Abstract
In this study, we synthesized water-soluble hyperbranched poly(amido acid)s (HBPAAs) featuring multiple terminal CO2H units and internal tertiary amino and amido moieties and then used them in conjunction with an in situ Fe2+/Fe3+ co-precipitation process to prepare organic/magnetic nanocarriers comprising uniformly small magnetic iron oxide nanoparticles (NP) incorporated within the globular HBPAAs. Transmission electron microscopy revealed that the HBPAA-γ-Fe2O3 NPs had dimensions of 6–11 nm, significantly smaller than those of the pristine γ-Fe2O3 (20–30 nm). Subsequently, we covalently immobilized a bacterial γ-glutamyltranspeptidase (BlGGT) upon the HBPAA-γ-Fe2O3 nanocarriers through the formation of amide linkages in the presence of a coupling agent. Magnetization curves of the HBPAA-γ-Fe2O3/BlGGT composites measured at 300 K suggested superparamagnetic characteristics, with a saturation magnetization of 52 emu g−1. The loading capacity of BlGGT on the HBPAA-γ-Fe2O3 nanocarriers was 16 mg g−1 support; this sample provided a 48% recovery of the initial activity. The immobilized enzyme could be recycled 10 times with 32% retention of the initial activity; it had stability comparable with that of the free enzyme during a storage period of 63 days. The covalent immobilization and stability of the enzyme and the magnetization provided by the HBPAA-γ-Fe2O3 NPs suggests that this approach could be an economical means of depositing bioactive enzymes upon nanocarriers for BlGGT-mediated bio-catalysis.
Highlights
In the quest to develop enzyme immobilization technologies, magnetic nanoparticles (NPs) are often used as nanocarriers because they allow facile re-collection and definite repeatability of biocatalysts having long-term stability [1,2,3,4,5,6,7]
In this study we encapsulated γ-Fe2O3 NPs through co-precipitation of Fe2+/Fe3+ in the presence of aqueous NH4OH and a templating water-soluble hyperbranched poly(amido acid)s (HBPAAs) having a molecular weight of 10,100 g mol−1 (Scheme 1)
The efficacy of the dendritic HBPAA templates in controlling the organic/magnetic nanohybrids was achieved through growth of the NPs within the branched structure, where they were protected by the exterior functional groups
Summary
In the quest to develop enzyme immobilization technologies, magnetic nanoparticles (NPs) are often used as nanocarriers because they allow facile re-collection and definite repeatability of biocatalysts having long-term stability [1,2,3,4,5,6,7]. Surface-functionalized dendritic polymer/magnetic nanocarriers present many surfaces functional groups for covalent immobilization of natural enzymes, providing a means of facilitating product separation and sometimes improving the stability of biocatalysts. We prepared water-soluble hyperbranched poly(amido acid)s (HBPAAs), based on wholly aliphatic structure with terminal carbonyl functionalities, through a facile self-condensation synthesis [27]. Considering their water-solubility and dendritic characteristics (size controllability; molecular uniformity), we wished to explore the possibility of using such HBPAAs to prepare organic/magnetic nanohybrids exhibiting desired magnetization for further biological application as enzyme nanocarriers. We sought to immobilize a natural protein upon the multifunctional HBPAA-γ-Fe2O3 NPs as a route toward the development of magnetic biomaterial hybrids with potential applications in biocatalyst technology.
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