New nucleophilic catalysts for bright and fast peroxyoxalate chemiluminescence

Miniaturized detection applications based on chemiluminescence require fast reaction kinetics for optimum performance. In this work, high-intensity light from the analytically useful peroxyoxalate chemiluminescence reaction has been generated at high rates by employing both single-component and dual-component nucleophilic catalysis. 4-(Dimethylamine)pyridine and its derivatives were superior to all other bases in terms of reaction speed and intensity of the generated light and outshone imidazole, which hitherto has been considered as the best catalyst. The light intensity was related to the difference in pKa between the 4-aminopyridine catalyst and the leaving group of the reagent, and the optimum delta pKa was found to be close to 0. Similarly, high light intensities were obtained when mixtures of the imidazole analogue 1,2,4-triazole and the strong, nonnucleophilic base 1,2,2,6,6-pentamethylpiperidine acted as catalysts. The mechanism behind this was concluded to be a "base-induced nucleophilic catalysis", where the ancillary strong base assisted the production of the highly nucleophilic 1,2,4-triazolate anion, which as the actual catalyst then participated in the formation of a more reactive transient reagent. All the investigated catalysts reduced the light yield of the reaction due to base-catalyzed breakdown reactions of the reagents and/or intermediates. The intensity peak maximums of these bright and fast reactions typically appeared after less than 10 ms, whereafter the light decayed to darkness within a few seconds. These reaction characteristics are especially advantageous for sensitive detection applications where the observation volumes and times are limited, e.g., peaks emerging from a capillary-based separation process.