The synergistic self-assembly of biomolecules with polyoxometalates (POMs) has recently been considered as an effective approach to construct nano-biomaterials with diverse structures and morphologies towards applications in drug delivery, controlled release, tissue engineering scaffolds, and biomineralization, due to the unique features of the clusters in addition to many well-known inorganic nanoparticles. This review presents an overview of recent work focusing on the noncovalent co-assembly of peptides and POMs as well as their biological applications. In the co-assemblies triggered by the interaction between the components significant advantages are observed that POMs or peptides alone do not possess; examples include chiral recognition of hybrid metal oxides, the quick hydrolysis of peptides, and enhanced inhibition of Aβ aggregation. Finally, we outline a brief perspective on possible unresolved issues and future opportunities in this field.

Polyoxometalates (POMs) represent a type of typical polyanionic nanoclusters that can be utilized as inorganic bioactive materials; however, the detailed interactions of them with many target biomolecules such as peptides and proteins were not well clarified due to the complexity of the binding process. In the present study, the binding-induced physiochemical phenomena of a highly charged Eu-containing polyoxometalate, K13[Eu(SiW9Mo2O39)2] (EuSiWMo), with a model protein, bovine serum albumin (BSA), was identified upon the examination of luminescence of both the components during the titration. The large emission enhancement and subsequent quenching of the EuSiWMo were found in close relation to the amount of added BSA. Being different from the known binding type of less charged POMs, a distinct two-step binding process was concluded, and the possible mechanism was proposed through the analysis on the time-resolved fluorescence spectra, isothermal titration calorimetry (ITC), transmission electron microscope (TEM), and two-dimensional correlation spectroscopy (2D COS). The present results directed a new understanding for the charge numbers and existing state of POMs affecting the interaction with proteins, which is important to exploit the biological functionalities of POMs in related systems and the development of POMs as potential inorganic drugs.

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