Design,Syntheses And Electrochemical Sensing Properties Of Metal-Calix[4]arene Complexes

Food and drug safety as well as environmental pollution are two important issues related to human health and ecological sustainable development.It is an urgent and challenging task to achieve sensitive,accurate and efficient detection of drugs and contaminants in medical,food and environmental fields.Compared with traditional detection methods,electrochemical detection methods have exerted a tremendous fascination on researchers’attention because of their outstanding advantages such as fast response,low cost,high sensitivity and miniaturization of instruments.In the development of electrochemical sensors,modified materials play the crucial role in the improvement of detection performances.Therefore,the synthesis of functional and more environmentally friendly sensing materials is the key factor for electrochemical sensing.Metal-calix[4]arene complexes have potential applications in gas storage and separation,organic catalysis and fluorescence detection due to their porous structure,catalytic activity and fluorescence characteristics,but their electrochemical properties are rarely studied.In order to explore their potential application in the field of electrochemical sensing,five metal-calix[4]arene complexes were synthesized,and different electrochemical sensors were prepared for rapid and accurate detection of baicalein,bisphenol molecules and heavy metal ions,respectively.The main research contents and results include:1.A new dumbbell-shaped metal-organic hybrid complex,[Co₄（TC4A）₂]·3DMF·Me OH（Co-TC4A）,was synthesized with the bowl-shaped p-tert-butylthiacalix[4]arene（H₄TC4A）.By a simple one-step solvothermal reaction method,Co-TC4A was embedded and dispersed in ordered mesoporous carbon（OMC）to give composite（Co-TC4A@OMC（1:1））.The synergistic effects between Co-TC4A and OMC drastically enhanced the catalytic efficiency,conductivity and specific surface area of the resulting materials.The glassy carbon electrode modified with Co-TC4A@OMC（1:1）composite（Co-TC4A@OMC（1:1）/GCE）was used in the electrochemical detection of baicalein with a wide linear range of 0.005–17.00μM,a high sensitivity of 8.96μAμM^-1and an ultra-low detection limit of 1.6 n M.In addition,this sensor can also be used for the determination of baicalein in the real drug（baicalein aluminum capsules）with satisfactory recovery.2.Based on H₄TC4A of the previous chapter,the lower edge of the calixarene was modified by four imidazole groups and the bridged sulfur atoms were oxidized to sulphones,resulting in the imidazole groups functionalized sulfonylcalix[4]arene-based ligand（L¹）.Then,a new porous 2D MOF[Zn₂（L）（IPA）（H₂O）]·2DMF·2Me OH·3H₂O（Zn-L-IPA）was synthesized by using L¹,isophthalic acid（H₂IPA）and Zn（Ⅱ）cations.Due to the introduction of hydrochloric acid into the solvothermal reaction,parts of C-O bond of L¹were broken and L¹converted into new ligand（H₂L）.Combined with the host-guest recognition strategy and the electrochemical detection method,a rapid,high-selective and ultrasensitive electrochemical sensing platform（Zn-L-IPA@GP/GCE）was fabricated by using Zn-L-IPA as the host to recognize and adsorb bisphenol guests（GP=graphite powder）.During the accumulation process,1D channels with specific size and structure of Zn-L-IPA showed different adsorption capacities for the three analogous bisphenol substances.Thus,the detection results of bisphenol F（BPF）and bisphenol A（BPA）showed wide linear ranges of0.005–10.50μM and 0.01–8.50μM,respectively,and extremely low detection limits of 0.2and 3.5 n M,respectively.While there was almost no current response to bisphenol S（BPS）.The density functional theory（DFT）calculation results demonstrated that the hydrogen bonding andπ–packing interactions dominated the combining effect between the Zn-L-IPA host and the bisphenol guest.The volume,dipole moment,electronic structure and geometry of guest molecules affect the selective adsorption of guest molecules in the 1D channels.3.Further,under different solvothermal conditions,the dumbbell-shaped tetranuclear bismuth cluster[Bi₄（TC4A）₂（μ₄-O）]·2NO₃·3DMF·3Me OH（Bi₄-TC4A）and the irregular sphere-shapeeight-nuclearbismuthcluster[Bi₈（TC4A）₅（en）₂（μ₃-OH）₂（μ₄-OH）₂]·5DMF·2Me OH（Bi₈-TC4A）were synthesized by the use of H₄TC4A.The constructed electrodes（Bi₄-TC4A/GCE and Bi₈-TC4A/GCE）were applied to detect Cd²⁺and Pb²⁺in aqueous solution by utilizing the unique advantages of Bi-based materials and calixarene ligands in the detection of heavy metal ions.Compared with Bi₄-TC4A/GCE,Bi₈-TC4A/GCE showed the senior detection performances with high sensitivities of 12.71 and 18.14μAμM^-1as well as low detection limits of 12.4 and 8.2 n M for Cd²⁺and Pb²⁺,respectively.Moreover,Bi₈-TC4A/GCE was employed to determine the contents of Cd²⁺and Pb²⁺in real soil and lake water samples.4.By the use of resorcin[4]arene modified by 4-mercaptopyridine（TMC4R）,1,4-benzenedicarboxylic acid（1,4-H₂BDC）and Co（II）cations,a new sulfur-containing nano-capsule-based3DMOF[Co₂（TMC4R）（1,4-BDC）₂（μ₂-H₂O）]·3DMF·CH₃OH·5CH₃CN·H₂O（Co-TMC4R-BDC）was synthesized.And the detection performances of four heavy metal ions(HMIs:Pb²⁺,Cu²⁺,Cd²⁺and Hg²⁺)was systematically evaluated on the Co-TMC4R-BDC modified electrochemical sensing platform（Co-TMC4R-BDC/GCE）.Under the optimized detection conditions,the HMIs sensing platform showed significantly enhanced electrochemical sensing behavior because the Co-TMC4R-BDC featured even-distributed sulfur atoms,special cavity structure and acceptable conductivity.Most strikingly,the limit of detection（LOD）values for Cd²⁺,Pb²⁺and Cu²⁺are up to 26.4,11.2 and 13.3 n M,respectively,which are lower than the standard level of drinking water from the World Health Organization.Moreover,the Co-TMC4R-BDC modified electrode possessed good stability,prominent reproducibility and great potential for the practical application.X-ray photoelectron spectroscopy（XPS）results confirmed that the exposed S atoms of the nano-capsule units effectively captured HMIs through the complexation between S atoms and HMIs.Further,DFT calculations indicated the presence of cation-πinteractions between phenyl rings and HMIs.Thereby,it is reasonable to infer that the synergistic effects accomplished the effective capture for the sensitive detection of HMIs.This work provides a feasible strategy for the capture and electrochemical detection of HMIs in an aqueous solution with the sulfur-containing nano-capsule shaped MOF.