Preparation And Properties Of Methoxy Poly（Ethylene Glycol）-Functionalized Lanthanide Nano-Assemblies And Their Supramolecular Hydrogels

In this paper,partially esterification derivative of pyromellitic acid（PMA）and methoxy poly（ethylene glycol）（MPEG,M_n=1,000）was designed and synthesized.In aqueous solution,well-dispersed Ln-PMA-MPEG were rapidly prepared through biomimetic mineralization using bovine serum albumin（BSA）as biologic initiator and Ln-PMA-MPEG as functional organic ligand with lanthanide ions(Ln³⁺).Hybrid supramolecular hydrogels could be in-situ fabricated by introducingα-cyclodextrin（α-CD）aqueous solution into the above-mentioned solutions.The structure and properties of Ln-PMA-MPEG and hybrid supramolecular hydrogels were characterized.Their applications in solvent recognition,water（trace water）detection,Fe³⁺ions detection and controlled drug release were fundamentally evaluated.First of all,the water-soluble partially esterified derivative（PMA-MPEG）was synthesized via esterification reaction between pyromellitic acid（PMA）and methoxy poly（ethylene glycol）（MPEG,M_n=1,000）by controlling the molar ratio of PMA to MPEG（[PMA]/[MPEG]=1:1.5）using 1,3-dicyclohexyl carbodiimide（DCC）as coupling agent and 4-（dimethylamino）pyridine（DMAP）and triethylamine as catalysts.The structure and properties of PMA-MPEG derivative were characterized by ~1H NMR,~1H NMR、FT IR、CMC、DSC etc..The esterification degree of PMA was found to be 1.4 MPEG chains per PMA molecule,and the CMC value was 4.63╳10^-4mg m L^-1.well-dispersed Ln-PMA-MPEG were rapidly prepared through biomimetic mineralization using bovine serum albumin（BSA）as biologic initiator and PMA-MPEG as functional organic ligand with lanthanide ions(Ln³⁺)in aqueous systems.The structure and morphology of PMA-MPEG and Ln-PMA-MPEG were characterized by ~1H NMR,FT IR,SEM and TEM.TEM images showed the individual Ln-PMA-MPEG exhibited approximately spherical morphology with particle sizes in the range from 60 to 100 nm.The particle sizes of the as-synthesized Ln-PMA-MPEG in the aqueous solution were in the range from110 to 450 nm.The particles of the Ln-PMA-MPEG in DMF were in the range from80-200 nm.Ln-PMA-MPEG have a trend to aggregate into larger nanoscale agglomeration in aqueous solutions.Ln-PMA-MPEG depict tunable photoluminescent properties via modulating the stoichiometry of Eu³⁺to Tb³⁺.Eu-PMA-MPEG display different emission colors in water,THF,acetone,ethanol and DMF for solvent recognition.Eu-PMA-MPEG and Eu/Tb-PMA-MPEG(Eu³⁺/Tb³⁺=1:1)are sensitive to the water or trace water in ethanol and DMF,so they could be used as fluorescent sensor or ratiometric fluorescent sensor for detection of water in solvents and Fe³⁺ions detection.Second,Ln-PMA-MPEG display good water-dispersity and stability in aqueous solutions due to the hydrophiphilicity of MPEG moieties.Hybrid supramolecular hydrogels could be in-situ fabricated by introducingα-CD aqueous solution into the above-mentioned solutions.the structure and properties of supramolecular hydrogels were characterized by FT IR,TGA,XRD,SEM,fluorescence spectrophotometer and rheometer etc..XRD confirmed that there existed the channel-type structure of the crystallineα-CD-PEG inclusion complexes formed betweenα-CD and the MPEG moieties in hydrogel systems.The rheological measurements showed that the obtained supramolecular hydrogels displayed a high degree of elasticity,with the storage moduli greater than 10~5Pa,and their viscosity greatly diminished when they were sheared.Both Ln-PMA-MPEG and the resulting supramolecular hydrogels showed tunable fluorescent properties,and their emission colors could be modulated from red to green via varying Eu³⁺,Tb³⁺and the molar ratio of Eu³⁺to Tb³⁺.The release profiles of BSA as model protein show that hybrid hydrogels exhibit outstanding controlled release behaviors lasting for about 45 days.