Self-assembled bionanoparticle polymer conjugates for building soft composite membranes
This project was focused on building a smart nanoporous membrane based on an assembly of bionanoconjugates. Horse spleen ferritin was chosen as a model protein scaffold to graft thermoresponsive polymers as Poly(N-isopropylacrylamide)(PNIPAAm) to it using the grafting from approach. PNIPAAm is a well known thermo-responsive polymer exhibiting a LCST of 32±C. After developing the well controlled atom transfer radical polymerization (ATRP) of NIPAAm in water at low temperature, the in-situ grafting of PNIPAAm from the ferritin was achieved. The grafting from approach consisted of two steps: the modification of ferritin into a macro-initiator by coupling the N-hydroxysuccinimide activated 2-bromo isobutyric acid ATRP initiator to the 72 addressable epsilon-amino end groups around ferritin polypeptide chains. It allows the modification of the majority of the amino sites of ferritin and induces a polymerization resulting in a higher grafting density. The condition of this chemistry has to be mild to prevent the denaturation of the proteins. The challenge was the preparation of monomeric conjugates with low polydispersity as ferritin aggregates in solution and perturbs the polymerization process. The resulting conjugates are well defined and show a thermo-responsive behavior with a Tc of about 31.5 ±C. The building of the membrane requires the crosslinking of the polymer matrix. The crosslinking was realized by a random copolymerization of NIPAAm with the monomer DMIAAm, (2-(dimethylmaleimido)-N-ethylacrylamide), a photocrosslinker. This photocrosslinker hosts a maleimide group able to form cyclobutane rings activated of UV irradiation and a sensitizer thioxanthone. The photocrosslinker is fully assimilated in the copolymer and decreases the lower critical solution temperature depending on its ratio. The assembly of the ferritin-P(NIPAAm-DMIAAm) conjugates at the solid-liquid interfaces on a mica sheet or silicon wafer creates a homogeneous thin polymer protein film. After crosslinking underUV irradiation while cooling the sample, the polymer matrix undergoes protein denaturation by the use of chaotropic agents and temperature to create nanopores in the membrane. The final membrane is a thin polymer film with monodisperse pores of about 16 nm of diameter and 2 nm depth carrying different functional groups. Such conjugates can also be assembled at the liquid-liquid interfaces forming porous micro-capsules as they reduce the interfacial tension and are able to stabilize oil droplets in solution. The ferritin-P(NIPAAm-DMIAAm) conjugates are interesting building blocks with adjustable properties able to produce functional and switchable nanoporous membranes and capsules.
info:eu-repo/classification/ddc/540, Ferritin, Membran, Chemie, horse spleen ferritin, PNIPAAm, ATRP, self-assembly, membrane
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