Phthalate dianion

Gorsuch and Hercules 109> stated that certain discrepancies between the fluorescence spectrum of 3-amino-phthalate dianion and the chemiluminescence spectrum of luminol are partly due to reabsorption of the shorter-wavelength chemiluminescence light by the luminol monoanion. These authors confirmed the results of E. H. White and M. M. Bursey 114> concerning the very essential solvent effect on luminol chemiluminescence the relative intensity of the latter in anhydrous DMSO/t-BuOK/ oxygen was found to be about 30,000 times that in DMSO/28 mole % water/potassium hydroxide/oxygen. 

The emission maxima of luminol chemiluminescence and of 3-amino-phthalate dianion in some solvents are listed in Table 3 ... 

Table 3. Chemiluminescence maxima of luminol and fluorescence maxima of 3-amino-phthalate dianion (after J. Lee and H. H. Seliger 115>)...

Similarly the N-methylacridone derivative 59 yielded chemiluminescence which was about a third that of 58. In this case the donor part of the molecule, i.e. the phthalic hydrazide, cannot produce a fluorescent product at all, but on its oxidation excited phthalate dianions very probably are produced 124>. From a series of other compounds of this type (60, 61, 62)... 

The CL reaction of luminol (5-amino-2,3-dihydro-1,4-phthalazinedione) (1) is one of the more commonly used nonenzymatic CL reactions and has been extensively studied [49, 57-59], It is well known that the luminol CL reaction is catalyzed by many kinds of substances, e.g., ozone, halogen-Fe complex, hemin, hemoglobin, persulfate, and oxidized transition metals. The most acceptable scheme is shown in Figure 10. Luminol forms a six-membered ring of peroxide (3) from a diazaquinone intermediate (2) and then, by the decomposition of 3, N2 gas and the Si-excited state of the phthalate dianion are produced, yielding... 

Nevertheless the fluorescence efficiency of the substituted phthalate dianion is a decisive factor in luminol type chemiluminescence. Since one can expect that the carboxylates of higher condensed aromatic hydrocarbons would exhibit high fluorescence efficiencies, a series of naphthalene-, anthracene- and homologuous o-dicarboxylic acid hydrazides have been synthesized and their chemiluminescence investigated. In the tables in Appendix, p. 205 some of these hydrazides synthesized since 1968 are listed. 

In all chemiluminescence reactions of cyclic diacyl hydrazides investigated so far the respective (substituted) phthalate dianions are the emitters. 

The decomposition of the endoperoxide via the o-xylene derivative (48) in an intramolecular electron transfer mechanism would also give the substituents a decisive role in the excitation step itself - not only affecting the fluorescence efficiency of the phthalate dianion. A high fluorescence efficiency is of course a necessary, but not sufficient, requirement in luminol type chemiluminescence [9, 16],... 

Electrodes based on 9 but no nucleobase derivative [3.0 wt% 9 bis(2-ethylhexyl) phthalate ( dioctyl phthalate , DOP) as the membrane solvent] showed similar potentiometric responses to 5 -GMP and 5 -AMP (Figure 8a), which is not surprising because cation 9 cannot interact specifically with the base pairing site of nucleotides. The EMF slope (-29 mV decade" 0.1 M HEPES-NaOH buffer solution, pH 6.8) was much greater than in case of the electrode based on the macrocyclic pentaamine 1 (-15 mV decade" ) and corresponds to the slope as expected for a dianion according to the Nemstian equation. Extraction experiments confirmed that at this pH it is indeed the dianion that enters the organic phase. 

It appears that there may be several paths leading to eventual generation of electronically excited state products from luminol. In non-protic solvent, in particularly DMSO, the reaction apparently proceeds through the intermediate luminol dianion [33]. Reaction of the dianion with oxygen results in the formation of 3-aminophthalate in the excited state (42). White and Roswell (1970) have shown that under these conditions the chemiluminescence is due to emission from the excited phthalate. 

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