Kinetics Study on Reaction of Atenolol with Singlet Oxygen by Directly Monitoring the ¹O₂ Phosphorescence

The pharmaceutically active compound atenolol, a kind of \beta-blockers, may result in adverse effects both for human health and ecosystems if it is excreted to the surface water resources. To effectively remove atenolol in the environment, both direct and indirect photodegradation, driven by sunlight play an important role. Among indirect photodegradation, singlet oxygen (¹O₂), as a pivotal reactive species, is likely to determine the fates of atenolol. Nevertheless, the kinetic information on the reaction of atenolol with singlet oxygen has not been well investigated and the reaction rate constant is still ambiguous. Herein, the reaction rate constant of atenolol with singlet oxygen is investigated directly through observing the decay of the ¹O₂ phosphorescence at 1270 nm. It is determined that the reaction rate constant between atenolol and ¹O₂ is 7.0×10⁵ (mol/L)^-1\cdots^-1 in D₂O, 8.0×10⁶ (mol/L)^-1\cdots^-1 in acetonitrile, and 8.4×10⁵ (mol/L)^-1\cdots^-1 in EtOH, respectively. Furthermore, the solvent effects on the title reaction were also investigated. It is revealed that the solvents with strong polarity and weak hydrogen donating ability are suitable to achieve high rate constant values. These kinetics information on the reaction of atenolol with singlet oxygen may provide fundamental knowledge to the indirect photodegradation of \beta-blockers.