Mechanistic Studies on the Salicylate‐Catalyzed Peroxyoxalate Chemiluminescence in Aqueous Medium

Abstract

The peroxyoxalate reaction is one of the most efficient chemiluminescence transformations known and the only system occurring by an intermolecular chemically initiated electron exchange luminescence (CIEEL) mechanism with confirmed high quantum yields. The peroxyoxalate chemiluminescence (PO‐CL) is mainly studied in anhydrous organic medium; however, for bioanalytical application, it should be performed in aqueous media. In the present work, we study the peroxyoxalate system in a binary 1,2‐dimethoxyethane/water mixture with bis(2,4,6‐trichlorophenyl) oxalate (TCPO), bis(4‐methylphenyl) oxalate (BMePO) and bis[2‐(methoxycarbonyl)phenyl] oxalate (DMO), catalyzed by sodium salicylate, in the presence of rhodamine 6G as activator. Reproducible kinetic results are obtained for all systems; emission decay rate constants depend on the salicylate as well as hydrogen peroxide concentration, and the occurrence of a specific base catalysis is verified. Although singlet quantum yields determined are lower than in anhydrous media in comparable conditions, they are still considerably high and adequate for analytical applications. The highest singlet quantum yields are obtained for the “ecologically friendly” derivative DMO indicating that this derivative might be the most adequate substrate for the use of the peroxyoxalate system in bioanalytical applications.

Mechanistic Study of the Peroxyoxalate System in Completely Aqueous Carbonate Buffer

“…This is in agreement with results obtained before for the reaction in anhydrous conditions (4,5,(15)(16)(17). The singlet quantum yield at infinite activator concentration of Ф S ∞ = (5.8 AE 0.2) × 10 -7 E mol -1 is significantly lower than yields commonly determined in anhydrous media (3,16,17,32) however, comparable to quantum yields observed in partially aqueous media (25,26,42). The perhydrolysis and the hydrolysis pathway, which lead to light emission and dark TCPO decomposition, respectively, have the same bimolecular rate constants (Table 1 and Scheme 3).…”

“…This is in agreement with results obtained before for the reaction in anhydrous conditions (4,5,15–17). The singlet quantum yield at infinite activator concentration of Ф S ∞ = (5.8 ± 0.2) × 10 –7 E mol –1 is significantly lower than yields commonly determined in anhydrous media (3,16,17,32) however, comparable to quantum yields observed in partially aqueous media (25,26,42).…”

“…These low quantum yields should be caused by a lower efficiency of the chemiexcitation step of the peroxyoxalate reaction in aqueous media (1)(2)(3). This situation has been observed before for other peroxyoxalate reaction systems (24)(25)(26)42), as well as other chemiluminescence reactions (1-3); however, no general explanation could be given up to date.…”

“…Although the peroxyoxalate reaction mechanism has been studied mainly in anhydrous media, our group has shown recently that this reaction is viable in aqueous media, using lutidine, borate, salicylate and phosphate catalysts (24)(25)(26)42) Both specific base catalysis, in the case of salicylate, and general base catalysis, in the case of lutidine and phosphate, have been observed, without a clear way to predict which one will happen in a given condition (i.e., solvent type, nature of the base).…”

Water Effect on Peroxyoxalate Kinetics and Mechanism for Oxalic Esters with Distinct Reactivities

“…Using ACTs with distinct photophysical and electronic properties, it was also possible to confirm the involvement of the CIEEL mechanism (21) in the chemiexcitation step of this transformation (7). However, few mechanistic studies have been carried out involving the peroxyoxalate system in aqueous systems, even though it is an essential analytical chemiluminescent method (22–25).…”