Assembly Regulation And Photothermal Antibacterial Investigations Of Molybdenum-containing Polyoxometalates And Biofunctional Molecules

Polyoxometalates(POMs)are a class of metal oxide inorganic nanoclusters.They are built from connections of MO_x polyhedra,where M is generally an early transition metal in its high oxidation state.POMs have nanoscale dimensions and high negative charge overall characteristics,which have shown excellent magnetic,redox,luminescence,and catalytic properties.These remarkable physical and chemical properties make them widely used in the fields of catalysis,materials science,macromolecular crystallography,and medicine.The Na₁₅[Mo^VI₁₂₆Mo^V₂₈O₄₆₂H₁₄(H₂O)₇₀]·400H₂O(abbreviated as Mo₁₅₄)is a giant ring-shaped molybdenum-containing polyoxometalates with very well-defined chemical composition and structural morphology.Due to the intervalence charge transfer(IVCT)between Mo(V)and Mo(VI),it can produce effective absorption at 748 nm,which can be used for photothermal therapy in the near-infrared region.However,naked POMs inevitably bind to proteins or other biomolecules in practical applications,which may cause different degrees of cytotoxicity.Therefore,in order to reduce the biotoxicity and improve its structural stability and photothermal conversion efficiency,we adopted a co-assembly scheme of positively charged biocompatible molecules with POMs to encapsulate POMs through electrostatic interactions to enhance their photothermal properties and optimize the biocompatibility of the material and reduce toxicity.In this paper,the biomolecular--TK-14 peptide and Spermine(Spm)were respectively assembled with Mo₁₅₄ to construct a structurally stable supramolecular assembly,and then investigate their photothermal antibacterial properties.(1)Assembly regulation and photothermal antibacterial investigations of Mo₁₅₄and TK-14:Mo₁₅₄ was assembled with TK-14 peptide,and the Mo₁₅₄/TK-14 assembly was characterized by Zeta potential,dynamic light scattering(DLS)and TEM.Its absorption at 808 nm was significantly enhanced;and the photothermal conversion efficiency was increased from 30.3%of Mo₁₅₄ to 38.6%under 808 nm laser irradiation.When Mo₁₅₄ and Mo₁₅₄/TK-14 assembly were used in antibacterial experiments,it was found that the biofilm formation rates of S.aureus treated with Mo₁₅₄ and the assembly were 97.6%and 24.6%,respectively;and the bacterial viability were 92.9%and 20.2%.This result indicated that Mo₁₅₄/TK-14 assembly had significantly enhanced inhibition of biofilm formation and antibacterial effect than Mo₁₅₄.After 808 nm laser irradiation,the assembly could further reduce the biofilm formation rate and bacterial viability to 7.7%and 4.4%.This result indicates that the assembly can greatly improve the photothermal antibiofilm and antibacterial effects.(2)Assembly regulation and photothermal antibacterial investigations of Mo₁₅₄and Spm:In view of the antibacterial properties against S.aureus of spermine,a typical representative molecule of biogenic amines,it was assembled with Mo₁₅₄ to construct new materials with synergistic photothermal enhanced antibacterial effect.The structure and morphology were characterized and analyzed by Zeta potential,dynamic light scattering(DLS)and TEM,respectively.It was found that the absorption at 808 nm of the Mo₁₅₄/Spm assembly was enhanced,and the photothermal conversion efficiency could be improved to 35.4%.The biofilm formation rates of S.aureus treated with Spm and the assembly were 79.8%and 50.3%,respectively;and the bacterial survival rates were 41.8%and 10.4%.Under the 808 nm laser irradiation,the assembly can further reduce the biofilm formation rate and bacterial viability to49.1%and 6.2%.The result shows that the assembly indeed has obvious assembly-induced aggregation and photothermal synergistic effects,which can greatly improve the photothermal antibacterial and antibiofilm properties of the material.The research in this thesis provides a new strategy for designing efficient photothermal-enhanced antimicrobial composites.