Imidazole chemiluminescence peroxyoxalates

Hadd AG, Robinson AL, Rowlen KL, Birks JW. Stopped-flow kinetics investigation of the imidazole-catalyzed peroxyoxalate chemiluminescence reaction. J Org Chem 1998 63 3023-31. 

Most peroxyoxalate chemiluminescent reactions are catalyzed by bases and the reaction rate, chemiluminescent intensity, and chemiluminescent lifetime can be varied by selection of the base and its concentration. Weak bases such as sodium saUcylate or imidazole are generally preferred (94). 

An indirect method has been used to determine relative rate constants for the excitation step in peroxyoxalate CL from the imidazole (IM-H)-catalyzed reaction of bis(2,4,6-trichlorophenyl) oxalate (TCPO) with hydrogen peroxide in the presence of various ACTs . In this case, the HEI is formed in slow reaction steps and its interaction with the ACT is not observed kinetically. However, application of the steady-state approximation to the reduced kinetic scheme for this transformation (Scheme 6) leads to a linear relationship of l/direct measure of the rate constant of the excitation step. 

Stevani and coworkers prepared and characterized a peracid intermediate, 4-chloro-pheny 1-0,0-hydrogen monoperoxalate (57) and found that no chemiluminescence was observed in the presence of activators (i.e. rubrene, perylene and DPA) and the absence of a base. Based on this result, the authors excluded 57 and similar peracid derivatives as HEI in the peroxyoxalate system. Moreover, 57 only emits light in the presence of an activator and a base with pK > 6, suggesting that a slow chemical transformation must still occur prior to the chemiexcitation step. Kinetic experiments with 57, using mainly imidazole, but also in the presence of other bases such as potassium 4-chlorophenolate, f-butoxide and l,8-bis(dimethylamino)naphthalene , showed that imidazole can act competitively as base and nucleophilic catalyst (Scheme 41). At low imidazole concentrations, base catalysis is the main pathway (steps 1 and 2) however, increasing the base concentration causes nucleophilic attack of imidazole catalyzed by imidazole to become the main pathway (steps la and 2a). Contrary to the proposal of Hohman and coworkers , the... 

The peroxyoxalate system is the only intermolecular chemiluminescent reaction presumably involving the (71EEL sequence (Scheme 44), which shows high singlet excitation yields (4>s), as confirmed independently by several authors Moreover, Stevani and coworkers reported a correlation between the singlet quantum yields, extrapolated to infinite activator concentrations (4> ), and the free energy involved in back electron-transfer (AG bet), as well as between the catalytic electron-transfer/deactivation rate constants ratio, ln( cAx( i3), and E j2° (see Section V). A linear correlation of ln( cAx( i3) and E /2° was obtained for the peroxyoxalate reaction with TCPO and H2O2 catalyzed by imidazole and for the imidazole-catalyzed reaction of 57, both in the presence of five activators commonly used in CIEEL studies (anthracene, DPA, PPO, perylene and rubrene). A further confirmation of the validity of the CIEEL mechanism in the excitation step of... 

Imai et al. studied the catalytic effect of imidazole and other bases on the peroxyoxalate chemiluminescence reaction for HPLC [49]. The peak height of dipyridamole obtained using the eluent containing buffers was largest at pH 7, a few times less at pH 6 and pH 5, 100 times less at pH 4,... 

Stevani CV, Lima DF, Toscano VG Baader WJ. Kinetic studies on the peroxyoxalate chemiluminescence reaction imidazole as a nucleophilic catalyst. J Chem Soc Perkin Trans 2 1996 989-95. 

Imai K, Nishitani A, Tsukamoto Y, Wang WH, Kanda S, Hayakawa K, Miyazaki M. Studies on the effects of imidazole on the peroxyoxalate chemiluminescence detection system for high performance liquid chromatography. Biomed Chromatogr 1990 4 100-204. 

Imai, K., Chemiluminescence detection in flow systems. Biomed. Chromatog. 4, R1 (1990). Imai, K., Nishitan, A., Tuskamoto, Y., Wang, W. H., Kanda, S., Hayakawa, K., and Miyazaki, M., Studies on the effects of imidazole on the peroxyoxalate chemiluminescence detection system for high performance liquid chromatography. Biomed. Chromatog. 4,100-104 (1990). Ireland, D. C., and Samuel, D., Enhanced chemiluminescence ELISA for the detection of antibody to hepatitis B virus surface antigen. J. Biolumin. Chemilumin. 4, 159-163 (1989). 

Sun Y, Wada M, Al-Dirbashi O, Kuroda N, Nakazawa H, Nakashima K. High-performance liquid chromatography with peroxyoxalate chemiluminescence detection of bisphenol A migrated from polycarbonate baby bottles using 4-(4,5-diphenyl-lH-imidazol-2-yl)benzoyl chlorine as a label. J Chromatogr B 2000 749 49-56. 

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