Measurement and characterization of singlet oxygen production in copper ion-catalyzed aerobic oxidation of ascorbic acid.
Production of singlet molecular oxygen ((1)O(2)) in the aerobic oxidation of ascorbic acid catalyzed by copper ion was measured and characterized using [4'-(9-anthryl)-2,2':6',2''-terpyridine-6,6''-diyl]bis(methylenenitrilo)tetrakis(acetate)-Eu(3+) (ATTA-Eu(3+)) as a highly sensitive and selective time-resolved luminescence probe for (1)O(2). The (1)O(2) produced in the reaction was further characterized and confirmed by (i) chemical trapping of (1)O(2) with 9,10-diphenylanthracene (DPA), the corresponding endoperoxide was detected by HPLC and (ii) spin trapping of (1)O(2) with 2,2,6,6-tetramethyl-4-piperidinol (TMP-OH), the corresponding free radical of TMP-OH oxide (TMPO) was detected by electron spin resonance (ESR) spectroscopy. The effects of deuterium oxide, sodium azide and histidine on the (1)O(2) signal were investigated. The mechanism investigation of (1)O(2) production implied that the ascorbic acid-Cu(I) complex formed in the reaction could be an important intermediate for the (1)O(2) production. The reaction of ascorbic acid with copper ion monitored by (1)H NMR and absorption spectroscopy demonstrated the formation of a copper ion-ascorbic acid complex. Except for Cu(2+) and Cu(+)-ascorbic acid systems, no detectable (1)O(2) was produced in other transition metal cation-ascorbic acid systems in the studied range.
Song
Bo
B
Department of Analytical Chemistry, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, PR China.
Wang
Guilan
G
Yuan
Jingli
J