Spectroscopic investigations on the effect of N-Acetyl-l-cysteine-Capped CdTe Quantum Dots on catalase

•The interaction between CdTe QDs (QDs-612) and catalase (CAT) is spontaneous.•The predominant force of the binding is hydrophobic interaction.•The interaction changes the secondary structure of CAT.•Tryptophan residues of CAT expose to a hydrophilic environment.•QDs-612 could affect the function of CAT by decreasing its catalytic activity.

Quantum dots (QDs) are recognized as some of the most promising semiconductor nanocrystals in biomedical applications. However, the potential toxicity of QDs has aroused wide public concern. Catalase (CAT) is a common enzyme in animal and plant tissues. For the potential application of QDs in vivo, it is important to investigate the interaction of QDs with CAT. In this work, the effect of N-Acetyl-l-cysteine-Capped CdTe Quantum Dots with fluorescence emission peak at 612 nm (QDs-612) on CAT was investigated by fluorescence, synchronous fluorescence, fluorescence lifetime, ultraviolet–visible (UV–vis) absorption and circular dichroism (CD) techniques. Binding of QDs-612 to CAT caused static quenching of the fluorescence, the change of the secondary structure of CAT and the alteration of the microenvironment of tryptophan residues. The association constants K were determined to be K288K = 7.98 × 105 L mol−1 and K298K = 7.21 × 105 L mol−1. The interaction between QDs-612 and CAT was spontaneous with 1:1 stoichiometry approximately. The CAT activity was also inhibited for the bound QDs-612. This work provides direct evidence about enzyme toxicity of QDs-612 to CAT in vitro and establishes a new strategy to investigate the interaction between enzyme and QDs at a molecular level, which is helpful for clarifying the bioactivities of QDs in vivo.

Graphical abstractN-Acetyl-l-cysteine-Capped CdTe Quantum Dots with fluorescence emission peak at 612 nm (QDs-612) could interact with catalase (CAT) which leads to conformational and functional changes of the enzyme. The potential toxicity of QDs-612 to CAT was investigated by multi-spectroscopic techniques. Binding of QDs-612 to CAT caused static quenching of the fluorescence, the change of the microenvironment of tryptophan residues and the secondary structure of CAT. The interaction between QDs-612 and CAT was spontaneous through hydrophobic force with about 1:1 stoichiometry. Besides, the CAT activity was also inhibited for the bound QDs-612. This work clarifies the fact that QDs-612 can not only contribute to the conformational changes of CAT but also alter the enzyme function.Figure optionsDownload full-size imageDownload as PowerPoint slide