing superoxide in the reaction with dioxygen. 

The second system to be described is the CL obtained in the transformation of lucigenin and related derivatives here, too, the mechanisms which lead to chemiexcitation are still discussed in the literature. Finally, we will concentrate our discussion on one of the most efficient CL systems known, the peroxyoxalate reaction. After a brief discussion of kinetic results obtained with the different peroxyoxalate substrates, we will focus mainly on studies which attempt to elucidate the structure of the high-energy intermediate in these reactions and describe the experimental evidence obtained with respect to the mechanism of the excitation step. 

The mechanism of 1,2-dioxetane formation in the reaction of lucigenin with hydrogen peroxide suggests a nucleophilic attack of peroxide anion on position 9 of the acri-dinium ring, followed by deprotonation and subsequent formation of 1,2-dioxetane ring... 

The mechanism of the chemiluminescence of la in reactions with singlet oxygen or ozone in homogeneous media has also been investigated in connection with that of lucigenin. The light emitter of the chemiluminescence of la was found to be the... 

Hundreds of ECL reactions have been reported, and many are spectroscopically simple enough to be understood in these terms. Others offer emission bands due to excimers [excited dimers such as (DMA), where DMA is 9,10-dimethylanthracene], exciplexes [excited-state complexes, such as (TPTA BP ), where TPTA is tri-p-tolylamine and BP is benzophenone], or simply decay products of the radical ions. More complicated mechanisms are obviously needed to describe such situations. Many studies involve radical ions of aromatic compounds, but others have dealt with metal complexes such as Ru(bpy)3 [bpy = 2,2 -bipyridine], superoxide, solvated electrons, and classical chemiluminescent reagents, such as lucigenin (1-5). 

A very thorough examination [9] of this mechanism has added useful corroborative detail. The salient features described by these workers are that the reaction is first order in lucigenin with the rate expression (L = lucigenin) ... 

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