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A peroxotitanium complex (later PTC) which is obtained by reacting hydrogen peroxide (H2O2) with TiCl4 or TiOSO4•nH2O is well-known as an important intermediate during the TiO2 preparation by the peroxo sol–gel method. Recently, peroxo-modified photocatalysts have been demonstrated to have their visible light photo-degradation activities significantly improved, while the PTC has been used in synthesizing these materials. Interestingly, peroxo-modified photocatalysts can degrade organic molecules in the dark in the presence of H2O2, suggesting that these kinds of materials could be potential peroxidase-mimics. However, such interrelationship has gained little attention in the field of catalysis chemistry and furthermore an enzyme-like activity of the PTC itself has not been studied yet. Therefore, we investigated to characterize the catalysis of the PTC as a new peroxidase mimic and explore its application value.
According to our research results, the PTC catalyzed the reaction between H2O2 and o-phenylenediamine (OPD) under the pH range of 3~6(optimum pH: 4.8). PTC's stability in the absence of OPD increased with decreasing the pH, temperature, and the catalyst concentration and with increasing the H2O2 concentration, perhaps due to the PTC's condensation. In addition, the PTC's catalysis was strongly inhibited by some hydroxyalkanoic acids including citrate and lactate, enabling to apply the PTC to quantify the hydroxyalkanoic acids that are of physiological and biochemical significance. Finally, the investigation on the apparent kinetic characteristics of PTC's catalysis, radical species confirmation and inhibitory effects of some organic acids against the PTC's catalytic activity has shown that the PTC should have one reaction center to oxidize OPD directly.
The research results have been published in the journal "Catalysis Science & Technology" under the title of "Peroxidase-like activity of a peroxotitanium complex and its inhibition by some hydroxyalkanoic acids" (https://doi.org/10.1039/d2cy00101b).