The Study Of Defects Structure And Host-Guest Interaction In Metal-Organic Frameworks

Metal-organic frameworks(MOFs)are porous crystalline materials with promising applications in molecular adsorption,separation and catalysis.It has been discovered recently that the existence of structural defects introduced unintentionally or by design could have significant impact on their properties.However,the exact chemical composition and structural evolution under different conditions at the defects are still under debate.At the same time,the existence of defects in MOFs may influence the host-guest interaction of loaded molecules in MOFs.In first work,we performed multidimensional solid-state nuclear magnetic resonance(SSNMR)to elucidate an important scenario of MOF defects,uncovering the dynamic interplay between residual acetate and water.We discovered that acetate molecules coordinate to a single metal site monodentately and pair with water at the neighboring position.The acetates are highly flexible which undergo fast libration as well as a slow kinetic exchange with water through dynamic hydrogen bonds.The dynamic processes under variable temperatures and different hydration levels have been quantitively analyzed by SUPER and CODEX experiments.The integration of SSNMR and computer simulations allows a precision probe into defective MOF structures with intrinsic dynamics and disorder.Certain MOFs may have low cytotoxicity and high biocompatibility which make them favorable candidates as drug/gene delivery carriers.In the second work,we found that the defects in UiO-66 allow remarkably high loading of bioactive molecules.Combined with solid-state NMR techniques and molecular dynamics simulations,we revealed that the phosphate groups of the biomolecules bond to the defect sites in UiO-66.The loading of different biomolecules in the defective MOF is influenced by the number of phosphate groups,the geometry of functional groups,and the volume of biomolecules.The dynamic processes of phosphate groups have been quantitatively analyzed by SSNMR to determine the strength of host-guest interaction.Breast cancer skeletal metastases is a severe cancerous disease.In our last work,we designed a bone targeting immuno-stimulating MOF(BT-isMOF)which successfully inhibits bone damage by cancer cells in the murine model.BT-isMOF utilizes the defects in MOF to load immunostimulatory DNA oligomers(CpG)and is covered with bone-targeting zoledronic acid(ZOL).We proved the bone-targeting effect of BT-isMOF in vitro and in vivo and showed that BT-isMOF can suppress activity of osteoclasts and enhance M1 macrophage differentiation.Our results offer a new strategy for the further therapeutic applications of MOF materials in the treatment of cancer.