Molecular Recognition on the Multisite Binding Surface of the Keplerate {Mo72Fe30} Giving Supramolecular Texturing and Modulating the Function of Guest Molecules

Molecular recognition underlies structure formation in supramolecular architectures either in materials or in living systems. Here, we used the nanoscale nontoxic Keplerate-type polyoxometalate (POM) {Mo72Fe30} as a template for the recognition of two different guest molecules [tetracycline (TC) and doxorubicin (DOX)] on the textured surface. By means of single crystal X-ray analysis and X-ray photoelectron spectroscopy (XPS), we revised the key features of the {Mo72Fe30} structure, showcasing the guest dimolybdenum units' {Mo2} location under the hexagonal pores and dynamic exchange of these units during dissolution in an aqueous medium. Based on the clarified POM structure, we demonstrated how the small differences between the TC and the DOX molecules can be recognized by the Keplerate surface, revealing the nature of the binding sites─{Mo6}/{FeO6} for TC and {FeO6} for DOX. Furthermore, using the Monte-Carlo method, we calculated the statistical distribution of the guest molecules in the stoichiometric compounds {Mo72Fe30}@TC12 and {Mo72Fe30}@DOX12, displaying the supramolecular ordering of the DOX species and randomization of the TC as a result of different coordinations to the POM surface. The produced {Mo72Fe30}@TC12 and {Mo72Fe30}@DOX12 associates were evaluated for bioactivity, showing how their interaction with POM can modulate the biological function of guest molecules.

Association of Keplerate-Type Polyoxometalate {Mo72Fe30} with Tetracycline: Nature of Binding Sites and Antimicrobial Action

The association process between the tetracycline (TC) antibiotic molecule and Keplerate-type nanocluster polyoxometalate (POM) {Mo72Fe30} was studied in aqueous solution. The novel supramolecular ensemble {Mo72Fe30}@TC12.5 was produced, its composition and structure were revealed by means of elemental analysis (C, N, H) and vibrational spectroscopy (IR and Raman). Based on the spectral data, the POM structure’s integrity was confirmed and binding sites of TC with the Keplerate {Mo72Fe30} surface were found. Due to thermogravimetric analysis (TG) and in-situ Raman spectroscopy during the process of {Mo72Fe30}@TC12.5 thermal destruction, we showed a significant change in the phase composition of POM’s destruction products after association with TC. The antibacterial activity of the obtained complex {Mo72Fe30}@TC12.5 was examined. The experimental results allowed us to note the partial inhibition of TC’s antibacterial activity owing to the coordination of TC to FeIII centers, in turn, which hinders the participation of TC in coordination via Mg2+ of ribosomal subunits 30S in bacteria.

Coordinative interaction between nitrogen oxides and iron–molybdenum POM Mo72Fe30

The process of adsorption of nitrogen monoxide and dioxide by the giant Keplerate nanocluster Mo₇₂Fe₃₀ was studied in detail under ambient conditions and air/argon atmosphere.