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Abstract
An antioxidant material composed of halloysite nanotubes (HNTs), protamine sulfate polyelectrolyte (PSP), and superoxide dismutase (SOD) enzyme was prepared by self-assembly of the PSP and SOD biomacromolecules on the nanoparticulate support. The structural, colloidal and biocatalytic features were assessed. Adsorption of PSP on the oppositely charged HNT surface at appropriate loadings gave rise to charge neutralization and overcharging, which resulted in unstable and stable dispersions, respectively. The formation of a saturated PSP layer on the HNT led to the development of positive surface charge and to remarkable resistance against salt-induced aggregation making the obtained HNT-PSP hybrid suitable for immobilization of negatively charged SOD. No enzyme leakage was observed from the HNT-PSP-SOD composite indicating sufficient structural stability of this material due to electrostatic, hydrophobic, and hydrogen bonding interactions taking place between the particles and the biomacromolecules. Enzymatic assays revealed that SOD kept its functional integrity upon immobilization and showed high activity in superoxide radical dismutation. In this way, stable antioxidant bionanocomposite dispersions were obtained, which can be used as antioxidants in heterogeneous samples.
Highlights
Antioxidant enzymes are the most efficient defense systems against reactive oxygen species (ROS), which are responsible for the development of several diseases including cancer due to their high reactivity against lipids and other cell constituent biomolecules.[1]
An antioxidant nanocomposite consisting of halloysite nanotubes (HNTs) with selfassembled protamine sulfate polyelectrolyte (PSP) and superoxide dismutase (SOD) biomacromolecules on the outer surface was developed
The aggregation of the particles was tuned by varying the PSP dose, and stable dispersions were observed once the amount of the PSP biomacromolecule was high enough to cover the entire outer surface of the HNTs
Summary
Antioxidant enzymes are the most efficient defense systems against reactive oxygen species (ROS), which are responsible for the development of several diseases including cancer due to their high reactivity against lipids and other cell constituent biomolecules.[1]. Despite the opposite sign of charge of the particles, one can conclude that the dispersion characteristics of HNT and HNTPSP are very similar, and both nanotubes form stable dispersions below 30 mM KCl. HNT-PSP was selected for the SOD immobilization process as stronger enzyme adsorption is expected on their positively charged surface than in the case of negatively charged bare HNT. The analysis of the spectra revealed that the spectrum measured for the supernatant obtained after SOD adsorption on HNT-PSP was similar to the one of the reference sample devoid of SOD molecules This finding clearly shows that the enzyme quantitatively adsorbed on the HNT-PSP, and that no partitioning between the bulk and surface occurred, when an enzyme loading of 10 mg/g is applied. The formation of a protein corona on the particle surface usually further improves the colloidal stability of the nanocomposites.[58,59]
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