Synthesis,Characterization And Properties Of Organic-inorganic Hybrid Compounds Based On Molybdenum And Tungsten Polyoxometalates

Polyoxometalates(POMs for short)not only have diverse structures,but also have good redox activities and excellent transport capabilities of electron and proton,which is promising candidates for catalysis,antitumor,antibacterial and antiviral fields.However,there are some disadvantages of individual pure inorganic POMs clusters,in terms of catalysis: 1)specific surface area is relatively small preventing the entry of active centers;2)low selectivity and poor separation ability from liquid;in terms of drugs: 1)high toxicity;2)poor stability under physiological conditions,resulting in a bad application in clinical trials.In the current experimental studies,the surface of POMs could be modified by organic groups to design multifunctional compounds using covalent attachment or electrostatic interactions.Thiosemicarbazones(TSCs)have a variety of biological activities(anticancer,antiviral,antibacterial,etc.)and strong coordination ability(with NNS tridentate coordination system,which can coordinate with different valence states and different types of metal ions),and the –NH– and –NH2 groups contained in TSCs have potential catalytic activity.This organic-inorganic hybrid material not only have the advantages of organic materials and POM,but also may generate new structures and excellent synergistic effects,thereby achieving special applications that are difficult to achieve in other aspects.This paper focuses on the synthesis of POM-based complexes and their potential applications in the catalysis and antibacterial fields,which is divided into two parts:(1)design and synthesis of homopolyoxometalates organic-inorganic compounds modified by 2–acetylpyridine thiosemicarbazones,the oxidation reaction of amine to imine and antibacterial activities;(2)design and synthesis of heteropolyoxometalates Keggin-type organic-inorganic compounds modified by 2–acetylpyrazine thiosemicarbazones and the study of antibacterial activities and mechanism.In the first chapter,three isopolyoxometalate-based organic-inorganic compounds were synthesized by controlling different temperatures,reaction ratios,p H values and solvents using the solvothermal method.The structure and composition of the compounds were characterized and properties were studied as follows:The homopolyoxometalate [M6O19]2–(M=Mo,W)and [W10O32]4– compounds were synthesized using 2–acetylpyridine thiosemicarbazones(HL1)as ligands.Three inorganic-organic hybrid compounds [Co(L1)2]2[Mo6O19](1),[Co(L1)2]2[W6O19](2)and [Ni(HL1)2]2[W10O32](3)were synthesized using HL1,Ni(Cl O4)2·6H2O/Co(NO3)2·6H2O and Na2 Mo O4·2H2O/Na2WO4·2H2O at a certain ratio,solvent,p H values and temperatures,and the as-synthesized single crystals were characterized by X-ray single crystal diffractions,inductively coupled plasma(ICP),elemental analysis(EA),infrared spectrum(IR),ultraviolet spectrum(UV-vis),X-ray powder diffraction(XRD),X-ray photoelectron spectroscopy(XPS)and scanning electron microscope(SEM).Moreover,the reaction performance of 1 for catalyzing amine to imine was studied,and various experiments(the amount of solvent,oxidant,and catalyst of the reaction)were regulated to explore the optimal reaction conditions.The results showed that 1 can be subjected to a cycle experiment and cycled three times with skeleton stability and high catalytic yield.The kinetics of catalytic reaction has been further studied,and the apparent rate constant is K' = 0.2338 L mol–1 h–1.In addition,in-vitro antibacterial experiments were performed on the compounds 1–3,which showed good antibacterial activity against both E.coli and S.aureus.Comparing minimum inhibitory concentration(MIC),the MICs of the three compounds were lower than those of single component,the amoxicillin trihydrate positive reference and kanamycin sulfate negative reference.This exhibits that the three compounds have a good application prospect in the field of practical chemical material preparation and biomedicine.In the second chapter,three heteropolyoxometalate-based organic-inorganic compounds were designed and synthesized by controlling different temperatures,reaction ratios,p H values and solvents using the solvothermal method.The structure and composition of the compounds were characterized and properties were studied,and the possible antibacterial mechanism was discussed systematically.The specific contents are as follows:The heteropolyoxometalate [PM12O40]3–(M=Mo,W)compounds were synthesized using 2-acetylpyrazine thiosemicarbazones(HL2)as ligands.Three inorganic-organic hybrid compounds [Ni(L2)(HL2)]2H[PMo12O40]?4H2O(4),[Co(L2)2]3[PMo12O40](5)and [Co(L2)2]3[PW12O40](6)were synthesized using HL2,Ni(ClO4)2·6H2O/Co(NO3)2·6H2O and Na2MoO4·2H2O/Na2WO4·2H2O at a certain ratio,solvent,p H values and temperatures,and the as-synthesized single crystals were characterized by X-ray single crystal diffractions,inductively coupled plasma(ICP),elemental analysis(EA),infrared spectrum(IR),ultraviolet spectrum(UV-vis),X-ray powder diffraction(XRD),X-ray photoelectron spectroscopy(XPS)and scanning electron microscope(SEM).Moreover,these three compounds maintain stability in the p H range of 4.0?10.0,1.0?9.0 and 2.0?10.0.At the same time,the antibacterial properties of these three compounds were investigated.Compounds 4,5,and 6 all showed lower MICs.The MICs of 4 to S.aureus is about 125?250 times of the reference drug,and the MICs of 5 and 6 to S.aureus is about 16?1000 times of the reference drug.Compound 5 has lower MICs value than 6,probably because the skeleton of [PMo12O40]3? has higher redox properties than [PW12O40]3?.The compounds 4,5,and 6 had better antibacterial activity against E.coli and S.aureus by the time-killing experiments.Different compounds had different degrees of sensitivity to bacteria,compound 4 could completely kill bacteria in 6 hours,while 5 and 6 can completely kill bacteria in 4-6 hours.In addition,compound 5 was selected to explore the possible antibacterial mechanism and E.coli was taken as an example.From the mechanism exploration experiments,it can be seen that the interaction of various components can damage the cell membrane integrity,causing the leakage of proteins,the decrease of dehydrogenase activity,the accumulation of reactive oxygen species(ROS)and depletion of glutathione(GSH),etc.These combined reasons ultimately lead to the death of bacteria.