Lucigenin reactions

The CL enhancement of the lucigenin reaction with catecholamines in the presence of HTAH micelles was used for determination of dopamine, norepinephrine, and epinephrine [42], However, the presence of an anionic surfactant, SDS, inhibits the CL of the system. The aforementioned CL enhancement in the presence of HTAH can be explained in the following way the deprotonated forms of the catecholamines are expected to be the principal species present in aqueous alkaline solution due to the dissociation of the catechol hydroxyl groups, and to react with lucigenin to produce CL. The anionic form of the catecholamines and the hydroxide ion interact electrostatically with and bond to the cationic micelle, to which the lucigenin also bonds. Therefore, the effective concentration of the... 

Du, J. X. Li, Y. H. Guan, R. Chemiluminescence determination of chromium(III) and total chromium in water samples using the periodate-lucigenin reaction. Microchim. Acta 2007, 158, 145-150. 

YIII.1.3 Influence of MiceUe Forming Agents on the Lucigenin Reaction... 

A distinct increase in the chemiluminescence quantum yield of the lucigenin reaction was observed in the presence of cetyltrimethylammonium bromide (CTAB), compared with the reaction performed in an isotropic medium [12]. The effect of CTAB depends on the ratio of the lucigenin/CTAB-concentration. 

A number of chemiluminescent reactions may proceed through unstable dioxetane intermediates (12,43). For example, the classical chemiluminescent reactions of lophine [484-47-9] (18), lucigenin [2315-97-7] (20), and transannular peroxide decomposition. Classical chemiluminescence from lophine (18), where R = CgH, is derived from its reaction with oxygen in aqueous alkaline dimethyl sulfoxide or by reaction with hydrogen peroxide and a cooxidant such as sodium hypochlorite or potassium ferricyanide (44). The hydroperoxide (19) has been isolated and independentiy emits light in basic ethanol (45). 

Classical chemiluminescence from lucigenin (20) is obtained from its reaction with hydrogen peroxide in water at a pH of about 10 Qc is reported to be about 0.5% based on lucigenin, but 1.6% based on the product A/-methylacridone which is formed in low yield (46). Lucigenin dioxetane (17) has been prepared by singlet oxygen addition to an electron-rich olefin (16) at low temperature (47). Thermal decomposition of (17) gives of 1.6% (47). 

Me Capra in particular proposed n> that the chemiluminescence reactions of a large number of organic compounds had this concerted dioxetane decomposition step as key reaction in the production of electronically excited products, namely acridinium salts 25,26,27) indolylperoxides 28>, activated oxalic esters 29>, diphenyl carbene 30>, tetrakis-dimethylamino-ethylene 31 32>, lucigenin 33>, and substituted imidazoles 23>. 

Lucigenin 71 chemiluminescence is more complicated than that of luminol and related compounds due to the presence in the reaction mixture of several species capable of emission 135>. N-Methylacridone 72, however, has been established as the primary excited product (for references see 0 p. 90) from which energy transfer occurs to the other species 3>. 

Because of the close relations between lucigenin, N-alkylacridones, and other 9-substituted acridines, it appears appropriate to consider the chemiluminescence reactions of all these compounds simultaneously. 

In view of the increasing interest in the radical ion chemiluminescence 71 has also been investigated to see whether radical ions play an essential role here, especially by E. G. Janzen et al. 136,137,138) The reaction pathway to N-methylacridone 72 was thought to proceed perhaps via a homolytic cleavage of the lucigenin carbinol base 74, yielding N-methylacridone radical anion 75. 

The lucigenin radical 78 is not involved, according to Janzen and coworkers 136), in the direct formation of this cyclic peroxide one would, however, expect a reaction of 78 with oxygen radical anion to be a possible way of forming the cyclic peroxide, although lucigenin radicals were not detected in the presence of hydrogen peroxide. 

The dioxetane derivative 79 may be formed as intermediate in the brilliant chemiluminescence reaction between 10,10 -dimethyl-9,9 -bi-acridylidene and excited-singlet oxygen 125>. Chemiluminescence also occurs when potassium cyanide is added to lucigenin solutions in the... 

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. 

Figure 5 Chemiluminescent reaction of lucigenin proceeding via a dioxetane intermediate.

Several N-methyl-9-acridinecarboxylic acid derivatives (e.g., 10-methyl-9-acridinecarboxylic chloride and esters derived therefrom [39]) are chemiluminescent in alkaline aqueous solutions (but not in aprotic solvents). The emission is similar to that seen in the CL of lucigenin and the ultimate product of the reaction is N-methylacridone, leading to the conclusion that the lowest excited singlet state of N-methylacridone is the emitting species [40], In the case of the N-methyl-9-acridinecarboxylates the critical intermediate is believed to be either a linear peroxide [41, 42] or a dioxetanone [43, 44], Reduced acridines (acridanes) such as N-methyl-9-bis (alkoxy) methylacridan [45] also emit N-methylacridone-like CL when oxidized in alkaline, aqueous solutions. Presumably an early step in the oxidation process aromatizes the acridan ring. 

HTAC and HTAH have been used as surfactants in the chemiluminescence reaction of lucigenin (10,10 -dimethyl-9,9 -biacridinium dinitrate) with biological reductants (such as fructose, glucose, ascorbic and uric acid) or hydrogen peroxide [38],... 

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. 

Figure 6 Chemiluminiscent reaction of lucigenin. (From Ref. 49 with permission.)...

Figure 8 Dependence of the relative CL intensity upon the final molar concentration of HTAH observed from the reaction of 3.3 X 1CT4M lucigenin with (A, solid line) 200 mg/L glucose and ( , dashed line) 48 mg/L fructose. (From Ref. 38 with permission.)...

Riehl et al. also characterized the CL system lucigenin-hydrogen peroxide-A-methylacridone in the presence of different cationic surfactants such as HTAC, S-ClV-dodecyl-A lV-dimethylammonio) propane-1-sulfonate, and DODAB [41], Enhancement factors (ratio between CL intensity in the presence of organized medium and CL intensity in the absence of organized medium) of CL intensity were found of 3.4, 2.5, and 1.6, respectively. The alterations in CL intensity are explained in terms of the effect of the different surfactants on the rate of the reaction and on excitation efficiency. 

However, surfactants have been used not only to enhance the signal of CL systems, but also to avoid problems of solubility in these systems. Thus, Klopf and Nieman have used SDS, at a submicellar concentration, to solubilize the product (TV-mcthylacridonc) of the CL reaction of lucigenin, due to its insolubility in water [9], In this way the appearance is avoided of solid deposits in the observation cell and in other components of the flow system. 

One of the nonionic surfactants most used as an enhancer of chemiluminescent reactions is Brij-35. This surfactant increases the reaction of lucigenin with catecholamines by a factor of 2.6 compared with the CL intensity in an aqueous medium [42], This enhancement can be explained in the following way it is known that oxygen from the polyoxyethylene chains in Brij-35 can react with sodium ion to form an oxonium ion, by which means the polyoxyethylene chains act as an oxonium cation. In this way the increase in CL intensity due to Brij-35 can be attributed to the same effect described for the micelles of a cationic surfactant. 

When the influence was studied of different surfactants on the CL intensity of the reaction of lucigenin with isoprenaline, it was found that while cationic surfactants such as HTAH and HTAB and anionic surfactants such as SDS decrease the CL signal, the presence of Brij-35 increases the signal by a factor of 2.1 compared to that obtained in an aqueous medium [61]. As a result, a quite sensitive analytical method has been established for determination of isoprenaline, using Brij-35 as a CL enhancer. Application of the method has been satisfactorily verified with the determination of isoprenaline in pharmaceutical preparations. 

One of the few zwitterionic surfactant used in CL reactions is /V-dodccyl-MA-dimethyl-ammonium-3-propane-l-sulfonate (SB-12). Particularly, SB-12 has been assayed in the study of the CL reaction of lucigenin with various biological reductants [10]. The results show that SB-12 enhances CL intensity of the luci-genin-glucose and lucigenin-fructose systems by factors of 3.0 and 1.5, respectively, compared to the intensity obtained in aqueous medium. In these conditions detection limits were found for-both analytes of 0.7 X 10 4 and 2.5 X 10 5 M, respectively. 

The dismutation (disproportioning) of two free radicals is accompanied by release of a portion of reaction energy as a light quantum. As the quantum yield of such a process is extremely low, the detection of this type of chemiluminescence is technically complicated. Several compounds like lucigenin and luminol have a high quantum yield after reaction with peroxide radicals. Therefore, they are widely used for the detection of these radicals, particularly in the examination of phagocyting cells. 

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