Singlet oxygen has developed much interest since the early 1960’s for its connection with photooxidation, DNA damage, photodynamic therapy, and polymer science. Photosensitized generation of singlet oxygen is relatively simple and controllable; requiring just the presence of oxygen, light (of appropriate wavelength), and a photosensitizer capable of absorbing and using the energy to excite molecular oxygen to its singlet state. Singlet oxygen production has been monitored in many studies by the RNO method of Kraljic and El Mohsni; which uses the bleaching of p-nitrosodimethylaniline (RNO) in the presence of imidazole. There have been many variations of the RNO method, but not much investigation of the efficiency of the assay. Since this assay is widely used in kinetic analysis, it is important to recognize how well the assay describes the processes it measures.
In this research, UV-Vis spectroscopy and multivariate data analysis methods are used to assess the standard RNO method of Kraljic and El Mohsni for monitoring the production of singlet oxygen by Rose Bengal in homogeneous, biorelevant, and microheterogeneous media. Rose Bengal is a xanthene dye that efficiently transfers energy from its excited triplet state to the triplet ground state of molecular oxygen (in methanol), making it one of the most studied photosensitizers, and a useful sensitizer for assessing the quality of a singlet oxygen trap.
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