Self-Assembly of Protamine Biomacromolecule on Halloysite Nanotubes for Immobilization of Superoxide Dismutase Enzyme

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.

Layered double hydroxide-based antioxidant dispersions with high colloidal and functional stability

“…Note that added polyelectrolytes below the ASP were strongly adsorbed on the oppositely charged particles, i.e., no free polyelectrolyte could be found in the solution phase. 46 Similar charging behaviour has been reported earlier for oppositely charged particle-polyelectrolyte systems, 32,35,45 including LDH particles. 10,47,48,51,52 Beside these generic findings in the tendency of the zeta potentials, system specific effects were also observed.…”

“…Both bare LDHs are negatively charged and possess low charge (s is À5 and À16 mC m À2 for EA-LDH and EtOH-EA-LDH, respectively), which is typical for natural inorganic particles. 35,47,60 Similarly, relatively low magnitude of charge was determined for the EtOH-EA-LDH/PEI (+16 mC m À2 ) and EtOH-EA-LDH/PS (+6 mC m À2 ), while the former one is slightly higher due to the higher abundance of the protonated primary amino groups. Note that these charges were determined at the slip plane and that counterion condensation contributed to this low charge.…”

“…PAAm-co-DADMAC is a quaternary polyammonium salt and it also contains non-charged PAAm blocks in its chain possessing, therefore, the lowest line charge density. These polyelectrolytes have been proven as effective stabilizing or aggregating agents for colloidal particles; 33,35,46,60,61 however, no systematic colloidal stability studies were reported for LDHs. To assess the charging features at the slip plane, the electrophoretic mobilities were converted to zeta potentials using eqn (S4) ESI.…”

“…In turn, the activity of the materials strongly depends on the surface area, which can be improved by stabilization of the nanocomposites in the dispersions. Synthetic (e.g., polyacrylates, 32 polyamines 33 and polystyrenes 34 ) and natural (e.g., polypeptides, 35 polysaccharides 36 and humic substances 37 ) polyelectrolytes have been proven to be excellent stabilizing agents for nano-or colloidal particles in various applications including drug delivery, 38 wastewater treatment 39 and dye production. 40 Comprehensive studies carried out using surface sensitive techniques have revealed that their adsorption on oppositely charged surfaces is rather strong and irreversible.…”

Chitosan-Grafted Halloysite Nanotubes-Fe3O4 Composite for Laccase-Immobilization and Sulfamethoxazole-Degradation

“…In addition, HNTs-M-chitosan (1%) in solution have good colloidal stability. Since potential applications take place in dispersions, particle aggregation should be prevented, in order provide homogeneously distributed primary particles of high surface area [ 35 , 36 , 37 ]. Moreover, Figure 2 B presents the ABTS oxidation spectra by free laccase and immobilized laccase on HNTs-M-chitosan (1%).…”