Generating Singlet Oxygen Bubbles: A New Mechanism for Gas–Liquid Oxidations in Water

Abstract

Laser-coupled microphotoreactors were developed to bubble singlet oxygen [1O2 (1Δg)] into an aqueous solution containing an oxidizable compound. The reactors consisted of custom-modified SMA fiber-optic receptacles loaded with 150-μm silicon phthalocyanine glass sensitizer particles, where the particles were isolated from direct contact with water by a membrane adhesively bonded to the bottom of each device. A tube fed O2 gas to the reactor chambers. In the presence of O2, singlet oxygen was generated by illuminating the sensitizer particles with 669-nm light from an optical fiber coupled to the top of the reactor. The generated 1O2 was transported through the membrane by the O2 stream and formed bubbles in solution. In solution, singlet oxygen reacted with probe compounds (either 9,10-anthracene dipropionate dianion, trans-2-methyl-2-pentanoate anion, N-benzoyl-D,L-methionine, and N-acetyl-D,L-methionine) to give oxidized products in two stages. The early stage was rapid and showed that 1O2 transfer occurred via bubbles mainly in the bulk water solution. The later stage was slow, it arose only from 1O2-probe molecule contact at the gas/liquid interface. A mechanism is proposed that involves 1O2 mass transfer and solvation, where smaller bubbles provide better penetration of 1O2 into the flowing stream due to higher surface-to-volume contact between the probe molecules and 1O2.

Superhydrophobic Photosensitizers. Mechanistic Studies of 1O2 Generation in the Plastron and Solid/Liquid Droplet Interface

“…23,48 Surface C provides similar functionality as such a singlet oxygen generator. Dry Pc particles alone, physically removed from the liquid, lead to the generation of singlet oxygen and its diffusion into the liquid droplet.…”

Bacterial Inactivation by a Singlet Oxygen Bubbler: Identifying Factors Controlling the Toxicity of 1O2 Bubbles

“…The change from fast to slow stages in an anthracene endoperoxidation reaction was also seen, after a similar time, in our previous work. 7 …”

“…7 The glass sensitizer was ground to 150 μm-sized particles. The device was filled with 35 mg of the sensitizer particles (total number of particles = 14,700).…”

Mechanistic and Kinetic Study of Singlet O2 Oxidation of Methionine by On-Line Electrospray Ionization Mass Spectrometry

“…To avoid the interferences in photooxidation experiments, one approach is to use heterogeneous photosensitization in which sensitizers are isolated from reaction solution and the sensitizer-generated 1 O 2 is delivered through space [33] or via bubbles [34]. We have adopted another approach based on a chemical reaction to produce radical-free, Bclean^1O 2 .…”