Reevaluation of analytical condition using highly singlet oxygen sensitive/selective reagent in aqueous-/non-aqueous solution

The spin-trapping ESR (ST-ESR) method, which observes unstable radicals as stable spin adducts using electron spin resonance (ESR), is an effective experimental method for evaluating chemical reactions involving radical reactions. For instance, reactive oxygen species (ROS) such as hydroxyl radicals and so on is trapped well by spin-trapping reagent like as DMPO. In this research, we considered the analytical conditions of generation and detection of singlet oxygen. All conditions were decided based on the viewpoints of high usability for the singlet oxygen scavenging/quenching evaluating method. In addition, all experimental conditions were examined with a solvent-independent measurement method. In this study, a nonaqueous solution is N,N-dimethylformamide (DMF), and an aqueous solution is phosphate buffer solution (PBS, 100 mM pH 7.4). In each solvent CDCl3 or D2O was added at a 10 vol.% ratio respectively. Because heavy solvent was previously reported as an extending lifetime of singlet oxygen. The experimental conditions of singlet oxygen were examined by two different generation/detection methods. Photosensitization method using organic dye and thermal decomposition method by naphthalene derivative endoperoxide were studied as generation method, and 4,4’-bis (1-p-carboxyphenyl-3-methyl-5-hydroxyl) pyrazole (DRD156) and 2,2,5,5-tetramethyl-3-pyrroline-carboxamide (TPC) were studied as detection reagent, respectively. As a result, DRD156 and thermolysis method was good combination for singlet oxygen generation and detection in aqueous solution (around neutral condition) and nonaqueous solution.