No abstract

The chemiluminescence of the Cypridina luciferin analog, 2‐methyl‐6‐(p‐methoxyphenyl)‐3,7‐dihydroirnidazo[1,2‐a]pyrazin‐3‐one (MCLA), with O2 (1Δg) generated by the retro‐Diels‐Alder reaction of 3‐(4′‐methyI‐l'‐naphthyl)‐propionic acid endoperoxide was studied in an aqueous solution with pH 7.12 at 37°C. The retro‐Diels‐Alder reaction occurs with a first‐order rate constant of (4.16 ± 0.13) × 10−4/s to quantitatively yield O2 (1Δg) and 3‐(4′‐methyl‐l'‐naphthyl (‐propionic acid. MCLA consumed equimolar amounts of O2 (1Δg) with a second‐order rate constant (6.96 ± 0.27) × 108/M/s to emit light in an aqueous solution with pH 7.12 at 37°C. The chemiluminescence spectrum was identified as the fluorescence spectrum of 2‐acetylamino‐5‐(p‐methoxyphenyl)pyrazine (OMCLA), a major chemiluminescence reaction. Chemiluminescence spectra and product yields for MCLA reactions with O21Δg, with O2 (3Σ−g) and with superoxide anion radicals are identical, suggesting that all of these reactions occur via a common MCLA‐2‐hydrope‐roxide intermediate formed by a combination of MCLA radicals and superoxide anion radicals. We have established practical use of NEPO as an O2 (1Δg) source and MCLA as a biological probe for detecting O2 (1Δg).

The formation of carbonyl oxides in the singlet oxygen (1O2) oxidation of phenyldiazomethanes 1 has been investigated mechanistically. Product ratios of N2/N2O, which are indicative of the selectivity in the carbonyl oxide/ketone formation, were determined by gas chromatography/mass spectrometry (GC/MS). The yields of carbonyl oxides were not affected by changing solvents but were significantly increased with the increasing electron-donating ability of substituents on diazomethanes. Rate constants for the quenching of 1O2 by 1 as determined by monitoring the emission of 1O2 at 1270 nm were also insensitive to solvents. These results suggest the predominant formation of 1,2,3,4-dioxadiazole intermediates by the cycloaddition of 1O2 to 1 followed by its cycloreversion, the selectivity of which is controlled by the relative stability of resulting carbonyl oxides. The formation of carbonyl oxides, observable from its transient absorption at ∼400 nm, was in good agreement with the decay of 1O2 within the experimental error, indicating that the 1,2,3,4-dioxadiazoles are a highly labile intermediate with the lifetime of less than 100 ns.

No abstract

Product ratios of N2/N2O as an indicator for carbonyl oxide formation in the 1O2 oxygenation of phenyl diazomethanes were not affected by protic solvents but were significantly increased by electron-donating substituents. A mechanism is suggested in which 1,2,3,4-dioxadiazole intermediates are formed by the cycloaddition of 1O2 and diazomethanes and its cycloreversion is controlled by the relative stability of resulting carbonyl oxides.