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Most of the chemistry in nanoporous materials with small pore sizes and windows takes place on the outer surface, which is in direct contact with the substrate/solvent, rather than within the pores and channels. Here, we report the results of our comprehensive atomistic molecular dynamics (MD) simulations to decipher the interaction of water with a realistic finite ∼5.1 nm nanoparticle (NP) model of ZIF-8, with edges containing undercoordinated Zn metal sites, vs a conventionally employed pristine crystalline bulk (CB) model. The hydrophobic interior surface of the CB model imparts significant dynamical behavior on water molecules with (i) increasing diffusivity from the surface toward the center of the pores and (ii) confined water, at low concentration, showing similar diffusivity to that of the bulk water. On the other hand, water molecules adsorbed on the surface of the NP model exhibit a range of characteristics, including “coordinated”, “confined”, and “bulk-like” behavior. Some of the water molecules form coordinative bonds with the undercoordinated Zn metal centers and act as nucleation sites for the water droplets to form, facilitating diffusion into the pores. However, diffusion of water molecules is limited to the areas near the surface and not all the way to the core of the NP model. Our atomistic MD simulations provide insights into the stability of ZIFs in aqueous solutions despite hydrolysis of their outer surface. Such insights are helpful in designing more robust nanoporous materials for applications in humid environments.
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Surface Coating of ZIF‐8 Nanoparticles with Polyacrylic Acid: A Facile Approach to Enhance Chemical Stability for Biomedical Applications
Abstract Nanoparticles of zeolitic imidazole framework‐8 (ZIF‐8 NPs), which are the subclass of metal‐organic frameworks consisting of Zn ion and 2‐methylimidazole, have been identified as promising drug carriers since their large microporous structure is suited for encapsulating hydrophobic drug molecules. However, one of the limitations of ZIF‐8 NPs is their low stability in physiological solutions, especially in the presence of water and phosphate anions. These molecules can interact with the coordinatively unsaturated Zn sites at the external surface to induce the degradation of ZIF‐8 NPs. In this study, herein a facile approach is reported to enhance the chemical stability of ZIF‐8 NPs by surface coating with polyacrylic acid (PAA). The PAA‐coated ZIF‐8 (PAA‐ZIF‐8) NPs are prepared by mixing ZIF‐8 NPs and PAA in water. PAA coating inhibits the degradation of ZIF‐8 NPs in water as well as phosphate‐buffered saline over 6 days, which seems to be due to the coordination of carboxyl groups of PAA to the reactive Zn sites. Furthermore, the PAA‐ZIF‐8 NPs loaded with the anticancer drug doxorubicin (Dox) show cytotoxicity in human colon cancer cells. These results clearly show the feasibility of the PAA coating approach to improve the chemical stability of ZIF‐8 NPs without impairing their drug delivery capability.
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- Award ID(s):
- 2102848
- PAR ID:
- 10580179
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Macromolecular Bioscience
- Volume:
- 25
- Issue:
- 2
- ISSN:
- 1616-5187
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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