Tunable Aggregation-Induced Emission of Polyoxometalates via Amino Acid-Directed Self-Assembly and Their Application...

In this work, through the aqueous phase self-assembly of an Eu-containing polyoxometalate (POM), Na₉[EuW₁₀O₃₆]·32H₂O (EuW₁₀) and different amino acids, we obtained spontaneously formed vesicles that showed luminescence enhancement for EuW₁₀ and arginine (Arg), lysine (Lys), or histidine (His) complexes, but luminescence quenching for EuW₁₀ and glutamic acid (Glu) or aspartic acid (Asp) complexes. The binding mechanisms between them have been explored at the molecular level by using different characterization techniques. It was found that EuW₁₀ acted as polar head groups interact with the positively charged residues for alkaline amino acids, protonated amide groups for acidic amino and nonpolar acid aminos through electrostatic interactions, and the remaining segments of amino acids served as relatively hydrophobic parts aggregated together forming bilayer membrane structures. Moreover, the different influences of amino acids on the fluorescence property of EuW₁₀ revealed that the electrostatic interaction between the positive charged group of amino acid and the polyanionic cluster dominates the fluorescence properties of assemblies. Furthermore, a turn-off sensing application of the EuW₁₀/Arg platform to probe dopamine (DA) against various other biological molecules such as neurotransmitters or amino acids was also established. The concept of combining POMs with amino acids extends the research category of POM-based functional materials and devices.