Dioxetanes chemiluminescence quantum yields

Scheme 28) Quantum yields of lucigenin oxidation by hydrogen peroxide in alkaline media are comparable with the values obtained in luminol oxidation (1.24 x 10 E mol ) ° . However, the use of other peroxides, such as tcrt-butyl hydroperoxide, results in a decrease of chemiluminescence quantum yields of two orders of magnitude, confuming the hypothesis that a 1,2-dioxetane is the HEI, since its formation would be impossible with alkyl peroxides . 

For the experimental determination of the 0, it is necessary to quantify the light output of the direct chemiluminescent process. The experimental definition of the direct chemiluminescence quantum yield is given in Eq. 36, that is, the initial rate of photon production (/q ) per initial rate of dioxetane decomposition k )[D]o). Alternatively, the total or integrated light intensity per total dioxetane decomposed can be used. The /t )[Z)]o term is readily assessed by following the kinetics of the chemiluminescence decay, which is usually first order. Thus, from a semilogarithmic plot of the emission intensity vs. time, the dioxetane decomposition rate constant kjj is obtained and the initial dioxetane concentration [Z)]o is known,especially if the dioxetanes have been isolated and purified. In those cases in which the dioxetanes are too labile for isolation and purification, [/)]o is determined by quantitative spectroscopic measurements or iodometric titration. 

A very high chemiluminescence quantum yield (about eight times that of luminol) has been reported for the oxidation of N-methyl-9-benzyl acridinium chloride with potassium persulfate as catalyst [17]. Although no mechanism has been determined the reaction is reminiscent of the oxidation of 9-methyl acridine [15] in which the carbanion reacts with oxygen to produce the dioxetan which presumably decomposes in the accepted fashion for such compounds ... 

The synthesis of A-methylacridan dioxetane derivatives would be very promising for analytical application as chemiluminescence probes. Despite the high quantum yields... 

Several other examples of 1,2-dioxetane derivatives containing easily oxidizable groups have been reported and the high singlet quantum yield observed in their decomposition was attributed to the occurrence of the intramolecular CIEEL sequence Based on this concept, Schaap and coworkers have introduced the concept of induced chemiluminescence, which is very relevant for investigations into firefly luciferin bioluminescence and has led to the development of chemiluminescent probes widely used in immunoassays (Section N. 

Tetramethylammonium ozonide, 736 Tetramethyl-l,2-dioxetane (TMD) chemical titration, 1224 chemiluminescence, 1221, 1234 quantum yield standard, 1224, 1226 N,N, N, A -Tetramethyl-p-phenylenediamine hydrogen peroxide determination, 735, 631, 633... 

In the case of the reaction of dioxetanes la and 2 initiated by addition of TBAF/DMSO, significant differences in heat evolution were observed in the comparison between reactions in a coated quartz cell and in a transparent cell. The quantum yield of chemiluminescence measured by Schaap et al., for la is 0.25 which is high enough to measure difference in reaction heat between reactions in a coated quartz cell (Q5, Q6) and a transparent cell (Q7, Q8). The reaction heat differences measured for the coated and transparent cells by DSC method, AEl = Q5 - Q6 = 6.6 kcal/mol and AE2 = Q6 - Q7 = 5.5 kcal/mol represented the amount of reaction heat... 

In the presence of methoxy magnesium methyl carbonate, the chemiluminescence emission in pullulan and cellulose increased significantly. It may be attributed to the decomposition of dioxetanes, with higher quantum yield of emission, which were formed from peroxidation of terminal semiacetal groups in the presence of MgO. 

Dioxetanes are beginning to have a tremendous impact on chemiluminescent methodologies for clinically relevant analytes. This impact is due to the development of dioxetanes as enzyme substrates in enzyme-amplified assays similar to the type described in Section 1.3.2. The evolution of the current generation of highly efficient substrates merits some comment. Schaap and co-workers (S8) showed that the naphthalene silyl ether shown in Fig. 40a could be triggered by fluoride ions to give chemiluminescence with a quantum yield of 0.01. On the other hand, the /nefa-disubstituted phenyl derivative in Fig. 40b is extremely efficient in a CIEEL chemiluminescence process (for reasons outlined in the previous section) with a quantum efficiency of 0.45. Subsequent studies showed that the naphthalene derivative in Fig. 40a with an 0-acetyl group instead of the silyl ether, could... 

Dioxetane and 1,2-dioxetanone are key chemical structures in many chemiluminescent and bioluminescent systems. The molecular structure of these systems bears the chemiluminophore properties of the chemi/bioluminescent molecules based on them, providing a channel for a thermally activated chemical reaction that produces a compound in an electronically excited state.The efficiency of the chemiluminescent process in 1,2-dioxetane and dioxetanone is however low and requires an electron-donor group to increase the quantum yield of luminescence. In addition, it is observed experimentally that the triplet emission is significantly more favourable than singlet emission in these small systems. From a theoretical standpoint, the general aspects of the... 

The activation energy in this case varied from 87 to 93 kJ/mol in different solvents. From the temperature dependence, several competitive reaction paths for this dimethyl-dioxetanone decomposition were deduced, all having a biradical as first intermediate. Heavy-atom effects often play a role in dioxetan chemiluminescence. If DBA is used as fluorescer, the quantum yield is markedly greater than that observed when DPA is used - although the latter has a fluorescence efficiency of 0.89, compared with 0.1 for DBA. In both cases triplet-singlet energy transfer is the origin of the chemiluminescence. 

It is very difficult to follow these alternatives to the very well defined dioxetan route right through to the light emitting step. A variety of fates for the intermediate peroxide, and a variety of electron transfer mechanisms are possible. Very many heterocycles and fluorescent aromatic hydrocarbons are chemiluminescent in dipolar aprotic solvents with base in the presence of oxygen. The quantum yields are rarely high, and the identification of a single well defined pathway is extremely difficult. 

Other values of n also give chemiluminescent compounds, with an interesting but unexplained variation in quantum yields and spectra. The reaction mechanism has been studied [7, 8] with evidence provided for the suggestion [6] that the reaction occurs via the electron rich olefin (6) and presumably via the dioxetan... 

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