Sonochemiluminescence of lucigenin: Evidence of superoxide radical anion formation by ultrasonic irradiation

摘要

The sonochemiluminescence (SCL) behavior of lucigenin (Luc(2+)) has been studied in aqueous solutions irradiated with 500 kHz ultrasound. Compared with the SCL of a luminol system, a tremendously increased SCL intensity is observed from 50 mu M Luc(2+) aqueous solution (pH = 11) when small amounts of coreactants such as 2-propanol coexist. It is shown that SCL intensity strongly depends on the presence of dissolved gases such as air, O-2, N-2, and Ar. The highest SCL intensity is obtained in an O-2-saturated solution, indicating that molecular oxygen is required to generate SCL. Since SCL intensity is quenched completely in the presence of superoxide dismutase (SOD), an enzyme that can catalyze the disproportionation of O-2(center dot-), the generation of O-2(center dot-) in the ultrasonic reaction field is important in the SCL of Luc(2+). In this work, the evidence of O-2(center dot-) production is examined by a spectrofluorometric method using 2-(2-pyridyl)benzothiazoline as the fluorescent probe. The results indicate that the yield of O-2(center dot-) is markedly increased in the O-2-saturated solutions when a small amount of 2-propanol coexists, which is consistent with the results of SCL measurements. 2-Propanol in the interfacial region of a cavitation bubble reacts with a hydroxyl radical (center dot OH) to form a 2-propanol radical, CH3C:(OH)CH3, which can subsequently react with dissolved oxygen to generate O-2(center dot-). The most likely pathways for SCL as well as the spatial distribution of SCL in a microreactor are discussed in this study. (C) 2016 The Japan Society of Applied Physics