Redox-responsive polymers

Ferrocene is one of the most widely explored redox-responsive moieties that has been incorporated into a number of polymers to produce redox-responsive polymers and drug carriers, e.g., poly(ferrocenylsilane) (PFS) chains, which are composed of alternating ferrocene and silane units and can be reversibly oxidized and reduced by chemical and electrochemical means [90]. There are many other examples, including end-decorated homopolymer poly( -caprolactone)-ferrocene threaded onto a )8-cyclodextrin [91], redox-responsible hydrogel system synthesized by combination of / -cyclodextrin (/ -CD), dodecyl-modified poly(acrylic acid) [p(AA/Ci2)]. and ferrocenecarboxylic acid (FCA) [92], nanocapsules composed of a poly(vinylferrocene)-h/oc/c-poly(methyl methacrylate) shell [93] and amphiphilic block copolymers consisting of a hydrophilic poly(ethylene oxide) 

Hydrophilic domain with high cell affinity 

Polymers containing labile groups provide a beneficial opportunity 

Acid labile moieties inside polyanhydrides, poly(lactic/glycolic acid) (PLGA), and poly(b-amino esters) (PbAEs) induce redox responsiveness. Another typical redox-responsive pol mier is poly(NiPAAm-co-Ru(bpy)3), which can generate a chemical wave by the periodic redox change of Ru(bpy)3 into an oxidized state of lighter color. This redox reaction alters the hydrophobic and the hydrophilic properties of the potymer chains and results in swelling and deswelling of the potymer [103]. 

A number of redox-responsive polymers have been developed for drug delivery applications and have been used in many devices to control the delivery of drugs. 

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Huo M, Yuan J, Tao L, Wei Y (2014) Redox-responsive polymers for drug delivery from molecular design to applications. Polym Chem 5 1519... 

Mazurowski, M., Gallei, M., Li, J., Didzoleit, H., Stiihn, B., Rehahn, M. (2012). Redox-responsive polymer brushes grafted from polystyrene nanoparticles by means of surface initiated atom Transfer radical polymerization. Macromolecules, 45, 8970-8981. 

Yan, Y., Wang, Y, Heath, J. K., Nice, E. C., Caruso, F. (2011). Cellular association and cargo release of redox-responsive polymer capsules mediated by exofacial thiols. Advanced Materials, 25(34), 3916-3921. 

Sun, J.-T., Piao, J.-G., Wang, L-H., Javed, M., Hong, C.-Y., and Pan, C.-Y. (2013) One-pot synthesis of redox-responsive polymers-coated mesoporous silica nanopardcles and their controlled drug release. Macromol. Rapid Commun.,... 

In a study, polymeric nanoparticles (NPs) composed of a new redox-responsive polymer, poly(ethylene glycol]-b-poly(lactic acid] [MPEG-SS-PLA], were prepared to carry paclitaxel [PTX] for glutathione (GSH]-regulated drug delivery. The PTX-loaded MPEG-SS-PLA NPs were fabricated using an optimized oil-in-water emulsion/solvent evaporation method. The HPLC results revealed that the NPs released almost 90% PTX within 96 h when GSH presented at intracellular concentrations, whereas only a very small PTX amount was released at plasma GSH levels. The MTT assay results show that the NPs caused concentration- and time-... 

Elbert J, Mersini J, VUbrandt N, LedCTle C, Kraska M, Gallei M, Stuehn B, Plenio H, Rehahn M (2013) Reversible activity modulation of surface-attached grubbs second generation type catalysts using redox-responsive polymers. Macromolecules 46 4255—4267... 

In the area of ion sensing, cation recognition by electrodes containing functionalized redox-active polymers has been an area of considerable interest. Fabre and co-workers have reported the development of a boronate-functionalized polypyrrole as a fluoride anion-responsive electroactive polymer film. The electropolymerizable polypyrrole precursor (11) (Fig. 11) was synthesized by the hydroboration reaction of l-(phenylsulfonyl)-3-vinylpyrrole with diisopinocampheylborane followed by treatment with pinacol and the deprotection of the pyrrole ring.33 The same methodology was utilized for the production of several electropolymerizable aromatic compounds (of pyrrole (12) (Fig. 11), thiophene (13 and 14) (Fig. 11), and aniline) bearing boronic acid and boronate substituents as precursors of fluoride- and/or chloride-responsive conjugated polymer.34... 

Reported studies include various deposition and dissolution processes [876,908] and mechanistic studies of electrode processes at redox-active polymer-coated surfaces [909-912]. In a typical study of a polymer film containing ruthenium ions as redox-active centers, a cyclic voltammogram indicative of the one electron transfer at this center is observed as depicted in Fig. 5.144. The movement of ions needed for charge compensation in the film after a change of the redox state can be detected with PBD. The positive-going response during oxidation of the ruthenium center... 

The second approach involves using a separate redox-active group as the reporter group, with the polymer merely providing a convenient means for immobilizing the receptor onto an electrode surface (e.g., Compounds 42-44, Fig. 9). Thus, a more defined and controlled redox response to complexation can be envisaged, and a direct comparison with the performance of freely diffusing receptors is possible. 

Due to its high stability, the membrane of polymersomes has low fluidity, which leads to a very limited ttansport through the membrane. Thus, in order to allow for transmembrane transport, specific efforts are necessary. One option is the use of responsive polymer blocks, which allow a switching of the block from hydrophilic to hydrophobic, or vice versa. This can be achieved with thermo-responsive poly(Af-isopropylacrylamide) (PNIPAM), pH-sensitive amino-functionalized methacryl derivatives (e.g., poly(diethylaminoethyl methacrylate) (PDEAEM)), or the redox-sensitive poly(propylene sulfide) (PPS). 

Nakahata M, Takashima Y, Yamaguchi H, Harada A (2011) Redox-responsive self-healing materials formed from host-guest polymers. Nat Commun 2 511... 

Because of the redox responsiveness of the TTF hook guest, oxidation of these precipitates demonstrated the reversible nature of network formation as the amorphous precipitates could be dismpted and were observed to redissolve in solution. Reduction led again to the formation of NP precipitate and the chemical switching was demonstrated for several cycles. In addition, this property was further exploited as TTF is known to form much more stable pseudorotaxane complexes with blue box than with Np. A mixture of both TTF-AgNPs and Np-AuNPs with the blue box polymer 64 leads primarily to a silver-rich precipitate of AgNP aggregates as characterized by electron miaographs and electron dispersive analysis of the... 

Redox active polymer films are ideally suited to tackling these issues. The properties of many of these electroactive polymers, e.g., their conductivity, charge distribution, shape, etc., can be changed in a controlled and reproducible way in response to environmental stimuli, e.g., a change in the nature of the contacting solution, an applied voltage, light intensity, or mechanical stress. 

Both polymers show the characteristic redox responses of tetrathiafulvalene however, the behavior of PEDOT-TTF, where TTF is incorporated into the polymer chain, differs from that of the other polymer, where TTF moieties are pendant... 

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