Peroxidase Enzyme Mimetic-catalyzed ATRP And Its Application In Functional Materials Preparation

Enzymes are environmentally friendly, non-toxic and renewable natural products. It has been widely used in food processing, medical diagnostic devices, pharmaceutical engineering, textile processing and so on. As an useful biocatalysts, enzymes have been extensively used in the vast majority of macromolecular synthesis reactions. Thus, research and development of the enzyme-catalyzed polymer synthesis is desirable for the environment and contributes to “green chemistry” for maintaining sustainable society. Among the naturally occurring enzymes, oxidoreductases and hydrolases are two classical enzyme classes, which have been employed for the synthesis of different kinds of polymers. A common methodology in which hydrolases are employed catalysis for ring opening polymerization(ROP) or polycondensations to produce degradable polymers for biomedical applications. Controlled/living radical polymerization catalyzed by peroxidase or other oxidoreductases is a new emerging field. As a novel methodology of polymer synthesis method, more new applications are waiting for explore. As a synthesized peroxidase mimic, Dh HP-6 shows high peroxidase enzyme activity, and presents a lot of biological activities in improving cell survivals and inhibiting apoptosis against reactive oxygen species. Structure and properties of Dh HP-6 suggest that it might serve as a good candidate of ATRP catalyst, although no relevant work has been reported to the best of our knowledge. In the present work, we study the catalytic ability of Dh HP-6 in controlled radical polymerization. Dh HP-6 shows a powerful catalytic ability and a good tolerance to a wide range of p H values(from 3.0 to 11.0), demonstrating a great potential in the production of diverse polymers with different functional groups including epoxy, –COOH and –OH etc. via ARGET ATRP. While, for the first time, the combination of enzymatic ATRP with other chemical or enzymatic polymerization techniques will be reported herein. We demonstrate the double-enzymatic synthesis of block copolymers by the combination of e ROP and enzymatic ATRP, showing the first example on the synthesis of copolymers by the joint of different kinds of enzymatic polymerizations and proving Dh HP-6 a new promising environment benign ATRP catalyst. At last, this peroxidase mimetic catalytic atom transfer radical polymerization(ATRP) was first used to install tertiary amine-functionalized polymer brushes on the surfaces of mesoporous silica nanoparticles(MSNs) in a facile and highly efficient manner. The controlled release of loaded cargo in response to p H changes is further demonstrated. The main contents are as follows:Firstly, the catalytic ability of Dh HP-6 in atom transfer radical polymerization(ATRP) was explored. As Dh HP-6 is highly soluble in water, we first chose water solvable PEGMA500 as a monomer and sodium ascorbate as a reducing agent, and conducted the polymerization in PBS. As can be seen from the results the molecular weights of the resulting polymers increased linearly with monomer conversion and the PDI were relatively low. The polymerization rate was fast, and semilogarithmic kinetic plot of ln([M]0/[M]) vs. time changed linearly during the first 1.5 or 2.0 hours of the reaction, indicating that the concentration of the growing radicals was constant. Dh HP-6 also been explored to organic solvent for water insolvable monomer’s polymerization. Conditions for Dh HP-6 catalytic ATRP in organic solvent has been studied in detail. In order to confirm that the initiation was induced from ATRP initiator, we utilized polyethylene glycol(PEG, Mw=550) containing bromoisobutyrate(PEG-Br) to synthesize copolymers. Synthetic PEG-PGMA copolymers with lower molecular weight were identified by 1H NMR and GPC, which confirmed that the reaction was started from PEG-Br. Meanwhile, Dh HP-6 can act as an environmental benign ATRP catalyst in water or DMF–H2O mixed solvent, avoiding the use of toxic transition-metal-based catalysts.Subsequently, as e ROP is a well-established biocatalytic and clean process for the synthesis of degradable biomaterials. Herein, we investigated the double-enzymatic synthesis of block copolymers by the combination of enzymatic ATRP and e ROP. Poly(?-caprolactone)(PCL) is a kind of degradable polymer that can be used in drug delivery and tissue engineering, therefore we choose PCL as one useful fragment of the target copolymer for potential biological applications. Firstly, we synthesized hydroxyl group-containing 2-hydroxyethyl 2-bromoisobutyrate(HEBi B), and used this bifunctional initiator to initiate 3-caprolactone polymerization by e ROP to obtain PCL with ATRP initiator on the end of the polymer chain(PCL-Br), whose Mn was analyzed by GPC. After purification, we conducted Dh HP-6 catalyzed ATRP of GMA using PCL-Br as initiator. Analysis the Mn and PDI of PCL-PGMA by GPC revealed monomodal distribution with a clear shift to higher molecular weight after enzymatic ATRP of GMA. This suggests the absence of PCL-Br macroinitiator or homopolymerof GMA in the final copolymer products. Compared to PCL-Br, the molecular weight increased, and PDI was narrower than PCL-Br. Structure was confirmed by 1H NMR spectroscopy, which also indicates the successful preparation of PCL-PGMA copolymers through a combination of these two enzymatic polymerization methods. Use this methodology two more types of block copolymers with a biodegradable segment was been Synthesized, that PCL-PMAA and PCL-PHEMA. It is worth noting that the synthesized copolymer could be further functionalized to generate more novel polymer structure.Finally, in order to explore the controllability of SI-ATRP on materials surface, we further study the Dh HP-6 catalyzed polymerization on mesoporous silica nanoparticles(MSNs). We decorate the surfaces of MSNs with PDMAEMA polymer brushes by Dh HP-6 catalyzed SI-ATRP approach. The resulting organic-inorganic hybrid nanocarriers were fully characterized by FT-IR, TGA, XPS, XRD, SEM, TEM, elemental analysis, zeta-potential, and N2 adsorption–desorption isotherms, which demonstrated the successful coating of p H-responsive polymers on MSN surface. As a model drug Rhodamine 6G(Rh6G) was loaded in the mesopores of PDMAEMA brushes-MSN hybrid materials, and its controlled release in response to p H changes is further demonstrated. The green catalysis-mediated biocompatible organic-inorganic hybrid nanomaterials hold great potential in nanomedicine and cancer therapy.