PH-responsive brushes

Van Camp, W., Du Prez, F. E., Alem, H., Demoustier-Champagne, S., Willet, N., Grancharov, G., et al. (2010). Poly(acrylic acid) with disulfide bond for the elaboration of pH-responsive brush surfaces. European Polymer Journal, 46,195-201. 

This technology has been expanded to prepare intelligent nanocapsules with temperature-responsive cross-linked shells and pH-responsive brushes on their inner walls. These nanocapsules have been prepared by the surface-initiated atom transfer radical polymerization (SI-ATRP) technique with sihca NP as the sacrificial templates. The two-step, sequential SI-ATRP procedure provided the poly(tert-butyl acrylate) (PtBA) brushes on the inner walls of the temperature-responsive cross-linked poly(A-isopropylacryl-amide) (PNIPAA) shells. Then the ester groups in the nanocapsules were transformed chemically into carboxyl groups after etching the silica templates with HF (Mu and Liu, 2012). 

Figure 4.9 pH-responsive brushes of P2VP on silica nanoparticles (Tsyalkovsky et al., 2010). 

Recently, pH-responsive redox brushes have been described by Katz and Minko [61]. It has been shown that the electrochemical response of PVP-Os grafted to ITO completely disappears when going from pH 4 to pH > 6, which was attributed to film collapse due to deprotonation of pyridine units. The same effect was not observed for randomly adsorbed polyelectrolytes. 

Those nanoparticles (3LNPs) were fabricated via a pH-controlled hierarchical self-assembly of a tercopolymer brush (Schemes 10.2 and 10.3), which contained hydrophilic polycaprolactone (PCL) chains, water-soluble PEG chains, and pH-responsive poly[2-(iV,iV-diethylamino)ethyl methacrylate] (PDEA) chains. PDEA is a polybase that is soluble at low pH but insoluble at neutral pH [167-169]. The brush polymer was initially dispersed in a pH 5.0 solution where the PDEA chains were protonated and hence water-soluble. The hydrophobic PCL chains and drug molecules associated to form the hydrophobic core. The PEG and protonated PDEA chains formed a hydrophilic corona surrounding the core. After the solution pH was raised to 7.4, the PDEA chains were deprotonated and became hydrophobic, collapsing on the PCL core as a hydrophobic middle layer with only the PEG chains forming the hydrophilic corona (Scheme 10.3). 

FIGURE 36.6 In vitro release profiles of quercetin from folated nanoparticles (at pH 5.8 ( ) and 7.4 ( )) and nonfolated nanoparticles (at pH 5.8 (A) and 7.4 ( )) at 37°C (n = 3). (Reprinted from Eur. J. Med. Chem., 50, Khoee, S. and Rahmatolahzadeh, R., Synthesis and characterization of pH-responsive and folated nanoparticles based on self-assembled brush-like PLGA/PEG/AEMA copolymer with targeted cancer therapy properties A comprehensive kinetic study, 416-427. Copyright 2012, with permission from Elsevier Masson SAS.)... 

Khoee S, Rahmatolahzadeh R. Synthesis and characterization of pH-responsive and folated nanoparticles based on self-assembled brush-like PLGA/PEG/AEMA copolymer with targeted cancer therapy properties A comprehensive kinetic study. Fur J Med Chem. 2012 50 416-427. 

Wang M, Zou S, Gutain G, Shen L, Deng K, Jones M, Walker GC, Scholes GD, Winnik MA (2008) A water-soluble pH-responsive molecular brush of poly(NJ4-dimethylaminoethyl methacrylate) grafted polythiophtaie. Macromolecules 41 6993... 

PDMAEMA brushes were also prepared on the surface of the nanopores in freestanding silica colloidal membranes [61], which showed similar pH-responsive transport behavior [62]. The free-standing silica colloidal membranes were prepared from silica spheres that were calcinated for 4 h at 600 °C, and were then assembled into colloidal crystals by vertical deposition using 12 wt% colloidal solutions in ethanol. The colloidal films were sintered at 1050 °C for 12 h to produce durable free-standing membranes (Fig. 8.16), followed by rehydroxylation with tetrabutyl-ammonium hydroxide in water to restore the surface hydroxyl groups. 

The observed pH-responsive behavior may originate from the electrostatic interaction between the amine end-groups of the poly(L-alanine) bmsh and the residual amines on the silica surface in a manner similar to that described earlier for other types of surface-immobilized polymer brushes [21, 68]. It is possible that at low pH, both types of amine groups become protonated and their mutual repulsion leads to the polymer extension, as described above. Thus, at low pH, the polymer brush blocks a larger portion of the nanopore volume. As the pH is increased, the eleetrostatic... 

Jia, H., Wildes, A., Titmuss, S. (2011). Structure of pH-responsive polymer brushes grown at the gold-water interface dependence on grafting density and temperature. Macromolecules, 45, 305-312. 

Mi, L., Bernards, M. T., Cheng, G., Yu, Q., Jiang, S. (2010). pH responsive properties of non-fouling mixed-chaige polymer brushes based on quaternary amine and carboxyhc acid monomers. Biomaterials, 31, 2919-2925. 

Figure 5.6 (a) Schematic illustration of conformation changes of a pH-responsive polymer brush, (b) Response of a poly(methacrylic acid) brush (11 lun thick) modified quartz crystal... 

Another application of pH-responsive polymers was shown by de Groot et al. (2013), as shown in Figure 5.11. Surface-initiated atom transfer radical polymerization synthesized PMAA brushes were used to create pH-responsive nanoporous platforms. It was shown that at pH 4, gating of ions was allowed through the nano channels, whereas at pH 8, the pores were closed. The authors predict that their pH-re-sponsive channels have potential as electrochemical biosensors and in bioseperation technology. 

Switching transport through nanopores with pH-responsive polymer brushes for controlled ion permeability. ACS Applied Materials Interfaces, 5, 1400-1407. 

Sanjuan, S., Perrin, R, Pantoustier, N., and Tran, Y. 2007. Synthesis and swelling behavior of pH-responsive polybase brushes. Lanvmuir 23 5769-5778. 

Duner, G., Anderson, H., Myrskog, A., Hedlund, M., Aastrup, T., Ramstrom, O., Surface-Confined Photopolymerization of pH-Responsive Acrylamide/ Acrylate Brushes on Polymer Thin Films, Langmuir 2008,24,7559-7564. 

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