1.2- Dioxetanones structure

One is the concerted decomposition of a dioxetanone structure that is proposed for the chemiluminescence and bioluminescence of both firefly luciferin (Hopkins et al., 1967 McCapra et al., 1968 Shimomura et al., 1977) and Cypridina luciferin (McCapra and Chang, 1967 Shimomura and Johnson, 1971). The other is the linear decomposition mechanism that has been proposed for the bioluminescence reaction of fireflies by DeLuca and Dempsey (1970), but not substantiated. In the case of the Oplopborus bioluminescence, investigation of the reaction pathway by 180-labeling experiments has shown that one O atom of the product CO2 derives from molecular oxygen, indicating that the dioxetanone pathway takes place in this bioluminescence system as well (Shimomura et al., 1978). It appears that the involvement of a dioxetane intermediate is quite widespread in bioluminescence. 

The decomposition of dioxetanone may involve the chemically initiated electron-exchange luminescence (CIEEL) mechanism (McCapra, 1977 Koo et al., 1978). In the CIEEL mechanism, the singlet excited state amide anion is formed upon charge annihilation of the two radical species that are produced by the decomposition of dioxetanone. According to McCapra (1997), however, the mechanism has various shortfalls if it is applied to bioluminescence reactions. It should also be pointed out that the amide anion of coelenteramide can take various resonance structures involving the N-C-N-C-O linkage, even if it is not specifically mentioned. 

FMNH2 requirement in bacterial luminescence Crystallization of Cypridina luciferin Crystallization of firefly luciferin Cypridina luciferin in fishes the first cross reaction discovered Structure of firefly luciferin Discovery of aequorin and GFP (green fluorescent protein) Structure of Cypridina luciferin Concept of photoprotein Structure of Latia luciferin Dioxetanone mechanism proposed in firefly and Cypridina luminescence... 

Dimethyl-1,2-dioxetanone, chemiluminescence quantum yield, 1226-7 Dimethyldioxirane epoxidation atkenes, 37-44 deuteriation, 1143 O NMR spectroscopy, 184-5 preparation, 26, 1130-2 structure, 26... 

The following four-membered ring structures containing two oxygen atoms are known. Of these, the 1,2-dioxetanes 1 are most common and will form the majority of this chapter. 1,2-Dioxetanones 2 (a-peroxy lactones) and dioxetanimines 3 are rare but have been prepared and will be mentioned where relevant. 1,2-Dioxetenes 4, methylene-1,2-dioxetanes 5, and l,2-dioxetane-3,4-dione 6 have not been prepared in stable form and will only be discussed from a theoretical viewpoint. The isomeric 1,3-dioxetanes 7, l,3-dioxetane-2,4-dione 8, and methylene-1,3-dioxetanes 9 have also received attention from the theoretical viewpoint however, creditable chemical evidence for their existence is still lacking. 

Only experimental information obtained over the last decade has been incorporated within this section and the reader is directed to the previous version of this chapter <1996CHEC-II(1B)1041> for information prior to 1996. Over the last decade, there have only been reports on the characterization of 1,2-dioxetanes 1 and 2-dioxetanones 2 (a-peroxy lactones) consequently, this section contains no information for structures of type 3-9. 

Infrared (IR) spectroscopy is not characteristically definitive for the identification and structural proof of the dioxetane core. Dioxetanones 2 (a-peroxy lactones) such as 29 and 30, depicted in Section 2.16.3.1.4, show carbonyl stretching frequencies at 1835 and 1870cm-1, respectively <1997JOC1623, 1977JA5768>. 

Finally, we would like to sound out with one specific query that must have been on the minds of most readers. Do the related 1,3-dioxetanes (26) and 1,3-dioxetanones (27) behave similarly as the 1,2-dioxetanes and a-peroxylactones respectively It is embarassing to have to admit that essentially nothing is known about these novel structures. Besides a few unconvincing claims for stable 1,3-dioxetanes in the recent patent literature, these so far elusive molecules have been postulated as transient intermediates in a few reactions. Clearly, the 1,3-dioxetanes should be challenging target molecules for investigation to both the synthetic and mechanistic chemists during this decade. 

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 structure giving rise directly to the excited state is now clearly seen as a dioxetanone such as (2) or (22). Cyclisation of the alkyl hydroperoxide forms a strained per-ester - a very much stronger oxidant. Since the electron rich donor is part of the same molecule it is not surprising that reaction is thought to be instantaneous, precluding isolation. 

---