(513cs) Understanding the Induction Time Associated with the Photoreduction of Resazurin

Reduction of resazurin to resorufin by hydroxylamine in the presence of metal catalysts has been extensively used as a model reaction for evaluating the catalytic activities of metal nanoparticles. In particular, the photocatalytic reduction of resazurin in the presence of gold nanoparticles has been well studied to assess the catalytic efficiencies of gold nanoparticles. However the mechanism associated with this reaction is not completely understood yet. An interesting mechanistic feature of resazurin reduction by hydroxylamine is the induction time. Induction time is the time interval at the beginning of the reaction when no turnover of resazurin is observed. Once the induction time is over, the reaction starts. There has been a contradictory explanation about the origin of the induction time. The induction time observed during resazurin reduction in the presence of gold nanoparticles is previously attributed to the time required to surface restructuring of the gold catalysts. However, the induction time is observed even in the absence of the metal catalysts, hence the surface restructuring of the metal catalysts could not be the sole reason for the induction time. It is important to know the accurate mechanism of a reaction when it is employed as a model reaction in a catalytic study as most of the experimental data depends on the reaction mechanism. Therefore in this study we investigate the factors governing the induction time associated with the reduction of resazurin by hydroxylamine in the presence of gold nanoparticles as the catalyst. We systematically studied how the different factors such as concentrations of the catalyst, the dissolved oxygen as well as the hydroxylamine affecting the induction time. We found that the observed induction time during the resazurin reduction can be attributed to the autoxidation of hydroxylamine by dissolved oxygen. This autoxidation reaction can be catalyzed by gold nanoparticles.