Tartaric acid stabilized iridium nanoparticles with excellent laccase-like activity.

Iridium nanoparticles with an average size of 1.7 nm (Tar-IrNPs) were synthesized by the reduction of IrCl3 with NaBH4 in the presence of tartaric acid. As prepared Tar-IrNPs showed not only oxidase, peroxidase and catalase activities but also exhibited unprecedented laccase-like activity, which can catalyze the oxidation of the substrates o-phenylenediamine (OPD) and p-phenylenediamine (PPD) accompanied by significant color changes. The superb catalytic performance is evidenced by the fact that Tar-IrNPs can achieve better laccase-like activity with only 2.5% of the dosage of natural laccase. Furthermore, they also exhibited superior thermal stability and broader pH adaptability (2.0-11) over that of natural laccase. Tar-IrNPs can retain more than 60% of their initial activity at 90 °C, while the natural laccase has totally lost its activity at 70 °C. At a prolonged reaction time, the oxidation products of OPD and PPD can form precipitates due to oxidation induced polymerization. Thus Tar-IrNPs have been successfully used for the determination and degradation of PPD and OPD.

Protein-stabilized Ir nanoparticles with usual charge-selective peroxidase properties.

Selective removal of an organic compound in the coexistence of other constituents is a great challenge in separation and purification processes. In this work, bovine serum albumin (BSA)-stabilized iridium nanoparticles (IrNPs) were prepared via a facile one-step precipitation method. The resulting BSA-IrNPs were comprehensively characterized by TEM, XRD, XPS, UV-vis, FT-IR, and fluorescence spectroscopy as well as circular dichroism spectrometry. It was found that the nanoparticles with an average diameter of 3.6 nm were embedded in the aggregated protein matrix and the structure of the coating agent was maintained well on the surface of nanoparticles. The as-prepared nanozymes (BSA-IrNPs) exhibit strong peroxidase-like activity and can selectively catalyse the degradation of cationic compounds by H2O2 in the coexistence of other inorganic or organic substances at room temperature. Interestingly, the degradation of amino acids could be precisely controlled by adjusting the pH above or below their isoelectric points. The catalytic selectivity of BSA-IrNPs should be ascribed to the anchoring effect between the amidogen-containing molecules and BSA through electrostatic adsorption. The nanozyme also exhibits excellent reusability as it can be readily recycled from solution by static settlement or centrifugation. Therefore, BSA-IrNPs have great potential for the selective removal of cationic compounds and amino acids in a complex matrix.