Conformational Transformation of pH-Responsive Hairy Cellulose NanoCrystalloids in Salt-Free Dilute Solutions.

Among biomaterials, pH-responsive nanoparticles have promising potential for overcoming nonspecific therapeutic delivery by taking advantage of the pH gradient between physiological and pathological states. This article discusses pH-dependent conformations of an organic nano particle that has a needle-shaped body from crystalline cellulose, sandwiched between two amorphous regions from chemically nanoengineered dicarboxylated cellulose (DCC). Computational study on a single free DCC chain elucidated that in a salt-free dilute solution, the chain undergoes a major transformation between pH similar to 3 and similar to 6.3. Through this transformation, the DCC chain nature varies from globular neutral polymer to coiled quasi-neutral polymer and finally to rodlike polyelectrolyte. Study on the particle nanostructure indicated that, at pH similar to 3, the conformation of the amorphous regions is analogous to that of polymer brushes in poor solvents, whereas at pH similar to 5, the conformation changes to that of quasi-neutral polymer brushes in good solvents. For pH > 6.3, the conformation transforms into that of star-like polyelectrolytes. The height of the amorphous region exhibits a regressive trend up to pH similar to 6.3, followed by a progressive trend up to pH similar to 10. Study on the hydrodynamic properties revealed a sharp decline in the diffusion rate as the pH varies from similar to 3 to similar to 5, followed by a plateau for higher pH. It was demonstrated that, at pH similar to 3, the nanoparticle may form a coherent nanophase with a rodlike structure. These results may provide insight into designing pH responsive nanocelluloses with a controlled expansion and diffusion coefficient.