Abstract
REDOX responsive (nano)materials typically exhibit chemical changes in response to the presence and concentration of oxidants/reductants. Due to the complexity of biological environments, it is critical to ascertain whether the chemical response may depend on the chemical details of the stimulus, in addition to its REDOX potential, and whether chemically different responses can determine a different overall performance of the material. Here, we have used oxidation-sensitive materials, although these considerations can be extended also to reducible ones. In particular, we have used poly(propylene sulfide) (PPS) nanoparticles coated with a PEGylated emulsifier (Pluronic F127); inter alia, we here present also an improved preparative method. The nanoparticles were exposed to two Reactive Oxygen Species (ROS) typically encountered in inflammatory reactions, hydrogen peroxide (H2O2) and hypochlorite (ClO−); their response was evaluated with a variety of techniques, including diffusion NMR spectroscopy that allowed to separately characterize the chemically different colloidal species produced. The two oxidants triggered a different chemical response: H2O2 converted sulfides to sulfoxides, while ClO− partially oxidized them further to sulfones. The different chemistry correlated to a different material response: H2O2 increased the polarity of the nanoparticles, causing them to swell in water and to release the surface PEGylated emulsifier; the uncoated oxidized particles still exhibited very low toxicity. On the contrary, ClO− rapidly converted the nanoparticles into water-soluble, depolymerized fragments with a significantly higher toxicity. The take-home message is that it is more correct to discuss ‘smart’ materials in terms of an environmentally specific response to (REDOX) stimuli. Far from being a problem, this could open the way to more sophisticated and precisely targeted applications.
Highlights
Variations in REDOX potential can o en be associated to speci c biological environments and sometimes to pathological conditions,[1,2]materials responding to REDOX-active species can be used to perform biological targeting
The different chemistry correlated to a different material response: H2O2 increased the polarity of the nanoparticles, causing them to swell in water and to release the surface PEGylated emulsifier; the uncoated oxidized particles still exhibited very low toxicity
The molecular weight dispersity of these model linear polymers is clearly larger than when the disul de presence is carefully avoided (1.4–1.6 vs. z 1.1 with protected initiators and in situ reducing agents); a high MW shoulder can be spotted in the GPC traces (Fig. 1, le ): this is typical of polymers with internal disul des that are a clear visual marker of disul de-mediated chain transfer activity.[26]
Summary
Variations in REDOX potential can o en be associated to speci c biological environments and sometimes to pathological conditions,[1,2] (nano)materials responding to REDOX-active species can be used to perform biological targeting. 1 mL of nanoparticle dispersion in deionized water (concentration z 3.5 mg mLÀ1 1⁄4 0.35% wt.) was added to 10 mL of an aqueous solution of H2O2 or NaOCl (of an adequate concentration) and adjusted to pH 1⁄4 7.4 by the addition of concentrated NaOH (aq), to obtain a nal concentration of z 0.32 mg mLÀ1 of nanoparticles (1⁄4 4.3 mM in thioethers); the reaction was allowed to proceed at 37 C monitoring the timedependent changes in turbidity (optical density at a wavelength of 600 nm), particle size (DLS) and Nile Red uorescence (at 620 nm). Preparation of test materials: puri ed pristine PA4 or PBr4 nanoparticles (0.02 Pluronic/PS weight ratio; puri cation via ultra ltration as previously described; concentration around 40 mg mLÀ1 in deionized water) were diluted with cell culture medium to reach the desired nal concentration. The absorbance at 562 nm was nally recorded a er 2 hours incubation at 37 C
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