Chemiluminescence, definition

T.G. Chasteen. Chemiluminescence Definitions and Primer. Available at http //www. shsu.edu/ chm tgc/chemilumdir/Defme.html. 

Current methods for DNA detection usually require enzymatic amplification of the target DNA sequence prior to analysis. For example, the PCR technique selectively increases the concentration of the target sequence relative to unrelated sequences. PCR methods, however, introduce ambiguities resulting from contamination by different DNA sequence. Therefore, a definitive method is required for the analysis of a single, original DNA sequence. To achieve this objective, the sensitivity and speed of the chemiluminescent enhancement techniques described in this chapter must be improved. 

Recently, the synthesis has been reported of the novel bicyclic dioxetanes 22a-c , which possess a remarkable chemiluminescence efficiency in aqueous media. Of the dioxetanes 22a-c with the 3-hydroxy-4-isoxazolylphenyl functionality, the derivative 22a is the most suitable On triggering by NaOH in water, the dioxetane 22a displays the highest CIEEL yield (0.24 at 25 °C), whereas the efficiency of componnds 22b and 22c is much lower (0.064 and 0.015, respectively). Nevertheless, the latter are still snfficiently efficient triggerable dioxetanes and quite adequate for their use in aqneons media. Snch unprecedented results definitely merit further exploration. 

The chemiluminescence emission resulting from the oxidation of luminol (5-amino-2,3-dihydro-l,4-phthalazinedione) has been extensively studied since its discovery by Albrecht in 1928. Although luminol oxidation is one of the most commonly applied chemiluminescent reactions, to date no definitive mechanism is known . Efficient chemiluminescence emission is only observed when luminol (25) is oxidized under alkaline conditions. Depending on the medium, co-oxidants are required in addition to molecular oxygen for the observation of light emission, but under any condition, 3-aminophthalate (3-AP) and molecular nitrogen are the main reaction products (equation 10). 

Luminescence covers all emissions of light in the near IR, VIS and near UV spectral regions. The origin of the luminescence can be specified as photoluminescence , electroluminescence , chemiluminescence , or bioluminescence for example. These definitions depend on the mode of formation of the excited molecule which eventually emits the luminescence. 

Spectroscopic Probes of Cavitation Conditions. Determination of the temperatures reached in a cavitating bubble has remained a difficult experimental problem. As a spectroscopic probe of the cavitation event, MBSL provides a solution. High resolution MBSL spectra from silicone oil under Ar have been reported and analyzed (7). The observed emission comes from excited state C2 and has been modeled with synthetic spectra as a function of rotational and vibrational temperatures, as shown in Figure 7. From comparison of synthetic to observed spectra, the effective cavitation temperature is 5050 =L 150 K. The excellence of the match between the observed MBSL and the synthetic spectra provides definitive proof that the sonoluminescence event is a thermal, chemiluminescence process. The agreement between this spectroscopic determination of the cavitation temperature and that made by comparative rate thermometry of sonochemical reactions is surprisingly dose (6). 

A kinetic analysis of the results, based on (17) and its O+OH analog, is in satisfactory agreement with observations on a wide variety of flames. These flames are relatively cool, and the concentrations of H and OH exceed their equilibrium values even in the burned gases, so that the observed sodium emission is definitely chemiluminescent. The third order rate coefficients for excitation by H+H and H+OH are estimated to be 8 x 109 and 2x 1010 l2.mole-2.sec-1, corresponding to an efficiency near unity per triple collision. The possible importance of mechanisms of the type (14,15) has not been carefully studied. 

Since chemiluminescence is a very sensitive method of studying oxidative degradation, it has been used to measure the effect of stress on oxidation of polymers, i.e. stress-induced chemiluminescence (SCL). SCL is by definition a type of triboluminescence, and it is likely that SCL and other forms of tri-boluminescence can occur at the same time. SCL is, however, the only type of tribo-induced luminescence that is oxygen dependent and can therefore be sorted out by measurements in inert and oxidative atmospheres. 

A variant of the crossed-beam geometry, simpler but efficient in some cases, is the beam-gas arrangement. It leads usually to much larger signal than in the crossed-beam configurations, at the expense of a less accurate definition of the reaction kinematics. It is used fairly often to study the total cross-sections of chemiluminescent processes, especially when the species which is to be put into the beam is refractory, as are the transition metals [39, 40]. Reactions of alkaline earth metal atoms have been studied by this technique [41]. 

A similar correlation diagram can be drawn to interpret the exclusive observation of BaOH chemiluminescence in the reaction of Ba(6s6p P) with water [172]. Here again, the reaction of excited barium can be explained by H-atom migration and formation of the intermediate HBaOH. This mechanism definitely carries some generality since it has been used also by Oberlander and Parson to account for re-... 

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. 

The experimental procedure to determine 4>wa is quite analogous to that discussed for The experimental definition is given by Eq. 38, in which all the terms have been already defined. Again the dioxetane decomposition rate constant kj) is determined by following the first-order kinetics of the DPA-enhanced chemiluminescence decay. The initial or total DPA fluorescence intensity is standardized with a suitable light standard, usually with luminol or the scintillation cocktail. The photomultiplier tube should be corrected for wavelength response. ... 

The reactions occurring during the chemiluminescence of luminol are still not too well known. Several theories have been proposed, but the difficulty of identifying the intermediate products has thus far made it impossible to draw definite conclusions (5). Drew suggested that peroxides and ozonides are the intermediate products, but it is also possible that cellulose, which has always been looked upon as an inert carrier, takes an active part in the reaction. Thus the phenomenon in this form cannot be used as a basis for measurements, because one is never interested in a method, which, in order to furnish good results, must be extended over several hours. 

The excellence of the match between the observed MBSL and the synthetic spectra provides definitive proof that the sonoluminescence event is a thermal, chemiluminescence process. The agreement among these spectroscopic determinations5,6 of the cavitation temperature and to that made by comparative rate thermometry of sonochemical reactions4 is extremely good. 

These concepts have been applied by Ben-Shaul et al., 1972a, b to analysis of product energy distributions and to the definition of apparent temperatures for non-equilibrium product distributions. Their procedure may be illustrated with a treatment of vibrational distribution of products, as measured in infrared chemiluminescence studies. The quantities measurable in this case are and v. It is convenient to introduce fractional energies fx = EJE, where fT + fv + fR = 1. The probabilities actually determined are conditional probabilities P(/v ) for fixed . The surprisal is... 

Fig. 32 (179). Chemiluminescence assay of bovine erythrocuprein and different Cu2+-amino acid complexes at pJi 7.8. None Cu(Lys)2 50 nM Cu(His)a, 100 nM Cu-Tyr, 145 nM bovine erythrocuprein, 8 nM. The assay components were pipetted in a disposable scintillation vial at room temperature. The total volume was 2.22 ml. The assay mixture was composed of HEPES buffer, 50 mM xanthine, 0.33 mM catalase, 800 i.U. luminol, 1 mM The reaction was started with 0.08 units xanthine oxidase (definition as given by J. Cooper, P. A. Srere, M. Tabachnick and E. Rocker, Arch. Biochem. Biophys. 74 (1958) 306). The first reading was taken after 10 sec. During the counting the coincidence of the Packard scintillation counter was turned on. The background was 4 1 cpm...

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