Single-electron transfer from NADH analogues to singlet oxygen

Area of Science:

• Photochemistry
• Chemical Kinetics
• Biochemistry

Background:

• Singlet oxygen (O2(1 delta g)) is a reactive oxygen species implicated in various biological processes.
• Understanding its quenching mechanisms is crucial for elucidating its role in cellular environments.

Purpose of the Study:

• To determine the rate constants for physical and reactive quenching of O2(1 delta g) by nicotine and several NAD(P)H analogs.
• To investigate the involvement of one-electron transfer mechanisms in these quenching processes.

Main Methods:

• Laser flash photolysis was employed to measure quenching rate constants.
• Kinetic spectroscopy was used to detect reaction intermediates and products.
• Reaction with 1,4-benzoquinone confirmed O2 production.

Main Results:

• Rate constants for O2(1 delta g) quenching were determined for nicotine and reduced forms of nicotinamide adenine dinucleotide (NAD+), nicotinamide mononucleotide (NMN), nicotinamide adenine dinucleotide phosphate (NADP+), and nicotinamide hypoxanthine dinucleotide (NHyD).
• Evidence for one-electron transfer was observed for the reduced forms of NAD+, NMN, NADP+, and NHyD.
• Reactive quenching constituted approximately 60% of the total quenching for these four compounds.

Conclusions:

• Nicotine and NAD(P)H analogs can quench singlet oxygen through both physical and reactive pathways.
• One-electron transfer is a significant reactive quenching mechanism for reduced forms of NAD+, NMN, NADP+, and NHyD.
• These findings contribute to understanding the reactivity of singlet oxygen with biologically relevant molecules.